This article throws light upon the four major types of noise hazards. The types are: 1. Noise Nuisance 2. Physiological Hazards 3. Psychological Hazards 4. Effect of Wildlife.
Noise Hazard: Type # 1. Noise Nuisance:
Noise is an undesirable by-product of our industrial civilization. Excessive noise causes distraction, annoyance, and even torture to a tired or sick person. Noise undermines mental peace and destroys the health.
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Excessive noise produced in recent years by the supersonic aircraft has compelled the governments to introduce “Insulation Grant Schemes” in the UK and USA. Medical experts in the United Kingdom have estimated that one out of four man and one out of three women have developed neurosis as a result of exposure to excessive noise.
In the same way, every fifth patient admitted to the psychiatric wards of French hospitals lands there because of noise. According to the Ministry of Health, Canada, two million Canadians suffer from poor hearing due to exposure to high levels of noise.
The situation is so worse, in fact, that a leading expert, Dr. V.O. Knudson, has warned, “If the noise level we live with today continues to increase at the same rate for the next 30 years as it has for the last 30 years, it could become lethal”. Similar conclusions have been reached by psychologists, psychiatrists, scientists, medical experts, urban planners and other experts in related fields.
The ranges of noise levels in some important cities of the world and India (Tiwari and Ali, 1988A) are mentioned in Table 6. The upper noise levels (150 dB(A) and above) in this table refer, of course, to the aircraft noise near airports.
But even the lower limits are too high for the most of these cities when we remember that the daily exposure limit for 8 hours is merely 90 dB (A), as mentioned in Table 2. Even in a developing nation like India, the noise levels in New Delhi, Bombay and Calcutta are similar to those in London, Paris or Frankfurt.
Table 7 shows the percentage of people disturbed by various types of noise in Pattaya, Thailand (Thanh et al., 1978). It is clear from this table that, even in a relatively backward country like Thailand, noise pollution is no longer a mere academic problem. Table 7 shows that the majority of people are disturbed at home, outdoors and at work by traffic noise.
In addition to its harmful physiological and psychological effects, noise affects the quality of life and reduces the enjoyment of life at home and in the society. It is well known that noise interferes with speech and reduces the pleasure of conversation and music.
Table 8 shows such speech interference levels at selected distances. We find from this table, for example, that if the ambient noise level is 73 dB (A), one has to shout to be heard satisfactorily even at a distance of one metre.
Noise Hazard: Type # 2. Physiological Hazards:
The physiological and other hazards of noise are galore. Some of these (Srivastava and Gupta, 1988) are shown in Table 9. In the first place, noise can damage the ear. Depending upon its intensity and duration, the person exposed to noise may suffer from a temporary or permanent noise-induced hearing loss.
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The most commonly occurring damage to the ear is caused when a listener is exposed to continuous periods of high-intensity noise. In this case, the auditory sensitivity of the ear is reduced and the effect is known as “temporary threshold shift”.
If the industrial workers or other citizens are constantly subjected to high noise levels, however, the auditory shift is no longer temporary. In this case, the result is a progressive and irreversible deterioration in hearing. Besides progressive hearing loss, there may also be an instantaneous damage, known as “acoustic trauma”, which is usually caused by the high-intensity impulse noise.
We have shown in Table 10 the average hearing loss (Dix, 1981) in various profession in which the workers are exposed to high levels of noise. We note here as mentioned in the last entry of Table 10, that the normal average hearing loss for a person in the age group 50-60 years is 30 dB (A). But the hearing loss for workers in various professions listed in Table 10, in the same age group, ranges from 35 to 65 dB (A).
This extra hearing loss results from the long-term exposure to excessive noise. The effects on the hearing ability of various levels of hearing loss are given in Table 11. We find from this table that the workers in the professions listed in Table 10 will have difficulty with hearing the speech varying from “soft” to “loud’.
Excessive noise may cause many pathological disorders. Ultrasonic sound, for example, may affect the semi-circular canals of the inner ear and cause nausea and dizziness. On the other hand, infrasound (very low frequency sound) may cause resonance in body organs and produce decreased heart-beat, variation in blood pressure and breathing difficulties.
Frequencies in the mid- audible band are known to cause resonance in the skull. This affects the brain and the nervous system, leading to harmful effects on the thinking ability and co-ordination of limbs.
