Essay on Noise Pollution!
The word noise has come from the Latin word nausia and is usually defined as unwanted on unpleasant sound that causes discomfort. Noise pollution is defined as “the unwanted sound dumped into the atmosphere that leads to health hazards”.
Over the years the general incidence of noise has been increasing due to the development of engines, technological machineries in industry, jet planes etc. which have contributed to an increasing noisy environment.
The human ear receives sound waves and these sets up oscillations in the ear drum. These oscillations cause movements of the three ossicles or small bones (malleus, incus and stapes) in the middle ear, behind the ear drum. The oscillation is then passed into the inner ear to the auditory nerve and on to the brain for identification and interpretation of the sound.
The ear is able to analyse sounds into frequency components. The range of an 18 year old person with perfect hearing is between 20 Hz (infra-audible) to 20,000 Hz (ultrasonic). Normally hearing is more acute in the frequency range of 2,000 to 5,500 Hz, but it falls off rapidly below 200 Hz and above 10,000 Hz.
However, the ear’s sensitivity range varies considerably from person to person and also with the age of the concerned person. Old aged people experience a progressive hearing loss of high frequency sounds which is called ‘presbycusis’.
The ear is susceptible to damage if it receives high intensity noise. However, there are some protective devices through reflex action which the ear can perform only for short duration. If the ear is exposed to noise of 90 dB or more for longer period (>10 milliseconds), then the tympanic membrane contracts, thus reducing sound transmission.
If the ear is exposed to a noise of over 140 dB, then the middle ear muscles change the direction of movement of the ear ossicles, thereby decreasing the noise intensity that enters the inner ear. However, these reflex actions are valid for short durations only.
Measurements of Noise:
There are two most important parameters of noise —sound pressure and sound intensity. Sound pressure is measured in Newton’s per square meter (Nm−2). Sound intensity is expressed in watts per square meter (Wm−2) and it is the quantum of sound energy that flows through unit area of the medium in unit time.
However, the common scientific acoustic unit is the decibel (dB). The word decibel comes from deci meaning ten and bel is after the name of the scientist Alfred Graham Bell. It is not an absolute physical measurement unit like the gram, volt or meter etc., but it is a ratio expressed as a logarithmic scale relative to a reference sound pressure level.
The decibel is defined as:
The reference intensity used is the threshold of hearing which is a sound that can be first heard at a sound pressure of 2 × 10-5 Nm-2 or a sound intensity of 10−12 Wm−2. Table 4.25 illustrates the relationship between the three measurements.
Noise or sound is sometimes expressed in term of loudness, which cannot be measured, but it is a matter of personal judgement.
Noise meters:
There are several meters for the measurement of noise – sound level meter, noise analyser etc. The dB scale is in general use. It, however, is not sufficiently refined to take care of (1) peak noise levels, (2) duration of noise exposure, and (3) quality of noise, which are features of specific environmental noise situations. That is why other noise meters have been designed, based upon the decibel scale with proper refinements.
Some of these are:
L10 (18 hour) Index:
It is expressed in dB scale and is used for road traffic noise measurement adopted in U.K. It is the average hourly values of the noise level exceeded for 10 percent of the time over 18 hours between 6.00 and 24.00 hours, during any normal day. It takes account of peak noise values and fluctuation of noise depending on the type of vehicle and traffic density.
Effective Perceived Noise Level (Lepn):
International Civil Aviation Organisation (ICAO) has recommended this as the standard for aircraft’s noise evaluation. It is based on the scale equivalent to the dB +13. It takes care of the peak frequency jet aircraft noise as well as duration of aircraft flyovers.
Equivalent Noise Level (Leq):
This index is accepted by the International Organisation for Standardisation (ISO) and used for measurement and rating of noise in residential, industrial and traffic areas. An Leq of 90 dB is equal to steady noise level over the whole period of time or noise level steady at 93 dB for 50 percent of the time and zero percent noise for the remaining period.
Sources of Noise Pollution:
The sources of noise pollution may either be natural thunder or man-made.
Man-made sources are:
(A) Transports,
(B) Industrial operation,
(C) Domestic practices, and
(D) others.
