Dr Ahmed Abu Foul

Sound is a form of energy which is emitted by a vibrating

body and on reaching the ear causes the feeling of hearing

through nerves

Sounds produced by all vibrating bodies are not audible

The frequency limits of audibility are from 20 HZ to 20000

HZ

A sound generally consists of three inter-related elements-

the source the receiver and the transmission path

This transmission path is usually the atmosphere through

which the sound is propagated

Sound is a form of energy which is emitted by a vibrating

body and on reaching the ear causes the feeling of hearing

through nerves

Sounds produced by all vibrating bodies are not audible

The frequency limits of audibility are from 20 HZ to 20000

HZ

A sound generally consists of three inter-related elements-

the source the receiver and the transmission path

This transmission path is usually the atmosphere through

which the sound is propagated

The pressure waves spread out like ripples on a pond when a stone is

dropped into it except that sound waves fill the whole volume of air

whereas ripples are confined to the surface of the pond

Speed of Sound

In a free field sound propagates with the velocity c defined by

where TK and TR are the temperature in Kelvin and Rankin respectively

A simpler formula for the velocity of sound in air sufficiently accurate at

normal temperatures 0ndash30oC is

where TC is the temperature in centigrade

Example 1

Determine the speed of sound at 20oC (68oF) in both metric

and English units

Solution

The Kelvin temperature is TK = 2732 + 20 = 2932 K

and the Rankin temperature is TR = 4597 + 68 = 5277oR

The speed of sound c is then

Sounds of frequencies less than 20 HZ are called infrasonic

and greater than 20000 HZ are called ultrasonic

The intensity of sound is measured in sound pressure levels

(SPL) and common unit of measurement is decibel dB

The community (ambient) sound levels are measured in the A -

weighted SPL abbreviated dB(A)

If a source of sound emits the same pressure fluctuation in

all directions in free space the surface with the same level

of pressure will be concentric spheres

As the waves propagate outward the spheres become larger

and larger and the energy emitted by the source spread over

an ever larger surface causing the amplitude to decay like

1r2 where r is the distance from the source

Distance affects the intensity of sound For example if the sound

pressure level L1 in dB is measured at r1 meters then the sound

pressure level L2 in dB at r2 meters is given by

This is called geometrical decay Even if this did not happen sound

wave would decay anyway due to the small but finite viscosity of the

air and the absorbing capacity of most surfaces

Sound waves are characterized by their pressure amplitude and their

frequency

If the sound levels are measured in terms of pressure then

sound pressure level LP is given by

Lp=10XLog10(p2p0

2) = 20X Log10(pp0) in dB

The Lp is measured against a standard reference pressure Po =

2 x 10-5 Nm2 which is equivalent to zero decibels

The sound pressure is the pressure exerted at a point due to a

sound producing source

Definition of sound pressure

Example 2

If the distance from a noise source is doubled find out the

noise levels

Given r2 = 2r1

We have L2 = L1 - 20log10 (r2r1)

Substituting we get

L2 = L1 - 20 log10 (2r1r1)

L2 = L1 - 20 log10(2)

ie L2 = L1 - 20 x 0301

= L1 - 602

ie the noise level will decrease by 6 dB for doubling of

distance from the source

Example 3

The sound pressure level is measured at 5 x 10-4 Nm2 Find

out the noise level in dB

Addition of sound levels

The effective sound levels form two or more sources cannot be

simply added algebraically

For example the effective sound level from two air

conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)

but 60 + 3 = 63 dB(A) (See table 1)

Similarly the effective sound level of 57 dB 63 dB 63 dB 66

dB and 69 dB is 72 dB

The computation is illustrated below

Addition of sound levels

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example 1

Determine the speed of sound at 20oC (68oF) in both metric

and English units

Solution

The Kelvin temperature is TK = 2732 + 20 = 2932 K

and the Rankin temperature is TR = 4597 + 68 = 5277oR

The speed of sound c is then

Sounds of frequencies less than 20 HZ are called infrasonic

and greater than 20000 HZ are called ultrasonic

The intensity of sound is measured in sound pressure levels

(SPL) and common unit of measurement is decibel dB

The community (ambient) sound levels are measured in the A -

weighted SPL abbreviated dB(A)

If a source of sound emits the same pressure fluctuation in

all directions in free space the surface with the same level

of pressure will be concentric spheres

As the waves propagate outward the spheres become larger

and larger and the energy emitted by the source spread over

an ever larger surface causing the amplitude to decay like

1r2 where r is the distance from the source

Distance affects the intensity of sound For example if the sound

pressure level L1 in dB is measured at r1 meters then the sound

pressure level L2 in dB at r2 meters is given by

This is called geometrical decay Even if this did not happen sound

wave would decay anyway due to the small but finite viscosity of the

air and the absorbing capacity of most surfaces

Sound waves are characterized by their pressure amplitude and their

frequency

If the sound levels are measured in terms of pressure then

sound pressure level LP is given by

Lp=10XLog10(p2p0

2) = 20X Log10(pp0) in dB

The Lp is measured against a standard reference pressure Po =

2 x 10-5 Nm2 which is equivalent to zero decibels

The sound pressure is the pressure exerted at a point due to a

sound producing source

Definition of sound pressure

Example 2

If the distance from a noise source is doubled find out the

noise levels

Given r2 = 2r1

We have L2 = L1 - 20log10 (r2r1)

