The word ‘Noise’ is derived from the Latin word ‘nausea’ which means feeling of sickness at the stomach with an urge to vomit. The term noise may be defined in a number of ways.
(i) In acoustic, noise is defined as unwanted, unpleasant and annoying sound.
(ii) Noise is defined as unwanted, unpleasant, disagreeable sound that causes discomfort.
(iii) Noise is defined as the wrong sound, in the wrong place at the wrong time.
(iv) Noise is the sound incidental to our civilization and is without agreeable musical quality.
It is seen that a particular sound which is musical to someone, may be noise to another. However, if the sound is loud and it prolongs for a longer period of time, it becomes noise for all. The technological advancements such steam engines, diesel engines, jet engines, industrial machinery, traffic noise of moving trucks, buses, cars, and automobiles with blow horns, etc. are polluting the atmosphere with their continuous noise. So, now a day’s noise is considered as a component of environmental pollution having a potential to cause hazards to human health and communication.
Noise pollution – definition
Noise pollution is defined as the unwanted or offensive sound that unreasonably intrudes into our daily activities. Sound is measured in the unit called decibel (dB). The sound intensity from 0 to 100 dB is pleasant but when the sound intensity exceeds 120 dB, it causes noise. Sound intensity of 130 dB is the upper limit of the threshold of hearing and beyond this is the threshold of pain which may cause damage to ear and leading to hearing impairment. So, sound of more than 130 dB causes noise pollution.
Sources of Noise Pollution
Noise may originate either from natural sources or from anthropogenic activities. The natural sources of noise include thunder, cyclone, roaring of sea, etc. The manmade noise are mechanized automobiles, industries, trains, aero planes, social functions etc. It may be noted that the manmade noise is now doubling after every decade.
The manmade sources of noise pollution are classified into:
- Transport noise
- Industrial noise and
- Neighborhood noise.
- Transport noise
The main threat of noise comes from transport sector. The transport noise includes road traffic noise, rail traffic noise and aircraft noise.
(a) Road traffic noise
The chief causes of road traffic noise are the number of road vehicles and their high traffic speed. Faster moving vehicles produce high noise from their gear box, exhaust system, vibrations from their body, etc.
(b) Rail traffic noise
The noise from rail traffic is comparatively lower than that from road traffic. Introduction of diesel engines or electrical engines has reduced the intensity of rail traffic noise which was previously shown by steam engine. Besides use of welded tracks and improved coach suspension have contributed to the reduction in railways noise.
(c) Aircraft noise
Larger and faster aircrafts produce high noise intermittently during takeoff, landing and during flight. Noise generates from compressor and turbine and near jet exhaust. Jet engines create most noise around a radius of 16 km. Sonic boom is an important aspect of aircraft noise. Sonic boom occurs when an aircraft flies supersonically overhead.
- Industrial noise
The different machines of numerous industries, factories and mills produce a lot of high intensity sounds causing noise pollution. Some industrial processes like weaving, ship building, boiler making, pressing and blasting operations are more nosier. The operations in pneumatic drills, milling machines, cutters, printing press with an upward, downward and sideways movement and vibrations, cause lowering of hearing capacity to a large extent. The noise pollution is further magnified due to the installation of industries in compact places. For example, the workers near the heavy industrial blowers in steel industry are exposed to sound of 112dB for eight hours and hence suffer from occupational pollution.
- Neighborhood noise
This type of noise includes antisocial activities of neighbors like using of loud TV, stereo, radio sets, jazz music, fireworks parties, playing of children, barking of dogs, neighborhood brawls out of intoxication and industrial neighborhood noise etc. The machines used in house construction like concrete mixes, vibrators, bulldozers, heavy diesel lorry, building demolition activities also add to the noise pollution.
Effects of Noise Pollution
Noise is air-borne mechanical energy striking the human eardrum. A sound of 65dB is the noise level for conversation heart at a distance of one meter. A sound of 125dB gives the sensation of pain in the ear. If a noise of 90dB in the mid-frequency range reaches the ear for more than few minutes, then the sensitivity of the ear is reduced. The various effects of noise pollution on human beings may be classified in to two categories
- Auditory effects and
- Non-auditory effects.
The impairing of hearing which may cause immediate auditory fatigue finally leading to deafness is known as auditory effects.
These effects include interference with speech communication, annoyance leading to ill-temper, bickering, mental disorientation, violent behavior and a series of health hazards.
In addition to serious loss of hearing, noise also causes pathological (or psychological), non-pathological (or physiological) and vibrational disorders.
(a) Pathological disorder
- Exposure to high frequencies or ultrasonic sound above the audible range damages inner ear and induces nausea and dizziness in man.
