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The term noise is derived from the Latin word Nausea refering to the feeling of sickness in the stomach with an urge to vomit. Any unpleasant and unwanted sound is considered as noise. It is one form of pollution. Noise pollution can be defined as unwanted or offensive sounds that unreasonably intrude into our daily activities. It is responsible for various adverse effects. In recent years noise is recognized as a major pollutant on par with other chemical pollutants of air, water and biosphere. Noise has many harmful effects on man and the damage incurred is irreversible.
There are various sources of noises and the sources are broadly classified into industrial sources and non industrial sources. The noise dumped into the atmosphere by the industires due to the functioning of machineries form the industrial sources. On the other hand the noise associated with urban development; road, air and rail transport; loud speakers, radio and television stations, construction sites, neighbourhood and recreational noise levels, and activities associated with urban living generally lead to increased noise levels.
Sound is measured by several complex systems. The best known unit of measurement is the measurement of sound in decibel which is named after Sir Alfred Bell. The industrial noise survey of India recognized noise levels from 81dB to 120dB as permissible levels.
Loud noises (above 130 dB) can cause immediate and permanent damage to the muscles in the middle ear, altering the stiffness of the ossicles, damaging the hair cells of the cochlea and casuing the rupture of ear drum thereby reducing the efficiency of hearing.
Prolonged exposure to unpleasant noises may lead to severe mental distubances and violent behaviour. Noise is also partially responsible for the increased consumption of alcohol, drugs, tranquillzers and sleeping pills. Noise pollution further contributes to a few cardiovascular problems. Peptic ulcers and asthma are aggravated. Small vessels to glomerular circulation are subjected to vaso constriction and ultimately the output of urine is reduced. Persons exposed to excessive noise at work place have temporary impairment of hearing.
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