In the context of occupational noise-induced hearing loss (NIHL), the OSHA (and Indian DGFASLI) permissible exposure limit for continuous noise is 90 dB(A) for an 8-hour workday. If noise intensity increases by 5 dB(A) to 95 dB(A), the permissible exposure duration is halved to:
- A 6 hours
- B 4 hours ✓
- C 2 hours
- D 1 hour
Correct answer: B. 4 hours
Explanation
OSHA uses a 5 dB exchange rate (halving rate): for every 5 dB(A) increase in noise level above 90 dB(A), the permissible exposure time is halved. Thus: 90 dB(A) → 8 hours; 95 dB(A) → 4 hours; 100 dB(A) → 2 hours; 105 dB(A) → 1 hour; 115 dB(A) → 15 minutes maximum. WHO and NIOSH use a stricter 3 dB exchange rate with 85 dB(A) as the reference (equal energy principle), where doubling dose corresponds to 3 dB increase. NIHL primarily affects the 4,000 Hz frequency (4 kHz dip or notch on audiogram) before lower frequencies.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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