What is the OSHA PEL for asbestos exposure in construction (8-hour TWA)?

• A. 1.0 f/cc.
• B. 0.1 fiber per cubic centimeter (f/cc) averaged over an 8-hour work shift.
• C. 0.01 f/cc.
• D. 0.001 f/cc.

Answer: (B)

The main concept being tested is how OSHA sets an asbestos exposure limit for construction in terms of an 8-hour time-weighted average, measured in fibers per cubic centimeter. The limit is 0.1 f/cc, averaged over the work shift. This means a worker’s exposure, when averaged across the entire 8 hours, must not exceed 0.1 fibers per cubic centimeter. The idea behind this limit is to protect workers from the cumulative health risks of asbestos over a typical workday.

Think of it as a budget for exposure: if some parts of the day are noisier or more dusty, the higher concentrations there must be offset by lower concentrations later so the overall average stays at or below 0.1 f/cc. For example, if you’re exposed to 0.3 f/cc for 2 hours and 0.05 f/cc for 6 hours, the 8-hour TWA would be (0.3×2 + 0.05×6) / 8 = 0.1125 f/cc, which exceeds the limit. The unit f/cc simply means fibers per cubic centimeter of air.

Other numerical options would imply different levels entirely, but the official construction standard sets this 0.1 f/cc 8-hour TWA as the permissible exposure.