Modern life has given rise to a new form of pollution. The word noise is derived from the Latin 'nausea' meaning disgust. Noise is usually defined as undesired sounds producing an auditory sensation considered being annoying.
Noise is the unwanted sound, usually of high intensity and it causes irritation and discomfort. Sources of noise are many, but it is always higher in urban and industrial areas than the rural one. Industries expose their workers to high noise load for long period of work every day.
Road traffic particularly during peak hours is another noise pollution source to travelers as well as to the shopkeepers and residents of the concerned area. Uses of loudspeakers on almost all kinds of occasions like festivals and elections, worship, and during advertisements are common almost all the year round.
Noise is defined physically as a complex sound with little or no periodicity and psychologically as a sound under sired by the recipient. The American National Standards Institute defines noise as any 'undesired' sound or 'unwanted' sound or sound 'without value.' Its definition can be more appropriately stated as - "Noise is unwanted sound or sounds of a duration, intensity, or other quality that cause some kind of physiological or psychological harm to humans or other living things."
(1) 28 million people in USA have hearing loss and noise is one of the leading causes of hearing loss, especially in young people.
(2) Noise negatively affects learning and behaviour.
(3) Studies show that children's learning is negatively affected by noise in the classroom.
Level of Noise
Decibel is a ratio expressed on a logarithmic scale. This logarithmic scale takes care of wide range of sound power, intensity and pressure. The decibel (dB) scale begins from zero, which represents the faintest sound, which is audible to a normal ear.
Decibel (dB) is used in environmental noise pollution as a measure of sound power level, sound intensity level and sound pressure level. A decibel (One-tenth of a bel) is a physical unit based on the weakest sound that can be detected by the human ear. It is named after Alexander Graham Bel, the inventor of the telephone.
Recommended Noise Levels
Acceptable noise levels for outdoor and indoor as recommended by ISI (1954-1968). A permissible maximum outdoor noise level for urban residential areas is 35-45 dB. Ministry of Environment and Forest (India) has also notified the ambient standards in respect of noise in the Gazette of India on December 26, 1989.
It is seen that there is little difference between daytime standards and nighttime standards. Daytime standards for industrial zone and silence zone are 75 dB and 50 dB, respectively. Permissible notice exposure levels for various maximum allowable durations are given which are recommended by Occupational Safety and Health Administration (OSHA).
Causes of Noise Pollution
The sources of noise are more in urban and industrial areas than in rural areas. The sources in general may be stationary or mobile.
1. Stationary Sources
Use of loudspeakers on various occasions like festivals, elections, worships in temples, mosques and during advertisements, mining operations, use of bulldozers, drillers and dynamites to break rocks, household gadgets like vacuum cleaner, TV, radio, stereo, grinder, mixer etc., common vegetable and fish markets.
2. Mobile Sources
Road traffic, railway traffic, air traffic, navigation etc the sources of noise can be classified in following categories:
(1) Transportation / Traffic noise
(2) Industrial noise
(3) Noise from construction work
(4) Neighborhood noise
1. Transportation / Traffic Noise
The main threat of noise comes from transport. A survey in Delhi, Mumbai and Kolkata showed that daytime noises varied from 60 dB (A) in busy localities. In some heavy traffic areas, the average noise level reached up to 90 dB (A) even at nights.
(a) Road Traffic or Highway Noise:
The noise generated from highway traffic is one of the major sources of noise pollution. Highway noises are of two types, viz., noises generated by individual vehicles and noises generated by a continuous flow of vehicles of all types.
The noises from individual vehicles include noise from engine and transmission, exhaust noise, noise due to slamming of car doors and use of horn. Traffic speed is one of the major causes of noise. The other factors on which traffic noise depends are traffic density and a number of operating factors / conditions/type of vehicle. Heavy diesel engine vehicles are the noisiest vehicles on roads. It can be observed that sports car and motor cycles are notorious noise producers.
(b) Aircraft Noise:
Aircraft noise differs from road traffic noise in the sense that it is not continuous but intermittent. Noise is at a maximum during take-off and landing. Major cities around the world have banned or reduced flights at night and also prescribed noise limits.
(c) Rail Traffic Noise:
Noise from rail traffic is not a serious nuisance as compared to the road traffic and airport noise. The noise produced is generally, of lower frequency than that of road vehicles and further, most railway tracks run through rural areas. The impact of noise pollution by trains is felt maximum in buildings located beside railway tracks. The normal ambient noise level near rail tracks went up by 10-20 dB(A) during train movement.
2. Industrial Noise
In industries, noise is the by-product of energy conversion. The compressors, generators, furnaces, looms, grinding mills, release valves and exhaust fans are the most offending noise sources.
The common noise level in most units is 80-120 dB(A), which is really hazardous. Studies showed that 1.3 per cent of industrial workers suffer from tinnitus for noise exposure levels up to 80 dB.
3. Noise from Construction Work
Noise from construction sites is generally far worse than the noise originating from factories. There are two reasons for this - one is that construction (of roads, bridges, buildings, dams etc.) may become necessary anywhere and the other reason is that construction equipments are inherently noisy.
4. Neighbourhood Noise
It includes a variety of noise sources which disturb and annoy general public. The most I prominent is the indiscriminate use of loudspeakers in public functions, entertainments, festivals, I elections etc. The other sources include vacuum cleaners, TV, radio sets and washing machines I etc.
During the festivals especially Dipavali, fireworks push up the noise level up to 80-100 I dB(A) during evening hours, against the normal level of 50 dB(A).