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A short-term exposure limit (STEL) is the acceptable average exposure over a short period of time, usually 15 minutes as long as the time-weighted average is not exceeded. STEL is a term used in exposure assessment , occupational health , industrial hygiene and toxicology .
A short-term exposure limit is one that addresses the average exposure over a 15-30 minute period of maximum exposure during a single work shift. A ceiling limit is one that may not be exceeded for any time, and is applied to irritants and other materials that have immediate effects.
Threshold limit value − time-weighted average (TLV-TWA): The average exposure on the basis of a 8 hours per day, 40 hours per week work schedule. Threshold limit value − short-term exposure limit (TLV-STEL): A 15-minute TWA exposure that should not be exceeded at any time during a workday, even if the 8-hour TWA is within the TLV-TWA.
Limits for short-term exposure, such as STELs or CVs, are defined only if there is a particular acute toxicity associated with a substance. These limits are set by the American Conference of Governmental Industrial Hygienists (ACGIH) and the Occupational Safety and Health Administration (OSHA), based on experimental data.
There are three levels of PAC value (1 to 3) where each successive value is associated with an increasingly severe effect from a higher level of exposure. Each level is defined as follows: PAC-1 : Mild, transient health effects. PAC-2 : Irreversible or other serious health effects that could impair the ability to take protective action.
An occupational exposure limit is an upper limit on the acceptable concentration of a hazardous substance in workplace air for a particular material or class of materials. It is typically set by competent national authorities and enforced by legislation to protect occupational safety and health .
National Institute for Occupational Safety and Health (NIOSH) RELs are designed to protect the health and well-being of workers by recommending safe exposure levels. To really use these guidelines well, safety professionals need to understand the recommended exposure levels, how to measure them, and ways to make sure workers aren't exposed to harmful stuff.
PEL = Permissible Exposure Limit, the highest concentration permitted under US OSHA regulations; STEL = Short-Term Exposure Limit, the highest concentration permitted for short periods of time, in general 15–30 minutes; TWA = Time-Weighted Average, the average amount of an agent's concentration over a specified period of time, usually 8 hours