NOISE Pollution (in reference to Environmental Science, M.Sc. Program, TU)

Sunil Babu Khatry

2010

© 2010. All rights reserved. This revised lecture note contains the vital information that is the property of the instructor and institution. No part of the inside may be reproducible by the unauthorized recipients in any versions without permission.

Table of Contents

1. Basic Properties of Sound ________ 1

1.1 Wave Characteristics of Sound / Noise

(Sound Physics - Acoustics) _____________ 1

1.1.1 Law of Superposition _____________ 1

1.1.2 Diffraction ______________________ 2

1.1.3 Interference _____________________ 2

1.1.4 Inverse - Square Law ______________ 2

1.1.5 Doppler Effect ___________________ 2

1.2 Sound Pressure __________________ 3

1.2.1 RMS Nature of Sound _____________ 3

1.3 Sound Intensity __________________ 3

1.4 Sound Wave ____________________ 4

1.4.1 Waveform ______________________ 4

1.5 Categories of Waves ______________ 5

1.6 Noise __________________________ 6

1.6.1 Types of Noise ___________________ 6

1.7 Sound Pressure & Intensity ________ 7

1.8 Sound Pressure Level _____________ 7

1.9 Sound Intensity Level _____________ 7

1.10 Sound Pressure Level, Decibel

Approach ____________________________ 8

1.10.1 Sound Addition & Subtraction _______ 9

1.10.2 Other Units of Sound Pressure ______ 9

1.11 Psycho - Acoustics (Sound & Human

Ear Perception) ______________________ 12

1.12 Relationship between Indoor and

Outdoor Levels ______________________ 12

2. Sound Propagation Characteristic _ 12

2.1 Geometrical Spreading __________ 13

2.2 Meteorological Parameters & Sound

Propagation _________________________ 13

2.2.1 Attenuation ____________________ 14

Temperature Effect __________________ 14

Distance Attenuation _________________ 14

Ground Surface Effects _______________ 14

Trees Attenuation ___________________ 14

Topography Effect ___________________ 14

Reflecting Surfaces and Noise Barriers ___ 14

3. Noise Measurements & Monitoring 15

3.1 Selection of Noise Descriptors _____ 16

3.2 Methods ______________________ 16

3.3 Acoustic Weighting Networks _____ 16

3.4 Measurement Objectives _________ 17

General ___________________________ 17

OSHA Concept ______________________ 17

3.5 General Noise Inspection Data _____ 17

3.5.1 General Information _____________ 17

3.5.2 Health Inspection Data ___________ 17

3.5.3 Machine and / or Process Data. ____ 18

3.5.4 Building Data ___________________ 18

3.5.5 Employer Data __________________ 18

3.5.6 Hearing Loss Data _______________ 18

3.5.7 Additional Information Requirement 19

Preliminary Information ______________ 19

Work Analysis Information ____________ 19

3.6 Selection of Measurement Positions 20

3.6.1 Outdoor Measurement ___________ 20

3.6.2 Measurement around the Building _ 20

3.6.3 Measurements inside the Building __ 20

3.6.4 Measurement in Work Environments 20

3.7 Instrumentation ________________ 20

3.7.1 Audiometry ____________________ 20

3.7.2 Noise Dosimeter ________________ 22

3.7.3 Sound Level Meter ______________ 25

3.7.4 Octave Band Analyzers ___________ 26

3.8 Instrumental Performance (Effects of

the Environment) _____________________ 27

3.8.1 Temperature ___________________ 27

3.8.2 Humidity ______________________ 27

3.8.3 Atmospheric Pressure ____________ 27

3.8.4 Wind or Dust ___________________ 27

3.8.5 Magnetic Fields _________________ 28

4. Environmental Noise Sources _____ 28

4.1 Transportation Noise ____________ 28

4.1.1 Road Vehicles __________________ 28

4.1.2 Railway ________________________ 28

4.1.3 Aircraft ________________________ 28

4.2 Industrial Noise ________________ 29

4.3 Domestic Noise _________________ 30

4.4 Construction and Other Activities __ 31

4.5 Parks & School Playing Fields ______ 31

4.6 Discotheque Noise ______________ 31

5. Noise Analysis _________________ 31

5.1 Equivalent Sound Pressure Level, (LAeq,

T) 31

5.2 Day - Night Average Sound Pressure

Level, (Ldn) __________________________ 32

5.3 Sound Exposure Level, (SEL) _______ 32

5.4 Percentile Level, (L) _____________ 34

5.5 Traffic Noise Index ______________ 34

5.6 Noise Pollution Level, (NPL) _______ 35

5.7 Airport Noise Measurement ______ 35

6. Noise Criteria (NC) Curves _______ 35

7. Noise Control & Abatement Measures

38

7.1 Source Control _________________ 39

7.2 Transmission Path Control ________ 42

7.2.1 Acoustic Barriers & Panels _________ 43

7.2.2 Mufflers and Silencers ____________ 45

7.2.3 Absorbing Materials and Acoustic

Lining 45

7.2.4 Absorber _______________________ 46

7.2.5 Damping _______________________ 46

7.2.6 Diffusion _______________________ 46

7.2.7 Anechoic Chamber _______________ 47

7.3 Receiver Control ________________ 47

7.3.1 Hearing Protectors _______________ 47

7.4 Traffic Noise Abatement _________ 49

7.4.1 Noise Barriers ___________________ 49

7.4.2 Land Use Planning Measures _______ 49

7.4.3 Alternatives to Noise barriers: _____ 49

7.5 Response of Noise Pollution Control in

Nepal through Legislation, Plan & Policies _ 49

7.5.1 Related Legislation ______________ 50

8. Health Effects of Noise __________ 53

8.1 Human Ear _____________________ 54

8.1.1 Hearing and Mechanism of Hearing

Loss 54

8.1.2 Outer and Middle Ear Mechanism _ 54

8.1.3 Cochlear Mechanism ____________ 54

8.1.4 Degrees of Hair Cell Injuries_______ 54

8.2 Noise - Induced Hearing Effect _____ 55

8.3 Sensory Effects _________________ 56

8.4 Interference with Speech

Communication ______________________ 57

8.5 Sleep Disturbance Effects _________ 59

8.6 Psycho Physiological Effects _______ 59

8.7 Mental Health effects ____________ 60

8.8 Performance Effects _____________ 60

8.9 Effects on Residential Behavior and

Annoyance __________________________ 60

9. Criteria for Continuous and

Intermittent Noise __________________ 61

9.1 ISO 1999-1990 __________________ 61

9.2 Criteria for Impulse Noise _________ 62

9.2.1 Control of noise exposure in

workplaces. (Policy and guidance documents of

the International Labour Organization (ILO)): _ 62

9.2.2 Occupational Exposure Levels reported

and recommended by I-INCE ______________ 63

9.2.3 Occupational Exposure Levels

recommended by NIOSH __________________ 63

9.2.4 ACGIH Recommendation _________ 64

Noise Pollution, 513 - Page 1

1. Basic Properties of Sound

Community noise (called environmental

noise, residential noise or domestic noise) is

defined as noise emitted from all sources

except noise at the industrial workplace.

Main sources of community noise include

road, rail and air traffic; industries;

construction and public work; and the

neighbourhood. The main indoor noise

sources are ventilation systems, radio /

television media, office machines, home

appliances and neighbours.

In contrast to many other environmental

problems, noise pollution continues to grow

and an increasing number of complaints

accompany it from people exposed to the

noise. The growth in noise pollution is

unsustainable because it involves direct, as

well as cumulative, adverse health effects. It

also adversely affects future generations, and

has socio-cultural, aesthetic and economic

effects.

When noise levels change 3dB(A) or less, the

change is considered barely perceptible to

human hearing in a field situation. A 5dB(A)

change in noise level is clearly noticeable. A

10dB(A) change in noise levels is perceived as

a doubling or halving of noise loudness, and a

20dB(A) change is considered a dramatic

change in loudness1.

1.1 Wave Characteristics of Sound / Noise (Sound

Physics - Acoustics)

Noise is defined as "disagreeable or

undesired sound" or other disturbance.

Sound and noise constitute the same

phenomenon of atmospheric pressure

fluctuations about the mean atmospheric

pressure where the differentiation is quietly

subjective matters, i.e. sound to one person

literally be noise to others. Sound (or noise)

is the result of pressure variations, or

oscillations, in an elastic medium (e.g., air,

water, solids), generated by a vibrating

1 Highway Traffic Noise Assessment Summary State of

Alaska Department of Transportation and Public

Facilities, October 2006

surface, or turbulent fluid flow. Sound

propagates in the form of longitudinal (as

opposed to transverse) waves, involving a

succession of compressions and rarefactions

in the elastic medium. When a sound wave

propagates in air, the oscillations in pressure

are above and below the ambient

atmospheric pressure. Sound being to show

the wave characteristics like law of

superposition, diffraction, interferences,

inverse square law, etc.

1.1.1 Law of Superposition

According to the law when two or more

sound waves may propagate in the same

space simultaneously, the resultant sound

pressure variation at any point being the

algebraic sum of the instantaneous

Sunil Babu Khatry, Noise Pollution, 513 -Page, 2

pressure variations of each component

wave. Two waveforms combine in a

manner, which simply adds their

respective amplitudes linearly at every

point in time. Thus, a complex spectrum

can be built by mixing different Sine

Waves of various amplitudes. Fourier

analysis is a reverse case of addition.

Successive approximations of a saw tooth

wave by addition of harmonics with

amplitude inversely proportional to the

harmonic number.

1.1.2 Diffraction

Diffraction of sound wave is a phenomenon

of sound wave movement around an object

whose dimensions are smaller than or

about equal to the wavelength. As a result

of their capability of diffraction, low

frequency sounds are difficult to localize or

contain in an environment

High frequency sound (short wavelength)

do not diffracted around most obstacles

but are absorbed or reflected thereby

creating a sound shadow behind the object.

But, low frequency sounds have

wavelengths that are much longer than

most objects and barriers, and therefore

such waves pass around them undisturbed.

When the wavelength is similar to the

dimensions of the object (as with low

frequencies and buildings, or mid-range

frequencies and the head), the wave

diffracts around the object, using its edges

as a focal point from which to generate a

new wave front of the same frequency but

reduced intensity.

1.1.3 Interference

When sound waves from two different

sources at the same frequency strike one

another, pressure displacements occur

that are the sum and the difference of the

amplitude of the two waves.

Where the crests of one set of waves

coincide with the crests of another set, the

amplitude is increased. This is called

constructive interference (the lines

indicated by C on the diagram). Where the

crests of one set fall on the troughs of the

other, i.e. they are 180° out of phase, the

two will cancel one another and the

resulting amplitude is decreased. This is

called destructive interference or

cancellation (the lines indicated by D on

the diagram). Beats and phasing are

examples of interference results. The dead

spots occur when two waves of the same

frequency and amplitude travel in opposite

directions. Interference also causes ground

effect in outdoor situations.

1.1.4 Inverse - Square Law

The law elucidates that the mean - square

sound pressure level varies inversely as the

square of the distance from the source. The

general rule of thumb is that, under ideal

conditions (no reflecting surfaces or other

background sound or interference), a sound

level drops 6 dB for every doubling of the

distance from the source. If the two

distances in question are d1 and d2, then the

decibel difference DD is:

∆D = 10 log (d1/d2)2 = 20 log (d1/d2)

1.1.5 Doppler Effect

Diffr

action P

heno

men

on

Sunil Babu Khatry, Noise Pollution, 513 -Page, 3

In sound, a change of wavelength occurs when

the source has a translation motion.

For sound waves propagating in a medium,

the velocity of the observer and of the source is

relative to the medium in which the waves are

transmitted. The total Doppler effect may

therefore result from motion of the source,

motion of the observer, or motion of the

medium. The Doppler Effect is defined as “the

change in frequency of a wave that results

from an object‟s changing position relative to

an observer” (Gundersen). It states that “when

a sound is played, the precise sound that is

actually heard depends on if you are moving or

not” (Doppler Effect for Sound). This means

that in order to hear exactly the sound that is

being played, you must stand still and try not

to move. The second you move, the sound you

hear and the sound that is played will no

longer are the same thing. For the both cases

the same change of frequency for the same

speed of motion, provided this small compared

with the velocity of the waves.

1.2 Sound Pressure When a vibrating body moves in air, it

creates slight disturbances of the ambient

atmospheric pressure. The amplitude of

these pressure variations (i.e., their

maximum displacement from the ambient

atmospheric pressure) is called the sound

pressure variation, whereas the effective

pressure variation is 0.707. The oscillating

variations in sound pressure (called the

waveform of the sound) propagate in the

form of a sound wave.

When the amplitude of the vibrating body

is greatest, its velocity is zero (that is, it

has reached its outer limit of displacement

and is shortly motionless before returning

in the opposite direction). If the velocity is

zero, so is the pressure it exerts on the

medium (e.g. air) around it. Velocity (and

therefore pressure) is greatest mid-way

between the maximum displacement of the

vibrating body, and we can graph the

resulting relationship between amplitude

and sound pressure in the following way:

1.2.1 RMS Nature of Sound

Most sounds are not purely sinusoidal (purely

sine wave) vibrations. They vary in both

frequency and magnitude over time. The

RMS sound pressure is applied to quantify

their magnitude over a measurement time T.

The RMS sound pressure is obtained by

squaring the pressure (amplitude) at each

instant in time, summing the squared values

over the measurement time T, dividing by T

and taking the square root of the total, i.e.,

2PP rms

2

1

2

0

1

dttP

T

T

1.3 Sound Intensity The sound intensity is the energy

transmitted per unit time through a unit

area, thereby being a measure of the

magnitude of a sound. The unit of

measurement is the erg per second per

square centimetre, or the watt per square

meter. The threshold of hearing lies at 10-12

watts/m2, whereas the threshold of pain is

about 1 watt/m2.

The measurement of sound

24ππ

WI

Sunil Babu Khatry, Noise Pollution, 513 -Page, 4

intensity is its intensity level and is

measured logarithmically in decibels

because of the wide range of intensities

involved.

Sound intensity is proportional to the square

of the sound pressure, which, being easier to

measure is more commonly used as a basis

of sound measurement. Sound intensity in

free filed situations varies inversely as the

square of the distance from the sound

source.

1.4 Sound Wave

Sound is a mechanical energy from a

vibrating surface which spreads as spherical

or plane wave forms and is transmitted by a

cyclic series of compressions are rarefactions

of the sound transmitting media. The sound

results in a sound pressure longitudinal

wave that alternatively rises to a maximum

level.

Waves may be of two sorts, transverse and

longitudinal. While solids will transmit both

kinds, liquids and gases will transmit only

longitudinal waves and the study of sound

waves is thus largely concerned with this

type where the amplitude variations are in

the direction of propagation. Nevertheless,

as transverse waves are easier to display

graphically in two dimensions, sound waves

are usually shown as if they were for

instance on an oscilloscope (transverse

compression) and drops to a minimum level

(rarefaction). On striking the ear, it may be

heard as sound waves.

Sound pressure variation of a sine wave

showing the phase relationship between

pressure and particle displacement.

Amplitude (A) : the maximum

or minimum pressure.

Wavelength (λ) : the distance

between successive troughs or crests.

Period (T) : the time lapse between

successive peaks.

Frequency (f) : the number of

complete pressure variations or

cycles/second.

Relationship:

fP

1

f

c

Based on energy transmittance

characteristics they are categorized as

electromagnetic and mechanical waves. An

electromagnetic wave is a wave, which is

capable of transmitting its energy through a

vacuum whereas a mechanical wave is not

capable of transmitting its energy through a

vacuum.

The speed of propagation (c) of sound in air is

343m/s, at 20oC and 1 atmosphere pressure.

At other temperatures (not too different from

20oC), it may be calculated by using the

formula: C = 332 + 0.6Tc. Sound / noise results

from periodic disturbances of the air at room

temperature are propagated in air at a speed

of approximately 340m/s. In water (1500m/s)

and steel (5000m/s), the speed is much

greater.

1.4.1 Waveform

P

A

Press

Sunil Babu Khatry, Noise Pollution, 513 -Page, 5

The pattern of sound pressure S variation,

usually displayed as a two-dimensional

graph of pressure or amplitude against time.

For periodic waveforms, a single cycle or

period defines the waveform (also called

sound pressure function), particularly when

represented digitally. The simplest

waveform is the sine wave, since it has only

one frequency associated with it. More

waveforms that are complex can be

constructed from sine waves of various

frequencies by the law of superposition.

Common waveforms used in sound synthesis

are the triangle wave, square wave, saw

tooth wave and pulse wave. These audio

waveforms are often termed fixed waveforms

because of their lack of variation, whereas

acoustic waveforms are constantly varying.

The waveform represents the behaviour of the

sound in the time domain, and since its shape

is indicative of the frequency content of the

sound, waveform is sometimes used

synonymously with timbre, although not all

contributing factors to timbre can be

understood simply in terms of the waveform.

Examples: sine wave saw tooth wave, square

wave, triangle wave at 100 Hz and pulse wave

with a 1:4 duty cycle

1.5 Categories of Waves On the basis of the direction of the

movement of the individual particles of the

medium relative to the direction, waves are

categorized as transverse waves,

longitudinal waves, and surface waves 2. A

transverse wave is a wave in which particles

of the medium move in a direction

perpendicular to the direction, which the

wave moves, i. e. they are characterized by

particle motion being perpendicular to wave

motion. A longitudinal wave is a wave in

which particles of the medium move in a

direction parallel to the direction, which the

wave moves, i.e. they are always

characterized by particle motion being

parallel to wave motion. A surface wave is a

wave in which particles of the medium

undergo a circular motion. They are neither

transverse nor longitudinal waves.

2 Henderson, T. The Nature of a Wave, 2004

Sunil Babu Khatry, Noise Pollution, 513 -Page, 6

1.6 Noise

Noise can be defined as unwanted sound or

sound in the wrong place at the wrong time.

Noise is undesirable because it interferes

with speech and hearing, is intense enough

to damage hearing or is otherwise annoying.

The definition of noise as unwanted sound

implies that it has an adverse effect on

human beings and their environment,

including land structures, and domestic

animals. It also disturbs natural wildlife and

ecological systems. On the basis of acoustic

science, the sound level above 50dB (A) is

considered to be the noise. Under the basis of

various WHO reports, the observed sound

pressure levels are categorized according to

the following manner.

Category Level, (dB

A)

Uncomfortable > 100

Very high quality sound 80 - 99

Medium Sound 50 - 70

Silent sound 40

Daily maximum permissible noise

level

45 - 55

1.6.1 Types of Noise

Noise may be classified as steady, non-steady

or impulsive, depending upon the temporal

variations in sound pressure level. All

sounds are categorized in three major

classes,

Continuous sound (steady state)

Intermittent sound

Impulsive sound (impact)

A continuous sound is an uninterrupted

sound level that varies less than 5dBA

during the period of observation. The noise

of longer duration and low density such as

that from construction, traffic, a household

fan etc. are the typical examples of

continuous sound.

A continuous noise, which occurs

intermittently and has duration of more

than several seconds but then is

Pressure

40 dB

T

Duration

Duration

20 dB

T

Sunil Babu Khatry, Noise Pollution, 513 -Page, 7

interrupted for more than one second, is

intermittent noise, e.g., a dentist's drill.

A noise consisting of one or more bursts of

sound energy having a very short

duration, i.e., noise of short duration and

high density such as explosions, sonic

booms, artillery fire, hammering noise, etc

is impulsive noise. A more rigorous

classification of impulse sound would

require a change of sound pressure of

40dB(A) or more within 0.5 second with

duration of less than one second.

1.7 Sound Pressure & Intensity Sound intensity is a vector quantity and is

a measure of the rate at which work is

done on a conducting medium by an

advancing sound wave and thus the rate of

power transmission through a surface

normal to the intensity vector. It is

expressed as watts per square metre

(W/m2). In a free-field environment (no

reflected sound waves & well away from

any sound sources), the sound intensity is

related to the root mean square acoustic

pressure.

where ρc is the density

of air (kg/m3), and c is

the speed of sound

(m/sec). The quantity, ρc

is called the "acoustic impedance" and is

equal to 414 Ns/m³ at 20oC and one

atmosphere, P is rms sound pressure level in

pa and I is the acoustic intensity in watts per

square meter.

The rate at which energy transmitted by

sound waves is called the sound power (W)

and mathematically is obtained by

integrating the sound

intensity over an

imaginary surface

surrounding a source

in the specified frequency band.

For a sound producing uniformly spherical

waves (radiating equally in all directions)

in a non dissipative medium, the intensity

becomes, W = 4πr2I. Literally, I is

equivalent to P2, i.e. P2 = [W/4πr2] W/m2.

The sound pressure level at doubling the

distance from a point source decreases by

6dB.

1.8 Sound Pressure Level

Sound pressure level measures the

magnitude of the sound. It is a relative the

ratio between the actual sound pressure

and a fixed reference pressure. This

reference pressure is usually that of the

threshold of hearing which has been

internationally agreed upon as having the

value 0.0002 dynes/cm2. Sound pressure

level may be measured with a sound level

meter weighted according to a specific

frequency response pattern and termed as

sound level. Because the square of the

sound pressure is proportional to sound

intensity, SPL can be calculated in the

same manner and is measured in decibels.

;

Lp = 20log10Prms – 20log10Pref.

