Glossary / Exposure limits
Recommended exposure limit (REL)
Recommended exposure limit (REL) is an occupational exposure limit recommended by NIOSH, based on a review of the health evidence. RELs are advice for protecting workers and are not legally enforceable like OSHA's permissible exposure limits.
Explanation
NIOSH, the National Institute for Occupational Safety and Health, is a research agency and does not enforce workplace rules. It develops RELs and publishes them, with notes on measurement methods, in resources such as its pocket guide to chemical hazards. OSHA may use such recommendations when it considers new standards, but until then they remain recommendations.
Most RELs are expressed as a time-weighted average for up to a 10-hour workday during a 40-hour work week, which is a different basis from the 8-hour average that many OSHA limits use. Some RELs also have short-term or ceiling forms. Check the averaging period before comparing values.
RELs are valuable because they often reflect newer data than the older Permissible exposure limit (PEL) values. NIOSH marks substances it considers potential occupational carcinogens with a "Ca" notation, which is a signal to keep exposure as low as you reasonably can rather than treating the REL as a safe line. Safety managers use RELs, along with Threshold limit value (TLV) values and Occupational exposure limit (OEL) information from suppliers, to set internal targets.
Supplier SDSs may list RELs in Section 8 or may leave them out; content varies. A missing REL does not mean a chemical has no hazard.
What to do and watch for
- Use RELs as a benchmark when the OSHA PEL looks outdated.
- Check the averaging time before comparing a REL with a PEL or TLV.
- Remember that only the PEL is legally enforceable by OSHA.
Where it appears on an SDS
- Section 8: Exposure controls / personal protection. May list NIOSH RELs among the exposure limit values, with the averaging time and any notes.
SDS content and wording vary by supplier. This page is general reference and does not replace the current SDS for your product.