Substituting we get

L2 = L1 - 20 log10 (2r1r1)

L2 = L1 - 20 log10(2)

ie L2 = L1 - 20 x 0301

= L1 - 602

ie the noise level will decrease by 6 dB for doubling of

distance from the source

Example 3

The sound pressure level is measured at 5 x 10-4 Nm2 Find

out the noise level in dB

Addition of sound levels

The effective sound levels form two or more sources cannot be

simply added algebraically

For example the effective sound level from two air

conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)

but 60 + 3 = 63 dB(A) (See table 1)

Similarly the effective sound level of 57 dB 63 dB 63 dB 66

dB and 69 dB is 72 dB

The computation is illustrated below

Addition of sound levels

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Sounds of frequencies less than 20 HZ are called infrasonic

and greater than 20000 HZ are called ultrasonic

The intensity of sound is measured in sound pressure levels

(SPL) and common unit of measurement is decibel dB

The community (ambient) sound levels are measured in the A -

weighted SPL abbreviated dB(A)

If a source of sound emits the same pressure fluctuation in

all directions in free space the surface with the same level

of pressure will be concentric spheres

As the waves propagate outward the spheres become larger

and larger and the energy emitted by the source spread over

an ever larger surface causing the amplitude to decay like

1r2 where r is the distance from the source

Distance affects the intensity of sound For example if the sound

pressure level L1 in dB is measured at r1 meters then the sound

pressure level L2 in dB at r2 meters is given by

This is called geometrical decay Even if this did not happen sound

wave would decay anyway due to the small but finite viscosity of the

air and the absorbing capacity of most surfaces

Sound waves are characterized by their pressure amplitude and their

frequency

If the sound levels are measured in terms of pressure then

sound pressure level LP is given by

Lp=10XLog10(p2p0

2) = 20X Log10(pp0) in dB

The Lp is measured against a standard reference pressure Po =

2 x 10-5 Nm2 which is equivalent to zero decibels

The sound pressure is the pressure exerted at a point due to a

sound producing source

Definition of sound pressure

Example 2

If the distance from a noise source is doubled find out the

noise levels

Given r2 = 2r1

We have L2 = L1 - 20log10 (r2r1)

Substituting we get

L2 = L1 - 20 log10 (2r1r1)

L2 = L1 - 20 log10(2)

ie L2 = L1 - 20 x 0301

= L1 - 602

ie the noise level will decrease by 6 dB for doubling of

distance from the source

Example 3

The sound pressure level is measured at 5 x 10-4 Nm2 Find

out the noise level in dB

Addition of sound levels

The effective sound levels form two or more sources cannot be

simply added algebraically

For example the effective sound level from two air

conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)

but 60 + 3 = 63 dB(A) (See table 1)

Similarly the effective sound level of 57 dB 63 dB 63 dB 66

dB and 69 dB is 72 dB

The computation is illustrated below

Addition of sound levels

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

If a source of sound emits the same pressure fluctuation in

all directions in free space the surface with the same level

of pressure will be concentric spheres

As the waves propagate outward the spheres become larger

and larger and the energy emitted by the source spread over

an ever larger surface causing the amplitude to decay like

1r2 where r is the distance from the source

Distance affects the intensity of sound For example if the sound

pressure level L1 in dB is measured at r1 meters then the sound

pressure level L2 in dB at r2 meters is given by

This is called geometrical decay Even if this did not happen sound

wave would decay anyway due to the small but finite viscosity of the

air and the absorbing capacity of most surfaces

Sound waves are characterized by their pressure amplitude and their

frequency

If the sound levels are measured in terms of pressure then

sound pressure level LP is given by

Lp=10XLog10(p2p0

2) = 20X Log10(pp0) in dB

The Lp is measured against a standard reference pressure Po =

2 x 10-5 Nm2 which is equivalent to zero decibels

The sound pressure is the pressure exerted at a point due to a

sound producing source

Definition of sound pressure

Example 2

If the distance from a noise source is doubled find out the

noise levels

Given r2 = 2r1

We have L2 = L1 - 20log10 (r2r1)

Substituting we get

L2 = L1 - 20 log10 (2r1r1)

L2 = L1 - 20 log10(2)

ie L2 = L1 - 20 x 0301

= L1 - 602

ie the noise level will decrease by 6 dB for doubling of

distance from the source

Example 3

The sound pressure level is measured at 5 x 10-4 Nm2 Find

out the noise level in dB

Addition of sound levels

The effective sound levels form two or more sources cannot be

simply added algebraically

For example the effective sound level from two air

conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)

but 60 + 3 = 63 dB(A) (See table 1)

Similarly the effective sound level of 57 dB 63 dB 63 dB 66

dB and 69 dB is 72 dB

The computation is illustrated below

Addition of sound levels

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Distance affects the intensity of sound For example if the sound

pressure level L1 in dB is measured at r1 meters then the sound

pressure level L2 in dB at r2 meters is given by

This is called geometrical decay Even if this did not happen sound

wave would decay anyway due to the small but finite viscosity of the

air and the absorbing capacity of most surfaces

Sound waves are characterized by their pressure amplitude and their

frequency

If the sound levels are measured in terms of pressure then

sound pressure level LP is given by

Lp=10XLog10(p2p0

2) = 20X Log10(pp0) in dB

The Lp is measured against a standard reference pressure Po =

2 x 10-5 Nm2 which is equivalent to zero decibels

The sound pressure is the pressure exerted at a point due to a

sound producing source

Definition of sound pressure

Example 2

If the distance from a noise source is doubled find out the

noise levels

Given r2 = 2r1

We have L2 = L1 - 20log10 (r2r1)

