University Safety and Assurances

Occupational Exposure Values

Health-based Guidance Levels OSHA/ILHR Enforceable Standardsa
Concentration Averaging: TWAb TWAb TWAb
Workshift exposure: RELc TLVd PELe
Short-term exposure: STELf STELf STELf
Maximum exposure: Cg C C
Acutely Toxic: IDLHh -- --

a OSHA standards may not be exceeded by law. In Wisconsin, ILHR 32.361, adopts OSHA 29 CFR 1910.1000 (July 1, 1992 edition), for public sector employees.

b TWA (Time Weighted Average): The mean exposure concentration for a conventional 8-hour workday and a 40-hour workweek.

c REL (Recommended Exposure Limit): TWA for up to a 10-hour workshift during a 40-hour workweek, unless otherwise noted.

d TLV (Threshold Limit Value): TWA for an 8-hour workshift, unless otherwise noted.

e PEL (Permissible Exposure Limit): TWA that must not be exceeded during an 8-hour workshift during a 40-hour workweek.

f STEL (Short-Term Exposure Limit): The average exposure concentration for a 15-minute work period that should not (must not under OSHA) be exceeded at any time during the workshift. The time period for averaging exposure may vary depending on the chemical, but is most often 15-minutes.

g C (Ceiling): Maximum exposure concentration that should not (must not under OSHA) be exceeded at any time during a workshift.

h IDLH (Immediately Dangerous to Life and Health): Exposures that pose an immediate threat to life or health. The IDLH represents a concentration that for 30-minutes exposure would not impair escape (e.g., severe eye irritation) or result in irreversible health effects for an unprotected worker (i.e., in the event of a respirator failure, or during emergencies).

  • Air Contaminants 29 CFR 1910.1000, OSHA, 1995.
  • Chapter ILHR 32 Safety and Health Standards for Public Employees, Wisconsin Administrative Code, 1995.
  • Pocket Guide to Chemical Hazards, U.S. Department of Health and Human Services (CDC/NIOSH), 1997.
  • Threshold Limit Values for Chemical Substances and Physical Agents /Biological Exposure Indices, American Conference of Governmental Industrial Hygienists, 1998.