A. Transport:
Transport noises include:
(a) Road traffic,
(b) Aircraft
(c) Rail, and
(d) other transports.
(a) Road traffic:
The road traffic noise is generated by the vehicles plying on the road. Traffic noise is created by a continuous running of vehicles and produces disturbance to more people than any other noise source. Vehicle noise is generated through engine, horn, and body of the vehicle and fiction of tyres on road.
The road traffic noise has been increasing over the last decade due to number of reasons. The total number of road vehicles and hence the density of road traffic has been steadily increasing. In the last decade Kolkata has witnessed a rise of 63% in the number of vehicles (6.3% increases per year) about 45% of these new vehicles are two-wheelers.
One of the most important cause of noise on the road is the traffic speed. The faster the traffic travels the greater will be the volume of noise and modern road development policy is encouraging higher speed. However, the average vehicle speed on the roads of Kolkata has decreased from 22 kmh−1 to 18 kmh−1 due to increase of vehicles, particularly auto-rickshaw. Tyre noise increases with speed and a wet road can increase the noise by 10 db.
Road traffic noise fluctuates according to a number of operating factors. Vehicles produce noise from the gear box and exhaust system. Also according, to the degree of loading and age, heavy vehicles produce rattles, squeaks and vibrations. All vehicles produce more engine noise at faster speed.
A doubling of engine speed can increase the noise level by 13dB. Generally a heavy good vehicle produces twice as much noise as a private car. The actual pattern of traffic noise on a main road is complex. Heavy diesel-engine trucks are the noisiest vehicles on roads.
Noise levels of road traffic are often expressed on the L10 (18 hrs.) index. The residential road having vehicle passing at a speed of 3 mph bears the noise level of 60 dB, while the busy main road having traffic of 48 Kph generate noise at 70 db.
Additional transport noise is generated by the use of horn and screeching brakes. Air horns are most disturbing and have been banned. The Central Pollution Board of India has prescribed permissible sound levels for cities, divided into 4 zones (Table 4.26) These noise limits, however, are violated in all big cities of India, of which Kolkata being the worst case. The average noise level in the busy streets of Kolkata are 90dB between the rush hours that is during 10.30-12.00 hours and 18.00-19.30 hours.
(b) Aircraft noise:
Aircraft noise varies from road traffic noise in the sense that it is not continuous but intermittent. Over the last decade there has been increased nuisance of noise from subsonic aircrafts for several reasons. There are peak noise levels when air-crafts are flying overhead or are taking-off and landing at airports.
The peak frequency varies with the number and the type of aircraft and the operational height. Noise is produced mainly from aircraft engines. Table 4.27 shows the amount of noise generated by different types of aircraft.
(c) Rail traffic noise:
Noise from trains is not a serious nuisance compared to the previous types of traffic noise. The probable reason being that the rail noise is generally of lower frequency than that of road vehicles and also most railway track runs through rural areas.
However, buildings located besides railway tracks and where engine testing and shunting is carried out, are exposed to noise menace. The introduction of diesel and all-electric locomotives have somewhat reduced rail traffic noise.
(d) Other transports:
Noise emitted from other transports such as ship, bullock cart, rickshaw and cycle bell etc. are not significant. However, houses situated near the dock area and shipping yard may be affected by noise.
B. Industrial operation:
Industrial noise are the various types of noise emitted from the working of machineries in industries.
The nature of noise is complex and varies with the:
(i) Design,
(ii) Direction of movement of working parts, and
(iii) The method of mounting of machines.
Noise from machinery is often produced in three stages:
(i) Initial disturbance at the point of origin of the sound,
(ii) Amplification, often caused by the resonance of the machine parts or the work-piece on the floor, and
(iii) Radiation of the sound to the surrounding environment.
Industrial noise can be classified into three types:
(a) Impact and percussive noise:
It is produced by presses, punch and stamp machines, pneumatic drills, milling machines, cutters and routers
(b) Impact noise:
This type of noise is caused when two surfaces meet each other, sometimes at high speed. Vibration occurs at the point of contact followed by amplification and resonance.