Substituting we get

L2 = L1 - 20 log10 (2r1r1)

L2 = L1 - 20 log10(2)

ie L2 = L1 - 20 x 0301

= L1 - 602

ie the noise level will decrease by 6 dB for doubling of

distance from the source

Example 3

The sound pressure level is measured at 5 x 10-4 Nm2 Find

out the noise level in dB

Addition of sound levels

The effective sound levels form two or more sources cannot be

simply added algebraically

For example the effective sound level from two air

conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)

but 60 + 3 = 63 dB(A) (See table 1)

Similarly the effective sound level of 57 dB 63 dB 63 dB 66

dB and 69 dB is 72 dB

The computation is illustrated below

Addition of sound levels

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

If the sound levels are measured in terms of pressure then

sound pressure level LP is given by

Lp=10XLog10(p2p0

2) = 20X Log10(pp0) in dB

The Lp is measured against a standard reference pressure Po =

2 x 10-5 Nm2 which is equivalent to zero decibels

The sound pressure is the pressure exerted at a point due to a

sound producing source

Definition of sound pressure

Example 2

If the distance from a noise source is doubled find out the

noise levels

Given r2 = 2r1

We have L2 = L1 - 20log10 (r2r1)

Substituting we get

L2 = L1 - 20 log10 (2r1r1)

L2 = L1 - 20 log10(2)

ie L2 = L1 - 20 x 0301

= L1 - 602

ie the noise level will decrease by 6 dB for doubling of

distance from the source

Example 3

The sound pressure level is measured at 5 x 10-4 Nm2 Find

out the noise level in dB

Addition of sound levels

The effective sound levels form two or more sources cannot be

simply added algebraically

For example the effective sound level from two air

conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)

but 60 + 3 = 63 dB(A) (See table 1)

Similarly the effective sound level of 57 dB 63 dB 63 dB 66

dB and 69 dB is 72 dB

The computation is illustrated below

Addition of sound levels

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example 2

If the distance from a noise source is doubled find out the

noise levels

Given r2 = 2r1

We have L2 = L1 - 20log10 (r2r1)

Substituting we get

L2 = L1 - 20 log10 (2r1r1)

L2 = L1 - 20 log10(2)

ie L2 = L1 - 20 x 0301

= L1 - 602

ie the noise level will decrease by 6 dB for doubling of

distance from the source

Example 3

The sound pressure level is measured at 5 x 10-4 Nm2 Find

out the noise level in dB

Addition of sound levels

The effective sound levels form two or more sources cannot be

simply added algebraically

For example the effective sound level from two air

conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)

but 60 + 3 = 63 dB(A) (See table 1)

Similarly the effective sound level of 57 dB 63 dB 63 dB 66

dB and 69 dB is 72 dB

The computation is illustrated below

Addition of sound levels

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example 3

The sound pressure level is measured at 5 x 10-4 Nm2 Find

out the noise level in dB

Addition of sound levels

The effective sound levels form two or more sources cannot be

simply added algebraically

For example the effective sound level from two air

conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)

but 60 + 3 = 63 dB(A) (See table 1)

Similarly the effective sound level of 57 dB 63 dB 63 dB 66

dB and 69 dB is 72 dB

The computation is illustrated below

Addition of sound levels

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Addition of sound levels

The effective sound levels form two or more sources cannot be

simply added algebraically

For example the effective sound level from two air

conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)

but 60 + 3 = 63 dB(A) (See table 1)

Similarly the effective sound level of 57 dB 63 dB 63 dB 66

dB and 69 dB is 72 dB

The computation is illustrated below

Addition of sound levels

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Addition of sound levels

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Adding noise sources and subtracting

background noise

10 log 2 = 3 dB

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

To get a measure of the magnitude of the noise we need its

root mean square value over a couple of periods (say 1s)

It turns out that for uncorrelated sources the resultant rms

pressure is such that is such that p2 = p2A + p2

B

This is illustrated in the diagram shown in the following

Fig

Addition of sound levels

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Chart method ndash adding decibels

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Chart method ndash subtracting background noise

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

0 16 Hz 20 kHz 5 MHz

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Sound waves travel at a specific speed ndash the speed of sound

ndash which is roughly c = 343 ms in air

This speed depends very little on the frequency of the wave

high frequencies ie 12 kHz travel as fast as a 50 Hz wave

However these two parameters define another important

one the wavelength

If T is the period of the pressure fluctuation then its

frequency is f=1T and the wavelength is defined by

=cT=cf

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Wavelength is the distance between two successive wave fronts (like

the distance between two wave crests with sea waves)

