Workplace exposure standards (WES) are values that refer to the airborne concentration of substances at which it is believed that nearly all workers can be repeatedly exposed day after day without coming to harm.

A prescribed exposure standard (PES) means a workplace exposure standard or a biological exposure index that has the purpose of protecting persons in a workplace from harm to health and that is prescribed in—

1. regulations; or
2. a safe work instrument

Currently there are no WES prescribed in regulation and no Safe Work Instrument for WES/BEI. The WES and BEI values discussed in this consultation and all other WES in the WorkSafe WES/BEI book are not PES and are therefore guideline values. They are intended to be used by people with the appropriate knowledge, skills and experience to apply them for health risk assessment.

A robust sampling strategy is critical when applying WES to ensure a good understanding of exposure variations which always occur. Exposure levels are commonly variable even in work that is regular and consistent. Variation in worker exposure arises from variation in work activities, control methods and environmental conditions. Due to this variation, exposure measured on a single day may not reflect exposure on other days. Multiple samples generally allow for better understanding of the variation in exposure, and thus provide more detailed information for the risk assessment. However, even samples from multiple days may not reflect the true variation in exposure that may occur over the long term. With this in mind, the PCBU should take advice from a competent person on how exposure should be monitored in the workplace, including the sampling strategy. The sampling strategy must be designed to provide sufficient measurements to reflect the risk to the worker from the variation in exposure.

BEI (Biological Exposure Indices) are guidance values for assessing biological monitoring results.  Biological monitoring measures the concentration of a substance – or its breakdown products - in blood or urine or even exhaled air and the monitoring result is compared to the BEI established for the specific substance.

For substances that can be readily absorbed through skin as well as inhaled, biological monitoring may be the preferred exposure monitoring tool, as measuring air levels alone may not fully represent exposure. However, options on biological monitoring are limited as there are few biological exposure indices, compared to exposure standards for airborne monitoring. 

Biological and airborne exposure monitoring should not be confused with health monitoring. Exposure monitoring means the measurement and evaluation of exposure to a health hazard experienced by a person; and includes monitoring of the conditions at the workplace, and biological monitoring of the people. Health monitoring, in relation to an individual, means monitoring of the individual to identify any changes in his or her health status because of exposure to certain health hazards.

Health risk management must consider a number of aspects from identification, to assessment, to control, with exposure monitoring being just one part – not the only part that needs to be considered.

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

While PCBUs must understand and manage the risks of hazardous or toxic substances at work, we do not recommend untrained people use WES to assess exposure risk. WES are guidance for qualified occupational health practitioners.

Further information on WES, including the meaning of WES-TWA and WES-STEL, and BEI is provided in the Glossary sections of the relevant proposal documents.