(c) Aerodynamic noise:
Aerodynamic noise is caused by a blow lamp or torch, fans and dust extractors.
C. Domestic practices:
Noise from domestic appliances like washing machines, spin dryers, food mixers, sink waste grinders, blaring music systems and TV, faulty vacuum cleaner etc. are the sources of disturbance and annoyance in the neighbourhood. Domestic noise and industrial noise are collectively referred to as occupational noise. Some occupational noise levels are depicted in Table 4.28:
D. Other sources of noise:
Other sources of noise of less importance include:
(a) Loud-speaker:
For every occasion, whether it is religious or other public or private purposes, the use of loud-speakers is a common practice. Blaring loud-speakers during festivals, melas, election etc. produce noise ranging from 55 dB to 90 dB, ignoring the orders of the court.
(b) Construction work:
Noise produced during construction of roads, bridges, residential and commercial complexes etc. has been very disturbing for the general public.
(c) Crowded markets:
Crowded markets in various cities have become a source of noise pollution. Chattering, bargaining by buyers and peddlers, stopping and starting of vehicles etc. create a lot of noise.
(d) Theaters, circus and carnivals:
Various amusement places like theater, circus, carnival, dance hall, discotheque etc. are all sources of noise pollution to the neighbourhood.
(e) Atomic explosion:
Lot of noise is emitted from the site of experimental atomic explosion but these sites are situated in deserted areas.
(f) Religious festivals and rituals:
Various religious festivals such as Deepawali, Durga Puja, Ganeshotsav etc. involve a lot of noise. Noises from various religious rituals like Yajna, Kirtan, Koran path, Akhandapath, Gurubani, Azan, Navaratri etc. are sometimes loud and unbearable. The noise generated from bursting of crackers during Deepawali and other celebrations are often deafening and may cause health problems.
Effect of Noise Pollution:
The effects of noise pollution are numerous. All the hazardous effects of noise pollution are:
A. Hearing damage from noise exposure:
Undoubtedly noise can damage the ear and cause temporary or permanent noise induced hearing loss, depending upon the intensity and duration of the sound level. Continuous period of high intensity noise causes ear damage. If the ear receives noise level of >90 dB in the mid-high frequency range for more than a few minutes, then the auditory sensitivity is reduced – an effect called the temporary threshold shift.
This results in a sound of 4,000 Hz frequency requiring a noise level of 20 dB to be heard instead of 5 dB under normal conditions. Fig. 4.68 shows typical hearing loss due to varied period of exposure in noisy environment.
Other than progressive hearing loss there may be instantaneous damage or acoustic trauma. It is generally caused due to very high intensity, impulse type noise that can result from sudden excessive noise of about 150 dB or more like in case of an explosion.
Broadly, hearing loss from noise exposure can be temporary or permanent. Immediately after exposure to a noise of > 100 dB (for a brief period) there is a marked increase in the minimum level that one can hear (threshold) and subsequently, gradual recovery of hearing ability takes place. Such exposure to noise is said to be temporary.
When repeated exposures over extended periods take place, it leads to incomplete recovery and some permanent hearing loss. This permanent loss of hearing depends on the noise level and the pattern of exposure and recovery time. Table 4.29 shows permanent hearing loss by industrial workers:
Various degree of hearing loss results in various hearing problems. For instance, hearing loss of < 25 dB does not pose any problem in hearing, but hearing loss of > 25 dB causes hearing difficulty. Hearing loss of > 50 dB requires hearing aid, while complete deafness is noted in hearing loss of > 90 dB.
B. Pathological and psychological disorders:
Pathological effects from particular noise frequencies are:
1. High frequencies or ultrasonic sound above the normal audible range can affect the semicircular canals of the inner ear and cause nausea or dizziness.
2. Mid-frequency noises are known to cause resonance in skull and so affect the brain and nervous system with consequent effects upon thinking and coordination of the limbs.
3. Very low frequency noises cause resonance in body organs, producing effects of decreased heartbeat, and variation in blood pressure and breathing difficulties.
Very high noise levels may cause damage of various body parts as shown in Table 4.30.
