Per OSHA 29 CFR 1926.1101 determination of employee exposure shall be made from ____________ samples that are representative of the 8 hour TWA of each employee.

• A. Breathing Zone
• B. Ambient air
• C. Area samples
• D. Bulk samples

Answer: (A)

Exposure determinations for asbestos exposure are about what a worker actually inhales over the full shift. Because inhalation is the primary route of exposure and exposure can vary with location and activity, you need to sample where the worker is actually breathing—the breathing zone. Personal samples taken in the worker’s breathing zone capture the real concentration the worker is exposed to over the entire shift, making the result representative of the 8-hour TWA for that employee.

Ambient air or area samples measure general conditions in a space and may not reflect the worker’s exact inhaled dose, since the worker moves, works at different distances from the asbestos source, or uses PPE that changes exposure. Bulk samples are material samples, not air concentrations, so they don’t tell you how much asbestos fibers are in the air that someone would breathe.

So the correct approach is to use breathing-zone (personal) samples to accurately represent each employee’s 8-hour TWA exposure.