Permissible Exposure Limit (PEL)

A legal limit for exposure of an employee to a chemical substance or physical agent, such as high level noise. For chemical substances, usually expressed in TWA (time-weighted average, usually for 8 hours), STEL (short-term exposure limit (usually a 15-minutes average) and ceiling values that may not be exceeded at any time. The unit of measurement is usually ppm (parts per million) or