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Understand requirements for occupational exposure limits (OELs)

OELs are regulatory values which indicate levels of airborne exposure that are considered safe for a chemical substance in a workplace.

For airborne exposures, there are three types of limits in common use:

  • The time-weighted average (TWA) exposure limit - the maximum average concentration of a chemical in air for a normal 8-hour working day and 40-hour week.
  • The short-term exposure limit (STEL) - the maximum average concentration to which workers can be exposed for a short period (usually 15 minutes).
  • The ceiling value - the concentration that should not be exceeded at any time.

In addition, biological exposure indices (BEIs) represent the concentration of chemicals in the body that would correspond to inhalation exposure at a specific concentration in air.


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