Occupational Exposure Limits/Standards

An occupational exposure limit (OEL) is an upper limit on the acceptable concentration of a hazardous substance in workplace air for a particular material or class of materials. Occupational exposure limit values (OELs) are set to prevent occupational diseases or other adverse effects in workers exposed to hazardous chemicals in the workplace. OELs assume that exposed persons are healthy adult workers, although in some cases the OELs should also protect vulnerable groups – e.g. pregnant women or other more susceptible people. They are tools to help employers protect the health of workers who may be exposed to chemicals in the working environment. OELs are usually set for single substances, but sometimes they are also produced for common mixtures in the workplace, for example solvent mixes, oil mists, fumes from welding or diesel exhaust fume.

OELs have many different names across the world, all essentially meaning the same thing. In the USA, they are called PEL (Permissible Exposure Limits), in Australia and New Zealand, WES (Workplace Exposure Standards), and in the UK, they are called WEL (Workplace Exposure Limits). The American Conference of Governmental Industrial Hygienists (ACGIH) use the term TLV (Threshold limit values). Other countries may also have other terms.

An OEL (WES) can take one or all three forms:

  • Time-weighted average (TWA) – an 8-hour TWA exposure standard is the maximum average airborne concentrations of a particular substance permitted over an eight-hour working day and five day working week. The TWA is the most common of the exposure standards and, except where a peak limitation has been assigned, virtually all substances are listed with a TWA.
  • Short-term exposure limit (STEL) – a short-term exposure limit is the time weighted maximum average airborne concentration of a particular substance permitted over a 15-minute period. Exposure at the STEL should not be longer than 15 minutes and should not be repeated more than 4 times a day. There should be at least 60 minutes between successive exposures at the STEL.
  • Peak – a maximum or peak airborne concentration of a particular substance determined over the shortest analytically practicable period that does not exceed 15 minutes.

Australia – Current Workplace exposure standards (WES) can be found at the Safe Work Australia Hazardous Chemical Information System (HCIS). Australia is transitioning to the Workplace exposure limits (WEL). Until 1 December 2026, workplaces must still comply with the WES list. Contact your work health and safety regulator for further information. Further information on the transition to the WELs can also be found at Safe Work Australia.

New Zealand – Current Workplace exposure standards can be found on the Work Safe New Zealand website.

Contact an Occupational Hygienist or similar qualified/skilled professional to assist with measurement or estimation of contaminant levels. You can find an Occupational Hygiene Consultant in the following organisation’s directory:

Reference/s for further information and detail: