Permissible Exposure Limit (PEL) is a limit for occupational exposure to hazardous environments that include physical agents, loud noises, or chemical substances. These limits are established by OSHA and are typically given as a time weighted average (TWA) such as 8 or 10 hours. They may also be expressed as a workplace environmental exposure limit (WEEL). For example, the OSHA PELs for methyl chloride is 100ppm per 8-hour TWA.
Permissible Exposure Limits are enforced by legislation to protect occupational safety and health. They were originally established to protect employees who operate in work environments that may be hazardous. Certain substances that employees may be exposed to also can be classified as immediately dangerous to life or health (IDLH).
It should be noted that many of OSHA’s PELs are outdated and therefore inadequate to protect the health of workers, due to the fact that they were issued after the Occupational Safety and Health (OSH) Act in 1970, and have not been updated since. New developments in technology, science, and industry have indicated that the original limits do not sufficiently protect worker health.
Occupational exposure limits have also been adopted by NIOSH and ACGIH to accommodate additional substances. For example, the ACGIH PEL for exposure to ammonia is no more than 25 ppm over 8 hours. Some exposure limits are based on short term exposure limits (STEL). For example, the ACGIH PEL for short term exposure to ammonia is no more than 35 ppm.
OSHA’s PELs tables of regulatory limits and recommended limits have been annotated to accommodate some updated information. These annotated tables also provide a list of permissible exposure limits that may better protect workers. OSHA recommends that employers consider using alternative exposure limits as some established PELs may be hazardous, even if they are compliant. When using TWAs, it’s important to keep in mind that they are averages. OSHA recommends that employers consider all their options as they establish limits for the exposure of their workers.