Noise Pollution: The Sources And Classification

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The word ‘Noise’ is derived from the Latin word ‘nausea’ which means feeling of sickness at the stomach with an urge to vomit [1]. Sound that is unwanted or disrupts one’s quality of life is called as noise. When there is lot of noise in the environment, it is termed as noise pollution. Sound becomes undesirable when it disturbs the normal activities such as working, sleeping, and during conversations. The unit of sound intensity is 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. It is an underrated environmental problem because of the fact that we can’t see, smell, or taste it. Noise pollution is defined as the distressing noise that may harm the physical/mental activity of human being as well as animal life. Now days the matter of noise pollution is of prime concern. Noise is found almost everywhere. Some industrial locations have even louder continuous noise. Community noise is chiefly produced by transportation sources, most often airplanes and highway vehicles. Noise sources are also in public buildings and residences. Physically, there is no dissimilarity between sound and noise. Noise corresponds to undesired sound and any needless disturbance within a useful frequency band. The generation of most of the outdoor/ environmental noise in the world is mainly caused by industrial machines, transportation systems etc. as well as indoor noise generated by machines (especially in some workplaces), building activities, domestic appliances and music performances etc. The different countries have rules & regulation bodies against the harmful noise sources, but implementation seems to be indulgent. Noise laws and ordinances vary widely across the world.

Classification of Noise Pollution:

There are two kinds of noise pollution

  • Community Noise/Environmental Noise (non-industrial noise pollution).
  • Occupational Noise (industrial noise pollution).

Community Noise/Environmental Noise: Community noise (also called environmental noise, residential noise, or domestic noise) is defined as noise emitted from all sources, except noise at the industrial work place. Major sources of community noise are automobiles, construction work, loudspeakers, recreational activities, fireworks, etc.

Occupational Noise: Occupational noise is the amount of acoustic energy received by an employee’s auditory system when they are working in the industry. Occupational noise, or industrial noise, is often a term used in occupational safety and health, as sustained exposure can cause permanent hearing damage. Occupational noise is considered an occupational hazard traditionally linked to loud industries such as ship-building, mining, railroad work, welding, and construction, but can be present in any workplace where hazardous noise is present.

Intensity and Measurements

The loudness of noise is measured by decibels(db). Decibel scales are logarithmic rather than linear. Thus, the change from 40 db (a library) TO 80 db (a dishwasher or garbage disposal) represents a ten-thousand-fold increase in sound loudness. The frequency or pitch of a sound is also a factor in determining its degree of harm. High pitched sounds are the most annoying. The most common sound pressure scale for high pitched sounds is the A scale, whose units are written dbA. Hearing loss begins with prolonged exposure (eight hours or more per day) to 80 or 90 dbA levels of sound pressure. Sound pressure becomes painful at around 140 dbA can kill at 180 dbA.

Major Sources

Noise can come from many places. But the major sources are-

  • Household sources: Gadgets like food mixer, grinder, vacuum cleaner, washing machine and dryer, cooler, air conditioners, can be very noisy and injurious to health. Others include loud speakers of sound systems and TVs, iPod and ear phones. Another example may be your neighbor’s dog barking every night at every shadow it sees, disturbing everyone else in the apartment.
  • Social events: Places of worship, discos and gigs, parties and other social events also create a lot of noise for the people living in that area. In many market areas, people sell with loud speakers, others shout out offers and try to get customers to buy their goods. It is important to note that whey these events are not often, they can be called ‘Nuisance’ rather than noise pollution.
  • Commercial and industrial activities: Printing presses, manufacturing industries, construction sites, contribute to noise pollutions in large cities. In many industries, it is a requirement that people always wear earplugs to minimize their exposure to heavy noise. People who work with lawn mowers, tractors and noisy equipment are also required to wear noise-proof gadgets.
  • Transportation: One of the main threats of noise comes from transport sector. The transport noise includes road traffic noise, rail traffic noise and aircraft 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. 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. Larger and faster aircrafts produce high noise intermittently during take-off, 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.

Literature Review

Sound can be defined as a mechanical disturbance or an oscillation in pressure, stress, particle displacement, and particle velocity propagated in an elastic medium of such character as to be capable of exciting the sensation of hearing (15 ). Noise is sound that is intolerable.

