What is Noise Pollution?

Noise pollution

We hear various types of sound everyday. Sound is mechanical energy from a vibrating source. A type of sound may be pleasant to someone and at the same time unpleasant to others. The unpleasant and unwanted sound is called noise.

Sound can be propagate through a medium like air, liquid or solid. Sound wave is pressure perturbation in the medium through which sound travels. Sound pressure alternately causes compression and rarefaction. The number of compressions and rarefactions of the molecules of the medium (for example air) in a unit is described as frequency. It is expressed in hertz (Hz) and is equal to the number of cycles per second.

There is wide range of sound pressures which encounter human ear. Increase in sound pressures does not invoke linear response of human hear. A meaningful logarithmic scale has been devised. The noise measurements are expressed as sound pressure level (SPL) which is logarithmic ratio of the sound pressure to a reference pressure. It is expressed as a dimensionless unit, decibel (dB). The international reference pressure of 2*10-5 pa is the average threshold of hearing for a healthy ear. Decibel scale is a measure of loudness. Noise can affect human ear because of its loudness and frequency (pitch).

The central pollution control board (CPCB) committee has recommended permissible noise levels for different location as given in table.

AREA

CODE

CATEGORY OF
AREA
NOISE LEVEL IN dB (A) leq
DAY NIGHT

(A)

Industrial

75

70

(B)

Commercial

65

55

(C)

Residential

55

45

(D)

Silence zone 50

40

Noise standards recommended by CPCB committee

What are the sources of noise pollution?

The sources of noise can be classified as (I) Mobile sources and (ii) stationary sources. Mobile sources are various modes of transportation (like air, road, rail-transportation), and stationary sources include industrial operations, construction activities and celebrations (social/religious functions, elections etc.) electric home appliances. Sound level associated with different sources of sound are given in table.

High levels of noise have been recorded in some of the cities of the world. In Nanjing (China) noise level of 150 dB has been recorded, while in some other cities of the world these levels are: Rome 90dB, New York 88 dB, Calcutta 85 dB, Mumbai 82 dB, Delhi 80 dB, Kathmandu 75dB.

What are the effect of noise?

Noise causes the following effects.

  1. Interferes with man’s communication: In a noisy area communication is severely affected.
  2. Hearing damage: Noise can cause temporary or permanent hearing loss. It depends on intensity and duration of sound level. Auditory sensitivity is reduced with noise level of over 90 dB in the mid-high frequency for some than few minutes.
  3. Physiological and psychological changes: Continuous exposure to noise affects the functioning of various systems of the body. It may result in hypertension, insomnia (sleeplessness), gastro-intestinal and digestive disorders, peptic ulcers, blood pressure changes, behavioral changes, emotional changes etc.

Control of noise pollution

  1. Reduction in sources of noise: sources of noise pollution like heavy vehicles and old vehicles may not be allowed to ply in the populated areas.
  2. Noise making machines should be kept in containers with sound absorbing media. The noise path will be interrupted and will not reach the workers.
  3. Proper oiling will reduce the noise from the machinery.
  4. Use of sound absorbing silencers: silencers can reduce noise by absorbing sound. For this purpose various types of fibrous material could be used.
  5. Planting more trees having broad leaves.
  6. Through law: legislation can ensure that sound production is minimized at various social functions. Unnecessary horn blowing should be restricted especially in vehicle-congested areas.

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