The measurement used by the Occupational Safety and Health Administration in evaluating workplace exposure during an 8 hour period is:

• A. PEL
• B. LC50
• C. TLV-C
• D. STEL

Answer: (A)

Permissible Exposure Limit (PEL) is the measurement OSHA uses to evaluate a worker’s exposure over an 8-hour period. It’s an 8-hour time-weighted average, meaning the concentration is averaged across the full shift to reflect typical exposure even if levels fluctuate during the day. PELs are enforceable regulatory limits set by OSHA, guiding when controls or interventions are needed.

Other terms describe different concepts not tied to the 8-hour average. LC50 is a toxicology marker for lethality in 50% of test organisms, not workplace exposure. TLV-C refers to a ceiling limit, an instantaneous maximum exposure that should not be exceeded at any time. STEL is a short-term exposure limit, usually applied to a 15-minute period, not the full 8 hours.