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Work environment

Noise

Why it is important problem?

1.7 million workers in the U.S. between 50-

59 years of age have compensable noise-

induced hearing loss

About 17% of the working population are

employed in jobs with noise exposure higher

than the OSHA standard of 85 dBA

In Poland ~13 milion citizens are in risk

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Occupations under hazardous conditions in Poland,

2011

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Sound

Sound

Normal Atmospheric Pressure

Sound

Pressure

A pressure wave traveling through air, water or othermedia that the human ear can detect.

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Sound radiates outward from the source

in all directions and the sound intensify

diminishes with distance from the source

Sound characteristics

Frequency

Number of times per

second a vibrating

body traces one

complete cycle of

motion

Cycles/second =

Hertz ( Hz) = f

Sound chaaracteristics

Wavelength (λ)

Distance measured between two analogous

points on two successive parts of a wave

Distance a sound wave travels in one cycle

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Sound characteristics

Velocity (c)

The speed at which analogous pressure points on

successive parts of a sound wave pass a given point

Speed of sound is always equal to the product of

wavelength and the frequency

c = f * λ

Speed of sound

344 m/s in air

1433 m/s in water

3962 m/s in wood

5029 m/s in steel

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Sound characteristics

Sound Pressure Level (Lp)

the sound pressure referenced to 20 µPa,

which is the threshold of hearing at a

reference frequency of 1000Hz

Unit: decibel [dB]

Lp = 10 log (p/p0)2

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Decibel

One dB is the minimum difference in

loudness that is usually perceptible

By definition, the decibel is a dimensionless

unit used to express the logarithm of the

ratio of a measured quantity to a reference

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Source

Threshold of Hearing (TOH)

Rustling Leaves

Whisper

Normal Conversation

Busy Street Traffic

Vacuum Cleaner

Large Orchestra

Walkman at Maximum Level

Front Rows of Rock Concert

Threshold of Pain

Intensity

Level

0 dB

10 dB

20 dB

60 dB

70 dB

80 dB

98 dB

100 dB

110 dB

130 dB

# of Times

Greater Than

TOH

100

101

102

106

107

108

109.8

1010

1011

1013

Military Jet Takeoff 140 dB 1014

Instant Perforation of Eardrum 160 dB 1016

Distance Vs Loudness (db)

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65

70

75

80

85

90

0 1 2 3 4 5 6 7 8 9 10

Distance from Origin

Lo

ud

ness (

db

)

How Much Does the Sound Intensity

Diminish with Distance from the Source?

Distance 1 or D1

Distance 2 or D2

The Change in the Decibels from D1 to D2 is 20 * log (D2/D1)

When the distance doubles, the decline is ~ 6 db

Why Does the Sound not Decline as

Computed?

Sound is reflected from

the concrete floor

Sound is reflected from

the block walls

Sound is reflected from

other objects

Hearing

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Hearing sense functions

Main defense sense – receive far signals independly

from their layout

Localize pottentally dangerous objects in space

(direction and distance)

Specific sounds alarm for the whole organismus

(„fight or escape”)

Homing system for sight

Interpersonal communication

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HOW DO WE HEAR?

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SOUND RECEPTORS

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Audiogram

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Noise

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Noise

Any unwanted sound or vibratory energy

Noise Induced Hearing Loss

Exposure to noise causes a

loss of sensitivity to high

frequency (high pitch)

sound

Continued exposure

results in damage to mid

frequency region

One can experience

progressive high

frequency hearing loss

and not be aware of it

until it becomes severe

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Noise is possibly annoying,

but it is not physically painful

The effects of noise on hearing loss

occur slowly, unnoticed from day to

day exposure to equipment

surrounding workers

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Fellow Workers on most construction projects

also do not wear hearing protection

Hearing protection might be regarded

as a bother to many construction

workers

Noise measuring

A weighted scale

Gives a single number measure of noise level by

integrating sound levels at all frequencies

Gives a scale for noise level as experienced or

perceived by the human ear

Sound level meter – dosimeter - Measures and

stores sound level measurements and

integrates these measurements over time,

providing an average noise exposure reading for

a given period of time

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Noise classification

infrasonic (2-50 Hz)

