Dr. Rashmi Rekha Patra

A Primer on Noise Pollution

A Primer on Noise Pollution

It is high time to make a Noise about Noise.

The ubiquity of noise and its generally obvious nuisance effect have caused many people to be apprehensive about its adverse effects on public health. High intensity sound which is undesirable is called noise. Not only it is annoying but also it produces emotional and behavioural changes in man.

Now-a-days the ambient noise level of the environment has risen both with increasing population density and with increasing use of machinery as a substitute for human and animal muscle-power. The increased noise level is felt in most of the occupational settings.

Since noise is an undesirable factor in our living environment, it is a subject of interest from the stand point of public health. There is normally some loss in productivity in high noise fields. The productivity loss in Germany due to noise was estimated to be 0.2% of GDP (Gross Domestic Product) (Wicke, 1986) which amounted to $2.084 billion US dollars. This represents an economic loss for the society in general, and for the industry and citizen in particular. Therefore, infact, noise results in total loss and should warrant more attention than it gets today.

Heavy industries such as iron and steel production, fabrication and mining etc display high levels of sound; so do refineries and chemical plants, though in the latter instances relatively few people are exposed to high levels of noise.

Automobile plants especially with forging and stamping sections, saw-mills, furniture factories, textile mills and the like often employ large numbers of workers in buildings with high noise levels throughout. Hearing impairment of such employees is usually noticed.

Necessity compels many people to accept at least to tolerate noisy conditions both at work place and at home. Urban areas in general, are more noisy than suburban or rural, and industrialised areas more than residential. In a residence noise comes from noise generating equipment, such as air-conditioners, fans, household appliances and is present for a long time due to increasing use of such equipment. However, one of the prime reasons for noisy residences is due to the Television and music players playing at a loud volume and the increasing use of mobile phones at higher volumes which are held closer to the ear.

Apart the human induced noise ie Anthropophony, noise is generated due to Geophony which is non biological sounds due to nature like wind, thunder etc and also due to Biophony ie sounds made by non-human species like animals, birds, insects etc.

Among the loudest noise generated due to Geophony can be from thunder and at times from volcanic eruptions. Similarly the loudest sounds from the Anthropophony can be due to a Jack hammer operating, Jet aircrafts taking off etc.

F1 cars emit high noise

F1 cars emit high noise

Noise is measured in the unit of decibel dB (named after Alexander Graham Bell, the inventor of telephone). One decibel is equivalent to the faintest sound that can be heard by the human ear. Sound consists of repeated alternate compressions and expansions of air. The pitch of the sound is determined by the number of vibrations per second (ie. the frequency), and the intensity of the sound (related to its loudness) is determined by the amplitude of the vibrations. Sound reaches the ear usually through pressure waves in air; a remarkable structure converts this energy to electrical signals which are transmitted to the brain through the auditory nerves. Barring injury or disease, the human ear carries out its work throughout the life. It can detect vibratory motion so small as to approach the magnitude of the molecular motion of the air. Coupled with the nerves and brain, it can detect frequency differences of sound sources; can also analyse and correlate such signals.

A perfect human ear can hear sounds from between the range of 20Hz to 20kHz. However most of the people over a period of time lose out on the ability to hear higher frequencies due to increased exposure to noise in our day to day life and/or in our work places.

Sound Pollution

Sound Pollution

Studies show that noise above 70dB creates stress in an average human and it reaches annoying proportions at 80dB. A 120 dB noise level is quite painful to the ears and if it persists for sometime then it can lead to hearing disorders. Permanent damage occurs a levels exceeding 140dB. In urban areas the noise levels exceed 90dB over long stretches of time. Average traffic noise is in excess of 80dB, with peaks of over 110 dB from loud horns.

At noise level of 75 to 80 dB, there is first constriction of peripheral blood vessels with a consequent increase in blood flow to the brain, a change in breathing rate, changes in muscle tension and gastrointestinal motility and sometimes glandular reactions detectable in blood and urine.

At a slightly higher level, and especially for intermittent or impulsive noise, another non-auditory response appears – the startle effect – which results in pulse rate and blood pressure change, release of stored glucose from liver into the blood stream (to meet the energy demand) and increase in the production of adrenalin. At noise levels above 125 dB, the electroencephalographic records show distorted brain waves and there is often interference with vision.

Temporary threshold shift (TTS) or temporary hearing loss occurs when a person hears a sudden severe noise such as explosions or other high-intensity sound. The hearing mechanism comes back to normal after a brief period, provided the noise was not loud enough to cause permanent damage, such as immediate deafness by rupturing the ossicles. Any damage of the cochlea or the auditory nerve is irreparable.

There is some evidence to suggest that the TTS induced by initial exposure to noise is of the same order of magnitude as the permanent loss – ie. “noise-induced permanent threshold shift” (NIPTS) – that is experienced by the same person after five to ten years of continuous occupational exposure to the same noise.

Robert Alex Baron (1964) for the first time pointed out that noise has damaging physiological and psychological effects on human beings. A research team of the University of Chicago revealed that excessive noise produced due to aircraft landing or taking off caused tiredness, irritability, insomnia and nausea among the crew members of the aircraft carriers. In some extreme cases, changes in electroencephalogram brain wave patterns were found along with blurred vision.

Apart from physical effects, noise has also some psychological effects of which irritation and annoyance are most common. It is an established fact that high noise levels bring about heart disorders. However, human response to noise displays a systematic qualitative pattern, but quantitative responses vary from one individual to another because of age, health, temperament and the like; and with the same individual, they vary from time to time because of change in health, fatigue and other such factors. Variation is greatest at low to moderately high sound levels; at high levels, discomfort is felt by almost everyone.

As with other environmental hazards, further studies are needed to characterise quality and quantity of community noise exposure, particularly as it relates to hearing loss and many other deleterious effects of noise on the exposed community. Where there is a community consensus that these noises are a public nuisance, there are grounds to seek its abatement.

Dr. Rashmi Rekha Patra
Latest posts by Dr. Rashmi Rekha Patra (see all)