For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is

about 7cm so there is a significant different

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

What happens when a sound source such as a pistol is fired

out-of-doors in the absence of any nearby reflecting

surfaces as is seen in Fig 4

The sound waves will travel through the atmosphere from

the pistol to the receiver) who will only hear one crack

The farther the receiver is away the later the crack will

arrive and the weaker it will be

The direct sound wave is the only sound heard

The sound wave arrives at time t t = Rc

where R is the distance between the source and the receiver

and c is the speed of sound

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

If there is a large wall or building at a distance near the firing position as

evidenced in Fig 5 the receiver will hear a different sound

The first sound wave will be from the direct arrival and the second sound

wave from the reflected arrival off of the wall

The two sound waves will arrive at

t1 = R1c and t2 = R2c

The human ear is able to recognize individual sound impulses if they are

separated by a time period of about 50 ms

If the time difference between the direct sound and the reflected sound is

greater an echo will be heard if the time difference is less only one

modified crack will be heard as evidenced in Fig 5

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example 6

Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Sound and human hearing ndash Frequency

Humans are less sensitive to low frequency sound and more

sensitive to high frequency sound Therefore sometimes the

dB scale is adjusted to take this into account

A-weighting (db(A)) adjusts overall scale so it better matches

what the human ear would hear

C-weighting (dB(C)) adjusts scale for loud or low frequency

sounds

B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo

the A-weighted factors and C-weighted factors (rarely used)

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Sound Level Meters are the instruments commonly used to

measure environmental noise

They have 3 main components

1 A microphone

2 Some filtering electronics (the weighting networks) and

3 Display

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Equivalent sound level (Leq) can be applied to any

fluctuation noise level

Itrsquos the constant noise level that over a given time expand

the same amount of energy as the fluctuating level over the

same period

Leq = 10 log Σ 10Li10(ti)

- n the number of samples taken

- Li the noise level in dBA of the ith sample

- ti fraction of total sample time

i=n

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Given two machines producing 80 dB each

what is the total SPLT

SPLT is the total sound pressure level

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example 7

The noise levels at a particular location are 65dB 70dB and

78dB measured during an hour of the day Find out the

average noise levels at the location

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Consider the case where a noise level of 90 dBA exists for 10 mins

and is followed by a reduced noise level of 70 dBA for 30 mins What

is the equivalent continuous equal energy level for the 40 mins

period Assume a 5-min sampling interval

Solution if the sampling time is 5 mins then samples (n) is 8 and the

fraction of total sample time (ti) for each sample is 18 = 0125

Σ = (109010)(0250) + (107010)(0750)

= (25 x 108) + (750 x 106) = 258 x 108

and finally we take the log to find

Leq = 10 log (258 x 108) = 8411 or 84 dBA

2

t=1

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Physically there is no distinction between sound and

noise

Sound is a sensory perception and the complex

pattern of sound waves is labeled as noise music

speech etc

Noise has become a very important stress factor in

the environment of man

Sound and Noise

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Sound that is unwanted or disrupts onersquos quality of life is

called as noise When there is lot of noise in the

environment it is termed as noise pollution

Sound becomes undesirable when it disturbs the normal

activities such as working sleeping and during

conversations

It is an underrated environmental problem because of the

fact that we canrsquot see smell or taste it

World Health Organization stated that ldquoNoise must be

recognized as a major threat to human well-beingrdquo

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Normal level of tolerance is 80 dbA

Sound level below and above this is considered to be as noise pollution

Any sound above 80 dB can cause hearing loss

The loss is related to the intensity and length of exposure

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Sound levels about 90 dBA with exposures of 8 hrs per day

will produce permanent hearing loss after many years

Increased blood pressure and hypertension were shown to

occur at sound levels of 85 dBA

Increased risk of hypertension for people living in areas

with road or air traffic noise at outdoor equivalent sound

levels above 70 dB(A) based on exposure between 600

am and 1000 pm

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Harmful Effects of Noise Are Related to the Noise

Dose

Is the Noise Harmful

Ask Yourself

How Loud How Long How Many Times

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Intensity of Noise (how loud)

Duration of Noise Exposure (how long)

Frequency (how many times during the day are they

exposed to such a noise)

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Regulated as an 8 hour Time Weighted Average

(TWA)

An 8 hr TWA of 90 dBA is designated as a Noise

Dose of 100

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

5 dB Halving Rule

For Each 5 dB Increase in Noise In order to be

Equivalent to the Previous Dose You Must Half the

Allowable Exposure Time

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over frac12 Hour TWA Period

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

OSHA Noise (permissible exposure limits PEL)

Presently industry is governed by noise regulations

adopted by OSHA (Occupational Safety and Health

Administration)

PEL same as originally adopted in 1971

ndash Criteria level (PEL) 90 dBA

ndash Threshold level 90 dBA

- Practical implication mdash Can be exposed to 89 dBA

forever

ndash Exchange rate 5 dB

bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

The 5 dB Rule Can Be Useful in Estimating

Whether a Noise or an Activity Would Result in

Employees Being Exposed to Noise In Excess of the

PEL

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

An Employee Must Enter a Pump Room and

Conduct Preventative Maintenance

The Small Portable Sound Level Meter Reads 105

dBA Inside the Pump Room

How Long Could the Employee Stay in the Pump

Room Without Exceeding the Dose Equivalent

Noise Exposure of 90 dBA over an 8 hour TWA

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Employee Noise Exposure for 1 Hour at 105 dBA