After substituting the internationally agreed

value of reference pressure level of [20µPa =

2*10-5Nm-2]. The minimum acoustic pressure

audible to the young human ear judged to be

in good health, and unsullied by too much

exposure to excessively loud sound, is

approximately 20 x 10-6Pa or 2 x 10-10

atmosphere [since 1 atm. = 101.3 x 103Pa],

Lp = 20log10Prms + 94dB

1.9 Sound Intensity Level The rate at which energy is transmitted by

sound waves is called the sound power (W)

measured in watts. The average sound

power per unit area normal to the

direction of propagation of a sound wave is

termed the acoustic or sound intensity (I).

So, the sound intensity level is defined as

Substituting an internationally agreed

reference intensity (Wo) of 10-12Wm-2 in the

above equation,

LI =10log10I + 120dB

2

0

2

10log10P

PLp

ref

rmsp

P

PL 10log20

rLLM

WP 2log10

Sunil Babu Khatry, Noise Pollution, 513 -Page, 8

=

=

= LW - 20 log r – 11, where, LW: sound power

level in dB for 10-12W. Similarly, for non

point sources, the reduction is 3dB for

doubling of distance. i.e,

where, = Sound power per meter .

1.10 Sound Pressure Level, Decibel Approach

Because the square of the sound pressure is

proportional to sound intensity, SPL can be

calculated in the same manner and is

measured in decibels (dB). The decibel is 1/10 th of Bel.

Sound power doesn't provide practical units

for sound or noise measurement due to it's

tremendous range and the human ear doesn't

respond linearly to increase in sound

pressure. The human responses are

essentially logarithmic. The sound pressure

level is a measure of the air vibrations that

make up sound. All sound pressures are

referenced to a standard pressure that

corresponds roughly to the threshold of

hearing at 1000Hz. So, the sound pressure

level indicates how much greater the

measured sound is than this threshold of

hearing. Sound pressure levels cannot be

added or averaged arithmetically

because they are measured on a

logarithmic scale.

Sound pressure level (SPL) is the

logarithmic ratio of the sound pressure to a

reference pressure (20µpa). The sound

pressure is converted to sound pressure level,

which is measured in decibel. The equation

for sound pressure level is as follows:

The table below can be used to find the

correction for distance such as in the case of

distances quoted in noise measurement

specifications, assuming ideal conditions. Take

the given distance on the left-hand column

and find the correction in the vertical column

under the distance for which the correction is

desired. Add the correction to the given level

to find the corrected level.

Table of sound levels L (loudness) and

corresponding sound pressure and sound

intensity

Sound

Sources

Examples

with

distance

Sound

Pressur

e

Level

Lp

dBSPL

Sound

Pressur

e p

N/m2 =

Pa

Sound

Intensity I

W/m2

Jet aircraft, 50

m away 140 200 100

Threshold of

pain

130 63.2 10

Threshold of

discomfort

120 20 1

Chainsaw, 1 m

distance

110 6.3 0.1

Disco, 1 m from

speaker

100 2 0.01

Diesel truck, 10

m away

90 0.63 0.001

Kerbside of

busy road, 5 m

80 0.2 0.0001

Vacuum

cleaner,

distance 1 m

70 0.063 0.00001

Conversational

speech, 1 m

60 0.02 0.000001

Average home 50 0.0063 0.0000001

Quiet library 40 0.002 0.00000001

Quiet bedroom

at night

30 0.00063 0.000000001

Background in

TV studio

20 0.0002 0.0000000001

0

2

10

4/log10

W

rW

2

0

2

10log10P

PLp

2

10

0

10 4log10log10 rW

W

8log10 rLLM

WP

MWL

Sunil Babu Khatry, Noise Pollution, 513 -Page, 9

Rustling leaves

in the distance

10 0.000063 0.00000000001

Threshold of

hearing

0 0.00002 0.000000000001

A decibel (dB) is a unit of measurement,

which indicates the relative amplitude of a

sound (pitch & loudness). The zero on the

decibel scale is based on the lowest sound

level that healthy, unimpaired human ear

can detect. Sound levels in decibels are

calculated on a logarithmic basis. An

increase of 10dB represents a ten-fold

increase in acoustic energy, while 20dB is

100 times more intense and 30dB is 1000

times more intense, etc.

1.10.1 Sound Addition & Subtraction

Two SPL measurements in decibels may be

combined with the aid of the following chart.

The difference in decibels between the two

readings is found on the upper scale, and the

corresponding correction appears opposite it

on the lower scale. This correction is added to

the higher SPL to give the combined

measurement. Multiple readings may be

combined by repeating this process. For

example, equal SPL readings (0 on top scale)

produce a 3.0 increase when combined. A 5 dB

difference (say between 60 and 65 dB)

produces a 1.2 dB increase (66.2 dB for the

same example). A 10 dB difference requires a

0.4 dB correction, and so on.

Subtraction of sound pressure level can be

made for the calculation of sound due to

specific activities or machine operation at

certain background sound pressure level,

where background noise must be subtracted

from total noise to obtain the sound produced

by a machine alone. The method used is

similar to that described in the addition of

levels.

1.10.2 Other Units of Sound Pressure

For perceived loudness (N) a unit is prescribed

as sone such that loudness is a subjective

measure of the sound pressure. It is also the

frequency based unit. At a frequency of 1kHz,

one phone is defined to be equal to 1dB of

sound pressure level LP above the nominal

threshold of hearing (20μPa = 2 * 10-5Pa). One

sone is equivalent to 40 phons which is defined

as the loudness level NL of a 1kHz tone at

40dB sound pressure level. The number of

sones to a phon was chosen so that a doubling

of the number of sones sounds to human ear

like a doubling of the loudness, that also

corresponds to increasing the sound pressure

level by 10dB or increasing the sound pressure

by a factor 3.16

Sunil Babu Khatry, Noise Pollution, 513 -Page, 10

Corrected Distance (ft)

Given

Distance

(ft)

3 5 10 15 20 25 30 40 50 60 70 80 90 100

3 0 - 4.4 -10.5 -14.0 -16.5 -18.0 -20.0 -22.5 -24.4 -26.0 -27.4 -28.5 -29.5 -30.5

5 4.4 0 - 6.0 - 9.5 -12.0 -14.0 -15.6 -18.1 -20.0 -21.6 -22.9 -24.1 -25.1 -26.0

10 10.5 6.0 0 - 3.5 - 6.0 - 8.0 - 9.5 -12.0 -14.0 -15.6 -16.9 -18.1 -19.1 -20.0

15 14.0 9.5 3.5 0 - 2.5 - 4.4 - 6.0 - 8.5 -10.5 -12.0 -13.4 -14.5 -15.6 -16.5

20 16.5 12.0 6.0 2.5 0 - 1.9 - 3.5 - 6.0 - 8.0 - 9.5 -10.9 -12.0 -13.1 -14.0

25 18.0 14.0 8.0 4.4 1.9 0 - 1.6 - 4.1 - 6.0 - 7.6 - 8.9 -10.1 -11.1 -12.0

30 20.0 15.6 9.5 6.0 3.5 1.6 0 - 2.5 - 4.4 - 6.0 - 7.4 - 8.5 - 9.5 -10.5

40 22.5 18.1 12.0 8.5 6.0 4.1 2.5 0 - 1.9 - 3.5 - 4.9 - 6.0 - 7.0 - 8.0

50 24.4 20.0 14.0 10.5 8.0 6.0 4.4 1.9 0 - 1.6 - 2.9 - 4.1 - 5.1 - 6.0

60 26.0 21.6 15.6 12.0 9.5 7.6 6.0 3.5 1.6 0 - 1.3 - 2.5 - 3.5 - 4.4

70 27.4 22.9 16.9 13.4 10.9 8.9 7.4 4.9 2.9 1.3 0 - 1.2 - 2.2 - 3.1

80 28.5 24.1 18.1 14.5 12.0 10.1 8.5 6.0 4.1 2.5 1.2 0 - 1.0 - 1.9

90 29.5 25.1 19.1 15.6 13.1 11.1 9.5 7.0 5.1 3.5 2.2 1.0 0 - 0.9

100 30.5 26.0 20.0 16.5 14.0 12.0 10.5 8.0 6.0 4.4 3.1 1.9 0.9 0

Decibel corrections for variations in distance from source. An example: a sound source of 60 dB is measured at

50 feet; if the measurement were at 15 feet, the level would be 60 + 10.5 = 70.5 dB under ideal conditions.

Sone 1 2 4 8 16 32 24

Rela

tiv

e R

es

po

ns

e,

dB

Frequency, Hz

A

B

C

B & C

- 5

- 20

- 45

20 100 500 2000 10000

Response characteristics of the three basic ANSI weighting characteristics (networks)

Sunil Babu Khatry, Noise Pollution, 513 -Page, 11

Phon 40 50 60 70 80 90 100

Sound Source Sound Presure,

(Pa)

Sound

Pressure

Level, dB

reference to

μPa

Loudness,

sone

Threshold of pain 100 134 ~ 676

Hearing damage during short term

effect 20 120 ~ 250

Jet, 100m distant 6 - 200 110 - 140 ~ 125 - 1024

Jack Hammmer 1m distance /

Discotheque 2 100 ~ 60

Hearing damage during long term

effect 6 * 10-1 90 ~ 32

Major road, 10m distance 2 * 10-1 - 2 * 10-1 80 – 90 ~ 16 - 32

Passenger car, 10mdistance 2 * 10-2 - 2 * 10-1 60 – 80 ~ 4 - 16

TV set at home level, 1m distance 2 * 10-2 60 ~ 4

Normal talking, 1m distance 2 * 10-3 - 2 * 10-2 40 - 60 ~ 1 - 4

Very calm room 2 * 10-4 - 6 * 10-4 20 – 30 ~ 0.15 - 0.4

Leaves' noise, calm breathing 6 * 10-5 10 ~ 0.02

Auditory threshold at 2kHz 2 * 10-5 0 0

Sones dBA Sones dBA

0.2 21.5 1.8 34.8

0.3 22.5 1.9 35.3

0.4 23.5 2.0 35.8

0.5 24.4 2.1 36.4

0.6 25.3 2.2 37.0

0.7 26.3 2.3 37.5

0.8 27.2 2.4 38.0

0.9 28.2 2.5 38.4

1.0 29.2 2.6 38.8

1.1 30.2 2.7 39.3

1.2 31.1 2.8 39.8

1.3 32.0 2.9 40.2

1.4 33.0 3.0 40.6

1.5 33.5 3.1 41.1

1.6 33.9 3.2 41.5

1.7 34.4 3.3 42.0

dBA = 33.22 × log (sones) + 28 with a possible accuracy of ± 2 dBA

Sunil Babu Khatry, Noise Pollution, 513 -Page, 12

1.11 Psycho - Acoustics (Sound & Human Ear Perception)

Sound can be also defined as the pressure

variation that the human ear can detect.

The response of the human ear to sound /

noise depends on both the sound frequency

and the sound pressure level. The sounds of

a single frequency are pure tones. Most

environmental sounds consist of a large

number of frequencies. Generally, human

ears are less sensitive to low frequencies

(<250Hz) than mid frequency (500 – 1kHz).

The lowest frequency sound that can be

detected by human ear is at about 20Hz and

the highest for a young person, is up to

18kHz. With age, the ear is most receptive

to sounds between 500Hz and 4kHz of which

500Hz to 2kHz is the frequency range of

speech. The sound frequency less than 15Hz

are not audible as they be felt as vibration

only and commonly known as infrasonic, and

is not considered damaging at levels below

120dB. Old listeners cannot hear the lower

frequency sound greater than 15Hz and less

than 20Hz. Sound characterized by

frequencies in excess of 20kHz is called

ultrasound and is not considered damaging

at levels below 105dB.

1.12 Relationship between Indoor and Outdoor Levels

The contribution of outdoor noise to indoor

noise levels is usually small. That pan of a

sound level within a building caused by an

outdoor source obviously depends on the

source's intensity and the sound level

reduction afforded by the building.

Although the sound level reduction

provided by different buildings differs

greatly, dwellings can be categorized into

two broad classes-- those built in warm

climates and those built in cold climates.

Further, the sound level reduction of a

building is largely determined by whether

its windows are open or closed. Table 6.2

shows typical sound level reductions for

these categories of buildings and window

conditions, as well as an approximate

national average sound level reduction.

Sample measurements of outdoor and indoor

noise levels during 24-hour periods are

depicted in Figure 6.2. Despite the sound

level reduction of buildings, indoor levels are

often comparable to or higher than levels

measured outside. Thus, indoor levels often

are influenced primarily by internal noise

sources such as appliances, radio and

television, heating and ventilating

equipment, and people. However, many

outdoor noises may still annoy people in

their homes more than indoor noises do.

Indeed, people sometimes turn on indoor

sources to mask the noise coming from

outdoors.

2. Sound Propagation Characteristic

Sound travels through air in waves with

the characteristics of frequency and

wavelength. If a sound is created at a

Table: Typical Sound Level Reductions of

Buildings

Climates Windows

Opened Windows Closed

Warm Climate 12dB 24dB

Cold Climate 17dB 27dB

Fig. 6.2: Comparison of Sound, Indoor /

Outdoor

Sunil Babu Khatry, Noise Pollution, 513 -Page, 13

Cool air

Warm air

Day time [ Bending away of sound wave]

point, a system of spherical waves

propagates from that a point outward

through the air at certain speed.

Geometric attenuation of sound has been

taken place as the wave spreads; the

height of the wave or the intensity of

sound at any given point diminishes due to

the spreading amount of energy. The point

source propagation of sound wave follows

the inverse square law. This is applicable

to the sound waves emissions from aircraft

and from a single vehicle.

When there is a continuous stream of

noise sources, line-source propagation

occurs. The propagation is no longer

characterized by a spherical or

hemispherical spreading of sound. The

reinforcement by the line of point sources

makes the propagation field either a

cylindrical shaped or half-cylindrical

planes.

2.1 Geometrical Spreading For the geometrical spreading of sound from

a coherent source - an attenuation of 6dB

per doubling of distance for spherical

expansion from a point source, 3dB per

doubling of distance for cylindrical

expansion from an infinite line sources and

parallel loss free propagation from an

infinite area source3. For sources of finite

size, there is a near field where the above is

approximately true and a far filed where the

expansion is spherical. In community noise,

however, incoherent sources are often more

important and the treatment of geometrical

spreading from incoherent sources has been

extended in recent years to cope with

multivehicle problems, particularly road

traffic and railway noise.

As the disturbance spreads geometrically

its effect will decrease with its distance

from the sound source but the diminution

in sound intensity will also be affected by

the damping of the sound waves by the

transmitting medium. This effect may

arise in the atmosphere and is influenced

3 A. Lara Saenz, R.W.B. Stephens, Noise Pollution,

Effects and Control, John Wiley & Sons, Chichester,

New York, Brisbane, Toronto, Singapore, 1986

by the degree of humidity and the

frequency of the sound. It is of particular

importance in a closed space, such as a

concert hall, where the geometrical

spreading is almost eliminated. Here it

becomes desirable from the musical and

speech intelligibility points of view to

introduce sound absorbing material or

resonator devices at the walls or ceiling to

reduce the prolongation of a given sound,

i.e. to control the reverberation of the

sound.

2.2 Meteorological Parameters & Sound Propagation

Noise level is attenuated due to rain, mist,

fog or snow, e.g., 0.5dB /km reduction in

fog. The variable temperature or wind

speed gradients can result in large

variations in noise levels at distances

greater than 100m from a noise source.

When upwind of the source or when the

temperature decreases with height, the

sound waves are refracted away from the

Warm air

Cool air

Night Time [Bending of sound waves

towards ground]

Sunil Babu Khatry, Noise Pollution, 513 -Page, 14

ground, resulting in decreased sound

levels. The opposite occurs when

downwind or when there is a temperature

inversion.

The effects of temperature inversions are

negligible for short distances but may

exceed 10dB at distances over 800m.

Typically, meteorological attenuations

range over ± 6dB up to a frequency at

0.5kHz and ± 10dB above 0.5kHz.

2.2.1 Attenuation

The sound pressure level from a non-

directive (diffuse) source is attenuated

(reduced) by geometrical spreading and

environmental conditions between the

source and receptor. When sound travels

through a medium, its intensity

diminishes with distance. In idealized

materials, the spreading of the wave only

reduces sound pressure (signal amplitude).

Natural materials, however, all produce

an effect, which further weakens the

sound. This weakening results from

scattering and absorption. Scattering is

the reflection of the sound in directions

other than its original direction of

propagation. Absorption is the conversion

of the sound energy to other forms of

energy. The combined effect of scattering

and absorption is called attenuation. The

amplitude change of a decaying plane

wave can be expressed as. In this

expression Ao is the amplitude of the

propagating wave at some location. The

amplitude A is the reduced amplitude

after the wave has travelled a distance Z

from that initial location. The is the

attenuation coefficient. The term e is

Napier's constant, which is equal to

approximately 2.71828.

Temperature Effect

Sound speed increase with temperature in

air. For moderate temperature differences,

this increase may be taken to be roughly

0.6m/s for each degree centigrade rise.

Distance Attenuation

The extent of geometrical spreading of sound

pressure depends on the type of source and

the existence of nearby boundaries.

Doubling of the distance gives 3dBreduction

for a line source or 6dB for a point source.

Ground Surface Effects

Acoustically soft ground surfaces (grass,

cultivated land, gravel) absorb sound energy

and reduce the received sound levels.

Acoustically hard surfaces (concrete, water)

reflect sound waves and absorb little sound

energy. The extent of the sound attenuation

from acoustically soft surfaces varies with

frequency and the heights of the noise

source to the recipients. The attenuations

range from 0 to more than 20dB per 100m.

However, grass gives high attenuation

values at low frequencies (0.3 to 1kHz)

where noise control is usually difficult.

Trees Attenuation

The little sound reduction is provided by

thin belts of trees. A wide (>50m) and dense

with foliage down to ground level is required

for significant sound absorption. A reduction

of about 0.1dB/m thickness may be achieved.

Topography Effect

This varies with the closeness of the sound

waves to the ground surface; all ground

attenuation may be lost across a valley.

Reflecting Surfaces and Noise Barriers

The sound level near a hard smooth vertical

surface (building façade) is the result of both

direct and reflected sound waves.

Immediately at the surface the combined

effects give an increased sound level of 6dB,

reducing to about 3dB within about 1m of

the surface. The effect of the vertical surface

decreases as the measuring point is moved

away and become negligible than about 10m.

Practical attenuations from noise barriers

seldom exceed 10 to 15dB.

Sunil Babu Khatry, Noise Pollution, 513 -Page, 15

4Sound Field Characteristic

Sound

Field Description

Free field A region in space where

sound may propagate free

from any form of obstruction.

Near field

The near field of a source is

the region close to a source

where the sound pressure and

acoustic particle velocity are

not in phase.

The sound field does not

decrease by 6 dB each time

the distance from the source

is increased (as it does in the

far field).

The near field is limited to a

distance from the source

equal to about a wavelength

of sound or equal to three

times the largest dimension

of the sound source

(whichever is the larger)

Far field

Far field of a source begins

where the near field ends and

extends to infinity. Note that

the transition from near to

far field is gradual in the

transition region.

In the far field, the direct

field radiated by most

machinery sources will decay

at the rate of 6 dB each time

the distance from the source

is doubled.

For line sources such as

traffic noise, the decay rate

varies between 3 and 4dB.

Direct

field

The direct field of a sound

source is defined as that part

of the sound field, which has

not suffered any reflection

from any room surfaces or

obstacles.

Reverbera

nt field

The reverberant field of a

source is the sound field

radiated by a source, which

has experienced at least one

reflection from a boundary of

4 ISO 12001

the room or enclosure

containing the source.

3. Noise Measurements & Monitoring

For noise measurements & monitoring

purpose, the emphasis should be given in

selection of appropriate noise descriptors

after that only it becomes easiness for the

data volume will be known.

Most commonly, environmental sounds are

described in terms of an average level that

has the same acoustical energy as the

summation of all the time varying events,

which is energy equivalent sound / noise

descriptor called as equivalent sound

pressure level (Leq). The most common

averaging period is either hour, twelve

hours or twenty-four hours. The selected

measuring instruments should generate

the output data within ± 1dB range.

Various computer models are used to

predict environmental noise levels from

sources (roadways, airports, etc). The

accuracy of the predicted models depends

upon the distance between the receptors

and the source. Close to the noise source,

the models are accurate to with about plus

or minus 1 to 2 dB.

Since the sensitivity to noise increases

during the evening and at night because

excessive noise interferes with the ability

to sleep. So, twenty four hour descriptors

have been developed that incorporate

artificial noise penalties added to quiet-

time noise events.

Community Noise Equivalent Level

(CNEL): It is a measure of the exposure of

the cumulative noise exposure in a

community, with a 5dB penalty added to

evening (7:00pm ~ 10:00pm).

Day / Night Average Sound Pressure Level

(Ldn): It measures the average day – night

average sound pressure level with 10dB

Sunil Babu Khatry, Noise Pollution, 513 -Page, 16

night time penalty for (20:00hrs ~

07:00hrs).

3.1 Selection of Noise Descriptors

• Traffic Noise: Equivalent Sound Pressure

Level (Leq); Percentile Level (Lmin, L90, L50,

L10, Lmax); Traffic Noise Index (TNI) & Day

Night Average (Ldn).

• Industrial Noise: Equivalent Sound

Pressure Level (Leq); Day Night Average

(Ldn); Sound Exposure Level (SEL) – TWA;

Maximum Sound Pressure Level (Lmax);

Median Sound Pressure Level (L50);

Background Sound Pressure Level (L90).

