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Exposure Limits

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The American Conference of Governmental Industrial Hygienists (ACGIH) has their Threshold Limit Values (TLV's). The National Institute for Occupational Safety and Health (NIOSH) has their Recommended Exposure Limits (REL's). The Occupational Safety and Health Administration (OSHA) has their Permissible Exposure Limits (PEL's). How are the three related?


The ACHIH has had their TLV's for over 50 years. When the OSHA act was promulgated on Dec. 29, 1970, the Federal Government was looking for existing consensus standards and industry specifications to include in the new rules. These rules were compiled by OSHA throughout 1971. In addition to the ACGIH, other safety and health standards were obtained by OSHA such as the American National Standards Institute (ANSI) specifications, the Compressed Gas Association (CGA), the American Welding Society (AWS), the National Fire Protection Association (NFPA) etc.

OSHA found the existing ACGIH TLV's from1969 and incorporated them into the first industrial hygiene rules in 1971 and performed their first inspections in 1972. The ACGIH had always adopted their TLV's as recommendations and guidelines, however, and did not want them to be used as code requirements subject to Federal Regulations, enforcement and citations. However, OSHA was successful in using the OSHA PEL's for enforcement throughout the 1970's and early 1980's. However, after the initial promulgation of the standards it became more difficult for OSHA to adopt new standard updates as a public hearing and advance notice of proposed rulemaking was now required to update or add new standards.

According to an OSHAletter of interpretation 08/05/1993 - Compliance and Enforcement Activities Affected by the PELs. Decision, OSHA was finally able to update the standards in the late 1980's:

"On January 19, 1989, the Occupational Safety and Health Administration (OSHA) updated its existing Air Contaminants Standard, 29 CFR 1910.1000. OSHA amended existing PELsfor 212 substances to more protective levels, increased an existing PEL for one substance, set new PEL for 164 substances that were not previously regulated, and after consideration, left the existing PELs of 51 substances unchanged. In addition, the existing PEL for 172 substances were not considered in the rulemaking and remained unchanged. The PEL were consolidated in a single table, Table Z-1-A, which also included the existing 1971 PELs under the "Transitional Limits" columns. The regulation permitted the use of any reasonable combination of compliance methodology until December 31, 1992."

The final rule was the subject of several legal challenges, and on July 7, 1992, the U.S. Court of Appeals, Eleventh Circuit, vacated the 1989 PELs listed in the "Final Rules" columns of Table Z-1-A of 29 CFR 1910.1000. Since that time, a stay of the Court's mandate implementing this decision allowed OSHA to continue to enforce the 1989 PELs while further legal action was considered.

Under the OSHA Act each State can apply to operator and enforce their own State OSHA program. Approximately half of the States currently enforce their own regulations. By law they must be at least as strict as OSHA but can be more restrictive. The other half of the States are under Federal OSHA.

State Plans

Those States with their own State plans, as listed on OSHA's website ( include:

Note: Of the list above The Connecticut, New Jersey, New York and Virgin Islands plans cover public sector (State & local government) employment only.

Many of the States have adopted the more restrictive limits for the air contaminants, rather than going with the Federal new PEL requirements.

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