Would Be the Dose Equivalent Exposure of 90 dBA

for an 8 Hr TWA

Administrative Controls

Likewise Limiting Employee Exposure Time to

Noise Can Help Reduce the Possibility of Hearing

Loss

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Hearing Conservation Amendment to PEL

1048714 Hearing Conservation Amendment (HCA) 1981ndash1983

1048714 Recognition that PEL was not protective

ndashAction level = 50 of PEL = hearing conservation program

require

ndashCriteria level = 90 dBA

ndashThreshold level = 80 dBA

ndashExchange rate = 5 dBA

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Table 1 presents permitted exposure times for various

noise levels

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

To calculate a permissible duration that is not addressed in this

table use the following equation

Where T is the permissible duration (in hours) and L is the

measured sound level (in dBA)

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

For mixed or varying-level noise the exposure may

not exceed a daily noise dose (Dt) of unity as

expressed in Eq (2)

where Dn is the actual duration of exposure at noise

level n and Tn is the noise exposure limit for noise

level n from Table 1

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Impact noises are generated by machines such as drop

hammers and punch presses and exposure to such noises must

not exceed a 140-dB peak sound pressure level

The peak sound pressure level also determines the maximum

number of impacts per day that an employee may be exposed

to as indicated in Table 2

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

If an employee is exposed to both steady noise and impulsive

noise throughout the day the combined effect can be handled

quite simply

For predictive purposes one needs to treat the ratio of the

number of impacts Nn at a given peak sound pressure level to

the maximum number of impacts allowed at that level and add

this fraction to the steady level calculation

The combined fractions from all sources should not exceed

unity

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Furthermore a hearing conservation program must be

implemented that will include at least an annual audiometric

test for employees exposed to noise levels greater than 85 dBA

for 8 h or whose noise dosage Dt meets or exceeds 05

Such a plan protects the workers by monitoring potential

deterioration of their hearing and protects employers from

unwarranted claims of damaged hearing prior to employment

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

Answer Borderline since dose = 100

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example

Given four hrs of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the PEL (Is this person

overexposed compared to PEL)

1048714 Answer No since dose lt100

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example

Given four hours of 90 dBA exposure two hours of 95

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Yes since dose is gt50

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example

Given four hours of 80 dBA exposure two hours of 90

dBA exposure and two hours of 85 dBA exposure

what is the dose using the HCA (Does this person

need to be in a hearing conservation program)

Answer Borderline since dose = 50

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Example 10 A group of factory workers are subjected to the following sound levels

daily

In addition they are exposed to 12 impulsive events from various

sources that have a sound level of 130 dB (peak) The workers are off-

site for lunch from 12 noon until 1 PM Determine if it is permissible for

the workers to work in this environment

The noise dosage from all events is

D = 316+1606+316+146+121000 = 0772

Therefore the workers can work in this environment but they should

have their hearing checked periodically because their exposure is greater

than 05

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Noise Exposure

In evaluating worker exposure to noise the industrial

hygienist should answer two main questions

1 Is the OSHA PEL met or exceeded

2 Does the worker need to be in the hearing

conservation program

Modern dosimeters calculate dose both ways

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

TLV and REL for Noise

The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as

follows

ndash Criteria level = 85 dBA

ndash Threshold level = 80 dBA

ndash Exchange rate = 3 dBA

American Conference of Industrial Hygienists (ACGIH)

The National Institute for Occupational Safety and Health (NIOSH)

These guidelines are

much more

protective

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Employee Noise Exposures Often Depend on How

Close They Are to the Noise Source

Distance

Noise Quickly Decreases as You Move Away from

the Noise Source

6 dB Double Distance Rule

Noise Will Decrease 6 dB Each Time You Double

the Distance (free field point source only)

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Reducing the Action Level for Extended Work shifts

If a worker works longer than an 8‐hour shift the action level

(AL) for hearing conservation is reduced proportionally from

85 dBA using the following equation

Example

A worker works a 1075‐hour shift in a car parts

manufacturing plant What will be the workerrsquos reduced AL

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Converting a Single Dose Measurement to an 8‐hour TWA Sound Level

A dose measurement can be converted to an 8‐hour TWA sound level

using the following equation

Where the dose is a percentage and the TWA is on an A‐weighted scale

Example

A factory hires a health and safety consultant to measure the noise

exposure of the workers The consultant writes a report that states that

workers are exposed to a 183 dose according to the general industry

standard Convert this dose into an 8‐hour TWA

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Sources of noise

The sources of noise may vary according to daily activities

They sources may be

Domestic (movement of tools cutting and shedding of

fruitsvegetables etc)

Natural (shores birdsanimal shouts wind movement sea

tide movement water falls etc)

Commercial (vendor shouts automobiles aero planes

marriages laboratory machinery etc)

Industrial (generator sets boilers plant operations trolley

movement transport vehicles pumps motors etc)

The noise levels of some of the sources are summarized at the

following table

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Typical noise levels of some point sources

