Noise Control Practices

Dr. Wesam Al Madhoun

Noise

Before We Discuss Noise Control Let’s Review Some Noise Concepts

Noise Measurements Noise Levels are Expressed as Decibels (dB)

DEVICEdBAComputer37 - 45

Refrigerator40 - 43

Cloths Dryer56 – 58

Garbage Disposal76 - 83

Vacuum Cleaner84 - 89

Leaf Blower95 - 105

Circular Saw100 - 104

1+1+1 Does Not Equal to 3

The Decibel is a Logarithmic Unit of Measure So We Can’t Simply Add Numbers.

“Shake and Roll”

How We Perceive Noise

High Frequency Noise

Power Tools, Saws, Grinders

Other High RPM Equipment

Sudden Release of Pressure

High Frequency Noises Deflect Easier, Are Easier to Shield, Are Easier to Insulate.

Low Frequency Noise

Power Presses

Pumps, Compressors

Other Low RPM Equipment

Low frequency Noises Can Travel Around and Through Objects and Are Harder to Shield and Absorb

Harmful Effects

Harmful Effects of Noise Are Related to the Noise Dose

Is the Noise Harmful?

Ask Yourself:How Loud, How Long, How Many Times?

Noise Dose is a Combination

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)

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%

First Rule of Thumb

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

Equivalent Dose of 90 dBA Over an 8 Hour TWA Period

95 dBA over 4 Hour TWA Period

100 dBA over 2 Hour TWA Period

105 dBA over 1 Hour TWA Period

110 dBA over ½ Hour TWA Period

Duration (How Long)

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

Example

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?

Answer

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

Watch Where You’re Standing

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)

6 dB Rule Would Not Apply

6 dB Rule Would Not Apply

Distance From the Noise Source

Is It Possible to Move the Employee Workstation or the Noise Source?

Moving the Employee or the Noise Source Doesn’t Eliminate the Loud Noise, it Just Reduces the Employee Exposure to it!

Think Out Loud

In Moving the Source, Have You Created a Problem for Someone Else?

Isolation Methods

Can You Isolate the Noise Source or The Employee From the Noise Source?

Enclosing the Employee

The Cab of Heavy Earth Moving Equipment

is a Good Example. They are Insulated (and

Air Conditioned).

Isolation Methods

Install Barriers Between the Employee

and Noise Source

Enclose the Noise Source

Enclose the Employee

Think Out Loud

Be Careful When Constructing Barriers or Enclosures.

Noise May be Deflected Backwards Off the Barriers or the Walls of the Enclosure Which Can Increase the Noise Intensity on the Noise Source Side.

Employees who Must Service Equipment or Conduct Work in Those Areas May Now be Exposed to Greater Noise than Before

Deflection of Sound Waves in Enclosure Creates Louder Noise

Noise Absorbing Material

The GoodNoise is Absorbed, It’s Gone, It Wouldn’t Bother Anyone Anymore

High Frequency Noises are Easier to Absorb

The Bad

Some Types Can be Fragile

Some Types Can be Hard to Clean

Some Can Be Expensive

The Ugly

Some Types Can Be Very Expensive

Some Types Won’t Hold Up to Chemicals or Moisture

Some Types Can be Combustible

Climate

Ease of installation

Durability - resistance to degradation from

compression, moisture, decomposition, etc.

Ease of replacement at end of life

Cost effectiveness

Toxicity

Flammability

Environmental impact and sustainability

Consideration of materials used

Brick

Glass

Hardwood

Softwood

Fiberglass rigid panel

PolystyreneCementitious foam

Air-entrained concrete

Transmitting Vibration

Noise and Vibration Can Be

Transmitted to Other Surfaces Which

Then also Transmits Noise

Controlling Noise Generated by Vibration Sources

Springs, or Isolation Material under Motors and Large Equipment

Ensure Plates, Covers, Doors, and Access Panels are Securely Attached

Bent or Warped Shafts on Motors and Fans Can Create Vibration

Bad Bearings, Flywheels, Pulleys, Fan Blades, and Belts

By the Way

Poor Maintenance Can Be a Major

Source of Noise Exposure and One

Which is Often Consider Economically

Feasible.

Controlling Noise Created By Released Air

Muffler systems on Pneumatic Equipment When Available

Reduce Air Pressure if Possible

Discourage the Use of Compressed Air for Cleaning Purposes

You May Not Be The First Person To Ask

Contact the Manufacturer of the

Equipment and Request Assistance

in Determining Ways to Help

Decrease Noise Output of the

Machines

Hearing Protection

Hearing Protection is not a Noise Control Method

Hearing Protection does not Reduce Employee Noise Exposure,

It Reduces the Potential Harm Which Could Otherwise Result in an Unprotected Employee

Hearing Protectors

Like Respirators, They are Only Effective if Used Properly

Ear Plugs and Other Types of Hearing Protection Have Limitations on How Much Protection They Can Provide

Noise Management Strategy

The techniques employed for noise control can be broadly classified as:

Control at source

Control in the transmission path

Using protective equipment.

