Measures of exposure limits for chemicals in the workplace include TLV-TWA and TLV-STEL. The term "time-weighted average" (TLV-TWA) refers to the average chemical concentration that a worker can be exposed to over the course of an 8-hour workday and a 40-hour workweek without suffering negative health effects.1. The phrase "short-term exposure limit" (TLV-STEL) refers to the highest concentration of a chemical to which a worker can be exposed for a brief period of time (often 15 minutes) without experiencing harmful health consequences.

The TLV-TWA for gasoline in the USA is 300 ppm, and the TLV-STEL is 500 ppm3. This means that during the course of an 8-hour workday, employees can be exposed to gasoline at quantities up to 300 ppm without experiencing any negative health impacts. However, workers may experience negative health consequences if they are exposed to gasoline for brief periods of time (about 15 minutes) at concentrations exceeding 500 ppm3. 

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