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What are Workplace Exposure Standards?

workplace exposure standards

Airborne contaminants are common in many workplaces across Australia (and around the world).

Work processes can release harmful substances such as gases, vapours, fumes, mists, or dusts into the air. Biohazards, such as viruses and bacteria, can also be a threat. These are known as airborne contaminants and they can adversely affect workers' health and wellbeing.

Exposure can occur through inhalation, skin or eye absorption, ingestion, or injection. Inhalation is the most common route of exposure.

Employers and persons conducting a business or undertaking (PCBUs) must eliminate or minimise risks in the workplace, so far as is reasonably practicable. This includes protection from airborne contaminants. PCBUs must ensure workers (and others at the workplace) are not exposed to levels of airborne contaminants above their workplace exposure standard (WES). Source: Safe Work Australia

In this article, we'll explain the ins and outs of workplace exposure standards.

What are Workplace Exposure Standards?

A workplace exposure standard - abbreviated to WES - is an upper limit of the concentration of a hazardous substance permissible in the workplace air. These standards aim to protect employees from the adverse effects of hazardous substances commonly found in workplaces. These substances include chemicals, gases, vapors, dust, and biological agents.

Airborne contaminants may be measured volumetrically in parts per million (ppm) or gravimetrically as milligrams per cubic meter (mg/m3) depending on the substance. Where both gravimetric and volumetric values are given, the volumetric (ppm) value should be used because it's not affected by temperature and pressure changes (Safe Work Australia).

The workplace exposure standards are generally set at the lowest airborne concentration that is unlikely to cause an adverse effect. Keep in mind that biological and immunological variations in humans mean that some people might experience adverse health effects well below the exposure standard.

In Australia, standards have been set for around 700 substances by Safe Work Australia. You can access the WES document here:

Safe Work Australia periodically reviews and updates these standards to align with the latest scientific evidence and international best practices. For example, the WES for welding fumes was recently reduced from an 8-hour time-weighted average (TWA) of 5 mg/m3 to 1 mg/m3.

Health and safety regulations require that persons conducting business or undertakings (PCBUs) take all reasonably practicable steps to eliminate or minimize exposure to a level well below the exposure standard.

Air monitoring can help you determine if WES is being exceeded. Engage with professionals, such as certified occupational hygienists, who are qualified to perform and interpret air monitoring.

In some cases, qualitative tools and mathematical models can be used to estimate airborne contaminant levels. For example, the software “IH Mod”12 provides several mathematical models that can be used to calculate airborne concentrations. These tools should only be used by qualified professionals such as occupational hygienists.

Air monitoring, and sometimes qualitative tools, are useful because they help you:

  • implement effective controls

  • check that existing controls are effective

  • choose the right PPE, including respiratory protective equipment (RPE)

  • determine if health monitoring is required

  • investigate worker complaints

  • comply with improvement notices or recommendations by regulators and inspectors

Now that you know what workplace exposure standards are, let's look at the various types of standards.

Key Components of Exposure Standards

There are three types of exposure standards.

Time-Weighted Average (TWA)

workplace exposure standard silica
TWA for respirable crystalline silica (RCS)

A time-weighted average exposure standard is the average airborne concentration of a particular substance permitted over an eight-hour working day and a 5-day working week. TWAs are the most common types of exposure standards.

Where workers have a working day longer than eight hours, a working week longer than 40 hours or work shift rotations over either 8 hours a day or 40 hours a week, the TWA exposure standard may need to be adjusted to compensate for the greater exposure during the longer work shift and the decreased recovery time between shifts.

The Australian Institute of Occupational Hygiene (AIOH) has a free WES Adjustment Tool.

Short-Term Exposure Limit (STEL)

workplace exposure standards
STEL for carbon dioxide

Some substances can cause intolerable irritation, or other immediate effects, during brief exposure. A short-term exposure limit (STEL) is the maximum average concentration of a specific substance permissible over a 15-minute timeframe.

The STEL is designed to regulate short-term exposure and is a crucial supplement to the eight-hour time-weighted average (TWA) exposure standards,

Generally, STELs are established to minimize the risk of:

- acute irritation

- irreversible tissue changes/damages

- narcosis (unconsciousness)

Not all substances have a STEL.

Peak Limit

Peak limit for oxygen difluoride

Simply put, peak limits are the maximum airborne concentrations of a substance that must never be exceeded at any time.

Peak limits are set because some substances may cause acute, adverse effects after only a short exposure to high concentrations,

Not all substances have a set peak limit.

Other Information

The Safe Work Australia WES document also lists carcinogen risks and known factors that can increase risks to workers including skin absorption and sensitisation.

Acrylamide is a Carc. 1B, may be absorbed via skin and may be a sensitiser


A carcinogen is a substance, organism, or agent capable of causing cancer.

The three categories of carcinogens in the WES are:

  • Category 1A – Known to have carcinogenic potential for humans

  • Category 1B – Presumed to have a carcinogenic potential for humans

  • Category 2 – Suspected human carcinogen


High exposures to some substances can lead to allergic sensitisation affecting the skin or respiratory system. Once developed, very low exposures can provoke significant allergic reactions.

These substances are given the notation ’Sen'.

Sensitised workers should not be exposed further to the inciting substance.

Absorption Via Skin

For some substances, absorption through the skin may be a significant source of exposure.

These substances are given the notation 'Sk'.

Implementation and Compliance

Workplace safety requires a collaborative effort from employers, employees, and regulatory bodies. Employers and PCBUs must implement measures to control exposure and regularly monitor air quality to ensure compliance with workplace exposure standards.

Regular risk assessments are crucial to identify hazards and implement effective control measures.

Safe Work Australia, and state/territory work safe organizations, provide guidance on managing risks associated with exposure to hazardous substances using the hierarchy of controls (elimination, substitution, engineering controls, administrative controls, and personal protective equipment, including respiratory protective equipment).

If you can't reduce WES to below the recommended values, or you aren't sure if you're exceeding standards, respiratory protective equipment is usually necessary (in addition to other control measures). In some cases, depending on the nature of the work, RPE may always be required.

Don't forget - RPE needs to be fit-for-purpose and fit tested to ensure adequate protection. And employees must be trained on how to properly use and maintain their RPE (click here to learn more about our RPE course).

Wrapping Up

Workplace exposure standards are crucial to maintain safe and healthy workplaces.

By providing clear guidelines on maximum levels hazardous substances, these standards empower organizations to protect their employees from the adverse effects of workplace exposures.

You'll want to make sure you access and refer to these documents to ensure you're compliant and keeping workers safe:

Happy breathing :-)

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