OSHA sets exposure limits to control the permissible levels of exposure to a substance. These limits are usually expressed as what in the air over a prescribed period?

• A. Maximum concentration in the air over a prescribed period
• B. Average concentration over a shift
• C. Peak concentration
• D. Total exposure over shift

Answer: (A)

OSHA exposure limits are about how much of a substance can be present in the air workers breathe, averaged over a defined time. This is expressed as the maximum permissible concentration in the air over a reference period (the time-weighted average, typically 8 hours, or a short-term exposure limit for a brief period). So the focus is on the allowable concentration in air, averaged over time, not on a single peak moment or the total amount inhaled over a shift.