You may know about WES and BEI or heard other people talk about them – here is a brief explanation of what they are and why they are so important.

WES are levels of airborne substances it is expected most workers can tolerate repeated exposure to without coming to harm. We say ‘most’, not ’all’ workers as differences between people, such as genetic variation, may mean some are more at risk from exposure. In addition toxicology data on the risk of certain chemicals is often limited, so setting a suitable WES value can be difficult.

Prescribed exposure standards are an upper limit above which no worker should be exposed. These are prescribed in legislation or a safe work instrument. There are currently only two prescribed exposure standards - 1080 and methyl bromide. These are in WorkSafe’s WES book.

The rest of the WES in the book are guideline values for people qualified in occupational health practice and are for use in risk assessment. A good sampling strategy is critical when applying WES to ensure a good understanding of exposure variations which always occur. The PCBU should take advice from a competent person on how exposure will be monitored in the workplace. It is not good practice to compare one or two samples to a WES and determine if risk is managed based on that simple comparison.

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.

Biological monitoring measures the concentration of a substance - its breakdown products - in blood or urine. The monitoring result is compared to a standard established for the specific substance – known as its biological exposure index (BEI).

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 give the full exposure picture. However, options on biological monitoring are limited as there are only about 20 biological exposure indices, compared with over 700 exposure standards for airborne monitoring. 

Biological monitoring should not be confused with health monitoring, which determines any negative changes in the worker’s health. Health monitoring should ideally show no changes occurring, meaning control measures are effective and risk is being managed.

PCBUs must minimise exposure and monitor the conditions of the workplace where the exposure cannot be eliminated. Monitoring conditions of the workplace for the purpose of preventing illness is about assessing the worker exposure to hazardous or toxic substances. WES are an important tool 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 determine compliance. WES are guidance for qualified occupational health practitioners.

This is because professional judgement is required in making decisions regarding safety levels of exposure to chemical and physical agents at work.

Our latest consultation highlighted that:

  • some PCBUs do not have a good understanding of how WES are applied, nor of the importance of good exposure monitoring in health risk assessment  
  • there is misunderstanding about the difference between WES values and the regulatory ‘prescribed exposure standards’.

Other feedback related more specifically to proposed changes to hydrogen sulphide, nitrogen dioxide and synthetic mineral fibres.  

As a result we engaged with industry to better understand their point of view, explain our position and discuss good practice in health risk assessment and exposure monitoring. 

Following the consultation many participating PCBUs indicated they will review their health risk management / exposure monitoring programmes with a view to lowering exposures to these substances.  

We are also going to support some specific industries on health risk management, including hydrogen sulphide in fellmongers’ and geothermal energy production.

The new WES and BEI values were published in the 2018 WES/BEI book in late November. 11 WES values were reduced this year and 17 BEI were lowered or adopted.

In 2019 we will be consulting on proposed changes to 36 carcinogens, respiratory sensitisers and mutagens.

2018 WES review: Beryllium, cobalt, chromium (VI), manganese, nickel, perchloroethylene, Portland cement, synthetic mineral (vitreous) fibres, sulphuric acid, total welding fume, flour dust, hydrogen sulphide, nitrogen dioxide, propylene oxide, styrene.

2018 BEI review: Arsenic, benzene, carbon disulphide, carbon monoxide, chromium VI, ethyl benzene, fluorides, mercury (elemental), MOCA, MDI isocyanate, methyl isobutyl ketone, PCP, phenol, tetrahydrofuran, TDI isocyanate, toluene, trichloroethylene.