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

-Any kind of loud music can cause temporary and permanent hearing loss

-Items such as iPods can cause much damage to the ear

-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Impacts of noise Why trouble about noise Often neglected noise induces a

severe impact on humans and on living organisms Some of

the adverse effects are summarized below

Annoyance (disturbance) It creates annoyance to the receptors

due to sound level fluctuations (variations) The a periodic

sound due to its irregular occurrences causes displeasure to

hearing and causes annoyance

Physiological effects The physiological features like

breathing amplitude blood pressure heart-beat rate pulse

rate blood cholesterol are effected

Loss of hearing Long exposure to high sound levels cause

loss of hearing This is mostly unnoticed but has an adverse

impact on hearing function

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Impacts of noise

Human performance The working performance of

workershuman will be affected as theyll be losing their

concentration

Nervous system It causes pain ringing in the ears feeling of

tiredness thereby effecting the functioning of human system

Sleeplessness It affects the sleeping there by inducing the

people to become restless and loose concentration and

presence of mind during their activities

Damage to material The buildings and materials may get

damaged by exposure to infrasonic ultrasonic waves and

even get collapsed

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Noise levels

As mentioned before the sound pressures perceived by

human range from 20 Pa to 200 Pa

This range is enormous (huge) As the intensity is

proportional to the square of the pressure its range of

variation is even greater

When a quantity varies over several orders of magnitudes it

is usually more helpful to look at its Logarithm and this is

what people working with noise do

A number of these logarithmic levels are used

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Noise levels

Intensity Level LI=Log10(II0) (in Bell)

where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing

These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo

Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore

LI=10 Log10(II0) (dB)

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Leq Prediction

- Developed by the Ontario Ministry of Transportation and

Communication

Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S

where Leq = energy equivalent sound level during 1 hr (dBA)

Vc = volume of automobiles (four tires only) (vehhr)

Vt = volume of trucks ( six or more tires) ( vehhr)

D = distance from edge of pavement to receiver (m)

S = average speed of traffic flow during 1 hr (kmhr)

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

If a new road is being planned it is not possible to assess

experimentally the impact of the new road on existing

neighboring areas

In this case noise calculations taking into account the most

common effects have been standardized to predict pressure

levels at some distance

See for example

httpwwwnplcoukacousticstechguidescrtn

Control of Noise Pollution

The techniques employed for noise control can be

broadly classified as

1 Control at source

2 Control in the transmission path

3 Using protective equipment

1- Noise Control at Source

The noise pollution can be controlled at the source of

generation itself by employing techniques like

A Reducing the noise levels from domestic sectors

B Maintenance of automobiles

C Control over vibrations

D Low voice speaking

E Prohibition on usage of loud speakers

F Selection of machinery

G Maintenance of machines

80

The domestic noise coming from radio tape

recorders television sets mixers washing

machines cooking operations can be minimized by

their selective and careful operation

By usage of carpets or any absorbing material the

noise generated from felling of items in house can

be minimized

81

Regular servicing and change of vehicles will

reduce the noise levels

Fixing of silencers to automobiles two wheelers

etc will reduce the noise levels

PH 0101 UNIT 1 LECTURE 9 82

The vibrations of materials may be controlled using

proper foundations rubber padding etc to reduce the noise levels caused by vibrations

PH 0101 UNIT 1 LECTURE 9 83

Speaking at low voices enough for communication

reduces the excess noise levels

84

By not permitting the usage of loudspeakers in the

habitant zones except for important meetings

functions

Now-a-days the urban administration of the metro

cities in India is becoming stringent on usage of

loudspeakers

85

Optimum selection of machinery tools or equipment

reduces excess noise levels

For example selection of chairs or selection of

certain machinery equipment which generate less

noise (sound) due to its superior technology etc is

also an important factor in noise minimization

strategy

86

Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels

For example it is a common experience that many

parts of a vehicle will become loose while on a rugged path of journey

If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger

2- Control in the transmission path

The change in the transmission path will increase the length of

travel for the wave and get absorbed refractedradiated in the

surrounding environment The available techniques are briefly

discussed below

1 Installation of barriers

1 Design of building

bull Installation of panels or enclosures

bull Green belt development

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

1- Noise Control at Source

The noise pollution can be controlled at the source of

generation itself by employing techniques like

A Reducing the noise levels from domestic sectors

B Maintenance of automobiles

C Control over vibrations

D Low voice speaking

E Prohibition on usage of loud speakers

F Selection of machinery

G Maintenance of machines

80

The domestic noise coming from radio tape

recorders television sets mixers washing

machines cooking operations can be minimized by

their selective and careful operation

By usage of carpets or any absorbing material the

noise generated from felling of items in house can

be minimized

81

Regular servicing and change of vehicles will

reduce the noise levels

Fixing of silencers to automobiles two wheelers

etc will reduce the noise levels

PH 0101 UNIT 1 LECTURE 9 82

The vibrations of materials may be controlled using

proper foundations rubber padding etc to reduce the noise levels caused by vibrations

PH 0101 UNIT 1 LECTURE 9 83

Speaking at low voices enough for communication

reduces the excess noise levels

84

By not permitting the usage of loudspeakers in the

habitant zones except for important meetings

functions

Now-a-days the urban administration of the metro

cities in India is becoming stringent on usage of

loudspeakers

85

Optimum selection of machinery tools or equipment

reduces excess noise levels

For example selection of chairs or selection of

certain machinery equipment which generate less

noise (sound) due to its superior technology etc is

also an important factor in noise minimization

strategy

86

Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels

For example it is a common experience that many

parts of a vehicle will become loose while on a rugged path of journey

If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger

2- Control in the transmission path

The change in the transmission path will increase the length of

travel for the wave and get absorbed refractedradiated in the

surrounding environment The available techniques are briefly

discussed below

1 Installation of barriers

1 Design of building

bull Installation of panels or enclosures

bull Green belt development

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

80

The domestic noise coming from radio tape

recorders television sets mixers washing

machines cooking operations can be minimized by

their selective and careful operation

By usage of carpets or any absorbing material the

noise generated from felling of items in house can

be minimized

81

Regular servicing and change of vehicles will

reduce the noise levels

Fixing of silencers to automobiles two wheelers

etc will reduce the noise levels

PH 0101 UNIT 1 LECTURE 9 82

The vibrations of materials may be controlled using

proper foundations rubber padding etc to reduce the noise levels caused by vibrations

