Exposure limits usually represent the maximum amount or concentration of a chemical that can be present in the air during an eight-hour day without presenting a health hazard. Relying on several information sources, OSHA has established PELs for about 600 different chemicals. However, exposure limits may not always be adequate to protect you. When new information is evaluated, exposure limits may be changed. Jobs involving heavy physical exertion may cause a worker to breathe harder, taking in more air and, consequently, more airborne chemical.
PELs usually apply only to chemical concentrations in the air.
Inhalation standards may not protect against excessive exposure through skin or ingestion. Work with them requires protective clothing. Exposure limits do not take chemical interactions into account. The lower the limit, the more hazardous the substance. The MSDS will recommend the protective clothing required for working with that particular substance.