Exposure standards and atmospheric monitoring
Guidance on how to monitor exposure to hazardous substances in the air and how to measure their risks.
What are hazardous substances?
Hazardous substances are substances that can harm people's health. A hazardous substance generally means a substance that satisfies the criteria for hazard classification set out in Part 3 (Health Hazards) of the Globally Harmonised System of classification and Labelling of Chemicals. They come in various forms including fumes, dusts mists and vapours. These types of hazardous substances can become airborne.
Employers have a legal duty eliminate or reduce any risks associated with hazardous substances in the workplace. They must also ensure employees are not exposed to hazardous substances above the exposure standard.
There are proposed changes to some of SafeWork Australia's exposure standards scheduled for December 2026. They can be viewed on the SafeWork Australia website.
What is an exposure standard?
The amount of a certain substance in the air is called the airborne concentration. An exposure standard represents the airborne concentration of a particular substance in a person's breathing zone that must not be exceeded. Exposure standards are based on the airborne concentrations of individual substances that should neither impair the health of, nor cause undue discomfort to, nearly all people. The Australian exposure standards for airborne contaminants are set at the lowest concentration that is unlikely to cause ill health.
The exposure standards are reviewed and adjusted based on current scientific knowledge.
However, exposure standards don't draw a line between a healthy and unhealthy work environment. Differences in people's biology and individual susceptibility mean that some people may experience discomfort or adverse health effects below the exposure standard. That's why employers should keep exposure levels as low as reasonably practicable, even if they're already below the exposure standard.
SafeWork Australia website has a complete list of all the hazardous substances that have an exposure standard, which applies in Victoria. Other WHS laws referenced in this document do not apply in Victoria.
For every hazardous substance, employers must have a safety data sheet (SDS). An SDS provides health and safety information about a hazardous substance. Employers must have the SDS before the first delivery of the hazardous substance. The supplier of the hazardous substance must ensure that the SDS includes any relevant exposure standards.
The SDS should be made available to HSRs and employees who will come into contact with the substance. This should be part of the consultation process.
Types of exposure standards
There are 3 types of exposure standards. Some hazardous substances have more than one type of exposure standard.
- Time-weighted average (TWA)
This standard shows an airborne concentration averaged over an eight-hour working day. It applies to a 40-hour working week. A TWA is for hazardous substances that cause medium to long term health effects. If a worker is working overtime and more than 40 hours calculations of exposure must take this into account.
- Short term exposure limit (STEL)
A STEL is an airborne concentration averaged over 15 minutes. Some substances may cause irritation or other acute effects after short periods of exposure. A STEL is applied to a hazardous substance when such irritation or effects may occur and there are appropriate methods for monitoring over short periods. A STEL is for a substance that may cause some people short term health effects.
- Peak limitation
This standard shows the maximum airborne concentration that can be measured over a period no more than 15 minutes. This is for hazardous substances that cause short term health effects that can be immediately dangerous.
What if there is no exposure standard?
Even if SafeWork Australia hasn't set an exposure standard for a hazardous substance, it can still pose a health risk. When there is no exposure standard for a hazardous substance, you must control exposure by using the hierarchy of control and any other control measures specified in the OHS regulations.
For a substance that is not hazardous and doesn't have an exposure standard, then the employer must, so far as is reasonably practicable, provide and maintain a working environment that is safe and without risks to health. It is recommended that employers use the hierarchy of control to help them fulfil this duty.
What is atmospheric monitoring?
Atmospheric monitoring (or personal monitoring) is the only way to test whether employees are breathing in concentrations of a hazardous substance above the exposure standard. It's where a sample of air is taken in the employee’s breathing zone over a period of time to find out how much of the substance the employee is breathing in. This is then compared to the relevant exposure standard.
How long personal monitoring should be conducted for depends on which exposure standard is being used. For example, if you want to compare against a TWA exposure standard, then personal monitoring should be done for a representative work period that is at least half the shift, but preferably the entire shift. However, if you're measuring to compare against a STEL, then personal monitoring should be done for 15 minutes while the substance is used, preferably when exposure is likely to be at its highest.
An occupational hygienist can advise the employer on which type of monitoring is required.
Other types of air monitoring
Static monitoring
Static monitoring is also known as fixed position air monitoring. It tells you the concentration of a hazardous substance in a particular area and can show the potential exposure of other workers, not directly involved in the work task (for example, welding fumes).
