Permissible Exposure Limits (PELs) are regulatory limits on the amount or concentration of a substance in the air. OSHA defines PELs for over 500 chemical substances. These limits are intended to protect workers against the health effects of exposure to hazardous substances. PELs are usually given as a time-weighted average (TWA), which represents the average exposure over a standard workday (usually 8 hours) and workweek (usually 40 hours).