Audible (20Hz – 10 000 Hz)

ultrasonic (10-100 kHz)

Noise classification

Continous

Impact

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Noise classification

industrial

municipal

Traffic

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Industrial noise

Energetics

Wood industry

Stone treatment

Trade and servises

Metal industry

Mining

Entertainment places (i.e. clubs)

Food industry

Other

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Acoustic map of Wroclaw

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Noise influence on human organismus

Impact on hearing organ

Adaptation

Fatigue

Acoustic trauma

Physiological impact

Psychological – anxiety disorders,

deconcentration, longer reaction time

Hormonal

Equilibrium disorders

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Hearing loss

Prolonged exposure to sound

levels greater than 85 decibels

will result in hearing loss

Occupational hearing loss is the hearing

impairment of one or both ears, partial or

complete, that results from one’s employment

Acoustic trauma – damage to the sensorineural

elements of the inner ear due to injury

Noise-induced hearing loss – cumulative permanent

sensorineural hearing loss

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Damaging of Corti

aparatus

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Noise Exposure Factors

Intensity Loudness

Frequency

Duration Length of exposure

Distance from the source

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Noise Exposure Standards

Occupational Safety And Health

Administration’s(OSHA) Noise Standard,

Code of Federal Regulations Section 29, Part

1910 Sub Part 95 (CFR 29 1910.95)

Permissible Exposure Limit (PEL) - 90 dB

Polish law – 85 dB

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How can we easy estimate the noise

level? Rule of Thumb

If you have to raise your voice to be heard

by someone less than 1 m away, than you

need hearing protection

Signs of risk

Ringing in the ears

the need to shouting to the co-worker

temporary hearing loss

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Doubling Rate

The number of decibels of continuous noise

exposure which results in a halving of the

allowed exposure time

OSHA

8 hours at 90 dB

4 Hours at 95 dB

2 hours at 100 dB

1 hour at 105 dB

30 minutes at 110 dB

15 minutes at 115 dB

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Noise reduction methods

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Noise reduction methods

Technical

Emission reduction silent devices,

automatization, maintenance

Transmission reduction housings, screens, traps

Immission reduction personal hearing protection

Administrative

Law regulations

Organizational work time, breaks, workstation

layout

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Soundproofing housings

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Acoustic screens

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Acoustic screens and traps

Source of

noise

Reflecting

ceiling

Screen

Source of

noise

Sound

absorbing

material

Screen

Personal Hearing Protection

NRR - Noise Reduction Rating

In order to ensure maximum hearing

protection two variables are important:

the fit of the hearing protector

the importance of wearing the hearing protector

during the entire time the wearer is exposed to

excessive or dangerous noise levels

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Personal hearing protection

Types

Canal Caps

Earplugs

Ear Muffs

NRR of 22 NRR of 29 NRR of 30

DOUBLING UP!

Use of insert earplugs and circumaural earmuffs together

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Active method

Additional sound

source

Noise

Silence

Basic principles

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1. Reduce the noise level of the

source itself

Identify why the machine makes noise

Examine the possibility of making design

changes

1. Maintenance

2. Substitution of materials (plastic for metal)

3. Substitution of equipment

Maintenance

replacement or adjustment of worn or loose

parts

balancing of unbalanced equipment

lubrication of moving parts

use of properly shaped and sharpened

cutting tools

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Substitution of equipment

electric for pneumatic (e.g. hand tools);

stepped dies rather than single-operation

dies

rotating shears rather than square shears

hydraulic rather than mechanical presses

presses rather than hammers

belt conveyors rather than roller conveyors

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2. Enclose the source

This stops the sound emission at the source

Make sure the reduction is sufficient

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3. Increase the distance between the

source and nearby people

This will help to decrease the sound before

it reaches the people around it

Noise levels decrease approximately with

the square of the distance between the

source and the receiver

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4. Place sound-absorbing and

reflecting barriers in the noise path

Absorbing materials will help reduce the

sound level energy

Reflecting barriers will direct some of that

energy away from surrounding personnel so

that the sound wave will need to go a large

distance before encountering people

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