Noise Pollution Lecture - 4

Noise Pollution In the nineteenth century the developments of the steam engine, petrol engine and technological machineries in industry resulted in increasingly noisy environment. In the twentieth century this has been further accelerated by introduction of the diesel engine, turbo-prop and jet engines, high-tech machineries, construction site machineries and increase road traffic. Noise is considered to be one of the dimensions of pollution, which leads to degradation of the environment and also poses health and communication hazards. The common scientific acoustic unit is Decibel (dB). It is not an absolute physical unit like volt, meter etc. but it is ratio expressed as a logarithmic scale relative to a reference sound pressure level.

Decibel 1 Decibel (dB) = 10 log 10 Intensity measured Reference intensity

Noise Classification Noise can be broadly classified under three categories: –Transport noise i) Road traffic noise ii) Aircraft noise iii) Rail traffic noise –Occupational noise –Neighborhood noise Road traffic noise – vehicles on roads produce irritation for more people than any other noise source. Traffic noise has been increasing over the years continuously. This is because of steady increase of the number of road vehicles and consequently increase of road traffic density

Aircraft noise – It differs from road traffic noise in the sense that it is not continuous but intermittent. There are peak noise levels when aircrafts fly overhead or take off and land at airports the noise being produced from aircraft engines. Rail traffic noise- this is not a serious nuisance as compared to the previous types of traffic noise. The noise is generally of lower frequency than that of street vehicles and further more, most railway tracks run through rural areas. Of course, buildings located besides railway tracks are exposed to noise menace. The introduction of diesel and all-electric locomotive has greatly reduced rail traffic noise.

Neighbourhood noise - this implies variety of sources of noise, which disturb and annoy the general public by interfering with their comfort and welfare. Such sources are loud TV and radio sets, loud cassettes, loudspeakers in public functions and entertainments etc. Disco music and dance in late evenings cause noise nuisance to nearby residents.

Noise Pollution Hazards Noise is air-borne mechanical energy striking the human eardrum. While 65dB (A) is the noise level for conversation heard at a distance of one meter, 125 dB (A) gives the sensation of pain in the ear and 150 dB (A) might kill a human being. The most commonly occurring ear damage is brought about by continuous periods of intensity of noise. If a noise level exceeding 90 dB in the mid frequency range reaches the ear for more than a few minutes then the sensitivity of the ear is reduced.

In addition to progressive hearing loss there may be instantaneous damage or aquatic trauma. This arises from very high intensity impulse type noise due to explosion or sudden excessive noise of about 150 dB or more. Sonic booms or over- pressure from supersonic airliners are impulse type noise, which can have hazardous effects on the ears. Noise pollution can also cause pathological or psychological disorders. Pathological effects are produced by particular noise frequencies causing vibration or resonance in materials or human bodies. Higher frequencies or ultrasonic sound above the normal audible range can affect the semicircular canals or the inner ear and make one suffer from nausea and dizziness. Again very low frequency noise can produce resonance in the body organs giving the effects of reduced heartbeat, variations in blood pressure and breathing difficulties. Mid audible band frequencies and generate resonance in skull and hence affect the brain and nervous system having impact on thinking and coordination of the limbs. Moderate vibration can lead to pain; numbness and cyanosis (blue colouration) of fingers while sever vibration results in damage to bones and joints in the hands with swelling and stiffness.