PH 0101 UNIT 1 LECTURE 9 83

Speaking at low voices enough for communication

reduces the excess noise levels

84

By not permitting the usage of loudspeakers in the

habitant zones except for important meetings

functions

Now-a-days the urban administration of the metro

cities in India is becoming stringent on usage of

loudspeakers

85

Optimum selection of machinery tools or equipment

reduces excess noise levels

For example selection of chairs or selection of

certain machinery equipment which generate less

noise (sound) due to its superior technology etc is

also an important factor in noise minimization

strategy

86

Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels

For example it is a common experience that many

parts of a vehicle will become loose while on a rugged path of journey

If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger

2- Control in the transmission path

The change in the transmission path will increase the length of

travel for the wave and get absorbed refractedradiated in the

surrounding environment The available techniques are briefly

discussed below

1 Installation of barriers

1 Design of building

bull Installation of panels or enclosures

bull Green belt development

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

81

Regular servicing and change of vehicles will

reduce the noise levels

Fixing of silencers to automobiles two wheelers

etc will reduce the noise levels

PH 0101 UNIT 1 LECTURE 9 82

The vibrations of materials may be controlled using

proper foundations rubber padding etc to reduce the noise levels caused by vibrations

PH 0101 UNIT 1 LECTURE 9 83

Speaking at low voices enough for communication

reduces the excess noise levels

84

By not permitting the usage of loudspeakers in the

habitant zones except for important meetings

functions

Now-a-days the urban administration of the metro

cities in India is becoming stringent on usage of

loudspeakers

85

Optimum selection of machinery tools or equipment

reduces excess noise levels

For example selection of chairs or selection of

certain machinery equipment which generate less

noise (sound) due to its superior technology etc is

also an important factor in noise minimization

strategy

86

Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels

For example it is a common experience that many

parts of a vehicle will become loose while on a rugged path of journey

If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger

2- Control in the transmission path

The change in the transmission path will increase the length of

travel for the wave and get absorbed refractedradiated in the

surrounding environment The available techniques are briefly

discussed below

1 Installation of barriers

1 Design of building

bull Installation of panels or enclosures

bull Green belt development

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

PH 0101 UNIT 1 LECTURE 9 82

The vibrations of materials may be controlled using

proper foundations rubber padding etc to reduce the noise levels caused by vibrations

