Permissible Exposure Limits (PELs): These are regulatory limits on the amount or concentration of a substance in the workplace air. Reference Dose (RfD): An estimate of daily exposure to the human population that is likely to be without an appreciable risk of adverse effects during a lifetime. Threshold Limit Values (TLVs): Guidelines to assist in controlling health hazards in the workplace. Maximum Contaminant Levels (MCLs): Standards set by the EPA for drinking water quality.
