Noise Pollution Regulation and Control: Limits and Decibel Arithmetic
Noise Pollution Regulation and Control is a high-scoring area because the standards are table-driven. The exam tests category-wise limits, day/night definition, silence zones, loudspeaker rules and decibel arithmetic.
Ambient standards
The Noise Pollution (Regulation and Control) Rules, 2000 set Leq limits in dB(A): industrial 75 day/70 night; commercial 65/55; residential 55/45; silence zone 50/40. Day is 06:00–22:00 and night is 22:00–06:00. A silence zone is an area within 100 m of hospitals, educational institutions, courts and religious places; horns, loudspeakers and amplified sound are prohibited there except with permission.
Source rules
Loudspeakers are banned 22:00–06:00. For cultural or religious events, written permission may allow 22:00–24:00, but the sound must not exceed ambient by more than 10 dB(A). Firecrackers must not exceed 125 dB(A) at 4 m or 145 dB(C). DG sets need acoustic enclosures and are regulated by source standards, not the ambient table. Construction noise is controlled by local conditions and time restrictions.
Worked example
Four machines each produce 60 dB(A) at a boundary. Total = 10 log10(4 × 10^6) = 60 + 10 log10(4) = 66.0 dB(A). If a fifth 60 dB(A) source is added, total = 67.0 dB(A). Adding a 70 dB(A) source to a 60 dB(A) source gives 70.4 dB(A), because the louder source dominates.
Traps
Night is not 00:00–06:00; silence-zone distance is 100 m; dB(A) is not dB(C); Leq is energy-averaged, not arithmetic; a 3 dB rise doubles acoustic energy, while about 10 dB is perceived as twice as loud. Do not apply industrial limits to a residential boundary.