OSHA uses the term Permissible Exposure Limit (PEL) to define the maximum concentration of a listed contaminant to which an unprotected worker may be exposed. Depending on the contaminant, the PEL may reference an eight-hour, time-weighted average (TWA), a 15-minute short-term exposure limit (STEL) or an instantaneous ceiling (C) concentration that cannot be exceeded for any period of time. Individual states either follow federal regulations, or follow their own, state-specific permissible exposure limits. States may not publish or follow exposure limits that are more permissive than federal OSHA limits.
The ACGIH TLVs® are guidelines for workplace exposure to toxic substances. TLVs® are developed and designed to function as recommendations for the control of health hazards, and to provide guidance intended for use in the practice of industrial hygiene. But ACGIH TLVs® are frequently incorporated by reference into state, federal and many international regulations governing workplace exposure. They may also be cited or incorporated by reference in consensus standards of associations such as the National Fire Protection Association (NFPA), or American National Standards Institute (ANSI).
Given the potential for lawsuits, many employers have made the strategic decision to base their corporate health and safety programs on conservative applicable recognized standards. Since ACGIH recommendations are frequently more conservative than OSHA PELs, many programs, especially the programs of multinational or prominent corporations, use the ACGIH TLV®.