• Aircraft Noise: Noise Number Index (NNI)

& Noise Exposure Forecast (NEF);

Equivalent Sound Pressure Level (Leq).

• Community Noise: Equivalent Sound

Pressure Level (Leq); Percentile Level

(Lmin, L90, L50, L10, L5,Lmax); Day Night

Average (Ldn); Community Noise

Equivalent Level (CNEL).

• Shipboard Noise: Equivalent Sound

Pressure Level (Leq); Median Sound

Pressure Level (L50)

• Impulsive Noise: Maximum Sound

Pressure Level (Lmax).

3.2 Methods

Grab sampling (shortterm area monitoring

or spot measurement): by sound level

meter.

Full day monitoring (for industrial

workers): Applicable for personal as well

as area monitoring through dosimeter

(attaching dosimeter on a worker to assess

the full working day exposure to noise).

The appropriate exchange rate should be

mentioned

Frequency characteristic analysis: Sound

frequency spectral analysis should be

applicable for specified noise source.

Noise zoning (area monitoring): A noise

map or zoning based on collected

timeframe noise data.

HLPP: In order to conduct HLPP, the

audiometric tests should be undertaken

that covers baseline audiogram,

monitoring audiogram, retest audiogram,

confirmation audiogram followed by exit

audiogram.

3.3 Acoustic Weighting Networks

The human ear is not equally sensitive

to sound at different frequencies.

Acoustic weighting networks are

electronic filtering circuits built into the

meter to attenuate certain frequencies.

They permit the sound level meter to

respond more to some frequencies than

to other with a prejudice something like

that of the human ear. The acoustical

standards have established A, B and C

weighting characteristics. These

networks weight the contributions of the

different frequencies to the overall sound

level, so that sound pressure levels are

reduced or increased as a function of

Sunil Babu Khatry, Noise Pollution, 513 -Page, 17

frequency before being combined

together to give an overall level.

The A - weighting is most commonly

used and is intended to approximate the

frequency response of our hearing

system. It weights lower frequencies as

less important than mid-and higher-

frequency sounds. C - Weighting is

common and is a nearly flat frequency

response with extreme high and low

frequencies attenuated. The main

difference among them is that very low

frequencies are filtered quite severely by

the A network, moderately by the B

network and hardly at all by the C

network.

3.4 Measurement Objectives The type and the strategy of

measurement will depend strongly on the

objectives of the survey.

General

Investigating complaints

Assessing the number of persons

exposed.

Regulation compliance.

Land use planning and environmental

impact assessments.

Evaluation of remedial measures.

Calibration validation of predictions.

Research surveys.

Trend monitoring.

Note: The sampling procedure, measurement

location, type of measurements and the

choice of equipment should be accord with

the objective of the measurements.

OSHA Concept

Different objectives can be pursed for the

occupational survey systems. In order to

examine the different type of noise exposure,

it is necessary to precede systematic, taking

into consideration four activity related

factors: the principal task, job period,

activity location & work nature.

Determination of the noise emission of a

given machine or ensemble of machines;

Identification, characterization and

ranking of noise sources;

Verification that a given worker is or is

not exposed to a noise level above the legal

limits (compliance);

Prediction of the individual risk of hearing

loss

Note: If the objective is only compliance,

more measurements are made if the exposure

is around the OEL than when the exposure

level is below or even above the OEL.

3.5 General Noise Inspection Data

3.5.1 General Information

The general information of the location are

to be collected including the height from the

ground, distance from the reference point

(road, river, walls, or other retaining

structures), major noise sources, physical

observed conditions, weather condition. The

general view is enclosed in the photograph

too as well as in the sketch map.

3.5.2 Health Inspection Data

In addition to collect the general

information, the health status of the

employee is collected as in the following

manner:

Distance from the employee to the

primary noise source(s);

Need for the employee to be present or in

close proximity to the noise field;

Employee exposure time pattern;

Existence of any known employee

auditory problems (e.g., ear infections,

ringing in the ears, or trouble with

hearing after the work shift);

Employee's opinion of the practicality of

potential noise controls (considering

machine operation), where relevant;

Hearing protection provided and any

problems with its use or acceptance.

(Octave band levels and/or dBC and

dBA data may aid in the evaluation of

hearing protectors.); and

Time since the last audiometric

examination and frequency of such

examinations.

Sunil Babu Khatry, Noise Pollution, 513 -Page, 18

3.5.3 Machine and / or Process Data.

Type of machine, and a brief description

of it and/or the process, including

identifying numbers, sketches, and

photographs whenever possible;

Condition of the machine (e.g., age and

maintenance status);

Machine operation (e.g., speed, cycle

times, parts/minute, and materials

used);

Apparent existing noise and/or vibration

controls;

Source(s) and characteristics of the noise

(e.g., fan noise--discrete and broad band

components, continuous or

noncontinuous). (Octave band analyzers,

real time analyzers, and narrow band

analyzers may be useful in determining

sources of noise); and

Practical engineering and/or

administrative controls and estimated

costs of such controls

3.5.4 Building Data

Size and shape of the room;

Layout of equipment, work stations and

break areas;

Surface materials (e.g., ceiling/steel;

walls/cinderblock; floor/concrete);

Existing acoustical treatment;

Potential acoustical treatment;

Noise from other sources (spill-over

noise); and

Presence of barriers or enclosures.

3.5.5 Employer Data

What has been done to control the noise

(e.g., have consultants been used, is plant

noise monitored, and are controls

implemented)?

What is planned for the future?

Are administrative controls utilized?

How are they enforced?

3.5.6 Hearing Loss Data

Document the following when hearing loss is

used to support a citation:

The amount of the threshold shift and

date it was recorded;

Employee's exposure level;

Frequency and duration of employee's

exposure;

Length of employment;

Explanation of any follow-up measures

taken; and

Duration of audiometric testing

program.

Population workers exposure brief

Sunil Babu Khatry, Noise Pollution, 513 -Page, 19

3.5.7 Additional Information Requirement

Preliminary Information

For general ambient monitoring assessment

purpose the secondary information like,

major noise sources (traffic, horns, activity

related noise, etc.), geographical position,

general weather conditions should be

required.

Following completion of the initial tour, it is

advisable to obtain agreement with

managers and employees that the conditions

encountered are normal/average for a day‟s

activity. This should form the basis for

discussion in establishing the working

system seen during the tour and an analysis

of the working patterns; in particular, in

relation to those operators who have been

previously identified as being included as

subjects of the measurements for the noise

assessment. The information gathered can

be used for a variety of purposes such as:

Area characteristics (noise hot or cold

stops);

Individual noise sources and their

character identification;

Identifying of mechanized contributions

& population persons exposure;

Study plan formulation details

(measurements protocol);

Assessment status (individual,

representativeness, group assessment);

and

Choice of the instrumentation to be used

Work Analysis Information

The characteristics of the different

exposures should find out to identify those

factors responsible for any variations in the

noise exposure.

Situation of the operators (fixed post,

mobile post inside fixed zone, no fixed

post, etc.);

Nature of the tasks carried out by each

worker (or group of workers), and the

temporal

Breakdown of the assigned tasks;

Worker's environment

Noise type exposure (including

identification of rare acoustic events)

Probability exposure to intense short

duration noises

Noise Type

When conducting the noise surveys it is

important to establish the characteristic of

the noise sources depending or in

depending upon the environment under

consideration. Prior knowledge of the

character of the noise being assessed is

critical when selecting the most

appropriate measuring instrumentation.

However, noise can be characterized by the

following components:

Information, Strategic Exposure Assessment

Sunil Babu Khatry, Noise Pollution, 513 -Page, 20

Steady-Continuous: Cotton/textile mills

where there is little variation in

perceived level.

Non-steady fluctuating: Wood working

mill (particleboard process), where the

level rises sharply when boards are

being cut; concrete block machines.

Impulsive and impact: Drop forge,

hammer mill, power press shop.

Broadband: Constant energy content in

all frequencies (e.g. bottling plant)

Narrow band: Energy confined to

discrete frequency

Tonal: Discrete low or high frequency

Sudden bursts: High energy and short

duration

Infra sound: Sound at frequencies below

20 Hz.

Ultra sound: Sound at frequencies above

20,000 Hz.

3.6 Selection of Measurement Positions

Unless otherwise specified, the

measurement positions shall be selected as

follows:

3.6.1 Outdoor Measurement

For the general ambient noise, select

measurement positions shall, whenever

possible, at least 3.5m from any reflecting

structure such as building and 1.2 to 1.5m

above the ground. When measurements are

carried out on a street, measurement

positions shall be selected on the edge of

the sidewalk towards the carriageway in

the case where the sidewalk is provided,

and on the edge of the carriageway in the

case where there is no sidewalk at a height

1.2 to 1.5m above the ground for both

cases. If the influences of noise from

specific sources (e.g., factories, recreation

facilities, etc) are investigated, the

measurements shall be carried out at the

positions under consideration.

3.6.2 Measurement around the Building

When the influence of noise from external

sources on a building is considered, the

measurement positions shall be selected 1

to 2m apart from the façade of the building

and 1.2 to 1.5 m above each floor level of

interest. In the measurements of A-

weighted sound pressure level in front of

the window of the building, the

measurement position shall be 1m from the

window on its center line.

3.6.3 Measurements inside the Building

When the A - weighted sound pressure level

is measured inside the building, the

measurement positions shall be selected 1.2

to 1.5m above the floor, and at least 1m from

the reflecting surfaces such as walls.

3.6.4 Measurement in Work Environments

When the noise in a work environment such

as a factory and office is measured, the

measurement positions shall be selected at

the approximate positions of the worker‟s

ears. If the positions of the workers cannot

be specified, the measurements shall be

carried out at some representative positions

on line where they move, 1.2 to 1.5m above

the floor.

3.7 Instrumentation

Several sound measuring instruments

include noise dosimeters, sound level

meters, and octave-band analyzers. The uses

and limitations of each kind of instrument

are discussed below

3.7.1 Audiometry

Audiometric tests shall be pure tone, air

conduction, hearing threshold

examinations, with test frequencies

including 500, 1000, 2000, 3000, 4000,

6000 and 8000 Hz, and shall be taken

separately for the right and left ears.

Audiometric tests shall be performed by

an audiologist, or by an occupational

Sunil Babu Khatry, Noise Pollution, 513 -Page, 21

hearing conservationist certified by the

Council for Accreditation in

Occupational Hearing Conservation

(CAOHC) working under the supervision

of an audiologist or physician.

Audiometric tests shall be conducted

with audiometers that meet the

specifications of, and are maintained

and used in accordance with the

American National Standard

Specifications for Audiometers, ANSI

S3.6-1995 [ANSI 1995]. Audiometers

shall be given an annual comprehensive

calibration, a bimonthly acoustic

calibration check, and a daily functional

check whenever the audiometers are

used. The date of the last annual

calibration shall be recorded on each

worker's audiogram.

Audiometric tests shall be conducted in

a room where ambient noise levels

conform to all requirements of the

American National Standard Institute

Maximum Permissible Ambient Noise

Levels for Audiometric Test Rooms,

ANSI S3.1-1991 [ANSI 1991b], when

measured by instruments conforming to

the American National Standard

Specification for Sound Level Meters,

ANSI S1.4-1983 and S1.4A-1985, Type 1

[ANSI 1983; ANSI 1985] and the

American National Standard

Specification for Octave-Band and

Fractional-Octave-Band Analog and

Digital Filters, ANSI S1.11-1986 [ANSI

1986]. For permanent, on-site testing

facilities, ambient noise levels shall be

checked at least annually. For mobile

testing facilities, ambient noise levels

shall be tested daily, or each time the

facility is moved, whichever is more

often. Ambient noise levels shall be

recorded on the worker's audiogram or

made otherwise accessible to the

professional reviewer of the audiograms.

Steps in Audiometric Analysis

Method

a. Baseline Audiogram

For each worker in a HLPP, a baseline

audiogram shall be obtained prior to

employment or within 30 days of

enrollment in the HLPP.

Because the baseline audiogram is

intended to be the best estimate of the

worker's hearing before any exposure to

potentially harmful noise, the worker shall

not be exposed to workplace noise for a

minimum of 14 hours before the baseline

audiometric test. The required quiet

period shall not be substituted by the use

of hearing protectors.

b. Monitoring Audiogram, Retest

Audiogram, and Significant

Threshold Shift

On an annual basis, each worker's hearing

thresholds shall be monitored by an

audiometric test, which shall be conducted

during the worker's normal work shift. For

the purpose of this section, the audiogram

from this test is called the monitoring

audiogram.

At the completion of this test, the worker's

monitoring audiogram shall be examined

immediately to determine whether it

indicates any threshold shift (higher

threshold) in either ear that equals or

exceeds 15 dB at 500, 1000, 2000, 3000,

4000 or 6000 Hz as evidenced by a

comparison of that audiogram with the

worker's baseline audiogram.

If the monitoring audiogram indicates a

hearing threshold shift, a retest shall be

conducted immediately, following re-

instruction of the worker and refitting of

the earphones.

If the retest audiogram shows a shift of 15

dB or more at the same frequency in the

same ear as in the monitoring audiogram,

the worker shall be considered to have met

the significant threshold shift criterion for

the purpose of this section and shall be

given a confirmation audiometric test

within 30 days. This confirmation test

shall be conducted under the same

conditions as in a baseline audiometric

test.

Sunil Babu Khatry, Noise Pollution, 513 -Page, 22

c. Confirmation Audiogram and Fellow

- Up Action

If the worker's confirmation audiogram

shows a shift of 15 dB or more at the same

frequency in the same ear as in the

previous retest audiogram, the worker's

audiograms and other appropriate records

shall be reviewed by an audiologist or a

physician.

If this review confirms that the significant

threshold shift is persistent, the

significant threshold shift shall be

recorded in the worker's medical record,

and the confirmation audiogram shall be

used for the calculation of any subsequent

significant threshold shift in future years.

A worker whose significant threshold shift

is of any etiology other than noise, as

determined in this review, shall be

referred to the worker's physician. If the

probable etiology is of occupational noise

exposure, the employer shall take

appropriate action to protect the worker

from additional hearing loss due to

occupational noise exposure. Examples of

appropriate action include, but are not

limited to, re-instruction and refitting of

hearing protectors, additional training of

the worker on hearing loss prevention, and

reassignment of the worker to a quieter

work area.

d. Exit Audiogram

An exit audiogram shall be obtained for a

worker who is leaving employment or is

permanently rotated out of an

occupational noise exposure at or above 82

dBA, 8-hour TWA. The audiometric test

shall be conducted following a minimum of

14 hours of quiet.

3.7.2 Noise Dosimeter

a. Introduction

A dosimeter is like a sound level meter

except that it stores intermittent or varying

sound level measurements and integrates

these measurements over time, providing an

average noise exposure reading for a given

period, such as an 8-hour workday. It

measures and stores the sound levels during

an exposure period and computes the

readout as the percent dose or TWA. With a

dosimeter, a microphone is attached to the

employee's clothing and the exposure

measurement is simply read at the end of

the desired time. A reader may be used to

read-out the dosimeter's measurements.

b. Personal Noise Monitoring

It measures noise levels in those locations

in which the employee travels from an

employee‟s worn dosimeter. A sound level

meter can also be positioned within the

immediate vicinity of the exposed worker to

obtain an individual exposure estimate.

Such procedures are generally referred to

as "personal" noise monitoring.

c. Area Monitoring

Area monitoring can be used to estimate

noise exposure when the noise levels are

relatively constant and employees are not

mobile. In workplaces where employees

move about in different areas or where the

noise intensity tends to fluctuate over time,

noise exposure is generally more accurately

estimated by the personal monitoring

approach.

d. Specifications

Many dosimeters available today can

provide an output in dose or TWA using

various exchange rates (e.g., 3, 4, and 5

dB), 8-hr criterion levels (e.g., 80, 84, 85,

and 90 dBA), and sound measurement

ranges (e.g., 80 to 130dBA). The choice of

FAST or SLOW meter response on the

dosimeter does not affect the computed

noise dose or TWA when the 3-dB exchange

rate is used, but it will when other

exchange rates are used [Earshen 1986].

ANSI [1996a] specifies that the microphone

be located on the midtop of the worker's

more exposed shoulder and that it be

oriented approximately parallel to the

plane of this shoulder.

The noise dosimeters used shall meet the

American National Standards Institute

Sunil Babu Khatry, Noise Pollution, 513 -Page, 23

(ANSI) Standard S1.25-1978,

"Specifications for Personal Noise

Dosimeters," which set performance and

accuracy tolerances. For OSHA use, the

dosimeter must have a 5 - dB exchange

rate, use a 90 - dBA criterion level, be set

at slow response, and use either an 80 -

dBA or 90 - dBA threshold gate, or a

dosimeter that has both capabilities,

whichever is appropriate for the

evaluation.

e. Dosimeter Calculation

The noise dose provided by dosimeters can

be used to calculate both the continuous

equivalent A-weighted sound level (LA) and

the 8 - hour TWA for the time period

sampled, using the following formulas

9012.5t

D10log16.61AL

90100

D10log16.61TWA

where:

LA : the continuous equivalent A-

weighted sound level in decibels for

the time period sampled

D : dosimeter readout in percent noise

dose

t : the sampling time in hours

TWA : the 8-hour time-weighted average in

decibels, dBA

f Exchange Rate

The time / intensity relationship is referred

as the exchange rate. Sometimes it is also

referred as doubling rate, trading ratio,

and time - intensity trade off. So, the

exchange rate is the increase or decrease in

decibels corresponding to twice (or half) the

noise dose. This means that the sound level

of 90 dB produces twice the noise dose that

85 dB produces (assuming that duration is

held constant). The OSHA exchange rate is

5 dB. The exchange rate used by different

organizations is different.

Occupational Health and Safety

Association, OSHA exchange rate: 5dB

US Department of Navy exchange rate:

4dB

US Department of the Army and the

Department of the Air Force exchange

rate: 3-dB.

Instrument used by the National

Institute for Occupational Safety and

Health (NIOSH) and the Environmental

Protection Agency (EPA), as well as most

foreign governments also use a 3-dB

exchange rate ACGIH Physical Agents

Threshold Limit Values (TLV)

Committee recently revised its noise

TLV to also use the 3-dB exchange rate.

The hypothetical exposure situations

shown in table illustrate the relationship

between criterion level, threshold, and

exchange rate and show the importance

of using a dosimeter with an 80-dBA

threshold to characterize an employee's

noise exposure. For example, an

instrument with a 90-dBA threshold will

not capture any noise below that level,

and will thus give readout of 0% even if

the employee being measured is actually

being exposed to 89 dBA for 8 hours (i.e.,

to 87% of the allowable noise dose over

any 8-hour period).

Sunil Babu Khatry, Noise Pollution, 513 -Page, 24

Dosimeter Readout, In Percent of Measured Dose

Exposure conditions

Dosimeter with

threshold set at

90 dBA

Dosimeter with

threshold set at

80 dBA

90 dBA for 8 hours 100.0% 100.0%

89 dBA for 8 hours 0.0% 87.0%

85 dBA for 8 hours 0.0% 50.0%

80 dBA for 8 hours 0.0% 25.0%

79 dBA for 8 hours 0.0% 0.0%

90 dBA for 4 hours plus 80 dBA for 4 hours 50.0% 62.5%

90 dBA for 7 hours plus 89 dBA for 1 hour 87.5% 98.4%

100 dBA for 2 hours plus 89 dBA for 6 hours 100.0% 165.3%

* Assumes 5-dB exchange rate, 90-dBA PEL, ideal threshold activation, and continuous sound

levels.

Conversion from Percent Noise Exposure or Dose To 8-Hour Time-Weighted Average Sound Level

Dose or percent TWA (dBA) Dose or percent TWA (dBA)

50 85.0 90 89.2

55 85.7 95 89.6

60 86.3 100 90.0

65 86.9 105 90.4

70 87.4 110 90.7

75 87.9 115 91.1

80 88.4 120 91.3

85 88.8 125 91.6

Assumes 5-dB exchange rate and 90-dBA PEL.

Source: 29 CFR 1910.95.

Sunil Babu Khatry, Noise Pollution, 513 -Page, 25

3.7.3 Sound Level Meter

The sound level meter is the basic

measuring instrument for intensity of

sound at a given moment, indeed noise

exposures. It consists of a microphone, a

frequency selective amplifier, and an

indicator. At a minimum, it measures

sound level in dB SPL. An integrating

function may be included to automate the

calculation of the TWA or the noise dose.

Since sound level meters provide a

measure of sound intensity at only one

point in time, it is generally necessary to

take a number of measurements at

different times during the day to estimate

noise exposure over a workday. If noise

levels fluctuate, the amount of time noise

remains at each of the various measured

levels must be determined.

a. Frequency Weighting Networks

The responses of the sound level meter are

modified with frequency - weighting

networks that represent some responses of

the human ear. The A-scale, which

approximates the ears response to

moderate - level sounds, is commonly used

in measuring noise to evaluate its effect on

humans and has been incorporated in many

occupational noise standards.

Relative Response of Sound Level Meter Weighting Networks*

*Meters that are set to integrate or average sound do not use either the FAST or SLOW time constant; they will sample many times each

second. For a more detailed description of exponential time weighting, refer to Yeager and March [1991].

b. Exponential Time Weighting

A sound level meters response is generally

based on either a FAST or SLOW

exponential averaging. FAST corresponds

to a 125-millisecond (ms) time constant;

SLOW corresponds to a 1-s time constant.

The meter dynamics are such that the

meter will reach 63% of the final steady-

state reading within one time constant.