- Exposure to mid-audible frequency affects brain and nervous system having significant impact on thinking and coordination of limbs.
- Moderate vibration can lead to pain, numbness and cyanosis (blue coloration) of Fingers.
- Severe vibration results in damage to bones and joints in the hands with swelling and stiffness.
- Exposure to low frequency noise can reduce heart beat, variation in blood pressure and breathing difficulties.
(b) Non-pathological disorders:
These disorders are mainly seen in industries and other establishments which result in lower efficiency, reduced work rate, increased absenteeism and a higher potential for accidents and injuries. Noise also disturbs sound sleep of old people. Children exposed to excessive noise show signs of behavioral disorder which in later age manifest themselves in destructive nature.
(c) Vibration (physical vibration) disorder and Reynaud’s phenomenon:
- Noise from constant vibrations of hand tools like the hammer or drilling instrument creates ‘dead hands’ or ‘white fingers’ which is known as Reynaud’s phenomenon.
- Noise from moderate vibrations causes pain, numbness, and cyanosis.
- Noise from severe vibrations causes damage to bones, joints with swelling and stiffness.
Some of the important effects of noise pollution are outlined as given below:
- It causes contraction of blood vessels, makes the skin pale leads to excessive secretion of adrenaline hormone into blood thereby inducing high blood pressure.
- It may cause damage to heart, brain, kidney and liver.
- It induces contraction of muscles which ultimately leads to nervous breakdown, tension and even insanity.
- It induces anxiety, stress and fright which in turn causes increased heart beat, constriction of blood vessels, dilation of pupil of eye etc. by modulating the hormone content in blood.
- It damages some part of auditory system thereby causing the impairment of hearing.
- Excessive noise causes thickening of blood and changes in breathing amplitude.
- It is responsible for disturbing the entire biological system. For example, the internal wreckage caused by the roar of a jet engine includes gastric ulcer and thymus gland atrophy.
- It causes irritation, dissatisfaction, disinterest and affects work efficiency.
- Sudden and explosive sounds cause cracks in buildings and breaking of window doors and glasses.
- It causes chronic headache and irritability thereby reducing work efficiency.
- It brings about changes in the behavioral aptitude of birds and animals. For example, noise pollution discourages the annual visit of migratory birds to Alipore Zoo of Kolkata.
- It interferes with communication systems. For example, sometimes it becomes necessary to raise the volume of our TV set or radio to overcome the impact of external noise.
Prevention and Control of Noise Pollution
Noise produced from different sources has created a catastrophe to the entire living world specially to man. Hence, necessary steps should be taken to minimise the level of noise thereby protecting the living world from its detrimental effects.Few methods of minimising noise pollution are discussed below:
Industrial noise pollution control
The level of noise pollution due to industries can be lowered down by adopting the following techniques:
(a) Use of improved technique
The noise at source can be reduced by replacing noise producing machines with suitable improved technique. For example, the noise from exhaust fans can be decreased either by increasing the number of blades or by decreasing the rotational speed.
(b) Sound proofing
An insulating material may be applied on the noise producing machinery and equipment’s which causes sound proofing.
(c) Transmission control
The level of noise can be minimised by covering the walls of the room by sound absorber (e.g. acoustic tiles), introducing gaskets around the doors and windows, sealing all the outlets and putting carpet, drapery and acoustic materials inside the room.
(d) Creation of green vegetation cover
Plants and trees should be planted along highways, streets and industrial areas because the vegetation covers absorb and dissipate sound energy and acts as a buffer zone.
(e) Using protective devices
The use of ear plugs or ear muffs or even cotton balls by the worker in the industry can protect them from hazardous effects of noise pollution.
(f) Operations in open space
Noisy industrial operations should be conducted at open spaces far off from residential areas.
(g) Use of Building codes
Certain codes should be enforced which require sound proofing in the construction of industries, buildings and apartments.
Community noise control
- The community noise control includes minimization of noise from air traffic, transport system, building constructions etc. The noises from the above sources can be lowered by adopting the following procedures:
- The air traffic noise can be reduced either by suitable technique or by zoning the area around the airport and not allowing for the construction of houses or industries within 10 meters of the airport.
- The road traffic noise includes engine intake noise, exhaust noise, aerodynamic noise, noise from blowing of horns etc. Such type of noise pollution can be controlled by incorporating silencers in vehicles, maintaining speed limit prescribed for the vehicle and banning air horns.
- The loudspeakers, radio and music system should be operated at threshold intensity so that the noise level should not be hazardous to living organisms.
- Public awareness should be created to educate the common man about the harmful effects of noise pollution, through radio, television, etc.