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µî·ÏÀÏÀÚ: 2012-03-26 Á¶È¸¼ö : 1797   
Noise is unwanted sound which is often a source of great nuisance. It is the duration, pitch and loudness of sound which determines the discomfort and other ill-effects which noise causes Human ear is sensitive to sound levels ranging from 0 dB to 150 dB, however, sound levels beyond 70-80 dB cause plenty of discomfort, irritation and a variety of physiological disturbances.
1. Loss of hearing:
The most common ill-effect of noise pollution is impairment of hearing ability of an individual. Hearing ability of an individual is monitored by Audiometric tests, the most common technique of which is referred to as the Threshold technique. It is based on the determination of the minimum sound level which an individual can hear. Starting from a zero value the sound level is gradually raised.
The level of sound which an individual can just perceive is noted. This is followed by gradual lowering of volume of a louder sound and the level of sound which is no longer audible to the subject is recorded. An average of the two values is taken as the threshold of hearing of the individual concerned.
Prolonged exposures to loud noise can cause temporary or permanent loss of hearing. People working in noisy places such as industrial establishments, factories etc. often suffer from temporary loss of hearing. The ciliary cells in the inner ear are inactivated or numbed and the threshold of hearing of the subject is raised. If the loudness of noise is moderate or the duration of exposure is short, the damage is only temporary.
The auditory system recovers itself when the exposure ceases. In Audiometric tests, the phenomenon is referred to as Temporary Threshold Shifts or TTS. Longer exposures to louder noises may cause permanent shift in the threshold of hearing of an individual.
The individual in such cases suffers from partial but permanent loss of hearing. He is no longer able to hear low sounds which are audible to normal persons. This is caused by slow and chronic damage to ciliary cells in the inner ear. Still, medical science is of little help in such cases.
Very loud, sudden and impulsive noises, such as a bomb blast, are capable of causing acute damage to auditory system and an abrupt loss of hearing. With or without involvement of inner ear, it is the middle ear which is affected in most of the cases. High intensity sound waves damage the ear drums and may disrupt the delicate bony chain which carries sensation from ear drums to the inner ear. Very fine surgical techniques have been developed to restore the hearing ability where only middle ear is involved.
2. Other health effects of noise pollution:
Loud noise is a nuisance which affects sleep, concentration and work or performance of an individual. Work which needs a high degree of skill and precision is considerably affected. It may cause head ache, irritability and fatigue. It is interest¬ing to note that our Optical system is considerably affected by noise pollution. Dilation of pupils, impairment of night vision, and decrease in color perception ability are some of the effects caused by exposure to loud noise for long durations.
Noise affects our cardiovascular system also. Loud noises tend to decrease the output of blood from heart, cause arterial blood pressure to fluctuate and smaller blood vessels of the body constrict reducing the flow of blood to the organs concerned. Heart beat rate is affected. Changes in breathing amplitude have been reported due to sudden and impulsive noises. Eosinophilia, hyperglyaemia, hypokalemia and hypoglycaemia may also be caused by changes in blood circulation and other body fluids due to noise pollution (Kryter, 1970).


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