It is being recognized as a major pollution. It is often referred to as the ‘New Pollutant;’ but in fact, it is one of the oldest. Two thousand years ago, Horace complained about the noise that harassed the man of letters in the Eternal City (5). Noise bothered Julius Caesar so much that he banned chariot driving at night. In 1851, Arthur Schopenhauer wrote about the ‘disgraceful… truly infernal’ cracking of whips in German streets ( 18). English law (Act of 1864) allowed a householder to send away street musicians, and to this day they are required to keep moving. In a study published in October 1955, Fortune reported ‘a rising tide of noise (in/ U. S. streets, factories, homes, and skies’ and asserted that Americans ‘have decided that noise should be abated. ‘ The optimism was unwarranted. Today the level of everyday noise is increasing very quickly. The increasing rate is so fast that it is more than twice what it was in 1955, and the level continues to mount (18).

Although a few individuals have fought against noise for centuries, noise pollution has only recently come to the attention of the public. Scientific research has shown that noise has many bad impacts on human health. It may affect one’s health in subtle ways — both physiologically and psychologically. Dr. Samuel Rosen, clinical professor of otology (the science of the ear) at Mount Sinai School of Medicine and consulting ear surgeon at Mount Sinai Hospital in New York City, feels that unexpected or unwanted noises cause certain physical reactions — the pupils dilate, skin pales, mucous membranes dry, there are intestinal spasms, and the adrenals explode secretions. The biological organism is disturbed (8). Because of loud noise the blood pressure, the functions of the heart and the nervous system also get affected.

Dr. Alexander Cohen, director of the National Noise Study, a Public Health Service research program headquartered in Cincinnati, contends (17) that loud and continual noises not only damage the ears and cause hearing loss but also produce physiologic side effects, such as the narrowing of blood vessels near the surface of the body. Even loud conversation is enough to affect the nervous system and therefore provoke constrictions in a large part of the blood circulation system. Dr. Cohen confirms that hearing loss rises in proportion to noise levels and time of exposure (7)

Dr. John D. Dougherty of the Harvard School of Public Health and Dr. Oliver I. Welsh, chief of the Audiology Unit of the Veterans Administration Outpatient Clinic in Boston, made a study of the loss of hearing in high frequencies. They observed that many noise levels encountered in the community exceed standards found injurious in industry ( 3 ).

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According to Dr. Dougherty, the hair cells can regenerate themselves after noise exposure; but long-term exposure is likely to cause complete destruction. Dr. Dougherty has noticed increasing deafness in the general population. ‘There is incriminating evidence that community noise levels are causing hearing loss,’ he says. Even the average kitchen is guilty, he believes; the whirring and whining of kitchen machines is too loud for comfort and health. Also, on Dr. Dougherty’s guilty list in the rising decibel count are autos, trucks, buses, subways, power lawn mowers, and outboard motors. Sirens and police whistles, too, are dangerous to hearing, he asserts, because they affect the sensitive high frequency range (6).

A more exceptional type of hearing damage, called acoustic trauma or blast trauma, is caused when a sudden burst of noise, such as gunfire, ruptures the eardrum or disrupts the chain of small bones that transmits the sound within the ear to the auditory nerve. Explosive noise may also affect the inner ear, producing cochlear damage and permanent nerve deafness (15 ). Sonic booms are able to induce the typical startle reaction, similar to acoustic trauma, in human beings. Prolonged exposure to these sonic booms can result in health hazards, including deafness, cardiovascular, glandular, and respiratory malfunctions (8).

Psychiatrists and psychologists have recently noted the connection between excessive undesired noise and mental disorders. Drs. Rosen and Knudsen suggest that loss of hearing may in fact be the least serious impairment to the human organism caused by noise pollution. Both point out that one no longer has to work in a boiler factory to suffer noise-induced psychological and physiological damage. Day and night most of us are exposed to a general racket. These noises are now being recognized as a major factor in the celebrated tensions of modern living. Dr. Knudsen calls the total effect of the background roar of modern life ‘decibel fatigue,’ and says that millions of Americans suffer from it. Dr. Rosen believes that medical science will one day recognize an entire ‘noise syndrome’ — a family of symptoms related to unwanted or unexpected noises (15).

