Permissible Exposure Limits (PELs)

A PEL (also called an OSHAOccupational Safety and Health Administration (www.osha.gov). Federal agency within the U.S. Department of Labor with the responsibility of ensuring worker safety and health. PEL) is the maximum amount or airborne concentrationThe amount of a chemical present in a given weight or volume of air. Concentration of a gas in air may be expressed in units such as parts per million (by volume) or milligrams per cubic meter. of a substance to which a worker may be legally exposed. Most PELsPermissible Exposure Limits. A level of concern representing the adverse health effects of a hazardous substance on healthy adult workers. PELs are not available in CAMEO 365betÓéÀÖ. have been defined for substances that are dangerous when inhaled, but some are for substances that are dangerous when absorbed through the skin or eyes.

PELs are set by OSHA and are legal workplace exposure limits in the United States. Workers' exposure may not exceed these standards and OSHA has the power to warn, cite, and fine violators.

Note: PELs are not included in CAMEO 365betÓéÀÖ.

What are PELs?

A PEL is defined up to three ways:

  • Time-weighted average (TWA) concentration: The concentration of a contaminant averaged over a workday. It's measured in a workplace by sampling a worker's breathing zone for the whole workday. OSHA requires that the TWA should not be exceeded during any 8-hour workshift during a 40-hour workweek.
  • Ceiling value: A concentration of a toxicPoisonous; can injure or kill people or other organisms. substance in air that must not be exceeded at any time during the workday, per OSHA requirements. This value is often used in conjunction with the TWA.
  • Short-term Exposure Limit (STEL) value: A TWA concentration that OSHA requires not to be exceeded for longer than 15 minutes during a workday—even if the 8-hour TWA is within the standards. TWA-STELs are given for contaminants for which short-term hazards are known.

Below is a graph of concentration over an 8-hour day at a hypothetical workplace. During this day, the TWA and the ceiling value were not exceeded:

  • Excursions of concentration above the TWA line were balanced out by periods when concentrations were below the line.
  • While the ceiling value was reached, it was never exceeded.

A graph of exposure versus time at a hypothetical workplace.

Current PELs are listed in the Code of Federal Regulations (External link.Ìý²¹²Ô»å External link.). OSHA has also published External link., which show PELs alongside other common workplace exposure limits. Their website notes "OSHA's mandatory PELs in the Z-Tables remain in effect. However, OSHA recommends that employers consider using the alternative occupational exposure limits because the Agency believes that exposures above some of these alternative occupational exposure limits may be hazardous to workers, even when the exposure levels are in compliance with the relevant PELs." Read External link. on the OSHA website.

PEL Information in the NIOSH Pocket Guide

The External link. includes PELs, along with other information, for nearly 700 substances and substance groups. (Chemical-specific links to the NIOSH Pocket Guide are included on some chemical datasheets in CAMEO 365betÓéÀÖ.) In the NIOSH Pocket Guide, note that:

  • A TWA PEL is designated by "TWA" preceding the value.
  • A ceiling PEL is designated by "C" preceding the value.
  • A STEL is designated by "ST" preceding the value.

Part of the Benzene datasheet from the NIOSH pocket guide. The NIOSH RELs and OSHA PELs are marked.

PEL Information Online

  • External link.Ìý²¹²Ô»å External link. See the list of current PELs. (Any PEL value preceded by "(C)" is a ceiling value; others are TWA values.)
  • External link. See the list of current PELs alongside other common workplace exposure limits.