The meter indicator reflects the average

SPL measured by the meter during the

period selected. In most industrial

settings, the meter fluctuates less when

measurements are made with the SLOW

response compared with the FAST

response. A rapidly fluctuating sound

generally yields higher maximum SPLs

when measured with a FAST response.

The choice of meter response depends on

the type of noise being measured, the

intended use of the measurements, and

the specifications of any applicable

standard. For typical occupational noise

measurements, NIOSH recommends that

the meter response on a sound level meter

be set at SLOW.*

c. Microphones for Sound Level

Meters

Sunil Babu Khatry, Noise Pollution, 513 -Page, 26

The correct use of the microphone is

extremely important in obtaining accurate

measurements. Microphones come in

many types and sizes. A microphone is

typically designed for use in a particular

environment across a specific range of

SPLs and frequencies. In addition,

microphones differ in their directionality.

For example, some are intended to be

pointed directly at the sound; and others

are designed to measure sound from a

"grazing" angle of incidence. Thus users

should follow the sound level meter

manufacturer‟s instructions regarding the

type and size of microphone and its

orientation toward a sound. Also, care

should be taken to avoid shielding the

microphone by persons or objects [ANSI

1996a]. When measuring a diffuse sound

field, the person conducting the

measurement should hold the microphone

as far from his or her body as practical5.

d. Specifications

All sound level meters used shall meet

ANSI Standard S1.4-1971 (R1976) or

S1.4-1983, "Specifications for Sound Level

Meters," which set performance and

accuracy tolerances.

e. Purpose of Use

a. Sound level meters are used for the

following purposes:

To spot - check noise dosimeter

performance;

To determine an employee's noise dose

whenever a noise dosimeter is

unavailable or inappropriate;

To identify and evaluate individual noise

sources for abatement purposes;

To aid in the determination of the

feasibility of engineering controls for

individual noise sources for abatement

purposes; and

To evaluate hearing protectors.

5 Earshen 1986

b. For practical purposes, this procedure

should be followed for all sound level

measurements:

The microphone should be in the

monitored employee's hearing zone.

OSHA defines the hearing zone as a

sphere with a two-foot diameter

surrounding the head. Considerations

of practicality and safety will dictate

the actual microphone placement at

each survey location.

When noise levels at an employee's two

ears are different, the higher level must

be sampled for compliance

determinations.

Note: Sound level readings in a non - reverberant

environment should be taken in accordance with

the manufacturer's instructions.

3.7.4 Octave Band Analyzers

a. Introduction

Octave band analyzers are sound level

meters that has an octave or one - third

octave band filter attached or integrated

into the instruments. The assigned filters

are used to analyze the frequency content

of the noise. They are used to find out the

overall frequency content of noise in the

monitored area. Indeed they are also used

for the calibration of audiometers and to

determine the suitability of various types of

noise control.

They also can be used to select hearing

protectors because they can measure the

amount of attenuation offered by the

protectors in the octave-bands responsible

for most of the sound energy in a given

situation.

Octave - band analyzers segment noise

into its component parts. The octave-band

filter sets provide filters with the

following center frequencies: 31.5; 63;

125; 250; 500; 1,000; 2,000; 4,000; 8,000;

and 16,000 Hz.

The special signature of a given noise can

be obtained by taking sound level meter

readings at each of these settings

(assuming that the noise is fairly constant

over time). The results may indicate those

Sunil Babu Khatry, Noise Pollution, 513 -Page, 27

octave-bands that contain the majority of

the total radiated sound power.

b. Calibration

In normal operation, calibration of the

instrument usually requires only checking.

Prior to and immediately after taking

measurements, it is a good practice to

check, using a calibrator, the ability of the

sound level instrument to correctly

measure sound levels. As long as the sound

level readout is within 0.2 dB of the known

source, it is suggested that no adjustments

to the calibration pot be made. If large

fluctuations in the sound level occur (more

than 1 dB) then either the calibrator or the

instrument may have a problem.

3.8 Instrumental Performance (Effects of the Environment)

Temperature, humidity, atmospheric

pressure, wind, and dust can all affect the

performance of noise-measuring

instruments and their readings. Magnetic

fields can also affect the performance of

instruments. Each of these factors is

discussed below.

3.8.1 Temperature

Sound - measuring equipment should

perform within design specifications over

an ambient temperature range of -20°F to

140°F ( - 29°C to 60°C). If the temperature

at the measurement site is outside this

range, refer to the manufacturer's

specifications to determine if the sound

level meter or dosimeter is capable of

performing properly. Sound-measuring

instruments should not be stored in

automobiles during hot or cold weather

because this may cause warm-up drift,

moisture condensation, and weakened

batteries, all of which can affect instrument

performance.

3.8.2 Humidity

OSHA noise instruments will perform

accurately as long as moisture does not

condense or deposit on the microphone

diaphragm. If excessive moisture or rain is

a problem in a given exposure situation, the

Assistant Regional Administrator (ARA) for

Technical Support should be consulted.

3.8.3 Atmospheric Pressure Both atmospheric pressure and

temperature affect the output of sound

level calibrators; atmospheric pressure is

the more important of these two factors.

When checking an acoustical calibrator,

always apply the corrections for

atmospheric pressure that are specified

in the manufacturer's instruction

manual.

In general, if the altitude of the

measurement site is less than 10,000

feet above sea level, no pressure

correction is needed. If the

measurement site is at an altitude

higher than 10,000 feet, or if the site is

being maintained at greater-than-

ambient pressure (e.g., in underwater

tunnel construction), use the following

equation to correct the instrument

Air Pressure Correction reading:

)

B

30(5.0)

528

t 460(log10C

where:

C = correction, in decibels, to be added to

or subtracted from the measured

sound level

t = temperature in degrees Fahrenheit

B = barometric pressure in inches of

mercury

3.8.4 Wind or Dust

Wind or dust blowing across the

microphone of the dosimeter or sound level

meter produces turbulence, which may

cause a positive error in the measurement.

A windscreen should be used for all outdoor

measurements and whenever there is

significant air movement or dust inside a

building (e.g. when cooling fans are in use

or wind is gusting through open windows).

Sunil Babu Khatry, Noise Pollution, 513 -Page, 28

3.8.5 Magnetic Fields

Certain equipment and operations, such as

heat sealers, induction furnaces,

generators, transformers, electromagnets,

arc welding, and radio transmitters

generate electromagnetic fields that can

induce current in the electronic circuitry of

sound level meters and noise dosimeters

and cause erratic readings. If sound level

meters or dosimeters must be used near

such devices or operations, the extent of the

field's interference should be determined by

consulting the manufacturer's instructions.

4. Environmental Noise Sources

One of the many by-products of our

modern, industrialized society is the noise

produced by technology, and the adverse

effects of excessive noise on individuals are

well documented. The various

environmental laws, policies and

regulations deal with various types of noise

sources. The various sources of noise can

affect a community.

Transportation noise

Domestic noise

Industrial noise (other than motor

vehicles)

Construction and other non-domestic

noise. Note: It should be noted that equal values of LAeq,T

for different sources do not always imply the same

expected effect.

4.1 Transportation Noise Transportation noise is the main source of

environmental noise pollution, including

road traffic, rail traffic and air traffic. As a

general rule, larger and heavier vehicles

emit more noise than smaller and lighter

vehicles. Exceptions would include:

helicopters and 2- and 3-wheeled road

vehicles.

4.1.1 Road Vehicles The noise of road vehicles (heavy vehicles,

light vehicles, two wheelers, three

wheelers, etc) is mainly generated from the

engine and from frictional contact between

the vehicle and the ground and air. The

major types of vehicular noises are exhaust

noise, cooling fan noise, aerodynamic noise,

and intake noise, tire noise, honking horn

noise and loose metallic parts vibration

noise. In general, road-contact noise

exceeds engine noise at speeds higher than

60 km/h. The exhaust noise constitutes the

predominant source for normal operation

below 55km per hour for automobiles.

Diesel trucks are 8 to 10dB noisier than

gasoline - powered ones. The two stoke

motorcycles exhibit more high frequency

spectra energy content.

4.1.2 Railway Railway noise depends primarily on the

speed of the train, but variations are

present depending upon the type of

engine, wagons, and rails and their

foundations, as well as the roughness of

wheels and rails. Small radius curves in

the track, such as may occur for urban

trains, can lead to very high levels of high-

frequency sound referred to as wheel

squeal. Noise can be generated in stations

because of running engines, whistles and

loudspeakers, and in marshaling yards

because of shunting operations. The

introduction of high-speed trains has

created special noise problems with

sudden, but not impulsive, rises in noise.

At speeds greater than 250 km/h, the

proportion of high-frequency sound energy

increases and the sound can be perceived

as similar to that of over flying jet

aircraft.

4.1.3 Aircraft

Aircraft operations generate substantial

noise near both commercial and military

airports. Aircraft takeoffs are known to

produce intense noise, including vibration

and rattle. The landings produce

substantial noise in long low-altitude

flight corridors. The noise is produced by

the landing gear and automatic power

regulation, and when reverse thrust is

applied, all for safety reasons. The main

mechanism of noise generation in the

early turbojet-powered aircraft was the

turbulence created by the jet exhaust

mixing with the surrounding air.

Sunil Babu Khatry, Noise Pollution, 513 -Page, 29

In general, larger and heavier aircraft

produce more noise than lighter aircraft.

Multi-bladed turbo-prop engines can

produce relatively high levels of tonal

noise. The sound pressure level from

aircraft is, typically, predicted from the

number of aircraft, the types of airplanes,

their flight paths, the proportions of

takeoffs and landings and the

atmospheric conditions. Severe noise

problems may arise at airports hosting

many helicopters or smaller aircraft used

for private business, flying training and

leisure purposes. Special noise problems

may also arise inside airplanes because of

vibration. The noise emission from future

super jets is unknown.

A sonic boom consists of two types of

shock wave (discontinuities existence) in

the air, generated by an aircraft when it

flies at a speed slightly greater than the

local speed of sound. At supersonic speed,

the air in front of the aircraft is

undisturbed, and the sudden impulse at

the leading edge creates a region of

overpressure higher than atmospheric

pressure. This overpressure region

travels outward with the speed of sound

that creates a conically shaped bow wave.

A tail wave is produced by the tail of the

aircraft and is associated with a region

where the pressure is lower than the

atmospheric pressure due to the sideways

trailing of air behind the aircraft. An

aircraft in supersonic flight trails a sonic

boom that can be heard up to 50 km on

either side of its ground track, depending

upon the flight altitude and the size of

the aircraft (Warren 1972). A sonic boom

can be heard as a loud double-boom

sound. At high intensity it can damage

property.

4.2 Industrial Noise Industrial machinery and processes are

composed of various noise sources such as

rotors, stators, gears, fans, vibrating

panels, turbulent fluid flow, impact

processes, electrical machines, internal

combustion engines, etc. The mechanisms

of noise generation depend on the

particularly noisy operations and types of

equipments [crushing, riveting, blasting

(quarries and mines), shake out (foundries),

punch presses, drop forges, drilling, lathes,

pneumatic equipment (jack hammers,

chipping hammers, etc), tumbling barrels,

plasma jets, cutting torches, sandblasting,

electric furnaces, boiler making, machine

Bo

w w

ave

Tail w

av

e

Sonic boom hearing

Underpressure

Overpressure Sonic boom hearing

Sunil Babu Khatry, Noise Pollution, 513 -Page, 30

tools for forming, dividing and metal

cutting, such as punching, pressing and

shearing lathes, milling machines and

grinders as well as textile machines and

print machines, pumps and compressors,

drive units, hand guided machines, self

propelled working machines, in plant

conveying systems and transport vehicles].

Air jets: widely used , for example, for

cleaning, drying power tools and steam

valves can generate sound levels of

about 105dB.

Workers in a cigarette factory in Brazil

involved in compressed air cleaning

were exposed to sound level equivalent

to 92dB for 8 hours.

In the wood working industry the sound

level of saws can be as high as 106dB.

Average sound level range between 92

dB and 96dB in industries such as

foundries, shipyards, breweries,

weaving factories, paper and saw mills.

The recorded peak values were between

117dB to 136dB.

In most developing countries, industrial

noise levels are higher than those in the

developed countries.

Industrial Noise Level in Nepal

Ref.: Occupational Dafety & Health Project HMG /

Nepal, 2000/2001 & 2001/2002

Industry Activity Leq,

dB(A)

Balaju Aluminum, BID Spinning 90 - 98

Reliable Plastic, BID Molding 99 - 112

Plastic Industries, BID Molding 97

Nebico Biscuit, BID Grinding 100 - 104

Balaju Yantra Shala,

BID Cutting 104

Bottlers Nepal, BID Filling 96

Nepal Feed Industries,

BID Grinning 90 -95

Him Plastic, BID Cutting 100 - 103

Eastern Textile, Birgunj Loom 102

Birgunj Sugar Mill,

Birgunj Turbine 105

Hulas Steel, Bara Galvanizing 94

Mechanized industry creates serious noise

problems. It is responsible for intense noise

indoor as well as outdoors. This noise is due

to machinery of all kinds and often

increases with the power of the machines.

The noise may contain predominantly low

or high frequencies, tonal components, be

impulsive or have unpleasant and

disruptive temporal sound patterns.

Rotating and reciprocating machines

generate sound that includes tonal

components; and air-moving equipment

tends also to generate noise with a wide

frequency range.

The high sound pressure levels are

caused by components or gas flows that

move at high speed (for example, fans,

steam pressure relief valves), or by

operations involving mechanical

impacts (for example, stamping,

riveting, road breaking). Machinery

should preferably be silenced at the

source.

4.3 Domestic Noise Noise from domestic premises includes

mechanical devices noise (heat pumps,

ventilation system, lawn movers, and

vacuum cleaners), music and party

noise, band and drum practice, trail

bikes, revving motor vehicles,

hammering, and other non-mechanical

construction noise. When it interferes

with the enjoyment of an area by any

Sound Pressure Levels in manufacturing

Industries, Singapore, 1993

Sunil Babu Khatry, Noise Pollution, 513 -Page, 31

person living in or otherwise using it,

the noise becomes environmental harm.

Some types of indoor concerts and

discotheques can produce extremely

high sound pressure levels. Associated

noise problems outdoors result from

customers arriving and leaving.

Outdoor concerts, fireworks and various

types of festivals can also produce

intense noise. The general problem of

access to festivals and leisure activity

sites often adds to road traffic noise

problems. Severe hearing impairment

may also arise from intense sound

produced as music in headphones or

from children‟s toys.

4.4 Construction and Other Activities

Building construction and excavation

work can cause considerable noise

emissions. A variety of sounds come

from cranes, cement mixers, welding,

hammering, boring and other work

processes. Construction equipment is

often poorly silenced and maintained,

and building operations are sometimes

carried out without considering the

environmental noise consequences.

Street services such as garbage disposal

and street cleaning can also cause

considerable disturbance if carried out

at sensitive times of day. Ventilation

and air conditioning plants and ducts,

heat pumps, plumbing systems, and

lifts (elevators), for example, can

compromise the internal acoustical

environment and upset nearby

residents.

4.5 Parks & School Playing Fields

Noise generated by several planned parks

and schools on the age and number of

people utilizing the respective facility at a

given time, and the type of activities they

are engaged in school playing field

activities tend to generate more noise than

those of neighbourhood parks, as the

intensity of school playground usage tends

to be higher. At a distance of 100ft from an

elementary school used by 100 students,

average and maximum noise levels of 60

and 75dB respectively, can be expected. At

organized events such as high school

football games with large crowds and public

address systems, the noise generation is

often significantly higher. As with service

commercial uses, the noise generation of

parks and school playing fields is variable.

4.6 Discotheque Noise

Mainly, 6discotheque noise is night

occurrence problem, and has arisen

largely through the advancing of the audio

equipment industry. This development

has meant that large dance – hall bands of

live music and the accompanying size of

hall are no longer necessary. The type,

size and location of the hall has changed

for whole musical equipment is easily

transportable and only three to six players

or just a disc- jockey is required. It is

evident with sound peak levels which can

reach 120dB(A) and halls with inadequate

acoustic insulation that a local noise

problem is created. Particularly, the

heavy low frequency beat will penetrate

deeply into the environment.

5. Noise Analysis

5.1 Equivalent Sound Pressure Level, (LAeq, T)

Equivalent sound pressure level is the

logarithmic average steady state noise

level in a stated time period. According to

the equal energy principle, the effect of

combination of noise events is related to

the combined sound energy of those

events. So, the measure sums up the total

energy over same time period. Equivalent

continuous sound pressure level is gaining

widespread acceptance as a scale for the

6 Edt. Sanez, A. Lara & Stephens, R. W. B., Noise

Pollution, SCOPE, John Willey & Sons, Ltd.,

1986

Sunil Babu Khatry, Noise Pollution, 513 -Page, 32

measurement of long - term noise

exposure. It has been adopted for the

measurement of both community noise

exposure and hearing damage risk, i.e.

LAeq,T should be used to measure

continuous sounds such as road traffic

noise, industrial noises, ventilation

system noise, environmental noise as well

as aircraft and railway noise.

Calculation:

)

an/1010...

/102

a10

/101

a10(

n

1

10log10)

T(Aeq,L

dB(A)

Where,

L(Aeq, T) : Equivalent A - weighted sound pressure level for total time period T.

N : Total no of readings

a1 : Sound pressure level at first time interval

5.2 Day - Night Average Sound Pressure Level, (Ldn)

Day - night average sound pressure level (DNL) is the 24 hours average sound level, in

decibels, for the period from midnight to midnight, obtained after addition of 10dB to sound

levels in the nighttime from midnight to 7am and from 10pm to midnight. The nighttime

penalty is based on the fact that many studies have shown that people are much more

disturbed by noise at nighttime than at any time (Chanlet, 1973). This desicaptor is used for

impact assessment, noise zoning as well as in criteria development.

Mathematically,

]10 / 10) n(L

(10 0.375) 10 /

dL

10( 0.625[10 log 10dnL

dB (A)

Where,

Ld: Average Leq for the daytime (07.00 - 22.00hrs)

Ln: Average Leq for the nighttime (22.00 - 7.00hrs)

5.3 Sound Exposure Level, (SEL)

The value of A - weighted sound pressure

level of a steady state sound of one second

duration which has the same A - weighted

sound energy as that of a discrete noise

event under consideration is known as

sound exposure level. This measure is

applied for airport, railway and industrial

noise measures. The sound exposure level

shall be obtained from n values of A -

weighted sound pressure level sampled

Sunil Babu Khatry, Noise Pollution, 513 -Page, 33

during the measurement period by following equation:

dB(A)

Where,

T : ∆T.n(∆T is interval of sampling in second, N= 1/n)

To : 1 second

The relationship between the A – weighted sound exposure and the A – weighted equivalent

continuous sound level, Leq,T is

Where, T is expose time interval (=8hrs)

A noise exposure level normalized to a nominal 8-hour working day may be calculated from

EA,8h by using following equation:

Daily Personal Noise Exposure Level (LEP,d):

The daily personal noise exposure of a worker is expressed in dB(A) by using the following

formula:

Where,

T: Daily duration of a worker‟s exposure to noise (hours)

T0: 8hours

P0: 20µpa

PA: A – weighted instantaneous sound pressure in pascals to which is exposed, in air at

atmosphere pressure, a person who might or might not move from one place to another while at

work; it is determined from measurements made at the position occupied by the person‟s ears

during work, preferably in the person‟s absence, using a technique which minimizes the effect

on the sound field.

“Daily personal noise exposure of a worker LEP,d “ is the same as the term “ noise exposure

level normalised to a normal 8hr working day, LEX,8h

/10ai

L10

n

1

oT

T

10 log 10 SEL

Sunil Babu Khatry, Noise Pollution, 513 -Page, 34

Weekly average of the daily values (LEP,w): The weekly average of the daily values is found

using the following formula:

Where (LEp,d)k are the values of LEP,d for each of the m working days in the week being

considered.

If each work station "i" is exposed to a level LAeq,Ti in dB(A) for a relative duration Di (in%),

the reconstituted noise level is:

5.4 Percentile Level, (L)

A widely used method of recording the

variations in sound pressure level is that

of level distribution analysis, sometimes

called statistical distribution analysis.

This yields a graph of the percentage of

the total time for which any given sound

pressure level is exceeded.

When the A - weighted sound pressure

level that is exceeded for x% of the

measurement time interval, the level is

called as x percentile noise level. The

50-percentile level (L50) is called

median and 5 - percentile (L5) and 95-

percentile level (L95) are called the

upper limit and lower limit of the 90 -

percentile range respectively. L95

represents the background sound

pressure level whereas L10 represents

subjective annoyance. The various

measured sound pressure levels are

arranged in the increasing order and

the percentile position is calculated by

using the following formula:

100

1) (n%x a

5.5 Traffic Noise Index The sound pressure level from traffic

can be predicted from the traffic flow

rate, the speed of the vehicles, the

proportion of heavy vehicles, and the

nature of the road surface. Special

problems can arise in areas where the

traffic movements involve a change in

engine speed and power, such as at

traffic lights, hills, and intersecting

roads; or where topography,

meteorological conditions and low

background levels are unfavorable (for

example, mountain areas). The traffic

noise index (TNI) is based on the

weighted combination of the sound

levels (in dBA exceeded for 10 %, 50 %,

and 90 % of the time) according to the

formula:

)90 L-10 L ( 450 L TNI

This index reflects the conclusion that

traffic noise annoyance depends not only

upon the average or typical sound pressure

level (L50) but also upon the magnitude of

the fluctuation (L10 - L90). However, further

investigation revealed that, because of the

practical difficulties of predicting L 90 with

an adequate degree of confidence, the value

of TNI was susceptible to large errors. For

example, TNI - values decrease when the

traffic increases. Thus, TNI was

subsequently rejected in favor of L10 for

traffic noise compensation regulations7,

even though its correlation with annoyance

7 UK

Statutory Instrument, 1975

Sunil Babu Khatry, Noise Pollution, 513 -Page, 35

was shown to be inferior to that of TNI in

the original survey.

