What measurement does OSHA commonly use to evaluate workplace exposure during an eight-hour period?

• A. Permissible Exposure Limit
• B. Threshold Exposure Level
• C. Average Exposure Benchmark
• D. Recommended Exposure Limit

Answer: (B)

Measuring an eight-hour workplace exposure focuses on the eight-hour time-weighted average. The regulatory measure OSHA uses for this is the Permissible Exposure Limit (PEL). The PEL is the maximum average airborne concentration a worker may be exposed to over an 8-hour workday (and a 40-hour workweek). To determine compliance, you calculate the eight-hour TWA by weighting each concentration by the time spent at that level, summing, and dividing by eight hours. For example, exposure at 2 units for 4 hours and 4 units for 4 hours yields an eight-hour TWA of (2×4 + 4×4) / 8 = 3 units. If that eight-hour TWA equals the PEL, it’s at the limit; higher exposures require control measures. Other terms like Threshold Limit Value or Recommended Exposure Limit are not OSHA regulatory measures for an eight-hour period.