Noise Control at Source

Reducing the noise levels from domestic

sectors:

The domestic noise coming from radio, tape

recorders, television sets, mixers, washing machines,

cooking operations can be minimized by their

selective and judicious operation.

By usage of carpets or any absorbing material, the

noise generated from felling of items in house can be

minimized.

Maintenance of automobiles:

Regular servicing and tuning of vehicles will reduce the noise levels.

Fixing of silencers to automobiles, two wheelers etc., will reduce the noise levels.

Control over vibrations:

The vibrations of materials may be controlled using proper foundations, rubber padding etc. to reduce the noise levels caused by vibrations.

Low voice speaking: Speaking at low voices enough for communication reduces the excess noise levels.

Prohibition on usage of loud speakers: By not permitting the usage of loudspeakers in the habitant zones except for important meetings / functions.

Selection of machinery: Optimum selection of machinery tools or equipment reduces excess noise levels.

Maintenance of machines: Proper lubrication 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 driver/passenger.

Similarly is the case of machines. Proper handling and regular maintenance is essential not only for noise control but also to improve the life of machine.

Control in the transmission path

The change in the transmission path will increase the length of travel for the wave and get absorbed/refracted/radiated in the surrounding environment.

Installation of barriers:

Installation of barriers between noise source and receiver can attenuate the noise levels.

For a barrier to be effective, its lateral width should extend beyond the line-of-sight at least as much as the height.

The barrier may be either close to the source or receiver, subject to the condition that, R <<D or in other words, to increase the traverse length for the sound wave.

It should also be noted that, the presence of the barrier itself can reflect sound back towards the source.

At very large distances, the barrier becomes less effective because of the possibility of refractive atmospheric effects.

Design of building: The design of the building incorporating the use of suitable noise absorbing material for wall/door/window/ceiling will reduce the noise levels.

The approximate reduction of outside noise levels using typical exterior wall construction is given at Table 6.

Green belt development: The degree of attenuation varies with species of greenbelt.

The typical attenuation of noise levels by trees is presented at Fig. 7 (a) and (b).

The statutory regulations direct the industry to develop greenbelt four times the built-up area for attenuation of various atmospheric pollutants, including noise.

Using protection equipment

Protective equipment usage is the ultimate step in noise control technology, i.e. after noise reduction at source

and/or after the diversion or engineered control of transmission path of noise.

The first step in the technique of using protective equipment is to gauge the intensity of the problem, identification of the sufferer and his exposure to the noise levels.

The usage of protective equipment and the worker's exposure to the high noise levels can be minimized by -:

Job rotation: By rotating the job between the workers working at a particular noise source or isolating a person, the adverse impacts can be reduced.

Exposure reduction: Regulations prescribe that, noise level of 90 dB (A) for more than 8 hr continuous exposure is prohibited.

Persons who are working under such conditions will be exposed to occupational health hazards.

The schedule of the workers should be planned in such a way that, they should not be over exposed to the high noise levels.

Hearing protection: Equipment like earmuffs, ear plugs etc. are the commonly used devices for hearing protection.

Attenuation provided by ear-muffs vary widely in respect to their size, shape, seal material etc.

Literature survey shows that, an average noise attenuation up to 32 dB can be achieved using earmuffs.

Traffic Control Measures

Reducing road traffic noise at source:(a)imposing permissible noise emission limits;

(b) promoting the use of public transport; and

(c) cracking down illegal vehicle modifications such as muffler alterations

Land use planning:(a)zoning land and planning urban projects with the consideration of the noise factor;

(b) building bypasses and ring roads; and

(c) establishing buffer zones on each side of a road.

Resurfacing roads with low-noise materials:

Resurfacing roads with low-noise materials to reduce noise from tire friction.

Generally speaking, low-noise pavement can attain a reduction of noise from 3 dB(A) to 5 dB(A).

Installing double-glazed windows and air-conditioning for the affected residents

Adopting advanced construction methods

employing a jointless construction method for elevated roads and bridges; and

installing sound-absorbing panels on the underside of elevated roads.

Prohibition of certain vehicle types (usually trucks)

from a particular route or restricting vehicles from

operating during noise sensitive times of the day.

The prohibition of trucks from a major roadway can

produce up to an 8 to 10 dB reduction in noise, at

times providing an adequate traffic management

abatement measure.