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What are WES and BEI? 

Workplace exposure standards (WES) are values that state the concentration of substances in the air that most workers can be repeatedly exposed to without coming to harm.

Biological exposure indices (BEI) are guidance values for assessing biological monitoring results. Biological monitoring measures the concentration of a substance in blood, urine, or exhaled air. The monitoring result is compared with the BEI for the specific substance.

A prescribed exposure standard (PES) is a WES or a BEI that protects people in a workplace from harm to their health. It must be prescribed in: 

  • regulations, or 
  • a safe work instrument. 

There are no WES prescribed in regulation and no safe work instrument for WES and BEI. This means the WES and BEI values in this consultation and in the WorkSafe WES and BEI book are not PES. They are guideline values. You should use them if you have the appropriate knowledge, skills, and experience to apply them for health risk assessment.

The importance of sampling strategies for WES 

It is important you have a robust sampling strategy when applying WES to ensure you have a good understanding of exposure variations.

Exposure levels of airborne substances can often vary, even in work that is regular and consistent. How much a worker is exposed to a substance depends on variation in work activities, control methods, and environmental conditions. This means exposure measured on a single day may not reflect exposure on other days.

Taking many samples means you will better understand the variation in exposure and will mean more detailed information for the risk assessment. But even samples from different days still may not reflect the true variation in exposure that may occur over the long term. The Person Conducting a Business or Undertaking (PCBU) should get advice from a competent person on how to monitor exposure in the workplace, including the sampling strategy. The sampling strategy must be able to provide enough measurements to show the risk to the worker from the variation in exposure.

Biological monitoring for substances that can be absorbed or inhaled 

Some substances can be absorbed through skin or inhaled. You may prefer to use biological monitoring for these substances, as measuring air levels alone may not fully represent exposure. However, there are not many options for biological monitoring, as there are few BEI compared with WES.

Health monitoring

Biological and airborne exposure monitoring is not the same as health monitoring.

Exposure monitoring means measuring and evaluating a person’s exposure to a health hazard. It includes monitoring the conditions at the workplace, and biological monitoring of the people.

Health monitoring means monitoring a person for changes in their health because they have been exposed to certain health hazards.

Health risk management must consider many aspects, including identification, assessment, and control. Exposure monitoring is just one part that you need to consider.

Why use WES and BEI

PCBUs must minimise exposure and monitor the conditions of the workplace if it cannot eliminate exposure. WES and BEI are important tools for monitoring worker exposures.

Who should use WES and BEI

WES and BEI are guidance for qualified occupational health practitioners. We do not recommend that untrained people use WES and BEI to assess exposure risk.

More information

Further information on WES, including the meaning of WES-TWA and WES-STEL, and BEI is in the Glossary document on this page. 


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