5.6 Noise Pollution Level, (NPL)

Noise pollution level applies to any

environment, unlike those especially

concerned with aircraft and traffic.

However, it is incapable of determining

whether the noise being measured is

wanted or unwanted sound. The NPL level

is calculated by using following formula:

kσeqLNPL

Where,

Leq is the equivalent energy level measured

in dB(A), k is a constant which is

provisionally given the value 2.56, σ is the

standard deviation of instantaneous levels

in time.

5.7 Airport Noise Measurement

Noise number index (NNI) and noise

exposure forecast (NEF) are assigned for

airport noise measurement. These

parameters are calculated as follows:

Where, N = number of aircraft generate

noise during measurement. K = 88 for

daytime exposure [6am to 6pm] = 76 for

nighttime exposure [10pm to 6am).

NNI Guidelines

NNI = 20 Little degree of annoyance

(Degree 1)

NNI = 30 Little degree of annoyance

(Degree 2)

NNI = 50 Moderate degree of annoyance

(Degree 3)

Note: Four hours are missing for the

nighttime that is arbitrarily calculated as

NNI nighttime * 3/2.

6. Noise Criteria (NC) Curves

Noise Criteria Curves (NC-Curves)

developed by ASHRAE (American

Society of Heating, refrigeration and

Air conditioning Engineers) in 1957 are

the most widely used values for gauging

indoor building noise. These are curves

which were often used in the past to

assess steady industrial or community

noise. Machinery manufacturers to

specify machinery noise levels currently

use them in some cases. The

requirements are that the sound

pressures measured at each octave

band must be below the specified NC

curve (within a 2dB tolerance) if they

are to meet the NC rating.

Many specifications for target noise

levels and associated noise control

measures are also written based on the

Noise Criterion curves. The Noise

Criterion curves are octave band curves

with a single number rating attached to

each of them (see Figure 1). The

methodology of determining the NC

rating of a particular sound spectrum

requires plotting the octave band

spectrum under assessment against the

NC curves and selects the lowest NC

curve that has values that are higher or

equal to the ones assessed in all octave

bands. The NC curves provide both

quantitative and qualitative analysis of

the indoor noise levels through a single

number rating. Unlike the A-weighted

80 - N10

log 15 av. peak eq.

L NNI

K - N10

log 10 av. peak eq

L NEF

Sunil Babu Khatry, Noise Pollution, 513 -Page, 36

sound level, the Noise Criterion

provides some spectral information as

its level is determined by the level of

the highest NC curve that has a

tangency point in any octave band with

the sound spectrum under evaluation.

Figure no. 1

Fig2

Sunil Babu Khatry, Noise Pollution, 513 -Page, 37

The qualitative assessment of sound using

this criterion is not optimum as there are

many sound spectra that match the same

NC level. From Figure 2 one can see that

three completely different sound spectra

(SPL1, SPL2 and SPL3) could have the

same NC level (NC40 in this case). In terms

of qualitative assessment SPL1 is similar to

the sound of a constant volume HVAC

system; SPL2 is similar to the airflow noise

through a diffuser while SPL3 shows a

strong tonal character at 500 Hz. The

criteria are not a good reflection of the total

amount of sound energy in the spectrum

but rather of the energy in the tangency

band. Generally speaking is difficult to

compare two sounds based solely on their

NC levels without knowing their spectral

components.

Another short come of the Noise Criterion

is that it is defined for the octave bands

between 63 Hz and 8 kHz. This leaves un-

assessed the low frequency noise

components in 31.5 Hz and 16 Hz bands

that are usually associated with structure

borne noise and airflow turbulence noise in

ductwork systems that could induce

rattling of light fixtures, diffusers etc.

It is our experience that based on this

criterion, the threshold where the number

of complaints start to build-up is NC 42-43

for open plan offices. Whenever the noise

level in the space is above this limit, there

is a higher likelihood of complaints from

the people occupying the space. Based on

our experience and on data published by

others we found that the following NC

levels due to mechanical equipment

servicing the building, according to the type

of occupancy, provide good to acceptable

sound environments.

Building Occupancy Good Acceptable

Residences NC25 NC35

Appartements NC25 NC35

Hotel Rooms NC30 NC35

Executive Offices NC22 NC30

Conference Rooms NC22 NC30

Individual Offices NC30 NC35

Open Plan Offices NC38 NC42

Corridors NC40 NC45

Hospital Rooms NC23 NC33

Classrooms NC23 NC30

Auditoriums NC20 NC30

Theaters NC18 NC25

Concert Halls NC15 NC22

Recording Studios NC15 NC18

TV Studios NC18 NC26

Sunil Babu Khatry, Noise Pollution, 513 -Page, 38

7. Noise Control & Abatement Measures

In most countries, land - use planning and zoning is used to avoid conflicts between noise

sensitive buildings and noise - generating installation such as airports, road networks and

industrial plants. The planning involves decision on the future use of resources. Enforcement of

regulation is being made by supervision to ensure compliance with laws and regulations. The

source is the point at which noise originates, and the path is the line in air along with the noise

waves can be considered to the receiver or the ear. The final objective in noise control being to

reduce the noise reaching the receiver can be achieved by modifications at source, along path or

even the receiver or all the three.

Noise Control Measures

Source Control

Priority Order: I

(Source modification

by design)

Transmission Path

Priority Order: II

(Alteration and

controlling)

Receiver

Priority Order: III

(Personal protection

measure)

• Impact force reduction

• Radiating area reduction

• Speed & pressure reduction

• Frictional resistance

• Noise leakage reduction

• Isolation & dampen vibration elements

• Provide mufflers / silencers

Separation

Absorbing material

Acoustic lining

Barriers and panels

Transmission loss

Enclosure

Work schedule alteration

Ear Protection

Sunil Babu Khatry, Noise Pollution, 513 -Page, 39

Control technology should aim at reducing

noise to acceptable levels by action on the

work environment. Such action involves the

implementation of any measure that will

reduce noise being generated and / or will

reduce the noise transmission through the

air or the structure of the work place. Such

measures include modifications of the

machinery, the workplace operations, and

the lay out of the work room. In fact, the

best approach for noise hazard at its source

of generation, either by direct action on the

source or by its confinement.

Prior to the selection and design of control

measures, noise sources must be identified,

and the produced noise must be carefully

evaluated. To adequately define the noise

problem and set a good basis for the control

strategy, the following factors hould be

considered:

Noise type

Noise level and temporal pattern

Frequency distribution

Noise source characteristics

Noise propagation pathway

Room acoustics (reverberation)

Methods for prevention and control of

sources of noise emissions depend on the

source and proximity of receptors. Noise

reduction options that should be considered

include:

Selecting equipment with lower power

levels.

Installation silencers for fans

Installation of suitable mufflers on

engine exhausts and compressors

components

Improving the acoustical performance

of constructed buildings, apply sound

insulation.

Installation of acoustic barriers without

gaps and with a continuous minimum

surface density (about 10kg/m2) in

order to minimize the transmission of

sound through the barrier. Barriers

should be located as close to the source

or to the receptor location to be

effective.

Installation of vibration isolation for

mechanical equipment.

Limiting the hours of operation for

specific pieces of equipment or

operations, especiallymobile sources

operating through community

Relocating noise sources to less

sensitive areas to take the advantage of

distance and shielding.

Sitting permanent facilities away from

community areas if possible

Taking advantage of the natural

topography as a noise buffer during

facility design

Reducing project traffic routing

wherever possible

Planning fight routes, timing and

altitude for aircraft flying over

community

Development of a mechanism to record

and respond to complaints

ISO 11690, Part 1: Noise control can be

implemented using various technical

measures. These measures are noise

reduction at the source, noise reduction

by preventing / attenuating its

propagation, noise reduction at specific

positions.

7.1 Source Control Source control normally is the best

method of control. The noise radiated

from a machine and transmitted through

structure - borne connections very much

depended upon the used materials. The

mechanics of sound wave generation may

differ in two main categories. One is the

surface motion of a vibrating solid and

other is turbulence in a fluid medium.

The main aim of control at the source is

to reduce driving forces, response and

area of vibrating surface and velocity of

fluid flow reduction. To control noise at

the source, it is first necessary to

determine the cause of the noise and

secondly to reduce it. Modification of the

noise generated often provides the best

means of noise control.

Sunil Babu Khatry, Noise Pollution, 513 -Page, 40

At the source noise can be controlled by

the appropriate design modification,

which can include reduction of

mechanical shock between moving parts,

reduction of noise resulting from out-of-

balance, friction between metal parts,

and vibration of large structures.

General Source Noise Control

Activities Control

Maintenance

Replacement or adjustment

of worn or loose parts

Balancing of unbalanced

equipment

Lubrication of moving parts

Use of properly shaped &

sharpened cutting tools.

Substitution

of materials

Replacement of steel

sprockets in chain drives

with sprockets made from

flexible polyamide plastics.

Substitution

of equipments

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.

Substitution

of equipment

parts

Modification of gear teeth, by

replacing spur gears with

helical gears – generally

resulting in 10 dB of noise

reduction)

Replace straight edged

cutters with spiral cutters

(e.g. wood working machines

- 10 dB(A) reduction)

Replace gear drives with belt

drives

Replace metal gears with

plastic gears (beware of

additional maintenance

problems)

Replace steel or solid wheels

with pneumatic tyres.

Working

method

In building demolition,

replace use of ball machine

alteration with selective demolition;

Replace pneumatic tools by

changing manufacturing

methods, such as moulding

holes in concrete rather than

cutting after production of

concrete component

Use remote control of noisy

equipment such as

pneumatic tools

Separate noisy workers in

time, but keep noisy

operations in the same area,

separated from non-noisy

processes

Select slowest machine speed

appropriate for a job - also

select large, slow machines

rather than smaller faster

ones

Minimise width of tools in

contact with workpiece (2

dB(A) reduction for each

halving of tool width)

Woodchip transport air for

woodworking equipment

should move in the same

direction as the tool

Minimise protruding parts of

cutting tools

Process

change

Mechanical ejectors for

pneumatic ejectors -hot for

cold working

Pressing for rolling or forging

Welding or squeeze rivetting

for impact rivetting

Welding for rivetting

Use cutting fluid in

machining processes

Change from impact action

(e.g. hammering a metal bar)

to progressive pressure

action (e.g. bending metal

bar with pliers as shown in,

or increase of time during

which a force is applied)

Replace circular saw blades

with damped

Replace mechanical limit

stops with micro-switches

Substitution

of mechanical

Electric motors for internal

combustion engines or gas

Sunil Babu Khatry, Noise Pollution, 513 -Page, 41

power

generation

and

transmission

equipment

turbines

Belts or hydraulic power

transmissions for gear boxes

Replacement

of worn

moving parts

Replace new rolling element

bearings for worn ones

Minimizing the number of noisy machine

running at any one time

Sunil Babu Khatry, Noise Pollution, 513 -Page, 42

7.2 Transmission Path Control

Another step in noise reduction can be

obtained by increasing the distance

between people and the noise source. This

can be achieved by planning the location of

transport facilities and, in industry, by the

careful selection of work sites. Sound

transmission can also be controlled by the

use of partitions or barriers. Reverberant

noise levels can be reduced by sound -

absorbing materials.

Control Modality:

Use of barrier (single walls), partial

enclosures or full enclosure of the entire

item of equipment

Use of local enclosures for noisy

components on a machine

Use of reactive or dissipative mufflers;

the former for low frequency noise or

small exhausts, the latter for high

frequencies or large diameter exhaust

outlets

Use of lined ducts or lined plenum

chambers for air handling system

Reverberation control – the addition of

sound absorbing material to reverberant

spaces to reduce reflected noise fields

Active noise control – involves

suppression, reflection or absorption of

the noise radiated by an existing sound

source by use of one or more secondary or

control system

Airborne vs Structure – Borne Noise

Control

The solution for airborne noise is controlled

by enclosement of the source, sound

absorbing material employment or by

increasing the sound transmission path

through double wall construction or

replacement of exhaust muffler.

Isolation of Noise & Transmission Loss

The noise generated by a source can be

prevented from reaching a receiver by

means of an obstacle to its propagation,

conveniently located between the source

and receiver by proper isolation. The

transimission loss is defined as TL =

log10Γ, where the transmission coefficient

is defined as the ratio of transmitted to the

energy If the receiving space is outdoors in

a "free" field, the noise reduction is equal to

the transmission loss. If the receiving space

is indoor, the noise reduction is given by

Transmission loss through a partition

depends on the type of material used and it

varies as a function of frequency. For usual

industrial noise, the transmission loss

through a partition increases by about 6 dB

for each doubling of its weight per unit of

surface area. Therefore, the best sound

isolating materials are those, which are

compact, dense, and heavy.

Enclosure

The approach of enclosure is applied to

control the structural borne noise to the

receiver. The wall of an enclosure may

consist of several elements, each of which

may be characterised by a different

transmission loss. Many enclosures require

some form of ventilation.

If a machine is enclosed, reverberant build-

up of the sound energy within the enclosure

will occur unless adequate sound

absorption is provided. The effect will be

an increase of sound pressure at the inner

Sunil Babu Khatry, Noise Pollution, 513 -Page, 43

walls of the enclosure over that which

would result from the direct field of the

source. A degradation of the noise

reduction expected of the enclosure is

implied.

If the sound source radiates predominantly

high-frequency noise, then an enclosure

with low resonance frequency panels is

recommended, implying a massive

enclosure. On the other hand, if the sound

radiation is predominantly low frequency in

nature then an enclosure with a high

resonance frequency is desirable, implying

a stiff but not massive enclosure.

Since the absorption coefficient of

absorbent lining is generally highest at

high frequencies, the high-frequency

components of any noise will suffer the

highest attenuation. Some improvement in

low-frequency absorption can be achieved

by using a thick layer of lining. However

the liner should, in many cases, be

protected from contamination with oil or

water, to prevent its acoustical absorption

properties from being impaired.

The enclosure walls should have a

transmission loss of about 20 dB, and the

most sound power reduction that can be

achieved is about 10 dB. However, noise

levels may in some cases be more greatly

reduced, especially in areas immediately

behind solid parts of the enclosure.

7.2.1 Acoustic Barriers & Panels

A sound shadow is created when a barrier

cuts the line of sight from a noise source to

a receiver. Sound waves tend to bend

around the top and the ends of a barrier.

The extent varies with frequency, the lower

the frequency the greater the diffraction

and the smaller the resulting attenuation.

The effective barriers must be as close as

possible either to the noise source or to the

receiver. They must be sufficiently high

and long to ensure that noise cannot get

around the ends. Sound transmission

through a barrier must also be minimized.

Typically, the barrier material requires a

minimum mass per unit area of about

10kg/m2. It is important to ensure that no

cracks or gaps are present in a noise

barrier. The steel pile and concrete panel

wall is American's standard noise wall.

The noise control measures for roads or

highways include construction of

barriers to obstruct or dissipate sound

emissions, elevated or depressed

highways, and the absorption effects of

landscaping (trees, bushes, and shrubs).

Construction of barriers can be an

effective approach for reducing highway

noise. The important factors like

relative height of the barrier, the noise

and the effected area, and the

horizontal distances between the source

and between the barrier and the noise-

affected area are considered in

designing the barriers.

The type of materials used in

construction of noise barriers and other

abatement measures should be an

engineering decision based on

economics, effectiveness and, to a

limited degree, visual impacts.

The effects of barriers are complex

functions of the difference between the

direct and deflected noise path lengths

and of wavelengths of the sound. The

) N 203 (10 log10A

Sunil Babu Khatry, Noise Pollution, 513 -Page, 44

approximate attenuation from a point

source by an infinitely long thin barrier

of sufficient mass to ignore direct

transmission can be determined as

follows:

A: attenuation in dB

Transmission Loss Values for common

Barrier Materials

Material Thickness

(inch)

Transmission

loss, dB(A)

a. Woods

Fir

½ 17

1 20

2 24

Pine

½ 16

1 19

2 23

Redwood

½ 16

1 19

2 23

Cedar

½ 15

1 18

2 22

Plywood ½ 20

1 23

Particle Board ½ 20

b. Metals

Aluminium

1/16 23

1/8 25

¼ 27

Steel

24ga 18

20ga 22

16ga 15

Lead 1/16 28

c. Concrete Masonry, etc.

Light concrete 4 38

6 39

Dense concrete 4 40

Concrete block 4 32

6 36

Cinder block

(hollow core) 6 28

Brick 4 33

Granite 4 40

d. Composites

Aluminum

faced plywood ¾ 21 - 23

Aluminum

faced particle

board

¾ 21 - 23

Plastic lamina

on plywood ¾ 21 - 23

Plastic lamina

on particle

board

¾ 21 - 23

e. Miscellaneous

Glass (safety

glass)

1/8 22

¼ 26

Fiber glass

/resin 1/8 20

Polyester with

aggregate

surface

3 20 -30

Noise barriers are non-porous, high density and

usually non-fibrous materials, which are generally

flexible or damped. The effectiveness of noise

barriers is expressed as sound transmission class

(STC).

Ref.: US Department of Housing and Urban

Development, 1985

Sound Transmission Class of

Materials STC

1 lb. density barrier material 26

1 lb. density transparent curtain 26

5/8" gypsum wallboard 30

3/16" steel wall 31

2" fiberglass curtain with 1 lb. barrier 29

2" thick metal panel (solid and

perforated) 35

4" thick metal panel (solid and

perforated) 41

12" thick concrete 53

3/8" plasterboard 26

22 gauge steel 25

Solid core wood door, closed 27

Concrete block wall, unpainted 44

wav elength

dif f erencepathN

Sunil Babu Khatry, Noise Pollution, 513 -Page, 45

STC: Single number rating derived from

decibel loss data at several frequencies.

7.2.2 Mufflers and Silencers

Mufflers and silencers are acoustic filters

through which the fluid noise is reduced.

They are either absorptive or reactive

mufflers. An absorptive muffler reduces

the noise due to the presence of fibrous or

porous material present. The priority is

given in reactive muffler where its shape

is especially designed geometry, which can

reflect or expand the sound wave with

resultant destruction.

Muffling devices may function in any one

or any combination of three ways: they

may suppress the generation of noise; they

may attenuate noise already generated;

and they may carry or redirect noise away

from sensitive areas.

Muffling devices based upon reflection are

called reactive devices and those based

upon dissipation are called dissipative

devices. A duct lined with sound

absorbing material on its walls is one form

of dissipative muffler.

Muffling devices are commonly used to

reduce noise associated with internal

combustion engine exhausts, high

pressure gas or steam vents,

compressors and fans. Conclusively, a

muffling device allows the passage of

fluid while at the same time restricting

the free passage of sound. Muffling

devices might also be used where direct

access to the interior of a noise

containing enclosure is required, but

through which no steady flow of gas is

necessarily to be maintained.

Insertion loss (IL) and transmission

loss (TL) are commonly used to describe

the effectiveness of a muffling system.

The insertion loss of a muffler is

defined as the reduction (dB) in sound

power transmitted through a duct

compared to that transmitted with no

muffler in place. Provided that the duct

outlet remains at a fixed point in space,

the insertion loss will be equal to the

noise reduction which would be

expected at a reference point external

to the duct outlet as a result of

installing the muffler. The

transmission loss of a muffler, on the

other hand, is defined as the difference

(in decibels) between the sound power

incident at the entry to the muffler to

that transmitted by the muffler.

7.2.3 Absorbing Materials and Acoustic Lining

The sound absorbing materials are applied

in noise-transmitted ducts, pipe chases, or

electrical channels, which can be reduced

effectively. For high frequency noise, the

noise reduction in the order of 10dB/m is

achieved at a lining of 2.5cm thickness in

the ducts. For low frequency sound wave,

the thickness of acoustic lining thickness

should be doubled.

The sound absorbing material like

acoustical tile, carpets, and drapes placed

on ceiling, floor, or wall surfaces can

reduce the noise level in most rooms by

about 5 to 10dB for high frequency

sounds, but only by 2 or 3 dB for low

frequency sounds. The different types of

absorbing materials are rated either by

their sabin absorption coefficient or by a

single number noise reduction coefficient.

The unit area of totally absorbent surface

is called a sabin.

Sunil Babu Khatry, Noise Pollution, 513 -Page, 46

7.2.4 Absorber

Absorber is used to reduce noise reflection

and to dissipate noise energy. The

absorber materials are porous fibrous and

sometimes covered with protective

membranes. Noise enters the absorber

and is partly dissipated (absorbed) within

the material. Some is transmitted through

and some are reflected. Absorber

8 NRC: Percentage of acoustical energy absorbed calculated as

an average of laboratory test data at several frequencies.

performance is expressed as a decimal

value. A perfect absorber is rated at 1.00.

The higher the decimal value the more

effective the absorber will be. The

effectiveness of an absorber is expressed

as noise reduction coefficient (NRC).

7.2.5 Damping

The damping treatment is applied to

reduce noise radiated from vibrating

surfaces. This treatment is sometimes

combined with absorbers. The

effectiveness is expressed as a loss factor

which is the damping / stiffness ration of a

material.

