Workplace Exposure Standard (WES)
Workplace Exposure Standard (WES) : The maximum concentration of a substance in a worker's breathing zone that, on the basis of present knowledge, will not cause adverse health effects. Three categories of Threshold Limit Value (TLV) exist: (a) The Threshold Limit Value - Time Weighted Average (TLV-TWA) - the time-weighted average concentration for a normal 8-hour work day and a 40-hour work week, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect. (b) Threshold Limit Value - Short Term Exposure Limit (TLV-STEL) - the concentration to which workers can be exposed continuously for a short period of time without suffering from (l) irritation; (2) chronic or irreversible tissue damage; or (3) narcosis of sufficient degree to increase the likelihood of accidental injury, impair self-rescue or materially reduce work efficiency, and provided that the daily TLV-TWA is not exceeded. It is not a separate independent exposure limit; rather it supplements the time- weighted average (TWA) limit where there are recognised acute effects from a substance whose toxic effects are primarily of a chronic nature. STELs are recommended only where toxic effects have been reported from high short-term exposures in either humans or animals. A STEL is defined as a 15-minute time-weighted average exposure which should not be exceeded at any time during a workday even if the 8-hour time-weighted average is within the TLV. Exposures at the STEL should not be longer than 15 minutes and should not be repeated more than once per day. An averaging period other than 15 minutes may be recommended when this is warranted by observed biological effects. (c) Threshold Limit Value - Ceiling (TLV-C) - the concentration that should not be exceeded during any part of the working exposure
No records Found