PH 0101 UNIT 1 LECTURE 9 83

Speaking at low voices enough for communication

reduces the excess noise levels

84

By not permitting the usage of loudspeakers in the

habitant zones except for important meetings

functions

Now-a-days the urban administration of the metro

cities in India is becoming stringent on usage of

loudspeakers

85

Optimum selection of machinery tools or equipment

reduces excess noise levels

For example selection of chairs or selection of

certain machinery equipment which generate less

noise (sound) due to its superior technology etc is

also an important factor in noise minimization

strategy

86

Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels

For example it is a common experience that many

parts of a vehicle will become loose while on a rugged path of journey

If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger

2- Control in the transmission path

The change in the transmission path will increase the length of

travel for the wave and get absorbed refractedradiated in the

surrounding environment The available techniques are briefly

discussed below

1 Installation of barriers

1 Design of building

bull Installation of panels or enclosures

bull Green belt development

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

PH 0101 UNIT 1 LECTURE 9 83

Speaking at low voices enough for communication

reduces the excess noise levels

84

By not permitting the usage of loudspeakers in the

habitant zones except for important meetings

functions

Now-a-days the urban administration of the metro

cities in India is becoming stringent on usage of

loudspeakers

85

Optimum selection of machinery tools or equipment

reduces excess noise levels

For example selection of chairs or selection of

certain machinery equipment which generate less

noise (sound) due to its superior technology etc is

also an important factor in noise minimization

strategy

86

Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels

For example it is a common experience that many

parts of a vehicle will become loose while on a rugged path of journey

If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger

2- Control in the transmission path

The change in the transmission path will increase the length of

travel for the wave and get absorbed refractedradiated in the

surrounding environment The available techniques are briefly

discussed below

1 Installation of barriers

1 Design of building

bull Installation of panels or enclosures

bull Green belt development

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

84

By not permitting the usage of loudspeakers in the

habitant zones except for important meetings

functions

Now-a-days the urban administration of the metro

cities in India is becoming stringent on usage of

loudspeakers

85

Optimum selection of machinery tools or equipment

reduces excess noise levels

For example selection of chairs or selection of

certain machinery equipment which generate less

noise (sound) due to its superior technology etc is

also an important factor in noise minimization

strategy

86

Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels

For example it is a common experience that many

parts of a vehicle will become loose while on a rugged path of journey

If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger

2- Control in the transmission path

The change in the transmission path will increase the length of

travel for the wave and get absorbed refractedradiated in the

surrounding environment The available techniques are briefly

discussed below

1 Installation of barriers

1 Design of building

bull Installation of panels or enclosures

bull Green belt development

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

85

Optimum selection of machinery tools or equipment

reduces excess noise levels

For example selection of chairs or selection of

certain machinery equipment which generate less

noise (sound) due to its superior technology etc is

also an important factor in noise minimization

strategy

86

Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels

For example it is a common experience that many

parts of a vehicle will become loose while on a rugged path of journey

If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger

2- Control in the transmission path

The change in the transmission path will increase the length of

travel for the wave and get absorbed refractedradiated in the

surrounding environment The available techniques are briefly

discussed below

1 Installation of barriers

1 Design of building

bull Installation of panels or enclosures

bull Green belt development

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

86

Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels

For example it is a common experience that many

parts of a vehicle will become loose while on a rugged path of journey

If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger

2- Control in the transmission path

The change in the transmission path will increase the length of

travel for the wave and get absorbed refractedradiated in the

surrounding environment The available techniques are briefly

discussed below

1 Installation of barriers

1 Design of building

bull Installation of panels or enclosures

bull Green belt development

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

2- Control in the transmission path

The change in the transmission path will increase the length of

travel for the wave and get absorbed refractedradiated in the

surrounding environment The available techniques are briefly

discussed below

1 Installation of barriers

1 Design of building

bull Installation of panels or enclosures

bull Green belt development

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

88

Installation of barriers between noise source and receiver can attenuate the noise levels

The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

PH 0101 UNIT 1 LECTURE 9 89

R D

Source Receiver

Barrier

Barrier close to source

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

D

Barrier

Receiver

Source

R

At very large distances the barrier becomes less effective because

of the possibility of refractive atmospheric effects

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

91

A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver

The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

Climate

Easy in installation

Durability - resistance to degradation from compression

moisture decomposition etc

Easy of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

Approximate reduction of outside noise provided by typical exterior wall construction

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

Hardwood

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

Softwood

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

Fiberglass rigid panel

Polystyrene Cementitious foam

Air-entrained concrete

Polystyrene Cementitious foam

Air-entrained concrete

Example 11

What barrier dimensions are necessary in order that

the barrier provide 20 dB attenuation at 500 HZ

From fig (next slide) we see that H2R must be at

least 10 ft in order to achieve the desired attenuation

This can be accomplished by selecting different values

for H and R for example

H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R

= 30 ft etc

104

Green belt development can attenuate the sound

levels

The degree of attenuation varies with species of

greenbelt

The legal regulations direct the industries to develop

greenbelt four times the built-up area for attenuation

of various atmospheric pollutants including noise

PH 0101 UNIT 1 LECTURE 9 105

Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise

The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following

(a) Job rotation (b) Exposure reduction (c) Hearing protection

106

By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced

(b) Exposure reduction

The schedule of the workers should be planned in such a

way that they should not be over exposed to the high noise levels

(c) Hearing protection

Equipment like earmuffs ear plugs etc are the commonly

used for hearing protection Attenuation provided by ear-

muffs vary widely in respect to their size shape seal material etc

Noise Management Strategy

Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)

where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)

Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values

THE END

HAVE A NICE DAY

104

Green belt development can attenuate the sound

levels

The degree of attenuation varies with species of

greenbelt

The legal regulations direct the industries to develop

greenbelt four times the built-up area for attenuation

of various atmospheric pollutants including noise

PH 0101 UNIT 1 LECTURE 9 105

Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise

The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following

(a) Job rotation (b) Exposure reduction (c) Hearing protection

106

By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced

(b) Exposure reduction

The schedule of the workers should be planned in such a

way that they should not be over exposed to the high noise levels

(c) Hearing protection

Equipment like earmuffs ear plugs etc are the commonly

used for hearing protection Attenuation provided by ear-

muffs vary widely in respect to their size shape seal material etc

Noise Management Strategy

Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)

where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)

Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values

THE END

HAVE A NICE DAY

PH 0101 UNIT 1 LECTURE 9 105

Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise

The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following

(a) Job rotation (b) Exposure reduction (c) Hearing protection

106

By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced

(b) Exposure reduction

The schedule of the workers should be planned in such a

way that they should not be over exposed to the high noise levels

(c) Hearing protection

Equipment like earmuffs ear plugs etc are the commonly

used for hearing protection Attenuation provided by ear-

muffs vary widely in respect to their size shape seal material etc

Noise Management Strategy

Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)

where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)

Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values

THE END

HAVE A NICE DAY

106

By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced

(b) Exposure reduction

The schedule of the workers should be planned in such a

way that they should not be over exposed to the high noise levels

(c) Hearing protection

Equipment like earmuffs ear plugs etc are the commonly

used for hearing protection Attenuation provided by ear-

muffs vary widely in respect to their size shape seal material etc

Noise Management Strategy

Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)

where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)

Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values

THE END

HAVE A NICE DAY

Noise Management Strategy

Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)

where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)

Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values

THE END

HAVE A NICE DAY

Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)

where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)

Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values

THE END

HAVE A NICE DAY

THE END

HAVE A NICE DAY