Noise is generally defined as an unwanted or undesirable sound and the release of unwanted sound into the atmosphere is called noise pollution.
High pitch sound produced by automobiles, machines, power plants, trains, helicopters, aero planes, jets, rockets, public broadcasting systems, T.V., sudden ratting of doors and windows, explosion of bombs, sound of crackers etc. are potent sources of noise pollution. Noise provides alarm system in man’s physical environment. It has been regarded as urban pollution. It has become serious in urban areas due to technologies increasing population, urbanization and industrialisation.
ADVERTISEMENTS:
It is associated with almost all human activities. In 1990, Nobel laureate Robert Koch said, “a day will come when man will have to fight merciless noise as the enemy of health and that day is not far off’. The noise should be taken not only as a factor of annoyance but also as a lethal partner of life. According to Dr. Vem O. Knudsen of university of California, noise, like smog is a slow agent of death. If it continues unabated for the next 30 years it could become lethal to an alarming degree.
Sound is a form of energy. Man is not only affected by the sound energy but also by sound pitch or frequency and intensity. Intensity of sound is measured in decibels (d = deci meaning 10, B for Bell, name of scientist Alfred Grahm Bell). Technically a dB is the amount of sound pressure that equals to 0.0002 microbars (energy of about 10-15 watts). One dB is the finest sound intensity which can be perceived by human ear and 180 dB is the maximum tolerance limit.
The frequency is defined as the number of vibrations and is denoted by Hertz (hz). One Hertz (hz) is equal to one vibration per second. Man can hear sound from 16 hz to 20,000 hz Less than 16 hz second is infra-audible and sound above 20,000 hz is ultrasonic, some animals however can perceive sounds that are not andible to man. Loudness of sound can also be expressed in sones. One sone is equal to 40 dB at a pressure of 1,000 hz. The loudness of noise is measured on a logarithmic scale called “decibel”.
Mathematically the decibel (dB) can be expressed as follows:
I dB = 10 log10 (P/p ref) or 10 x log 10 p/p ref.
Where, P = measured sound pressure in dynes /cm and, p ref = reference sound pressure which is equal to barely audible sound taken as 0.002 dynes /cm. As the decibel is measured on a log scale, rise of every 10 decibel would cause 10 fold change in sound intensity. For example, a sound level of 100 decibels has an intensity 10 times greater than a sound level of 90 dB. According to World Health Organization (WHO), a level of 45 dB is considered a safe noise level for city.
ADVERTISEMENTS:
By international standard, a noise level up to 65 dB may be taken as tolerable. Noise level above 80 dB causes noise pollution. Noise level above 100 dB becomes uncomfortable and beyond 120 dB it becomes painful. Sudden or intermittent noise IS more harmful than continuous noise. According to a report of National Physical Laboratory, India, the noise level is increasing at the rate of 1 dB per year.
Some important standards developed for noise levels in India are given in Tables 13.20 13.21, 13.22 and 13.23.
Effects of Noise Pollution:
Human response to noise varies from man to man according to age and temperament. It may vary even in the same individual from time to time because of change in health, fatigue and other conditions. The effects of noise on human beings can be related to physiological, behavioural and psychological responses.
When we hear a loud noise the blood vessels constrict, the skin pales, the pupil dilates, the eyes close, the voluntary and involuntary muscles tense, gastric secretions reduce and the blood pressure increases. The immediate reactions to noise which starts at noise level of 30 to 70 dB include constriction of peripheral blood vessels with a consequent increase in blood flow to the brain, change in breathing rate, change in muscle tension and gastrointestinal mobility.
ADVERTISEMENTS:
As these reactions can also be carried out by some other factors, they are called non-auditory reactions. At slightly higher noise level there is “startle effect” produced due to change in pulse rate and blood pressure, release of stored glucose from lever into the blood stream and the excess secretion of adrenalin hormone because of which fear reaction develops in body.
Some of the other effects of noise pollution are given below:
1. The short-term auditory effects of noise include some temporary loss in hearing at high noise levels. Explosions or other high intensity sounds may cause immediate deafness by rupturing the ear drums or damaging the cochlea. Continuous exposure at high noise level may cause some permanent damage.
2. Prolonged exposures to noise are known to lead to gradual deterioration of internal ear and to subsequent hearing loss or deafness. Scientists are of the opinion that constant occupational exposure to sound at higher frequency is dangerous for human beings.
3. Noise also clearly produces annoyance in human beings and can interfere with proper rest and sleep. Annoyance seems to increase with the loudness of the sound.
4. Noise also produces psychological effects in human being.
5. One important effect of noise is the vasoconstriction reflex in which small blood vessels of the body constrict and reduce the flow of blood.
6. Physiological effects of noise include dilation of the pupils, paling of skin, tensing of voluntary muscles, diminishing of gastric secretions, increase in diastolic blood pressure and the sudden injection of adrenalins into blood stream which increases neuromuscular tension, nervousness, irritability and anxieties. It can adversely affect the development of unborn babies.
7. Impulsive noise and thunders are worse than continuous noise which, if loud enough, may cause sudden hearing loss. Sudden noises also startle persons and lead to accidents. Supersonic booms produced by objects travelling faster than the speed of sound produce shock waves which deviate from atmosphere pressures.
Diseases Due To Noise Pollution:
Recently there has been growing evidence that noise in the range of 90 decibels and above may cause temporary or irreversible changes in the autonomous nervous system. Noise may be an important factor in many stress-related diseases, such as peptic ulcer and hypertension.
A brief summary of noise induced diseases are given below:
Deafness or impaired hearing:
This may occur due to continuous exposure to noise level of more than 90 dB. It may be temporary or permanent.
Auditory fatigue:
Continuous humming sound may cause side effects such as whistling and buzzing in the ears.
Irritation and annoyance:
Noise, sometimes, leads to emotional disturbances and makes people loose their temper.
Work efficiency:
It has been observed that people work efficiently in a quiet environment and noise reduces the efficiency of work.
Other health effects:
Noise is also associated with:
Rise in blood pressure (hyper tension)
Headache and giddiness
Sweating, nausea and fatigue
Difficulty in breathing
Disturbed sleep pattern
Psychological stress
Control of Noise Pollution:
Noise pollution can be checked by the following means:
i. Noise-generating factories should be located far away from the populated areas.
ii. Proper maintenance of machinery checks noise pollution.
iii. Use of pressure horns in automobiles in the densely populated areas should be banned.
iv. Loudspeakers and mikes should be banned from 10 pm to 6 am.
v. Firecrackers producing loud noise should be banned.
vi. Televisions, music systems, VCDs should be played at a low volume.
There is no separate law for noise pollution control in India. It has been suggested that cultivation of thick vegetation along the roadsides, railway tracts and industrial establishments may considerably reduce noise pollution.