Exposure standards - airborne contaminants

The WES can be found in the Workplace exposure standards for airborne contaminants (WES list).  Under the model work health and safety (WHS) laws, a person conducting a business or undertaking must ensure that no person in the workplace is exposed to an airborne contaminant at a concentration exceeding the WES. 

To establish if the WES has been exceeded for an airborne contaminant, the worker’s exposure is measured using air monitoring in their breathing zone. 

Types of workplace exposure standards

The WES can be found in the Workplace exposure standards for airborne contaminants (WES list).  Under the model work health and safety (WHS) laws, a person conducting a business or undertaking must ensure that no person in the workplace is exposed to an airborne contaminant at a concentration exceeding the WES. 

To establish if the WES has been exceeded for an airborne contaminant, the worker’s exposure is measured using air monitoring in their breathing zone. 
Types of workplace exposure standards
The WES are generally based on the ‘critical effect’ of an airborne contaminant. This is the lowest airborne concentration that someone can usually be exposed to before they have an adverse effect. The critical effect can be a short-term health effect, like nausea or dizziness, or a long-term health effect like organ damage or cancer.

There are 3 different types of WES values: 

  • Time Weighted Average (TWA). If the critical effect on a worker is chronic (long-term) or sub-chronic (medium-term), the substance is given a TWA value. This is an 8 hour time weighted average (a worker’s average airborne exposure in any 8 hour work shift of a 40 hour week). Most substances in the WES have a TWA.
  • Short Term Exposure Limit (STEL). If the critical effect of the substance is acute (short term), it is generally given a STEL value. This a 15 minute time weighted average. 
  • Peak Limitation (peak). If the critical effect of a substance is acute and very dangerous, it is given a Peak value. This is the maximum concentration over the shortest possible time frame that can be measured, to a maximum of 15 minutes.

Importantly, exposure standards do not identify the dividing line between a healthy and unhealthy work environment. Natural human biological variations and individual susceptibilities (such as an existing medical condition) mean a small number of people may still experience adverse health effects from exposure at levels below the WES. Therefore, exposure to airborne contaminants should still be kept as low as is reasonably practicable to protect workers and others in the workplace. 

For more information on using and understanding the WES list see our Guidance on the interpretation of Workplace exposure standards for airborne contaminants.

Changes to workplace exposure standards

Workplace exposure standards have been in place since 1995 and have been reviewed and updated from time to time. Most recently, the WES list was updated in October 2022 to reduce the WES for respirable coal dust, following a July 2020 update to reduce the WES for respirable crystalline silica.

However, the WES list is currently undergoing a broader review. 

Supporting Information