Permissible Exposure Limit

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The Permissible Exposure Limit (PEL or OSHA PEL) is a legal limit in the United States for personal exposure to a substance, usually expressed in parts per million (ppm), or sometimes in milligrams per cubic metre (mg/m³). Permissible Exposure Limits are defined by the Occupational Safety and Health Administration (OSHA).

Exposure is defined as a time-weighted average, usually abbreviated to TWA. This means that, for limited periods, a worker may be exposed to concentrations which are higher than the PEL, so long as the average concentration over eight hours remains lower.