Experiments, conducted by Dr. Jansen and at the University of Southampton in England, show that noises, even mild ones, make the pupils of the eye dilate. This can help explain why watchmakers, surgeons, and others who do close work are so bothered by noise: it affects their eyes so that they are constantly changing focus. This can cause eyestrain and headaches (3 ).

‘Sound’ may damage the body and mind even though it cannot be heard. Studies have been started by the French National Centre for Scientific Research in Marseilles concerning infrasound. Infrasound has a pitch or frequency of below 30 cycles per second and is thus inaudible to the human ear, but is still capable of harming the human organism. Persons affected by infrasound experience physiological effects similar to those caused by low-frequency mechanical vibration. Vertigo and nausea are attributed to the excitation of the semi-circular canals, and infrasound may also cause resonances of il_lternal organs producing intense irritation, visual disturbances, and interference with intellectual activity ( 15 ).

At the other end of the frequency scale are the ultrasounds which are also inaudible to the human ear but which may have other serious effects on the human organism. In an extensive survey of the auditory and subjective effects of industrial ultrasonic sources made in 1967, it was foundJhat unpleasant subjective effects, including headache, n3.usea, tinnitus, and fatigue were experienced by some persons and that temporary threshold-shift occurred. It is rumored that the latest exotic weapon for military use in Vietnam uses a type of ultrahigh, ultraloud sound. This weapon is a siren capable of emitting 200 decibels .A sound intense enough to literally ‘boil’ the inner ear (15 ).

Besides its biological and physiological effects, noise also has important physical effects. Take the Comet, England’s and the world’s first jet airliner. It was noise, in the form of acoustic fatigue, which grounded these planes in 1954. Noise generated through the fuselage caused tiny cracks in the metal, which grew until the fuselage split open, and because of pressurization, exploded. Acoustical fatigue is an important concern of aerospace engineers. Part of the testing of airplane and rocket components is to determine the effect noise will have on them ( 3 ).

The sonic boom is a special kind of noise which, because it is explosive in nature, is particularly damaging. Serious damage connected with sonic booms has been observed and reported in the Canyon de Chelly National Monument in Arizona, Bryce Canyon in Utah, Mesa Verde National Park in Colorado, and elsewhere.

The effects of noise can largely be alleviated or prevented and should be. Frank Kirschner, director of engineering of the Soundcoat Company, a Brooklyn firm whose rapid growth exemplifies the rising technological interest in quiet, does not believe that machines are naturally noisy, nor is noise an inescapable price of progress. Machines can be designed to be quiet, often with a careful selection of the materials.

Noise that is not or cannot be eliminated often can be contained. The Labor Department established a health code in MAY 1969 in which 90 decibels was set as the loudest continuous noise a workman should endure in an eight-hour day; the higher the decibel count, the less the exposure time. Companies that do not comply to the code could be barred from bidding on government contracts worth $10,000 or more. Noise levels can be reduced at the source by noise and shock absorbers or by requiring workers to wear earplugs or earmuffs and exposing them to shorter periods of high-level noise. West Point-Pepperell, Inc. chairman Joseph L. Lanier says the company’s voluntary earplug-earmuff program is being expanded to include workers in all areas where noise is excessive. J. C. Radcliff, supervisor of industrial safety at Ford Motor Company, says fewer than 50 percent of the eligible employees take advantage of the voluntary program. At Ford’s forging plant in Canton, Ohio, the decibel count can reach 120.

Perhaps what is needed is a whole set of anti-noise laws which follow the concept proposed by a well-known British economist ·· that all citizens have violable ‘amenity rights.’ These, explained Professor Ezra J. Mishan of the London School of Economics and Political Science, are the rights to peace and quiet, to privacy and clean air. Now, he said, the noise created by airlines, factories, motor vehicles, among others, is limited only by what authorities believe the people will put up with. And they put up with more and more as they become accustomed to the noise ·· or think they do (3).

Dr Vern 0. Knudsen, a physicist, a founder of the Acoustical Society of America and former Chancellor of the University of California, did not overstate the problems of today’s noise when he said: ‘NOISE IS A SLOW AGENT OF DEATH’ (15). 

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