7.2.6 Diffusion

Diffusion treatment is applied in

industrial and commercial architectural

reduction of noise. This treatment is used

Noise Reduction Coefficients

of Materials NRC8

Brick, unglazed 0.05

Concrete block 0.05

1/8" pile carpet 0.15

5/16" pile carpet and foam 0.35

Concrete floor 0.00

Plaster, smooth finish 0.05

Plywood paneling, 1/4" thick 0.10

Water surface (as in swimming

pool) 0.00

1" thick fiberglass curtain 0.70

3" thick "SONEX" wedge foam 0.86

4" thick smooth surface foam 0.89

4" thick metal panel 0.95

Sunil Babu Khatry, Noise Pollution, 513 -Page, 47

to reflect sound waves off convexly curved

or uneven surfaces for the purpose of

evenly distributing and blending the

sound over a broad area. In critical

listening area, diffusion can eliminate

sharp echoes without eliminating the

sound by absorbing it.

7.2.7 Anechoic Chamber

The anechoic chamber is the enclosure

provided to compensate the noise danger

from the sources. The walls of the

chamber should be massive and air tight

and provided with absorbent lining in the

interior part that will reduce the

reverberant buildup of noise within it.

Structural contact between the noise

source and the enclosure must be avoided,

so that the source of vibration is not

transmitted to the chamber walls.

7.3 Receiver Control Hearing protectors are the least desirable

option for preventive measures of noise.

However, if it is impossible to reduce noise

to a harmless level then some form of

hearing protecting devices (ear – plug, ear

– muffs, helmets) is required. Most of the

hearing protection devices reduce the

sound to 35dB. It should be noted that

protective ear devices do interfere with

speech communication and can also be

hazard in some situation. A correctly

selected hearing protector should provide

enough noise reduction to remove the risk

of hearing damage, and at the same time

allow communication with the

surroundings while ensuring the best

available of comfort.

7.3.1 Hearing Protectors

The best hearing protection for any

worker is removal of hazardous noise from

the workplace. Until that happens, the

best hearing protector for a worker is the

one he or she will wear willingly and

consistently. The hearing protector is a

device, which covers or fills the ears so

that the sound reaching the eardrum is

attenuated. Molded and pliable earplugs,

cup - type protectors and helmets are

commercially available hearing protectors.

The selected hearing protector should be

capable of reducing the noise exposure at

the ear to below 82 dBA, 8-hour TWA.

Hearing protectors should be used only

when engineering controls and work

practices are not feasible for reducing

noise exposures, or during the

implementation of engineering controls.

The best hearing protector is the one the

worker will wear all of the time because it

is comfortable, adequate noise reduction

(effective), and has minimal impact on

communication.

Different types and models of hearing

protectors are available for noise

protection. Mainly the foam type HP with

noise rating reduction, NNR 29dB,

premolded (NNR - 21 to 26dB), fiberglass

(NNR - 15 to 26 dB), custom (NNR - 15 to

24dB), semi aural (NNI - 19dB), earmuffs

(NNR - 23 to 25dB), Capmuffs (NNR - 21

to 23dB).

Estimation of A - weighted TWA for

hearing Protectors:

When dBA level is known:

When using a sound level meter set to

the A-weighting network: The obtained

representative sample of the A -

weighted exposures is used to calculate

the employee's TWA by subtraction 7

dB from the NRR, and further

deducting the remainder from the A -

weighted TWA to obtain the estimated

A - weighted TWA under the hearing

protector.

When using area monitoring procedures

and a sound level meter set to the A -

weighting network: The estimation A -

weighted TWA under the hearing

protector for the obtained

representative sound level data for the

area in question is done by subtracting

7 dB from the NRR, and finally

deducting the remainder from the A -

weighted sound level for that area.

When using a dosimeter that is not

capable of C - weighted measures: The

first step is the conversion of A-

Sunil Babu Khatry, Noise Pollution, 513 -Page, 48

weighted dose to an 8 - hour TWA.,

followed by deduction 7 dB from the

NRR. Further the remainder value is

subtracted from the A -weighted TWA

to obtain the estimated A -weighted

TWA under the hearing protector.

Hearing protection devices may be broadly

divided into three types and one special

type:

Earmuffs which cover the outer ear

and act as an acoustic barrier

sealing it against the head.

Earplugs which can be inserted into

the outer ear canal, thereby

blocking the propagation of

airborne sound to the middle ear.

Canal caps (semi-aural) which are

basically earplugs connected by

flexible headband. Canal caps

generally seal the ear canal at its

opening and they are used

extensively in the food industries.

Other special types are available

such as helmets with circumaural,

cups or muffs with communication.

Other brands are also now

available with electronic

amplification or with electronic

amplification or with active noise

reducing digital circuits.

Earplugs

Earplugs can be classified according to size,

shape and construction materials (custom

molded, premolded and expandable).

Premolded earplugs are made of soft

plastic / silicone

rubber and are

available in different

sizes. Generally,

they are available

with an attached

cord to prevent loss.

The wearer of these types can

experience a feeling of pressure or

discomfort due to their semi-solid

construction.

Custom molded earplugs are made of

soft rubber material, which is molded

into the individual‟s outer ear canal.

Depending on each wearer, a high

degree of

attenuation is

obtained.

Expandable

earplugs are

considered the most comfortable. Since,

they are porous

and soft and are

made from slow

recovery closed cell

foam. They offer

high attenuation

as their

expandable nature

against the outer ear canal and seal it

with less pressure.

Earmuffs

Ear muffs are made from rigid cups, are

mostly oval shaped, and are designed to

cover the external ear completely. The

effectiveness of ear muffs depends mainly

on the pressure exerted by the headband

and the cushion to head sealing. The

attenuation provided by ear muffs can be

greatly reduced when the muff seal is

displaced by the side arms of spectacles or

long hair.

Canal Caps (Semi – aural/ Banded Ear

Plugs)

Canal caps consist of flexible tips, made

from silicone, vinyl or foam in mushroom,

hollow bullet or conical shape, attached to a

lightweight plastic headband. They are

easily removed and replaced. They can be

used under the chin and behind the head.

Specific Types of Hearing Protectors

There are a number of hearing protectors

designed for special purposes. Active noise

control earmuffs have low frequency

nullification characteristics They provide

Sunil Babu Khatry, Noise Pollution, 513 -Page, 49

good attenuation at low frequencies (up to

20 dB) and also serve as classical passive

earmuffs with good attenuation at high

frequencies.

Advanced Earmuffs: Phones and wired-

up or connection through radio.

Additionally, they can be fitted with

acoustic frequency band-pass filters to

provide speech communication between

wearers, providing that the noise is out

of the speech frequency band.

Earmuffs: Reproduce music or

messages from external units. These

muffs have a peak limiting circuit (to

about 80 dB(A)) to avoid hazard.

7.4 Traffic Noise Abatement

7.4.1 Noise Barriers As fences / vegetation have minimal

effectiveness, the most common method is

the construction of noise barriers (reflective

or absorptive). Because noise barriers are,

open to the air above and around them,

sound bends over just as light bends around

the obstructions – through the principle of

diffraction. Diffraction limits the

effectiveness of any barrier to a maximum

noise reduction of 10 to 15 decibels,

independent of the material used. Typical

reductions usually range from 5 to 10

decibels. Refelective barrieras can diminish

more reduction capabilities when barriers

are on both sides of highway and are spaced

closer than 100ft apart.

7.4.2 Land Use Planning Measures Another option for controlling traffic noise

is to use administrative controls (zonning

regulations). Residential developments can

also be planned with buffer zones between

highways and residential buildings. These

buffer zones can commercial, industrial or

undeveloped areas.

7.4.3 Alternatives to Noise barriers: Traffic management / speed Restriction:

Traffic noise levels depend greatly on

the type of vehicles on the highway and

their speeds. Trucks generate more noise

than cars, especially when accelerating

and decelerating. Restricting trucks

from certain roadways, enforcing speed

restrictions, and minimizing or

synchronizing traffic signals, can thus

minimize noise.

Highway Design Options: Highway

design options to minimize traffic noise

include building road ways as far as

possible from noise – sensitive locations,

depressing roadways, and avoiding steep

inclines in roadways. Steep inclines in

roadways cause more noise to be

generated by vehicles, especially trucks,

as they accelerate uphill and decelerate

downhill. A level roadway elevation

avoids this extra noise generation.

Building highways ground level creates

natural barriers between the highways

and any noise sensitive locations.

Building Insulation: Sound insulation in

buildings, in the form of replacing

windows and doors, providing central

ventilation systems, and adding

insulation to attics (top floors), are only

considered for public buildings and

nonprofits institutional structures on a

case by case basis.

7.5 Response of Noise Pollution Control in Nepal through Legislation, Plan & Policies

In Nepal, there are no specific policies,

legislation or guidelines related to noise

Sunil Babu Khatry, Noise Pollution, 513 -Page, 50

pollution control. However, the need for

policies, plan and legislation of noise

pollution was clearly spelled out in Nepal

Environmental Policies and Action Plan

(NEPAP) in 1993. NEPAP was based on

Agenda - 21 that has addressed most of

the principles relevant to the country. It

refers to the declaration of principles by

United Nations Conference on

Environment and Development (UNCED)

held in Rio de Janeiro (June, 1992).

Principles like 11, 13, and 17 of Agenda -

21 followed by the NEPAP are relevant to

noise pollution control, which states that:

"Nation shall enact effective

environmental laws and developmental

law regarding liability and compensation

for the victims of pollution and other

environmental damage. Nation shall

undertake the environmental assessment,

as a national instrument for proposed

activities that are likely to have a

significant adverse impact on the

environment."

Eighth Five Year Plan (1992 - 1997) has

strongly emphasized on the importance of

EIA in developmental sector for

investigating development - related

pollution and to adopt proper technology to

minimize such pollution. Subsequently, the

Environmental Protection Act, EPA (1997)

and Environmental Protection Rules, EPR

(1997) were enacted. Similarly, Ninth Five

Year Plan (1997 - 2002) has laid more

emphasis on Pollution Prevention Strategy.

In the current Tenth Five Year Plan (2002 -

2007), it spells out about the long term

goals for pollution control in a sustainable

manner as well as envisages the

visualization of legal and fiscal mechanisms

for controlling industrial pollution and

deliberates focuses on research on

environmental friendly technologies. The

working policies adopted in the Tenth Year

Five Year Plan has clearly spelled out

about air, water and sound pollution

standards determination and programs of

implementation giving emphasis to an

effective monitoring system. It was for the

first time in the sixth five - year plan (1980

- 1985) that environment problem was

recognized as national issue. Environment

was regarded as an integral part of

development in the Seventh Five - Year

Plan (1985 - 1990).

7.5.1 Related Legislation

• The Environmental Protection Act,

1997: Environmental Protection Act, 1997

and Environmental Protection Rules, 1997

have made provision dealing with Initial

Environmental Examination (IEE),

Environmental Impact Assessment (EIA),

Prevention and Control of Pollution and

Protection of National Heritage and

Environmental Protection Area.

Section (7) - 1 of the Act refers to

"Prevention and Control of Pollution"

which states; "Nobody shall create

pollution or allow pollution to be caused in

such a manner which is likely to have

significant adverse impact on the

environment or likely to be hazardous to

human life and health, or shall not emits

sound, heat radioactive rays, wastes from

any mechanical devices, industrial

enterprises or any other places contrary to

the prescribed standard." Subsection (2-3)

of the section (7) of the Act has given full

authority to the concerned agency to

immediately penalize or prohibit activities

violating to section (7) - 1. The chapter (3)

of the Act has provided various provisions

under rules (15 - 20) for prevention and

control of pollution. Rule - 15 refers to

prohibition of emitting waste states that

"A person shall not emit or cause the

emission of noise, heat, radioactive

material and wastes from any mechanical

means, industrial establishment or any

other place in contravention of the

standard prescribed by the Ministry

through notification published in the

Gazette." Rule - 16 has enforced the

industries like chemical, food processing,

textile etc listed in Annex - 7 of the Act to

install equipment to reduce the pollution

under prescribed standard and to take

provisional or permanent certificate from

the concerned body (MoPE / MoEST). Rule

(17 - 20) has given provision of lodging

complained against pollution and

Sunil Babu Khatry, Noise Pollution, 513 -Page, 51

empowered the concerned body to issue

notice to control pollution and to carry out

sanitation and cleanliness activities.

• The Labor Act, 1991: The Labor Act,

1991 that is administrated by the

Ministry of Labor, is the main regulation

that regulates the working environment.

Chapter 5 of the Act deals with

occupational health and safety. Section 27

of chapter 5 requires the management to

make certain arrangements such as

reduction of noise pollution that would

adversely affect the health of workers.

Section 26 and 29 require for management

to provide protective clothing or devices to

workers handling excessive noise

producing equipment.

• Industrial Enterprises Act, 1992: As provided in industrial policy, these

act mandates to take license for the

industries listed in the Annex - 2 of the

Act if it causes significantly adverse

effect on defense, public health and

environment. Section 11 clearly provides

that licenses or registration certificates

shall contain provision regarding

concession, exception, facilities that will

be given to enterprise and prescribed

condition to be fulfilled by them. Section

13 mandates the Industrial Promotion

Board established under the Act, Section

12 to direct the industries to make

arrangements for controlling

environment pollution. Section 15 (k)

provides permission to grant up to 50%

of taxable income for the investment of

an industry on process or equipment

with the objective of controlling pollution

or environment. Section 25 (l) empowers

Nepal government to punish any person

for establishing any industry without

complying the condition mentioned in

the license or certificate of registration.

• Motor Vehicle and

Transportation Management Act,

1993: Section 23 of the Act empowers

the Government of Nepal to fix

necessary standard to examine pollution

that vehicle may cause and also to

determine whether or not the vehicle is

road worthy. Section 17 (l) enforces the

vehicle owner to examine the vehicle

under the measures prescribed in section

23, before registration and for taking

owner roadworthiness certificate.

Section 118 of the Act mandates the

traffic police department to put

restriction to drive any vehicle at any

public place for public security and

welfare of the common people. Under

this Act, Traffic Police Department has

recently (2003) declared Horn

Restriction Zone from Shaidgate to

Jamal in Kathmandu City. For violation

of this law, under the section 164 of the

Act, traffic police can impose fine

immediately from Rs 25 to Rs 200.

• Local Self Governance Act, 1999: Section 28(h) of chapter 4; part 2 of this

Act empowers the Village Development

Committee to take executive decision and

direction to make various programs

related to environmental protection.

Similar empowerments are given to

District Development Committees and

Municipalities in section 189(g) and

section 96(c) of chapter 1, part 3

respectively. Section 70 (h) of this chapter

8 of this Act clearly mandated the Village

Development Committee to punish any

person that carry out such activity as to

disturb peace in the neighboring place or

society by way of installing or through any

equipment or means of entertainment. A

similar mandate is also given to

Municipality under section 165(g).

• The Town Development Act, 1999: Clause 9 of this Act empowers the Town

Development Committee to regulate,

control or to prohibit any act or activity

that has an adverse effect on public

health or aesthetic of the town, or in any

way pollutes the environment. It contains

penalty provision in the form of fines for

the violation of the Act.

Sunil Babu Khatry, Noise Pollution, 513 -Page, 52

• National 9Transport

Management Plan and Policy

of Government, Long Term

Vision (Interim Plan

(2007/08-2009/10)): The long

term vision is to make the transport

system safe, affordable, organized,

non-polluting and service-oriented,

through qualitative increase in

vehicle and transport services,

thereby making a contribution

towards the overall development

and prosperity of the country.

9 Transport Management System of Nepal, Yuba Raj

Pandey, Ministry of Labour and Transport

Management, Kathmandu, Nepal February 2009

Sunil Babu Khatry, Noise Pollution, 513 -Page, 53

8. Health Effects of Noise

The health significance of noise pollution

specific effects are noise induced hearing

loss, sensory effects, speech intelligibility

effect, sleep disturbance effect,

psychophisiological effects, mental health

illness, performance effects and effects on

residential behavior and annoyance.

Sleep / clinical

Disorders

- Sleep apnoea - Chronic Insomnia

Effects on Health

Short Term - Increased risk of accidents - Blood Pressure - Stress of hormones

Medium term - Cardiovascular - Cognitive performance

Long Term - Mental - Cardiovascular - Immune system

Symptoms or Indicators of

disturbed sleep "Sleep

Disturbance"

- Don't be able to fall asleep

- Successive awakenings - No –resting sleep

Time

Stressors

- Environment - Psychological - Life style

Sunil Babu Khatry, Noise Pollution, 513 -Page, 54

8.1 Human Ear

8.1.1 Hearing and Mechanism of

Hearing Loss

Sound first enters the ear through the

outer canal (external auditory meatus or

ear canal). The sound then falls on

eardrum (tympanic membrane). The

eardrum vibrates under the influence of

the incident sound wave. These waves

then connected through a series of bones

(ossicles) that reduces the amplitude and

increase the force upon inner round

windows. This transmits the waves to

liquid borne pressure waves within the

circular canal (cochlea). The pressure

fluctuations within the liquid in the

cochlea excite small nerve cells (hair

cells). Each of these hair cells has its own

individual nerves and they are connected

together into the auditory nerves, which

then go off to the brain center.

8.1.2 Outer and Middle Ear

Mechanism

The outer ear collects sound waves

through the auricle (pinna) and the

external acoustic meatus that ends with

the tympanic membrane (eardrum). The

aural reflex is more responsive to

broadband sounds than to pure tones and

more responsive to lower frequencies than

to higher, and is most readily activated

and maintained by intermittent, intense

pulses. The middle ear muscle contraction

increases the impedance of the middle ear

resulting in an attenuated input of sound

energy through cochlea.

8.1.3 Cochlear Mechanism

The sensory cells (having hair like

projection - stereocilia) of the corti convert

the pressure wave into ionic and electric

events, which constitute a nerve impulse.

The inner hair cells serves as the pre-

synaptic sensory receptors and the outer

ones are believed to serve as an

amplification system due to their

contractile properties. The more hair cells

are being activated when the sound

intensity increases. There is an initiation

of action potentials in the sensory nerve

endings when the stereocilia of the inner

hair cells are bent. Finally, the brain

interprets the impulses from the place of

maximal stimulation of the organ of corti

as a particular pitch of sound.

8.1.4 Degrees of Hair Cell Injuries

The outer and middle ear is rarely

damaged by noise but there exists the

possibility of rupturing of eardrum

Sunil Babu Khatry, Noise Pollution, 513 -Page, 55

through explosive noise. The neural

damage involves the injury to the hair

cells that results of hearing loss. The

excessive shearing forces mechanically

damage the hair cells. The intense noise

stimulation forces the hair cells into high

metabolic activity, which overdrives them

to the point of metabolic failure and

consequent cell death. Once destroyed,

hair cells are not capable of regeneration.

The hair cells may be partially, severely

injured or totally degenerate at the

number of degrees of sound exposure. The

partial injury in corti is observed through

the distortion of pillar cells, swelling of

supporting cells and absence of hair cells.

In severely injury case, there is collapse of

corti, absence of hair cells and the

accessory cells swollen and distorted.

Ultimately, there is absence of nerve

fibers and corti organ in the stage of total

degeneration.

8.2 Noise - Induced Hearing Effect

Hearing disability may be assessed in

terms of difficulty in understanding

acoustic signals and speech. From a

hearing-deficit point of view, noise is

primarily described in terms of equivalent

continuous sound pressure level over

certain averaged period. It is generally

believed that the damage of risk is

negligible at noise exposure levels of less

than 75dB(A) (LAeq, 8h). The available

evidence indicates that the risk increases

when impulsive sound pressure reaches

130 - 150dB (peak level) or when their

noise emission level exceeds 115dB. The

addition of impulsive noise on a steady

noise may increase the risk for damage at

80 - 110dB (LAeq, 8h) and 100 - 130dB peak.

The noise-induced hearing loss

accompanied through hearing

impairment, temporary threshold shift

and permanent threshold shift.

Hearing impairment is typically

defined as an increase in the threshold of

hearing. Hearing sensitivity diminishes

with age, a condition is known as

presbyacusis. Hearing deficits may be

accompanied by tinnitus (ringing in the

ears). Noise - induced hearing

impairment occurs in the higher

frequency range (3000 - 6000Hz). It is

expected that environmental and leisure

time noise with a LAeq, 24h of 70 dB or

below will not cause hearing impairment

in majority of community people even

after a lifetime exposure. But for shooting

noise with LAeq, 24h levels greater than

80dB, there may be an increased risk for

noise-induced hearing impairment.

Noise-Induced Temporary Threshold

Shift (NITTS) is a reversible

phenomenon in audiometric threshold

when a person entering a very noisy area

may experience a measurable loss in

hearing sensitivity. This may recover

some time after returning to a quiet

environment. But this may depend on the

severity of the hearing shift, individual

susceptibility and type of exposure.

Noise - Induced Permanent

Threshold Shift (NIPTS) is recognized

when the recovery from NIITS is not

complete before the next exposure; there

is a possibility that some of the loss will

become permanent. NIPTS usually

involves a maximum loss at around the

frequency of 4000Hz. The first stages of

noise-induced hearing loss are often not

recognized because they do not impair

speech communication ability in quiet. As

the loss becomes more pronounced, there

arise the difficulty in speech reception

Sunil Babu Khatry, Noise Pollution, 513 -Page, 56

may be encountered, particularly in the

noisy environment. Hearing of important

sounds other than speech (door bells,

telephones, or electronic signals) may also

be impaired. With further advancement,

speech communication may be severely

affected.

