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Understanding permissible exposure limits

Lab Safety Advisor, March 25, 2008

Each hazardous chemical in your laboratory has a permissible exposure limit (PEL) assigned to it. It also has an action level. For example, the PEL for formaldehyde is 0.75 ppm. The action level is 0.5 ppm. If environmental monitoring over an eight-hour time-weighted average (TWA) exceeds 0.5 ppm then you need to implement your respiratory protection program. If the ppm for formaldehyde exceeds 2.0 ppm during a short term exposure level (STEL) that, too, requires you to launch your program.

Also, concerning formaldehyde exposure, remember that if you use air-purifying respirators with chemical cartridges or canisters that do not contain end-of-service-life indicators approved by the National Institute for Occupational Safety and Health (NIOSH), you must replace the cartridges or canisters at the end of the work shift. In addition, the canister or cartridge must be approved for use against formaldehyde and not be a generic cartridge. Employers may substitute an air-purifying, half-mask respirator for an air-purifying, full-face-piece respirator when they equip the half-mask respirator with a cartridge approved for protection against formaldehyde and provide the affected employee with effective gas-proof goggles.

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