Time-weighted Average
A time-weighted average is any of the following: * Permissible exposure limit, a legal limit in the United States for exposure of an employee to a chemical substance or physical agent such as loud noise. * Time-weighted average price In finance, time-weighted average price (TWAP) is the average price of a security over a specified time. TWAP is also sometimes used to describe a TWAP card, that is a strategy that will attempt to execute an order and achieve the TWAP or better. ...

Permissible Exposure Limit
The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agents such as high level noise. Permissible exposure limits were established by the Occupational Safety and Health Administration (OSHA). Most of OSHA's PELs were issued shortly after the adoption of the Occupational Safety and Health (OSH) Act in 1970. Chemical regulation is sometimes expressed in parts per million (ppm), but often in milligrams per cubic meter (mg/m3). Units of measure for physical agents such as noise are specific to the agent. A PEL is usually given as a time-weighted average (TWA), although some are short-term exposure limits (STEL) or ceiling limits. A TWA is the average exposure over a specified period, usually a nominal eight hours. This means that for limited periods, a worker may be exposed to concentration excursions higher than the PEL as long as the TWA is not exceeded and any applicable excursion l ...
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