Time-Weighted Average (TWA)

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Definition - What does Time-Weighted Average (TWA) mean?

A time-weighted average (TWA) refers to the average rate at which a worker is exposed to a contaminant or adverse condition (such as noise) without unpleasant or dire effects over a defined period such as an 8-hour day or 40-hour work week. Commonly, the time-weighted average is calculated to confirm that the concentration of a potentially hazardous substance during a normal 8 to 10 hour work day will not exceed regulatory or legal standards. Staying below a specified time-weighted average may also reduce the corrosion rate due to the presence of said substances.

Corrosionpedia explains Time-Weighted Average (TWA)

The time-weighted average represents the amount of time that workers and equipment in a given location are exposed to chemical substances when the concentration and time of exposure varies. Variables such as dose rate, duration and exposure time are all factored into the equation in order to arrive at the time-weighted average. For example, when a worker is exposed to varying doses of a chemical vapor for differing periods of time, the time-weighted average can be used to determine the worker's average exposure to that particular chemical.

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