Acoustic Trauma is a permanent

hearing loss that results from very brief

exposure to a very loud noise. In this

case, the outer and middle ear rarely

damaged by intense noise. The explosive

sounds can rupture the tympanic

membrane or dislocate the ossicular

chain.

Presbyacusis is the condition of hearing

loss especially ascribed to aging effects.

The greatest hearing loss takes place in

higher frequency. Study shows that this

phenomenon is more pronounced in man

rather than women for medium to high

frequency sounds. The presbycusis curves

for women and men show the average

threshold shift for pure tones as a

function of age10.

10 ASA Subcommittee Z24-X-2, "The Relations of

Hearing Loss to Noise Exposure," New York, 1954,

pp.16-17

8.3 Sensory Effects Physical ear discomfort of noise exposure

starts from sound pressure level 80 -

100dB and up. Persons with some ear or

sensorineual hearing disorders and

hearing - aid users may experience aural

pain on exposure at even lower levels.

Tinnitus and loudness conscription are

common sensory effects accompanying

temporary or permanent hearing

impairment. Both trends may be

experienced as the result of exposure to

very loud noise.

Aural Pain: In abnormal hearing

(inflammation), pain may be caused in

the eardrum or middle ear by sound

pressure level of about 80 - 90dB. The

threshold of pain for sound exposures in

normal hearing persons is in the region of

the sound pressure level of 110 - 130 dB.

The threshold for physical discomfort

called loudness discomfort level (LDL) or

uncomfortable loudness level (ULL) is in

the region of 80 - 100dB SPL. In many

cases of sensorineual hearing disorders

(Meniere’s disease), dysacusis symptoms

(lowering of the threshold of aural

discomfort and pain) may appear.

Some forms of Tinnitus are produced due

to the blood flow through the ear

structures. Certain sensorineural

Presbycusis curves for women and men

Sunil Babu Khatry, Noise Pollution, 513 -Page, 57

disorders, and most frequently noise -

induced hearing losses, are accompanied

by abnormal loudness perception

(loudness recruitment).

8.4 Interference with Speech Communication

Noise interference with speech bias

results in a great proportion of person

disabilities and handicaps such as

problems with concentration, fatigue,

uncertainty and lack of self-confidence,

irritation, misunderstandings, and

decreased work capacity, problems in

human relations, and number of reactions

to stress. The higher the level of the

masking noise and more energy it

contains at speech frequencies, the greater

will be the percentage of speech sounds

that are undetectable to the listener.

Many noises that are not enough intense

to cause hearing impairment can interfere

with speech communication. The

interference effect is a complicated

function of the distance between the

speaker and listener and the frequency

components of the spoken phonemes.

During relaxed conversation, the speech

level is approximately 55dB(A) and that

as the noise levels increase, people tend

to raise their voices to overcome the

masking effect. At a distance of 1m from

the speaker, relaxed conversation occurs

at a voice level of approximately 54 -

56dB(A) and normal and raised voices at

levels of approximately 60 and 66dB(A).

The speech level should exceed the noise

level by 15 to 18dB(A) for 100% sentence

intelligibility. When the speech level is

equal to noise level, intelligibility falls to

95%.

So, for normal conversation at about 1m

distances, the background noise should

not exceed 70dB(A). Shouted

conversations at the same distance are

possible up to about 85dB(A). To permit

normal conversation at distances of about

5 meters would require a background

noise level below 50dB(A). Satisfactory

telephone conversations need background

levels less than about 80dB(A). The

estimated sentence intelligibility, at

speaker-listener distances greater than

1m in the reverberant conditions found in

a typical living room. For 100% sentence

intelligibility, it is desirable for indoor

listening conditions, a background noise

level of less than 45dB(A).

Communication Impossible

Communication Difficult

Communication Possible

Max. Vocal Effort

Shout

Expected Voice Level

3 6 9

Talker to Listener Distance, m

Backgro

un

d

Nois

e, dB

(A)

100

120

hig

h

Low

40

Sunil Babu Khatry, Noise Pollution, 513 -Page, 58

Effects of Noise on People (Residence Land Use Only)

Day-

Night

Average

Sound

Level

Speech Interference

Average

Communit

y Reaction d

General Community

Attitude Towards Area

Effects a

Hearing

Loss Indoor Outdoor

Annoyance b

Qualitative

Description

% Sentence

Intelligibilit

y

Distance in

meter for

95%

Sentence

Intelligibilit

y

% of

Population

Highly

Annoyed c

75

may begin

to occur

98

0.5

37

very severe

Noise is likely to be the

most important of all

adverse aspects of the

community environment

70

will not likely

to occur

99

0.9

25

severe

Noise is one oft he most

important adverse

aspects of the community

environment.

65

will not

occur

100

1.5

15

significant

Noise is one of the

important adverse

aspects of the community

environment.

60

will not

occur

100

2.0

9

moderate

to slight

Noise may be considered

an adverse aspect of the

community environment.

55

will not

occur

100

3.5

4.0

-

Noise is considered no

more important than

various other

environmental factors.

11Notes: Research implicates noise as a factor producing stress-related health effects such as heart diseases,

high blood pressure and stroke, ulcers and other digestive disorders. The relationships between noise

and these effects, however, have not as yet been quantified.

a. Speech interference data are drawn from other US Environmental Protection agencies studies.

b. Depends on attitudes and other factors.

c. The percentage of people reporting annoyance to lesser extent is high in each case. An unknown small

percentage of people will report being highly annoyed even in the quietest surroundings. One reason is

the difficulty all people have in integrating annoyance over a very long time.

d. Attitudes or other non-acoustic factor can modify this. Noise at low levels can still be important problem,

particularly when it intrudes into a quiet environment.

11 Federal Interagency Committee on Urban Noise, 1980, p. D-2

Sunil Babu Khatry, Noise Pollution, 513 -Page, 59

8.5 Sleep Disturbance Effects

If the equivalent continuous sound

pressure level during the sleeping period

exceed 30 - 50dB(A), Leq indoors, the

negative effects on rapid eye movement

sleep occurs. For isolated exposures as low

as 45dB(A, max), awakenings, changes of

sleep depth have been shown. Exposure to

noise cans disturbances of sleep in terms

of difficulty to fall asleep, alteration of

sleep pattern or depth, and awakenings.

The other primary physiological effects

that can be induced by noise during sleep

are vegetative reactions (increased blood

pressure and heart beating rate, finger

pulse amplitude, vascoconstriction, and

change in respiration and cardiac

arrhythmia as well as body movement).

Exposure to nighttime noise can also

induce secondary effects or aftereffects,

that is, effects can be measured in the

morning or the day after exposure. They

include perceived sleep quality, increased

fatigue, decreased mood, and decreased

performance.

The time required to fall asleep is

considered as an important aspect of

noise - induced sleep disturbances. A

longer time to fall asleep was found in

sensitive as well as non - sensitive

adults at sound pressure levels of 50

and 60dB(A, max) road traffic noise. A

reduction in the time need to fall asleep

was found among children who slept in

a more quiet room and among adults

who slept with closed windows as

compared to sleeping with open

windows.

In young and middle aged persons,

awakening reactions start occurring

from at least 50 - 55dB(A, max) indoors,

probably at low levels (12.7% awakened

at 47dBA, max of road traffic noise).

Among one third of the exposed persons

(30.6% at 60dBA, max) about 10% of

the noise events would produce a wake

up at 65dB(A, max),

Body movements have been registered

as an objective indication of

disturbances of noise during sleep.

Large body movements have been found

to be associated with the number of

awakenings or sleep-stage shifts and

sleep depth. The probability of noise-

induced body movements increased

with increasing maximum sound

pressure level in the same manner as

the probability of awakening reactions.

There was a threefold increase in body

movements at 45, 50 and 60dB(A, max)

noise levels at 16 events per night, and

slightly lower increase at 64 events per

night.

Physiological reactions (effects on heart

rate, finger pulse and respiration rate)

have been observed during the exposure

to noise levels exceeding 40dB(A, max)

while sleeping. The heart beat rate

response (difference between

acceleratory and deceleratory phases)

during sleep to a single noise event can

be 20 to 30 beats.

8.6 Psycho Physiological Effects

It has been postulated that noise acts as a

general stressor and as such may activate

physiological systems leading to changes

such as increases in blood pressure and

heart rate and vasoconstriction. Many

Sunil Babu Khatry, Noise Pollution, 513 -Page, 60

studies indicated that workers exposed to

high levels of industrial noise for 5 to 30

year duration have significantly increased

blood pressure compared to workers in

control areas. There has been a tendency

for blood pressure to be higher among

persons living in airport vicinity and on

streets with higher levels of traffic noise.

Noise induced stress may increase the

excretion of magnesium which may

cause negative magnesium balance that

may produce progressive

vasoconstriction, vasospasm and

ischemia which may lead to

hypertension and coronary heart

disease.

The overall evidence for the effects of

noise on cardiovascular functioning is

suggestive of weak to moderate effects of

community noise on blood pressure.

8.7 Mental Health effects Exposure to high levels of occupational

noise has been associated with development

of neurosis and irritability. Actually, noise

might accelerate and intensify the

development of latent mental disorders.

The criteria have been classified for mental

health such as indices based on treatment

data, psychiatric signs and symptoms,

indicators of mood, well-being, satisfaction,

indices of functional effectiveness and role

performance, and indices derived from

notions of positive mental health. Anxiety,

emotional stress, nervous complaints,

nausea, headaches, instability,

argumentativeness, sexual impotency,

changes in general mood and anxiety, and

social conflicts, more general psychiatric

problems like neurosis, psychosis and

hysteria are the noise induced mental

health symptoms.

8.8 Performance Effects Acute noise exposure appears to disrupt

tasks. The chronic noise exposure impacts

reading acquisition in children. Various

findings showed that impaired reading and

word list performance, and long term recall

of a text in children was found in nearby

uncontrolled airport side schools.

8.9 Effects on Residential Behavior and Annoyance

Community reaction to noise may involve

considerably more than just annoyance.

People may feel a variety of negative

emotions when exposed to community noise

and may report anger, disappointment,

dissatisfaction, withdrawal, helplessness,

depression, anxiety, distraction, agitation

or exhaustion. Annoyance is a feeling of

displeasure associated with any agent or

condition known or believed by an

individual or a group to be adversely

affecting them.

Annoyance generally increases with

sound pressure level; it has been found

that communities vary considerably in

their reaction to the same sound level.

Differences between reactions in

different cities may be as great as the

equivalent of a 15dB difference.

Annoyance is generally related to the

direct effects of noise on various

activities, such as interference with

conversation, mental concentration, rest,

or recreation.

Sound environments produce a number

of social and behavioral effects on

residential behavior and annoyance

including: overt everyday behavior

patterns (opening windows, using

balconies, TV and radio use, writing

petitions, complaining to authorities),

human performance on specific test

tasks (school achievement, vigilance,

choice-reaction time, short-term memory,

air traffic control), social behavior

(aggression, unfriendliness, engagement

and participation), social indicators

(residential mobility, hospital

admissions, drug consumption, accident

rates), changes in mood (less happy,

more depressed mood, etc.)

Sunil Babu Khatry, Noise Pollution, 513 -Page, 61

9. Criteria for Continuous and Intermittent Noise

The statement in the occupational exposure

limit that the proposed OEL (85 dB(A)) will

protect the median of the population against a

noise-induced permanent threshold shift

(NIPTS) after 40 years of occupational

exposure exceeding 2 dB for the average of 0.5,

1, 2, and 3 kHz comes from ISO-1999-1990.

Today, A-weighted sound levels are in general

use in hearing damage risk criteria.

9.1 ISO 1999-1990

The ISO 1999-1990 standard provides a

complete description of NIPTS for various

exposure levels and exposure times. The 85

dB(A) limit for 8 hours is recommended by the

ACGIH and has found acceptance in most

countries. Because some countries still use 90

dB(A) or both for different steps of action and

indeed the early OEL was at 90 dB(A), a short

review of the ACGIH recommending an A-

weighted 8-hour equivalent level of 85 dB(A) is

in order.

The relationship between stress and strain with special regard to moderate variables

Sunil Babu Khatry, Noise Pollution, 513 -Page, 62

85 dB(A) vs. 90 dB(A): Permanent noise-

induced hearing loss is related to the sound

pressure level and frequency distribution of

the noise, the time pattern and duration of

exposure, and individual susceptibility. The

zero settings on the audiometer are based on

response levels derived from the testing of

large groups of young people. There is

general agreement that progression in

hearing loss at frequencies of 500, 1000,

2000, and 3000 Hz eventually will result in

impaired hearing, i.e., inability to hear and

understand speech.

a. NIOSH, 1972 Criteria for a Recommended

Standard–Occupational Exposure to Noise

(National Institute of Occupational Safety

and Health 1972) - Workers exposed for

more than 30 years to 85 dB(A)

b. U.S. Environmental Protection Agency

(EPA 1974) - an 8-hour level of 75 dB(A)

was established as the level that would

protect "public health and welfare with an

adequate margin of safety.

c. AAOO (American Academy of

Ophthalmology and Otolaryngology), 1979

- TLV includes 3000 Hz. Using ISO-1999,

the median amount of NIPTS after 40

years of exposure to 90 dB(A) is 2 dB for

the average of 500, 1000, and 2000 Hz.

The same 40-year exposure at 85 dB(A) for

the average of 500, 1000, 2000, and 3000

also is 2 dB. Thus, everything else being

equal, inclusion of 3000 Hz will drop the 8-

hour criterion level from 90 dB(A) to 85

dB(A). The criterion are as follows:

1.The average of the hearing threshold

levels at 500, 1000, 2000, and 3000 Hz

should be calculated for each ear.

2.The percentage of impairment for each

ear should be calculated by multiplying

by 1.5 percent the amount by which the

average hearing threshold level exceeds

25 dB(A). The impairment should be

calculated up to 100 percent reached at

92 dB(A).

3.The impairment then should be

calculated by multiplying the percentage

of the better ear by five, adding this

figure to the percentage from the poorer

ear, and dividing the total by six.”

3 dB(A) vs. 5 dB(A): If hearing damage is

proportional to the acoustic energy received

by the ear, then an exposure to a particular

noise level for one hour will result in the

same damage as an exposure for two hours

to a noise level which is 3 dB lower than the

original level. This is referred to the 3 dB(A)

trading rule and is generally accepted in

many parts of the world. However, 4 dB(A)

and 5 dB(A) rules exist in the USA.

Inclusion of 3000 Hz would dictate reducing

the 5 dB(A) trading relation to a lower

number. In some cases, this number might

even be slightly lower than 3 dB(A). In

summary, the equal energy rule (3 dB(A)

rule) appears to be a better predictor of noise

hazard for most practical conditions and is

strongly recommended by the TLV

Committee.

9.2 Criteria for Impulse Noise

Impacts or impulses referred to discrete noise

of short duration, less than 500 ms, where the

SPL rises and decays very rapidly. For

assessing impulse/impact noise was to allow

100 impulses or impacts per day at 140 dB(A),

or 1000 per day at 130 dB(A), or 10,000 per

day at 120 dB(A).

9.2.1 Control of noise exposure in workplaces. (Policy and guidance documents of the International Labour Organization (ILO)):

General Conference of the International

Labour Organization in 1977, provides that, as

far as possible, the working environment shall

be kept free from any hazard due to air

pollution, noise or vibration. Neither

Convention No. 148 nor the accompanying

Recommendation No. 156 concerning the

Protection of Workers against Occupational

Hazards in the Working Environment Due to

Air Pollution, Noise and Vibration, also

adopted in 1977, specify exposure limits for

Sunil Babu Khatry, Noise Pollution, 513 -Page, 63

noise at the workplace. As of June,1997, 39

countries have ratified the Convention No. 148

of which 36 have accepted its obligation in

respect of noise. The ratification of a

Convention by an ILO member State involves

the obligation to apply, in law and in practice,

its provisions. In the light of knowledge at the

time of publication, a warning limit value of 85

dB(A) and a danger limit value of 90 dB(A) are

recommended.

9.2.2 Occupational Exposure Levels reported and recommended by I-INCE

In 1997 the final report on “Technical

Assessment of Upper Limits on Noise in the

Workplace“ had been approved and published

by the International Institute of Noise Control

Engineering (I-

INCE). It comprises the results of a Working

Party started in 1992 to “review current

knowledge.

1. Limit of 85 dB(A) for 8 hour workshift for

jurisdiction desirable as soon as possible.

2. Maximum sound pressure level as limit of

140 dB for C-weighted peak..

3. Exchange rate of 3 dB per doubling or

halving of exposure time.

4. Efforts to reduce levels to the lowest

economically and technologically reasonable

values.

5. In the design stage consideration to sound

and vibration isolation between noisier and

quieter areas, significant amount of

acoustical absorption in rooms occupied by

people.

6. Purchase specifications for machinery

should contain clauses specifying the

maximum emission values.

7. A long-term noise control program at each

workplace where daily exposure exceeds 85

dB(A).

8. Use of personal hearing protection should

be encouraged when engineering noise

control measures are insufficient to reduce

daily exposure to 85 dB(A), should be

mandatory when exposure level is over 90

dB(A).

9. Employers should conduct audiometric

testing of workers exposed to more than 85

dB(A) at least every three years, test

results should be preserved in the

employee„s file.

9.2.3 Occupational Exposure Levels recommended by NIOSH

In 1972, NIOSH published Criteria for a

Recommended Standard: Occupational

Exposure to Noise, which provided the basis

for a recommended standard to reduce the risk

of developing permanent hearing loss as a

result of occupational noise exposure (NIOSH

1972). NIOSH has now evaluated the latest

scientific information and is revising some of

its previous recommendations (NIOSH

1998),as it is summarized in the foreword of

the new document.

NIOSH recommended exposure limit

(REL) of 85 dBA for occupational noise

exposure.

The excess risk of developing

occupational noise-induced hearing

loss (NIHL) for a 40-year lifetime

exposure at the 85 dBA REL is 8%,

which is considerably lower than the

25% excess risk at the 90 dBA

permissible exposure limit currently

enforced by the Occupational Safety

and Health Administration (OSHA)

and the Mine Safety and Health

Administration (MSHA).

NIOSH previously recommended an

exchange rate of 5dB for the

calculation of time-weighted average

exposures to noise, but it is now

recommending a 3-dBexchange rate,

which is more firmly supported by

scientific evidence. The 5-dB exchange

rate is still used by OSHA and MSHA,

but the 3-dB exchange rate has been

increasingly supported by national and

international consensus.

Sunil Babu Khatry, Noise Pollution, 513 -Page, 64

NIOSH recommends an improved

criterion for significant threshold

shift, which is an increase of 15 dB in

hearing threshold at 500, 1000, 2000,

3000,4000, or 6000 Hz that is repeated

for the same ear and frequency in

back-to-back audiometric tests.

9.2.4 ACGIH Recommendation

American Conference of Government

Industrial Hygienists (ACGIH) has

recommended threshold limit values (TLV) for

occupational noise. The OEL's refer to sound

pressure levels and exposure durations that

represent conditions under which it is believed

that nearly all workers may be repeatedly

exposed without adverse effect on their ability

to hear and understand normal speech.

Prior to 1979, the medical profession had

defined hearing impairment as an average

hearing threshold level in excess of 25 dB(A)

(ISO-7029-DIS) at 500, 1000, and 2000 Hz.

The limits that are given here have been

established to prevent a hearing loss at 3000

and 4000 Hz. The values should be used as

guidelines in the control of noise exposure and,

due to individual susceptibility, should not be

regarded as fine lines between safe and

dangerous levels. The proposed limits should

protect the median of the population against a

noise-induced hearing loss exceeding 2 dB(A)

after 40 years of occupational exposure for the

average of 0.5, 1, 2, and 3Hz.

a. LEX,8h < < OEL (OEL = 85 or 90 dB(A)): the

working conditions are acceptable legally.

b. LEX,8h > >OEL: the conditions are

unacceptable and control measures must

be implemented as soon as possible

c. LEX,8h � OEL: additional measurements

are needed to determine whether LEX,8h is

lower or higher than the OEL.

Sunil (a)

References

1. Acoustic Materials for Sound Insulation for industrial, commercial or architectural applications, Smock &

Schonthaler Industries, Insulation Sales Inc.

2. Birgitta Berglund, Thomas Lindvall (1995), Community Noise, Center for Sensory Research, Stockholm,

Sweden.

3. Brief Technical Notes on Sound & Noise Control, N9701: ESI Engineering, Inc.., Minnesota.

4. Brigitta Berglund, Thomas Lindvall, Dietrich H Schela, Guideline for Community Noise,

WHO/SDE/PHE/OEH.

5. Canter, MW., Environmental Impact Assessment.

6. Chawla Gr, Mehra ML, Katyal T, Satake M, Katyal Mohan, Nagahiro Himeji (1989): Environmental Noise

Pollution & its Control.

7. Corner O Leo (1991), Putting a lid on noise pollution: Mechanical Engineering Journal, USA.

8. Criteria For a Recommended Standard; Occupational Noise Exposure - Revised Criteria 1998, U.S. Department

Of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National

Institute for Occupational Safety and Health, Cincinnati, Ohio

9. Cunnif PF (1977), Environmental Noise Pollution.

10. Davis, Cornwel, Environmental Engineering.

11. Garg, SK, Sewage disposal & air pollution engineering.

12. Gerard Kelly, Environmental Engineering.

13. Guideline Values for Community Noise in specific Environment (1999), WHO.

14. Jones DM, AJ (1984), Noise & Socity.

15. Lord P & Thomas, Noise Measurement & Control.

16. Manella R & Mc Clintock, Noise in non linear dynamical system; Contemporary Physics, Vol. 31, No. 3.

17. Monitoring Noise Levels Non – mandatory Informational appendix - 1910.95 App G: Regulations (Standards –

29CFR), US Department of Labor, Occupational Safety & Health Administration.

