Threshold Limit Value-Ceiling (TLV-C) in occupational exposure is defined as:
- A The 8-hour time-weighted average concentration that should not be exceeded
- B The concentration that should not be exceeded even instantaneously at any time during work ✓
- C The peak concentration allowed for up to 15 minutes, up to 4 times per day
- D The concentration below which no adverse health effects are observed in lifetime exposure
Correct answer: B. The concentration that should not be exceeded even instantaneously at any time during work
Explanation
ACGIH defines three TLV categories: TLV-TWA = 8-hour time-weighted average for a 5-day work week; TLV-STEL = 15-minute short-term exposure limit not to be exceeded even for 15 minutes (up to 4 times/day, with 60-minute gaps); TLV-C = ceiling value — concentration that should NEVER be exceeded even instantaneously. TLV-C applies to fast-acting substances like HCN, CO, and irritant gases where even brief peaks can cause acute harm. Occupational exposure limits (OELs) in India are set by ACGIH TLV values adapted by the Factories Act and DGFASLI.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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