Preliminary idea about Noise Pollution

1. Swapnadip Roy, Assistant Professor, Department of Chemistry, Bankura Sammilani College
NOISE POLLUTION
The term “noise” is applied to the sound that causes irritation on hearing of Human
being. In fact, there is very little demarcation of sound and noise.
 Sound and its general features:
Sound comprises wave motion in an elastic medium like air, water or solids (metals,
plastics, wood, bricks, etc.). Sound waves travel through the medium from the source to
the recipient or listeners. The rate of the oscillations of the medium is known as the
frequency of the sound, the unit being hertz (Hz) or cycles per second. The frequency is
the measure of the pitch of the sound received by the listeners. High frequencies imply
high-pitched sound, which are more irritating to the individual than low frequencies.
The second parameter of sound is pressure, which is measured in Newton/Sq. meter
(Nm-2). The third parameter of sound is intensity, expressed in Watt/Sq. meter (Wm-2)
i.e., the quantum of sound energy that flows through unit area of the medium in unit
time.
 Noise and its measurements:
Two important parameters sound/noise are sound pressure and sound intensity. They
are measured in different units giving varying scale of magnitude. The common
scientific acoustic unit is the decibel (dB). It is not absolute physical unit, it is a ratio
expressed as a logarithmic scale relative to a reference sound pressure level.
1 decibel (dB) = 10 log 10 (intensity measured/reference intensity)
The logarithmic scale takes care of wide range of sound, pressure and intensities. The
reference intensity used is the threshold of hearing which means sound which can be
first heard at a sound pressure of 2 x 10-5 Nm-2 or sound intensities of 10-12 Wm-2.
 L10 (18 hour) Index:
This is used for traffic noise measurement, adopted in UK for noise legislation. The
index is expressed in dBA – it is the arithmetic average hourly values of the noise level
exceeded for 10% of the time over 18 hours between 06.00 and 24.00 hours on any
normal weekday. It includes peak noise values and fluctuation of noise depending on
the type of vehicle and traffic density.

2. Swapnadip Roy, Assistant Professor, Department of Chemistry, Bankura Sammilani College
 Noise Classification:
Noise can be broadly classified under three categories: (1) Transport noise, (2)
Occupational noise, (3) Neighbourhood noise.
 Transport Noise:
This can be sub-divided into (a) Road traffic noise, (b) Aircraft noise and (c) Rail traffic
noise.
(a) Road traffic noise: Vehicles on road produce irritation for more people than any
other noise source. Traffic speed is one of the major cause of noise. The noise
volume increases with increase in traffic speed. Traffic noise is accurately
measured in dBA and noise level is given on the L10 (18 hours) index.
Situation Avg.Traffic Speed(km/h) L10 (18 hours)index(dBA)
Residential road, parallel to
busy main road
48 60
18 m from busy main road 48 70
18 m from highway with
high volume of heavy
vehicles
96 80
3 m from main road in
residential area
48 80
The limits for diesel or petrol engined cars are 70 dBA in UK, 83 dBA in France and 80
dBA in India.
(b) Aircraft noise: It differs from road traffic noise in the sense that it is not
continuous but intermittent. There are peak noise level when aircrafts fly
overhead or take-off and land at airports.
(c) Rail traffic noise: This is not a serious nuisance as compared to the previous
types of traffic noise. The noise is generally of lower frequency than that of street
vehicles and furthermore, most railway tracks run through rural areas.
 Occupational Noise:
This is mainly produced by industrial machines and processes which affects millions of
people. It also includes noise from domestic gadgets e.g., washing machines, vacuum
cleaners etc. Industrial workers are exposed to noise for 8 hours per day and 6 days per
week. Noisy industrial processes and conditions cause hearing loss to the workers

3. Swapnadip Roy, Assistant Professor, Department of Chemistry, Bankura Sammilani College
involved. Millions of workers are victim of occupational noise for up to 1800 hours per
year and for 30 years of their lives.
 Neighbourhood Noise:
This implies variety of sources of noise which disturb and annoy the general public by
interfering with their comfort and welfare. Such sources are loud TV and radio sets,
loudspeakers in public function and entertainments etc. Disco music and dance in late
evenings cause noise nuisance to nearby residents.
 Permissible Noise Levels:
In this age, many people work and live in environments where the noise level is not
hazardous. But over the years, they suffer from progressive hearing loss and
psychological hazards including tension.
The maximum permissible noise levels are summarized as follows,
Situation Permissible noise (dBA)
Road traffic near residential areas 70
Ear protection to be worn 85
Factory work for 8-hr day & 6 day week 105
Prolonged noise causing permanent damage 100
Ear-drum rupture 180
Lung damage 195
 Effects of Noise Pollution:
The effect of noise on health is numerous. It can affect central nervous system, cause
nausea, vomiting, deafness, loss of appetite, loss of sleep and even cardiac failure.
 Hearing Damage and Noise Exposure:
There is no doubt that noise can damage the ear and cause temporary or permanent
noise-induced hearing loss, depending upon the intensity and duration of the sound
level. The most commonly occurring ear damage is caused by continuous periods of
high intensity noise. If the ear receives a noise level over 90 dB in the mid high
frequency range more than a few minutes, then the auditory sensitivity is reduced. The
effect is called the temporary threshold shift and can result in a sound of 4000 Hz
frequency requiring a noise level of 20 dB to be heard, instead of 5 dB under normal
conditions.

4. Swapnadip Roy, Assistant Professor, Department of Chemistry, Bankura Sammilani College
 Pathological and Psychological Disorders:
Pathological effects can result from particular noise frequencies causing vibration or
resonance in materials or people’s bodies. High frequencies, or ultrasonic sound above
the normal audible range, can affect the semi-circular canals of the inner ear and cause
nausea or dizziness. Alternatively, very low frequencies noise can cause resonance in
the body organs, producing the effects of decreased heart beat, variations in blood
pressure and breathing difficulties.
Non-pathological or psychological noise effects are also variable and very difficult to
measure. The mildest effect is often physical or mental fatigue and lack of
concentration. This effect is important in industrial situation, because it results in low
efficiencies, a reduced work rate, increased absenteeism, and a higher potential for
accident and injuries.