Static monitoring can help assess how effective risk controls are. For example, the placement of a static monitor near a local exhaust ventilation extraction point can help in determining the effectiveness of the local extraction system.
Static monitoring results should not be used to determine whether employees are breathing in concentrations of a hazardous substance above the exposure standard. However, they can provide useful information which, in combination with other factors, can help in deciding whether personal monitoring should be done on specific employees.
All atmospheric monitoring must be performed by someone with a strong knowledge of exposure standards and atmospheric monitoring. The results also shouldn't be directly compared to an exposure standard.
Real-time dust monitoring
Real-time dust monitoring devices can directly measure general dust levels in the air and give an immediate result. They can help assess the effectiveness of risk controls. Like static monitoring, real time dust monitoring results should not be used to determine whether employees are breathing in concentrations of a hazardous substance above the exposure standard. However, they can provide useful information which, in combination with other factors, can help in deciding whether personal monitoring should be done on specific employees.
All atmospheric monitoring must be performed by someone with a strong knowledge of exposure standards and atmospheric monitoring. The results also shouldn't be directly compared to an exposure standard.
When is atmospheric monitoring needed?
An employer must ensure that atmospheric monitoring is done if there is an exposure standard for a hazardous substance (or any of its ingredients) supplied to or generated at the employer's workplace, and either of the following are true:
- It's uncertain whether the exposure standard is (or may be) exceeded based on reasonable grounds
Situations where this may be the case include:
- When you don't have information available on potential exposure such as previous atmospheric monitoring reports or other sources of information that will provide guidance on likely exposure levels
- When you are unsure how effective your risk controls are
- When there are changes to work processes or practices that may affect employee exposure
- Atmospheric monitoring is needed to see if there is a risk to health
Situations where there could be a possible health risk include:
- When there are contaminated surfaces or strong odours in the work area
- People have reported symptoms which may be linked to hazardous substance exposure
Sometimes it's obvious that there's a health risk from exposure to a hazardous substance. In these cases, you must ensure that employees are not exposed to the hazardous substance above the exposure standard. You must do this by controlling exposure risks, in line with the hierarchy of control. Then you should use atmospheric monitoring to make sure the risk controls are effective.
The OHS Act requires that the employer monitor:
- The health of employees
- The conditions of the workplace
Any decisions about the procedures for monitoring must be made in consultation with employees or any health and safety representatives.
When is atmospheric monitoring not needed?
Atmospheric monitoring of a hazardous substance isn't needed if:
- the OHS Regulations also call for health monitoring, and
- that health monitoring includes biological monitoring.
This is because biological monitoring will provide an understanding of a person's overall exposure, including inhalation.
However, even when biological monitoring is required and is happening, you should still consider atmospheric monitoring. This is because it may allow for a better understanding of more recent exposures.
Who should perform atmospheric monitoring?
Atmospheric monitoring and the interpretation of results needs to be done by a competent person. This could be, for example, an occupational hygienist with a strong knowledge of exposure standards and atmospheric monitoring.
What should an air monitoring report contain?
A detailed written report should be provided and may contain information on several of the following areas, including:
- the background and purpose of the air monitoring program
- the processes evaluated, the work patterns and the workers and hazards involved
- the control measures in place and how they are performing
- photographs and diagrams where necessary
- what measurements were taken and how sampling was carried out (including sampling times, flowrates, calibration information and any laboratory raw data attached as an appendix)
- how and where samples were analysed, what method was used and the test results, including the 8-hour TWA concentrations calculated where the substance being measured has an 8-hour TWA exposure standard
- an interpretation of the test results and comparisons with exposure standards
- an opinion on compliance and what the results mean (for example, is the exposure standard likely to be exceeded?)
- an opinion on the risks to workers
- advice on relevant industry practice and known control measures
- recommendations for specific hazard control improvements based on measurements, observations and discussions to reduce exposure or further monitoring required.
You should also consider the guidance provided by the Australian Institute of Occupational Hygienists on writing occupational hygiene reports.
What to do with the results
Employers must ensure employees exposed to airborne concentrations are staying below the exposure standard. The results can also help you check how well current risk controls are working. This may mean that you need to review and revise any controls if they are not working as expected.
Records of air monitoring must be:
- given to all employees who have been (or may be) exposed to the hazardous substance as soon as possible, no matter what the results show
- kept for 30 years.
The results can be kept in any form, so long as they're readily accessible to employees, and presented in plain English.