Hazardous Material Exposure Limits and Terms

TLV ACCIH Threshold limit value The airborne concentration of a substance to which most workers can be exposed on a daily basis without adverse health effects. 

TWA ACCIH Time-weighted average The average concentration of a substance for a normal 8-hour workday and 40-hour workweek. 

STEL ACCIH OSHA Short-term exposure limit A 15-minute TWA that should not be exceeded at any time during the workday. There should be 60 minutes between each 15-minute exposure, up to four times a day. 

PEL OSHA Permissible exposure limit Limit based on 8-hour TWAs. Exposures below the PEL do not require respiratory protection. 

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Appendix H Hazardous Material Exposure Limits and Terms... 

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