The Definition of Permissible Exposure Limit (PEL)

Definition of Permissible Exposure Limit (PEL)

A permissible exposure limit (PEL) is the legally enforceable limit OSHA sets on how much of a hazardous substance or physical agent, such as noise, a worker may be exposed to. Most PELs are expressed as an 8-hour time-weighted average (TWA), although some are short-term exposure limits (STELs) averaged over 15 minutes or ceiling limits that must never be exceeded. PELs apply to airborne concentrations, typically measured in parts per million (ppm) or milligrams per cubic meter (mg/m³), and some carry a skin notation where absorption through the skin adds to the dose.

Most general industry PELs are listed in the Z-tables of 29 CFR 1910.1000. Substance-specific standards, such as those for lead, benzene, respirable crystalline silica and asbestos, set their own PELs along with an action level, monitoring and medical surveillance rules.

Key Facts About PELs

• Most of OSHA's PELs were adopted in 1971 from consensus limits of the time and have not been updated since.
• OSHA itself recommends that employers consider more protective limits, such as NIOSH RELs, ACGIH TLVs and Cal/OSHA PELs.
• State plans such as Cal/OSHA set many PELs that are lower than federal limits.
• The noise PEL is 90 dBA as an 8-hour TWA, with a hearing conservation trigger at 85 dBA.
• Employers must control exposures below the PEL using the hierarchy of controls, with respirators used where other controls are not feasible or sufficient.

Example of a Permissible Exposure Limit

A fabrication shop samples a welder's breathing zone for manganese fume. The result is below the OSHA ceiling PEL but above the ACGIH TLV, so the safety manager adds local exhaust ventilation to bring exposure under the more protective limit.

How to Comply With PELs

1. Inventory chemicals and physical agents using safety data sheets.
2. Conduct air monitoring to measure representative worker exposures.
3. Compare results with OSHA PELs and more current limits.
4. Reduce exposures with elimination, substitution, engineering and administrative controls.
5. Use respiratory protection where needed, and document results and corrective actions.

Related Terms

• Occupational Exposure Limit (OEL)
• Threshold Limit Value (TLV)
• Time-Weighted Average (TWA)
• Action Level
• Industrial Hygiene

Frequently Asked Questions: Permissible Exposure Limit

What is the difference between a PEL and a TLV?

A PEL is a legal limit enforced by OSHA. A TLV is a health-based guideline published each year by ACGIH. TLVs are not law in the U.S. but are often lower and more current than PELs.

Is staying below the PEL always safe?

Not necessarily. Because many PELs are decades old, some workers may still be harmed at concentrations below them. Many employers manage to the lowest available limit.

What happens if exposures exceed a PEL?

The employer must implement feasible controls to reduce exposure and provide respirators in the meantime. Exceeding a PEL can lead to OSHA citations.