Describe noise pollution with its health effects and control.

Noise Pollution

• It is measured in decibels (dB) on a logarithmic scale, with the dB(A) weighting used because it approximates the response of the human ear
• The logarithmic scale has a consequence students often miss — an increase of 10 dB represents a tenfold increase in sound energy and is perceived as roughly a doubling of loudness; and two sources of 60 dB together give 63 dB, not 120
• The sources — traffic, which is the largest contributor in cities; aircraft and railways; industry and machinery; construction; loudspeakers at religious and social functions; firecrackers; generators; and domestic and personal audio devices
• The INDIAN ambient standards should be quoted, in dB(A) for day (6 am to 10 pm) and night (10 pm to 6 am):
• Industrial area — 75 day, 70 night
• Commercial area — 65 day, 55 night
• Residential area — 55 day, 45 night
• Silence zone — 50 day, 40 night
• A silence zone is the area within 100 metres of a hospital, educational institution or court
• The health effects divide into auditory and non-auditory, and the non-auditory effects are the larger public health problem because they occur at levels far below those causing deafness
• Auditory effects:
• Temporary threshold shift — reversible hearing loss after exposure, recovering with rest
• Permanent threshold shift (noise-induced hearing loss) — irreversible sensorineural loss from repeated exposure
• Its characteristic pattern is a dip at 4000 Hz on the audiogram, appearing before the speech frequencies are affected, so the person is unaware of it and does not complain until the damage is advanced
• This is why audiometric screening detects what history does not, and is the basis of occupational hearing conservation
• Acoustic trauma from a single intense sound such as an explosion or firecracker, which may rupture the tympanic membrane
• Tinnitus, and masking of speech and warning signals, which itself causes accidents
• Non-auditory effects, which are the more important for the community — annoyance and irritability; sleep disturbance, which is the effect with the widest impact and occurs at quite modest night-time levels; interference with communication and with children’s learning and reading; reduced work efficiency and concentration; and cardiovascular effects — raised blood pressure, tachycardia and, on long-term exposure, increased ischaemic heart disease
• The cardiovascular effect operates through a chronic stress response and occurs during sleep even when the person does not wake, which is why night-time noise standards are stricter than daytime ones
• The control measures, arranged as the standard hierarchy:
• At the source — quieter machinery and maintenance, silencers and mufflers, vibration damping, restrictions on horns and on the use of loudspeakers, bans on firecrackers at night, and limits on generator noise
• Along the path — distance, enclosure of noisy machinery, acoustic barriers and green belts, sound-absorbing building materials, and zoning that separates industry and roads from housing, schools and hospitals
• At the receiver — ear plugs and ear muffs, rotation of workers to limit exposure duration, audiometric surveillance, and health education
• Protection at the receiver is the last resort and the least effective, since it depends on the individual using it correctly at all times
• The legal framework — the noise pollution (Regulation and Control) rules, 2000 under the Environment (Protection) Act, with restrictions on loudspeakers at night and provisions for silence zones