OSHA established Permissible Exposure Limits (PELs) for chemicals and other hazards (such as noise) to identify how long workers can be exposed to the hazards without suffering harm. Sound simple enough? It's not.
PELs are normally expressed in what are known as time-weighted averages (TWA), which describe the average exposure over a set period. In some cases, the chemical may also have short-term exposure limits (STELs) or ceiling limits. It’s entirely possible that a worker may be exposed to significantly higher levels of a chemical for a period of time during the eight hours. Those situations involve another term: the Excursion Limit.
The safety experts at Safety Management Group in Indianapolis have written an article that explains these limits and more. Although current PELs address only some 500 chemicals, other resources are available to help you address chemical safety in the workplace. The article discusses PELs, TLVs, BEIs and more, and includes information to help you make reasonable decisions about acceptable exposure levels in your workplace.