Psychological effects of noise are variable and very difficult to measure. The effects include mental fatigue and lack of concentration. Such effects are very important in industrial situations as it results in low efficiency, reduced work rate, increased absenties and prone to accidents and injuries.
Even certain psychological noise effects may impinge upon sleep. Children exposed to excessive noise often show behavioural disorder which, in subsequent years, may make them destructive in nature. This may also lead to the development of neurotic traits in the adult.
C. Effect on wildlife:
Effect of noise pollution on migratory birds is exemplified by the decline in number of migratory birds to habitats which have become noisy. Zoo animals are reported to be affected from traffic noise and they subsequently become dull, inactive and show other health deterioration.
Another example of the effect of noise was witnessed in case of snow leopards at Darjeeling breeding centre. At the time of GNLF movement, heavy bombing in the vicinity of that area had resulted in miscarriage of a female snow leopard.
D. Effect on Non-living Things:
High intensity noises result in breaking of window pane, loosening of wall plaster, cracks on walls and other effects.
Control of Noise Pollution:
Ears do have some protective reflexes that can reduce the amount of noise entering into the ear. By modification of the contraction of tympanic membrane, ear can accommodate high pitch sound for a moment. But prolonged exposure to high level noise (>60 dB) leads to gradual hearing loss in almost all aged people.
Few countries have, however, set up some standard for permissible noise level in indoor and outdoor environment. The number of statutes and regulations that have been brought into use since the late 1960s indicate that the government is aware of the problem.
The Environmental Protection Agency (US- EPA) as well as Department of Environment (DOE-UK) has set up some general standard for noise level which is given in Table 4.31. These noise standards are violated in most places.
However, noise pollution can be regulated by adopting the following measures:
1. Control of noise generation at source:
A number of measures has been taken up to reduce noise generation at source.
They are:
i) Modification of car engines and should be properly lubricated,
ii) Modification of aircraft machines,
iii) Introducing less noisy machines in place of noisy ones,’
iv) Banning the use of air horns,
v) Proper lubrication of wheels, designing and fabricating silencing devices and their use in various appliances,
vi) Conducting noisy operations, as far as possible in open places, far away from any residential area,
vii) Banning the use of loudspeakers in residential areas or public places,
viii) Banning the bursting of crackers,
ix) Setting industries at least 5 km away from residential areas,
x) Switching over to diesel and electric railways engines.
2. Setting up of statutory legal bodies for monitoring noise problems:
Statutory legal bodies for monitoring noise problems should be set up in major cities; silent zones should be set up; prohibition of entry of heavy vehicles in some central areas to be maintained. Also, the Central Pollution Control Board Committee recommended permissible noise level at various places in the country (Table 4.26), vide Ambient Air Quality Standards in respect to noise – Notification under Schedule III of Part III Section 3(i) of Extraordinary Gazette of India by the Ministry of Environment and Forests, Government of India, New Delhi, December 26, 1989. However, all these recommended standards of noise level has been violated and no legal measures could be taken up against the offenders due to lacunae of legal procedures.
3. Control of traffic flow:
Noise pollution can be controlled through proper traffic flow, control of traffic speed through speed breaker, banning of silencer less vehicles, prohibiting the use of old and mutilated vehicles etc. Many of these are considered to be adopted on emergency basis in all major Indian cities.
4. Creation of vegetation buffer zones:
It has been noticed that roadside planting of noise-absorbing foliage, like Ashok, Banyan, Neem, Casuarina, Tamarind, Coconut etc., can absorb sound of at least 6-10 dB.
5. Protection of exposed persons:
Workers exposed to noise pollution of > 85 dB in factories, airports etc. should use devices such as ear plugs and ear muffs to reduce noise pollution hazards. The general public should always try to avoid such noisy areas.
6. Education and awareness:
People must be educated through books, newspapers, articles, radio, T.V., popular lectures etc. about the health hazards of noise pollution. Various non-government agencies (NGOs) have now come forward for public awareness of noise reduction at source and also to make aware the people, of the hazardous effects of noise. The Society for Clean Environment, Mumbai, is noteworthy among them.