NOISE POLLUTION

Noise pollution is defined as unwanted or offensive sound that unreasonably intrudes into daily activities. Noise pollution is a problem that affects human health and contributes to a general deterioration of environmental quality.
Sound is measured in decibels (dB)
As per environment protection rules 1999, the permitted noise level is 125 dB.

SOURCES Sources are broadly classified into:
Outdoor  sources: Ex - Industries, Vehicular movement, Construction work, Defence equipment, Explosion, Loud speakers during festivals, high speed aircrafts, launching of Satellites using rockets, etc
Indoor sources: Playing radio or music loudly

EFFECTS: The effects due to excess noise pollution are listed below:
-Emotional or psychological effects such as irritability, anxiety, stress, lack of concentration and mental fatigue
-It has been observed that the performance of school children is poor in comprehension tasks when schools are situated in busy areas of a city due to high background noise.
-Noise interferes with normal auditory communication and may mask auditory warning signals increasing the rate of accidents especially in industries.
-Severe noise pollution may be extremely annoying or painful and hazardous. It lowers workers efficiency at work leading to low productivity and is the main reason for high accident rates on the job.
-Physical damage to the ear and temporary hearing loss called Temporary Threshold Shift (TTS) is experienced. In this case, people will be unable to detect weak sounds. However, hearing ability is regained within one month. Permanent hearing loss called Noise Induced Permanent Threshold Shift (NITPS) is a type of hearing loss from which there is no recovery

At sound level:
less than 80dB - no hearing loss occurs
80 to 130 dB   - temporary effects
more than 95 dB - approximately 50% people develop NIPTS
more than 105 dB - most people experience permanent hearing loss
more than 150 dB - physically ruptures human ear drum
more than 180 dB - kills a person

-Noise pollution may also cause harmful effect on circulatory system by raising blood pressure and altering pulse rates.

CONTROL OF NOISE POLLUTION
The four major concepts to control noise pollution are listed below followed by a brief explanation.
-Reduce noise at source
-Block path of noise
-Increase path length
-Protect recipient
Reduction of noise at source: This can be accomplished by:
-muffling vehicles and machinery to reduce noise
-using rigid sealed enclosures around machinery lined with acoustic absorbing material
-Isolating machines and their enclosures from the floor by using special spring mounts or absorbing mounts and pads
-Regular and thorough maintenance of operating machinery
-Regular lubrication and correct installation of bearings
-Proper highway planning and design are essential for controlling traffic noise.
Blocking path of noise: This can be accomplished by:
-Planting of trees around houses as they act as effective noise barriers
-Using highly absorptive interior finish material for walls, ceilings and floors decreases indoor noise levels
Increasing path length:
-Municipal land use ordinances pertaining to the location of airports make use of the attenuating effect of distance on sound levels
Protect the recipient:
-Specially designed ear plugs and ear muffs reduce the sound level reaching the ear drum by almost 40 dB
-Education, awareness among people and legislation regarding noise pollution should be widely publiced for control of noise pollution.
Eg: Ban on loud speakers from 10 pm to 6 am.