The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agent. For chemicals, the chemical regulation is usually expressed in parts per million (ppm), or sometimes in milligrams per cubic metre (mg/m3). Units of measure for physical agents such as noise are specific to the agent. Permissible exposure limits are established by the Occupational Safety and Health Administration (OSHA).
A PEL is usually given as a time-weighted average (TWA), although some are short-term exposure limits (STEL) or ceiling limits. A TWA is the average exposure over a specified period of time, usually a nominal eight hours. This means that, for limited periods, a worker may be exposed to concentrations higher than the PEL, so long as the average concentration over eight hours remains lower.
A short-term exposure limit is one that addresses the average exposure over a 15-30 minute period of maximum exposure during a single work shift. A ceiling limit is one that may not be exceeded for any period of time, and is applied to irritants and other materials that have immediate effects.
Famous quotes containing the words permissible and/or limit:
“Fences, unlike punishments, clearly mark out the perimeters of any specified territory. Young children learn where it is permissible to play, because their backyard fence plainly outlines the safe area. They learn about the invisible fence that surrounds the stove, and that Grandma has an invisible barrier around her cabinet of antique teacups.”
—Jeanne Elium (20th century)
“No one who cannot limit himself has ever been able to write.”
—Nicolas Boileau-Despréaux (1636–1711)