18. Monitoring Noise Levels Non-mandatory Information, Appendix1910.95 [Regulations standard - 29 CFR: app

G]: US Department of Labor, Occupational Safety & Health Administration 200 Constitution Avenue, NW

Wasihngton , DC 20210

19. NIOSH 919720, EPA (1973) & ISO (1971).

20. Noise & Health, Health Council of the Netherlands, 1994.

21. Noise Code (1998), Department of Environmental Protection, New York.

22. Noise Criteria (NC) Method: State of the Art Acoustics Inc., Ottawa, ON Canada K1J 9J3.

23. Noise Level Monitoring & Measurement: JIS C 1512/1983.

24. Noise Pollution, EPA Victoria, South Australlia.

25. Occupational Noise Exposure, Criteria For a Recommended, Standard Revised Criteria 1998: U.S.

Department Of Health And Human Services, Public Health Service, Centers for Disease Control and

Prevention , National Institute for Occupational Safety and Health Cincinnati, Ohio.

26. Occupational Noise Exposure, Recommendations for a Noise Standard, NIOSH, CDC, USA.

27. Poleto, David MY, Cost – Benefit Handbook: A guide for New York State’s Regulatory Agencies, Government

Regulatory Reform.

28. Protection of the Human Environment, Guidelines for Community, WHO.

29. Recommendations for a Noise Standard, Niosh, CDC, 1999.

30. Rosenstock, Linda (1996), Criteria for a Recommended Standard Occupational Nosie Exposure, Revised

Criteria, DHHS (NIOSH), Publication No. 96

31. Sound Level Meters, JIS Z 8731/1983.

32. Young H. D. & Scars F. W.; University Physics.

33. Wikimedia Foundation, Inc 2007

34. Henderson Tom (1996 – 2004), The Nature of Sound

35. Allan D. Pierce, Acoustics: An Introduction to its Physical Principles & Application, 2007 The Acoustical

Society of America

36. Sapkota, Balkrishna (2004), Fundamentals of Noise Pollution, Department of Physics, Pulchowk Campus,

Lalitpur

Sunil (b)

A. Annexure

Table 1: Guideline Values for Community Noise in Specific Environments

Specific environment Critical Health Effect(s) LAeq

[dB(A)]

Time

base

[hours]

LAmax

fast

[dB]

Outdoor living area Serious annoyance, daytime and evening

Moderate annoyance, daytime and evening

55

50

16

16

-

-

Dwelling, indoors

Inside bedrooms

Speech intelligibility & moderate

annoyance, daytime & evening

Sleep disturbance, night-time

35

30

16

8

45

Outside bedrooms Sleep disturbance, window open (outdoor

values) 45 8 60

School class rooms & pre-schools,

indoors

Speech intelligibility, disturbance of

information extraction, message

communication

35 during

class -

Pre-school bedrooms, indoor Sleep disturbance 30 sleeping-

time 45

School, playground outdoor Annoyance (external source) 55 during

play -

Hospital, ward rooms, indoors Sleep disturbance, night-time

Sleep disturbance, daytime and evenings

30

30

8

16

40

-

Hospitals, treatment rooms, indoors Interference with rest and recovery #1

Industrial, commercial shopping and

traffic areas, indoors and outdoors Hearing impairment 70 24 110

Ceremonies, festivals and

entertainment events

Hearing impairment (patrons:<5

times/year) 100 4 110

Public addresses, indoors and

outdoors Hearing impairment 85 1 110

Music and other sounds through

headphones/ earphones Hearing impairment (free-field value) 85 #4 1 110

Impulse sounds from toys, fireworks

and firearms

Hearing impairment (adults)

Hearing impairment (children)

-

-

-

-

140 #2

120 #2

Outdoors in parkland and

conservations areas Disruption of tranquillity #3

# 1: As low as possible.

# 2: Peak sound pressure (not LAF, max) measured 100 mm from the ear.

Sunil (c)

# 3: Existing quiet outdoor areas should be preserved and the ratio of intruding noise to natural background sound

should be kept low.

# 4: Under headphones, adapted to free-field values.

Table 2: Noise Abatement Criteria

Hourly A - Weighted Sound Level in Decibels (dBA)

Activity

Category Leq(h) Description of Activity Category

A 57 (Exterior)

Lands on which serenity and quiet are of extraordinary significance and serve

and important public need, and where the preservation of those qualities is

essential if the area is to continue to serve its intended purpose

B 67 (Exterior) Residences, churches, school, libraries, hospitals, motels, hotels, parks, picnic

and recreation areas, active sports areas and playgrounds

C 72 (Exterior) Developed lands, properties or activities not included in Categories A or B

D Not Applicable Undeveloped lands

E 52 (Interior) Residences, motels, hotels, public meeting rooms, schools, churches, libraries,

hospitals and auditoriums

Table 3: South Australia Environmental Noise Policy

Class of Machine

Maximum

permitted

Noise Level,

dB(A)*

Specified Times

Lawnmowers, poser equipment and their

drives (including saws, drills, tools,

compressors, pumps, swimming pool pumps

and filters, etc)

45

From 8pm on any night (except Saturday

night) until 8am on the following morning.

From 8pm on Saturday night until 9am on

the following Sunday morning.

Domestic air conditioners 45

From 10pm on any night (except Saturday

night) until 8am on the following morning.

From 10pm on Saturday night until 9am on

the following Sunday morning.

Some non – domestic noise sources are also controlled by this policy

Bird scaring devices 45

From 8pm on any night until 7am on the

following morning.

Garbage collection units, street sweepers,

hoggerso 60

From 8pm on any night (except Saturday

night) until 7am on the following morning.

From 8pm on Saturday night until 8am on

the following Sunday morning.

*: Measured at any place, other than the premises from which the noise emanates, where a person lives or works.

O: Mobile mulching machines

Sunil (d)

Ref.: Environmental noise, October 2004, EPA South Australia

Table 4: Construction Equipment Noise Ranges

Eq

uip

men

t P

ow

ere

d b

y In

tern

al C

om

bu

sti

on

En

gin

es

Eart

h M

ovin

g

Equipments Noise Level at 50ft,

dBA

Compactors (Rollers0 71 - 74

Front Loaders 72 - 83

Backhoes 72 - 92

Tractors 78 - 94

Scrapers, Graders 80 - 82

Pavers 87 - 89

Trucks 83 - 93

Ma

teri

als

Ha

nd

lin

g Concrete Mixers 74 - 85

Concrete Pumps 81 - 82

Cranes, Movable 74 - 85

Cranes, Derrick 87 - 90

Sta

tio

nary

Pumps 69 - 71

Generators 73 - 83

Compressors 76 - 87

Impact Equipment

Pneumatic wrenches 83 - 88

Jackhammers and Rock Drills 82 - 96

Impact Pile Drivers Peaks 95 - 104

Others

Vibrator 69 - 81

Saws 73 - 81

Ref: US Environmental Protection Agency, 1972, P. 2-108

Sunil (e)

Table 5: Long Term Health effects of Noise Exposure, Netherlands

Health Effects Observation threshold (levels above which effect starts)

Effect Situation Noise metric Level in

dB(A) Inside/outside

1. Sufficient evidence

Hearing damage

Work LAeq, 8hr 75 Inside

Sport LAeq,24hr 70 Inside

Hypertension

Work LAeq,8hr <85 Inside

Home LAeq,6-22hr 70 Outside

Ischemic heart diseases Home LAeq,6-22hr 70 Outside

Annoyance Home Ldn 42 Outside

Awakening Sleep SEL 55 Inside

Sleep stages Sleep SEL 35 Inside

Self reported sleep quality Sleep LAeq, night 40 Outside

School performance School LAeq, day 70 Outside

2. Limited evidence

Birth-weight - - - -

Immune system - - - -

Psychiatric admission - - - -

3. Lack of evidence

Congenital effects - - - -

Immune system Sleep - - -

Ref.: Noise and Health, Health Council of the Netherlands, September 1994

Sunil (f)

Table 6: Ldn Values that protect Public Health and Welfare with a Margin of Safety

Effect Level Area

Hearing Leq(24) < 70 dB All areas (at the ear)

Outdoor activity interference and

annoyance Ldn < 55 dB

Outdoors in residential areas and farms and

other outdoors areas where people spend widely

varying amounts of time and other places in

which quiet is a basis for use.

Outdoor activity interference and

annoyance Leq(24) < 55 dB

Outdoor areas where people spend limited

amounts of time, such as school yards,

playgrounds, etc.

Indoor activity interference and

annoyance Ldn < 45 dB Indoor residential areas

Indoor activity interference and

annoyance Leq(24) < 45 dB

Other indoor areas with human activities such as

schools, etc.

Ref.: www.avlelec.com, inc.; INTERNET MERCHANT SINCE 1997Protective Noise Levels Condensed Version of EPA

Levels Document

Table 7: OSHA Technical Manual for Dosimeter Readout, in Percent of Measured Dose

Exposure Conditions

Dosimeter with

threshold set at

90 dBA

Dosimeter with

threshold set at

80 dBA

90 dBA for 8 hours 100.0% 100.0%

89 dBA for 8 hours 0.0% 87.0%

85 dBA for 8 hours 0.0% 50.0%

80 dBA for 8 hours 0.0% 25.0%

79 dBA for 8 hours 0.0% 0.0%

90 dBA for 4 hours plus 80 dBA for 4 hours 50.0% 62.5%

90 dBA for 7 hours plus 89 dBA for 1 hour 87.5% 98.4%

100 dBA for 2 hours plus 89 dBA for 6 hours 100.0% 165.3%

* Assumes 5-dB exchange rate, 90-dBA PEL, ideal threshold

activation, and continuous sound levels.

Ref.: NIOSH [1972], EPA [1973], and the International Standards Organization (ISO) [1971]

Sunil (g)

Table 8: Estimated Excess Risk Percentage as a Function of Average Daily Noise Exposure Over a 40 - year Working Lifetime Reported From Various Organizations

Reporting Organization Average Daily Noise

Exposure (dBA) Excess Risk

ISO

90 21

85 10

80 0

EPA

90 22

85 12

80 5

NIOSH

90 29

85 15

80 3

Ref.: NIOSH [1972], EPA [1973], and the International Standards Organization (ISO) [1971]

Table 9: Motor Vehicles Noise, New York City - USA

Vehicle Characteristics

Column I

Speed limit of

35 mph or less

Speed limit of

more than 35 mph

1. Any motor vehicle with a manufacturer‟s gross vehicle rating of

eight thousand pounds or more and any combination of vehicles

towed by such motor vehicle

86 dB(A)

90 dB(A)

2. Any motorcycle other than a motordriven cycle

Before January 1, 1978 82 dB(A) 86 dB(A)

After January 1, 1978 78 dB(A) 82 dB(A)

3. Any other motor vehicle and any combination of vehicles towed by such motor vehicle

Before January 1, 1978 76 dB(A) 82 dB(A)

After January 1, 1978 70 dB(A) 79 dB(A)

Column II

4. Any motor vehicle with a manfacturer's gross vehicle rating of eight

thousand pounds or more and any combination of vehicles towed by

such motor vehicle

92 dB(A) 96 dB(A)

5. Any motorcycle other than a motor driven cycle

Before January 1, 1978 88 dB(A) 92 dB(A)

After January 1, 1978 84 dB(A) 88 dB(A)

6. Any other motor vehicle and any combination of vehicles towed by such motor vehicle

Before January 1, 1978 82 dB(A)

88 dB(A)

After January 1, 1978 76 dB(A) 85 dB(A)

Ref.: Noise Code, Department of Environmental Protection, New York City, March 1998

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Table 10: Ambient Noise Quality Zones, New York City - USA

S.N. Ambient Noise

Quality Zone Features

Ambient noise quality zones are the classified zones for the entire geographical area of the city on the

basis of those conditions, which affect the ambient noise levels.

N - 1 Low density residential areas RL presently designated as land-use

zones R - I, R - 2, and R - 3.

N - 2 High density residential areas RH presently designated as land-use

zones R - 4, R - 5, R - 6, R - 7, R - 8, R - 9, and R - 10.

N - 3

All commercial and industrial areas presently designated as land-

use zones C - I, C - 2, C - 3, C - 4, C - 5, C - 6, C - 7, C - 8, M - I, M -

2, and M - 3.

Other Other land-use zones be established, including special zoning

districts.

Ref.: Noise Code, Department of Environmental Protection, New York City, March 1998

Table 11: Noise Standards for Various Ambient Noise Quality Zones, New York City - USA

Ambient Noise Quality Zone Day-time standards

(7am - 10pm)

Night-time standards

(10pm - 7am)

Noise quality zone N-1 (Low density residential RL; land-use zones

R-1 to R-3) Leq, 1hr = 60 dB(A) Leq, 1hr = 50 dB(A)

Noise quality zone N-2 (High density residential RH; land-use zones

R-4 to R-10) Leq, 1hr = 65 dB(A) Leq, 1hr = 55 dB(A)

Noise quality zone N-3 (All Commercial and manufacturing land-use

zones) Leq, 1hr = 70 dB(A) Leq, 1hr = 70 dB(A)

Ref.: Noise Code, Department of Environmental Protection, New York City, March 1998

Table 12: OSHA Noise Exposure Limits for the Work Environment

Noise Exposure Level, dBA Permissible Exposure (Hours & Minutes)

85 16 hrs

87 12 hrs 6 min

90 8 hrs

93 5 hrs 18 min

96 3 hrs 30 min

99 2 hrs 18 min

102 1 hr 30 min

105 1 hr

108 40 min

111 26 min

114 17 min

115 15 min

118 10 min

121 6.6 min

124 4 min

127 3 min

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130 1 min

Note: Exposure above or below the 90 dB limit have been “time weighted” to give what OSHA believes are equivalent

risks to a 90 dB eight - hour exposure.

Ref.: Marsh, 1991, p 322

Table 13: Some Important International Regulations

1. Road Traffic Noise Regulations in Different Countries, Emission Values for

Residential Areas, dB(A)

Country Noise Index Type of Emission Values Daytime Rest time Nighttime

Australia L(10,18h)

Target values for new roads 60

-

55

Reduction measures at existing

roads 65 -

Austria

L(A, eq)

Planning values for new roads 50 - 55 40 - 45

Remedial measures at federal

roads 65 -

Canada Target values for new residential

areas

55 50

Denmark 55 -

- France Limiting values for noise reducing

programs 60

Germany Lr = L(A, eq) + k;

k = 0 … 3dB

Planning values for new

residential areas 50 - 55 40 - 45

Limiting values for new and

considerably altered roads 59 49

Remedial measures at federal

roads 70 60

England L(A, eq); L10, 18h

Target values for new dwellings 55 42

Strong presumptions against new

dwellings 63 57

Insulation regulations for new

roads 68

- Hong Kong L10

Planning values for new

residential areas 70

Italy L(A, eq) Limiting values in some towns 65

Japan L50 Environmental standards for roads 50 - 60 50 - 55 45 - 50

Republic of L(A, eq) Environmental standards 65 55

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Country Noise Index Type of Emission Values Daytime Rest time Nighttime

Korea

Netherlands

Preferred values for new roads 55 50 45

Maximum allowable value for new

roads 63 - 70 58 - 65 53 - 60

Maximum allowable level for

existing roads 73 - 75 68 - 70 63 - 65

Switzerland Lr

Planning values for new roads 55

-

45

Emission impact threshold 60 50

Alarm value 70 65

USA Ldn No restrictions for new residential

developments at roads 65

Ref.: Gottlob, 1994; Sapkota, Balkrishna – Fundamentals of Noise Pollution, 2004

2. Aircraft Noise Regulations in Different Countries

Country National Noise

Index L(Aeq, 24 h)dB Regulations

Australia

< 20 < 53 No restrictions

20 > 25 … 53 … 58 New dwellings with appropriate insulation

25 >58 New dwellings not allowed

Canada

≤ 25 ≤ 57 No restrictions

28 … 30 60 … 62 New dwellings with appropriate insulation

> 35 > 68 New dwellings not allowed

Denmark ≤ 55 ≤ 51 No restrictions

> 55 > 51 No new dwellings

> 60 > 56 Support of insulation measures at Airport

Copenhagen

France

< 84 < 62 No restriction (at some airports

84 – 89 62 – 71 Insulation for existing dwellings

Germany

< 62 < 62 No restrictions in some federal states

67 … 75 67 … 75 New dwellings only with improved insulation

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Country National Noise

Index L(Aeq, 24 h)dB Regulations

Noise level reduction (NLR) > 40 dB

> 75 > 75 No new dwellings, support of insulation at

existing dwellings (NLR > 45 dB)

England

≤ 57 ≤ 55 No restriction

57 … 66 57 … 64 No dwellings only with appropriate insulation

> 66 > 64 Strong presumptions against new dwellings

> 72 > 70 No new dwellings are allowed

> 69 > 67 Insulation schemes at London airport

Japan

< 70 < 54 No restriction

> 85 > 69 Insulation measures

Netherlands

≤ 35 ≤ 50 No restriction

> 35 > 50 Generally no new residential areas allowed

> 40 > 53 Generally no new dwellings allowed

40 - 50 53 - 60 Support of insulation at existing dwellings

(NRL = 30 - 35dB)

50 - 55 60 - 64 NRL = 35 - 40dB

New Zealand

≤ 55 ≤ 52 No restriction

55 - 65 52 - 62 No dwellings only with appropriate insulation

> 65 > 62 No new residential areas allowed (<35 EPN)

Norway

≤ 60 ≤ 55 No restriction

> 60 > 55 No dwellings only with appropriate insulation

60 … 70 55 … 65 Insulation measures

Switzerland

> 45 > 62 No new residential areas allowed

45 - 55 62 - 72 Support insulation: walls > 50dB, windows >

35

USA

≤ 65 ≤ 62 No restriction

65 - 70 62 - 67 New developments not recommended, NLR >

25dB

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Country National Noise

Index L(Aeq, 24 h)dB Regulations

70 - 75 67 - 72 New developments strongly dis - encouraged,

NLR > 25dB

> 75 > 72 No new development allowed

Ref.: Gottlob, 1994; Sapkota, Balkrishna – Fundamentals of Noise Pollution, 2004

3. Noise Standards, Philippines

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Ref.: Estimation and mapping of vehicular traffic-induced noise along a. bonifacio avenue and sumulong

highway in Marikina City, Aileen U. Mappala , Sheila Flor T. Dominguez-Javier

4. New Zealand Standard 6803

Time of week Time period Duration of works at a location

less than 14 days less than 20 weeks more than 20 weeks

LAeq(t) LAFmax LAeq(t) LAFmax LAeq(t) LAFmax

Noise limits at residential neighbours

Weekdays 0630-0730 65 dB 75 dB 60 dB 75 dB 55 dB 75 dB

0730-1800 80 dB 95 dB 75 dB 90 dB 70 dB 85 dB

1800-2000 75 dB 90 dB 70 dB 85 dB 65 dB 80 dB

2000-0630 45 dB 75 dB 45 dB 75 dB 45 dB 75 dB

Saturdays 0630-0730 45 dB 75 dB 45 dB 75 dB 45 dB 75 dB

0730-1800 80 dB 95 dB 75 dB 90 dB 70 dB 85 dB

1800-2000 45 dB 75 dB 45 dB 75 dB 45 dB 75 dB

2000-0630 45 dB 75 dB 45 dB 75 dB 45 dB 75 dB

Sundays and public holidays 0630-0730 45 dB 75 dB 45 dB 75 dB 45 dB 75 dB

0730-1800 55 dB 85 dB 55 dB 85 dB 55 dB 85 dB

1800-2000 45 dB 75 dB 45 dB 75 dB 45 dB 75 dB

2000-0630 45 dB 75 dB 45 dB 75 dB 45 dB 75 dB

Noise limits at commercial/industrial neighbours

0730-1800 80 dB - 75 dB - 70 dB -

1800-0730 85 dB - 80 dB - 75 dB -

In New Zealand, noise from most construction and maintenance, including roads, is managed in accordance with

New Zealand Standard NZS 6803:1999 ‘Acoustics – Construction Noise’. The NZTA manages and minimises

potentially unreasonable noise effects during state highway construction and maintenance, so far as is practicable,

in accordance with this standard. NZS 6803 provides the following guideline noise limits for construction and

maintenance works. These limits apply outside neighbouring buildings; one metre from the façades and 1.2 to 1.5

metres above the relevant floor level. Updated: Monday, March 1, 2010 - 10:29

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5. UK Special

For each time period there are two noise limits: an average (LAeq(t)) and a maximum (LAFmax) [acoustics terms]. For typical daytime

construction lasting less than 20 weeks, the guideline limits are 75 dB LAeq(t) and 90 dB LAFmax. The LAeq(t) noise limits for works

lasting less than 20 weeks

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Ref.: Workers Compensation Board of BC, Vancouver, ARSC Ref. No. 0135-20, Februrary 2000

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Ref.: Highway Traffic Noise Analysis and Abatement Policy and Guidance, US DOT, 1995

NIGHT NOISE GUIDELINES (NNGL) , FOR EUROPE , WHO 2007

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