Physical effects of increasing sound pressure levels have been discussed by Vaish (1973). Cardiovascular system is especially vulnerable to high levels of noise.
Workers exposed to high noise levels were found to have higher incidence of circulatory problems, cardiac diseases, hypertension, peptic ulcers, and neurosensory and motor impairment. Short term exposure to very high intensity noise may produce rupture of the ear drum. In this case, there is an intense pain, followed by prolonged loss of high tones (above 9,000 Hz).
Noise Hazard: Type # 3. Psychological Hazards:
In addition to the physiological effects mentioned above, high levels of noise give rise to many harmful psychological effects. The mildest psychological effects of noise are physical and mental fatigue and lack of concentration.
These effects are important in industries since they lead to lowered efficiency, reduced output, increased absenteeism and higher rates of accidents and injuries. The behaviour of a person is affected by excessive noise, although such effects are more difficult to quantify than actual hearing losses.
The chief behavioural effects of noise are:
(a) Annoyance
(b) Distraction and performance efficiency reduction
(c) Fatigue and
(d) Speech interference.
Laboratory experiments have shown that noise lowers the efficiency of workers. It has also been demonstrated (Broadbent, 1964) that people make more mistakes in their work when there is noise. Their working speed is not much affected by noise, but accuracy of work is reduced.
Most people find high-pitched and intermittent noises more annoying than the low-pitched and prolonged, steady noises. Sounds from unknown or unfamiliar sources are especially irritating. But irritation and annoyance are. merely the mildest psychological effects of noise. In a non-work environment (at home, for example), psychological effects of noise impinge upon sleep.
Every person requires a specific minimum period of regular sleep of good quality to maintain a healthy body and mind. The depth of sleep and its duration are important. Low frequency noise of even 50-60 dB (A) can affect the higher centres of the brain, and cause an alteration to normal sleep pattern and prevent deep sleep.
This noise may not wake the young and middle-aged people, but it may wake older people and prevent them from returning to sleep.
Excessive noise causes also psychosomatic disorders, tension-related diseases, mental illness and emotional distress. It has been medically confirmed that noise causes a loss of nervous energy, but the reaction varies widely in different individuals. High levels of noise make human beings more irritable and more susceptible to neurotic and irrational behaviour.
There appears to be a relationship between increased rate of crime and the increasing urban noise level. Among the most insidious aspects of noise pollution is the fact that an individual may be unconsciously building up nervous tension due to noise exposures.
This may cause the person thus exposed to noise suddenly to be catapulted into an act of violence or mental collapse by some seemingly minor sounds which drive him beyond the point of endurance.
Noise Hazard: Type # 4. Effect of Wildlife:
High levels of noise adversely affect not only human beings but even animals. Many birds, for example, live the place if it becomes too noisy, and go elsewhere to nest. There is a decrease in migratory birds to a place if it is subject to noise.
It was reported by the Director of Delhi Zoo that the zoo animals particularly, the deer’s, lions and rhinos are worst affected from the traffic noise. They become dull and inactive their health deteriorates, and their number does not increase. According to the Director of Delhi Zoo, the psychological and ecological consequences of noise could be serious from the point of view of their survival.
In a survey in Malaysia, it was observed that grizzly bears, musk-oxen and kangaroo rats are falling victims to noise pollution. According to a study conducted by the Environmental Protection Agency of Kuala Lumpur (Malaysia), the kangaroo rats have become more and more vulnerable to their predators – the venomous rattlesnakes.
The grizzly bears, on the other hand are said to be moving out of the area of their inhabitation, in search of other less noisy places. The noise affects their health, food habits and mating behaviour.
Selye conducted extensive studies on the physiological effects of noise on animals.
He exposed a group of rats to high levels of noise and observed the classic stress reaction triad, viz.:
(a) Atrophy of the thymus gland,
(b) Development of duodenal ulcers, and
(c) Swelling and discolouration to the adrenal glands.
Examination of the internal organ systems of the noise-exposed rats yielded the convincing evidence of stress reactions resulting from exposure to noise. It was found that every noise-exposed rat demonstrated at least one of the three stress reactions mentioned above In fact most of the animals were found to manifest all the three reactions.