User:SelahWillis/Permissible exposure limit

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Chemical regulation is expressed in parts per million (ppm) when the substance is a gas or vapor at standard temperature and pressure (STP) conditions. Examples of substances with a PEL expressed in ppm include acetic acid and hydrogen peroxide. If the substance is not a gas or vapor at STP, the PEL is expressed in milligrams per cubic meter (mg/m³). Examples of substances with a PEL expressed in mg/m³ include dichlorodiphenyltrichloroethane (DDT) and nicotine. The PELs for mineral dusts, such as mica and respirable quartz, are expressed in millions of particles per cubic foot of air (mppcf). Fibers are measured in fibers per cubic centimeter (f/cm³). Examples of substances monitored in f/cm³ are asbestos and tremolite. Units of measure for physical agents such as noise are specific to the agent. A list of OSHA regulatory limits as well as recommended limits can be found in OSHA annotated table Z-1, OSHA annotated table Z-2, and OSHA annotated table Z-3.

A short-term exposure limit (STEL) establishes the maximum time-weighted average exposure that a worker can experience over a 15-minute period. These STEL values are the highest concentration a worker can be exposed to within a 15-minute period. A ceiling limit (CL) is an established concentration that may not be exceeded for any time, and is applied to irritants and other materials that have immediate effects. An Action Level (AL) is the concentration of a substance at which steps must be taken to ensure that employees are being adequately protected from that substance. This value is typically one half the value of the current PEL, unless otherwise specified. An increase in exposure monitoring, medical surveillance, or biological monitoring must be implemented when this concentration is exceeded.

Permissible Exposure Limits are regulatory limits for chemical hazards in a workplace set by OSHA. U.S. States and Territories may operate their own workplace safety and health programs if the program is OSHA approved and as least as effective at protecting employees as OSHA programs. Individual organizations and workplaces may implement stricter guidelines for chemical use and exposure, but OSHA guidelines must be followed at the minimum. Permissible Exposure Limits are calculated as a time-weighted average based on a 8-hour shift worked 5 times per week. This means workers may be exposed to concentrations higher than a PEL during the work shift if the 8 hour TWA is lower than the PEL. When an employee works an extended or unusual work shift that is longer or more consecutive than a 8-hour shift worked 5 times per week, the employer must take this into consideration in regards to the PEL. This can be done by performing a continuous sample of the substance during the worst 8-hour work block of the extended work shift or by collecting multiple samples over the entire extended work shift.

Many factors contribute in establishing Permissible Exposure Limits. Threshold Limit Values (TLVs), often determined by the American Conference of Governmental Industrial Hygienists (ACGHI), is a key component in determining the PEL. Another group that contributes recommendations to OSHA is the National Institute for Occupational Safety and Health (NIOSH). NIOSH was established alongside OSHA by The Occupational Safety and Health Act of 1970 to research worker safety and health. Other things that contribute to determining the PEL are toxicity and particle size. When determining a PEL for chemical exposures that are chronic or have a delayed onset, long-term exposure data is reviewed. This includes epidemiological evidence and quantitative risk assessments specifically focused on long-term mean exposures or cumulative lifetime exposures.