Occupational exposure limit

An occupational exposure limit is a regulatory or advisory concentration limit for a hazardous substance in workplace air, usually defined over a specified averaging period.

Time-weighted average: An average exposure calculated across a specified period, often an eight-hour work shift. Many occupational exposure limits cap a shift-long average rather than every momentary concentration.
Permissible exposure limit: A legally enforceable workplace exposure limit established by a government authority. It is one specific kind of occupational exposure limit, distinguished by legal force.
Industrial hygiene: The discipline of anticipating, recognizing, evaluating, and controlling workplace health hazards. Industrial hygienists assess whether workplace conditions meet relevant exposure limits.
Risk assessment: A process for estimating the likelihood and severity of harm from a hazard under specified conditions. Risk assessments translate incomplete evidence into decisions about acceptable workplace exposure.
Short-term exposure limit: A maximum average airborne concentration permitted over a brief period, commonly 15 minutes. It limits brief high exposures that a shift-long average could conceal.
Threshold limit value: A set of workplace exposure guidelines published by the American Conference of Governmental Industrial Hygienists. These advisory values are often compared with legally enforceable limits.
Air sampling: The collection of air samples to measure contaminants in a specific environment. Workplace air sampling provides measurements that can be compared with concentration limits.
Uncertainty factor: A numerical adjustment used to account for gaps in evidence or differences among individuals. Limit-setting may use such adjustments when human data or exposure evidence is incomplete.
Ceiling limit: A concentration that must not be exceeded at any time during workplace exposure. Some substances require an instantaneous cap instead of an averaging period.
Recommended exposure limit: A workplace exposure limit recommended by the United States National Institute for Occupational Safety and Health. It illustrates how a technically grounded recommendation can differ from a binding rule.

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