ISPE Glossary of Pharmaceutical and Biotechnology Terminology

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TWA (Time Weighted Average)

The most frequently used exposure guideline term, is the average concentration of a chemical in air over the total exposure time – usually an 8-hour workday (OSHA PELs and ACGIH TLVs), and up to 10 hours in a 40hour workweek (NIOSH Recommended Exposure Limit (RELs).

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