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Overview :
The Time Weighted Average (TWA) for the exposure to a
chemical can be used when both the chemical concentration and time for exposure
varies over time. It is usually averaged over 8 hours, which is used as the
standard daily work shift.
time weighted average per time period =
= (((concentration at first level in ppm) * (number of hours
exposed)) + ((concentration at second level in ppm) * (number of hours exposed))
+ .... + ((concentration at nth level in ppm) * (number of hours exposed))) /
(time period in hours)
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