Under work health and safety regulations, many airborne contaminants are subject to workplace exposure standards. Based on scientific research into the health effects of different chemicals, the exposure standards are published by Safe Work Australia and regularly updated.
These exposure standards have legal force with penalties attached: persons conducting a business or undertaking (PCBUs) must ensure that no person in their workplace is exposed to an airborne contaminant at a concentration exceeding the relevant exposure standard. They must arrange air monitoring when necessary to determine if there is a risk to their workers’ health.
Note that while the exposure standards provide a legal limit, even concentrations below the exposure standards can potentially be a health hazard. For that reason, work health and safety regulations require that exposure to airborne contaminants be kept ‘as low as is reasonably practicable’ to protect workers and others in the workplace.
There are three different kinds of exposure standard, with some airborne contaminants being subject to more than one. An exposure standard can be defined as:
- 8-hour time-weighted average (TWA)
- short term exposure limit (STEL)
- peak limitation.
To understand exposure standards, it’s important to understand the differences between these three ways of defining them.
8-hour time weighted average
Most commonly, exposure standards are expressed as an 8-hour time weighted average or TWA. This is defined as ‘the maximum average airborne concentration of a substance when calculated over an eight hour working day, for a five day working week’. In other words, it’s permissible for the concentration of the contaminant to exceed the specified level for a short period of time, as long as the average level over a working day and week is below the limit.
Time-weighted averages reflect the fact that for many chemicals, negative health impacts mainly come about through continuing exposure over a period of time.
Short term exposure limit (STEL)
Some contaminants have a short term exposure limit as well as an 8-hour time-weighted average. The short term exposure limit is defined as ‘a 15 minute time weighted average exposure limit which must not be exceeded at any time during an eight hour working day, even if the exposure during the full day is less than the TWA exposure standard’.
Short term exposure limits reflect the fact that some chemicals have risks associated with high levels of exposure, even for a short period.
Peak limitation
Finally, some chemicals are so hazardous that even momentary exposure above a certain level is hazardous to health. For these chemicals, the exposure standard is expressed as a peak limitation, which is a concentration ‘not permitted at any time’.
How Airsafe can help
As our name implies, air quality monitoring is one of Airsafe’s core activities, and we have the equipment and expertise to monitor for a large variety of airborne contaminants, including respirable crystalline silica, diesel particulate matter, and other kinds of inhalable and respirable dust. Whatever the relevant exposure standards, our air monitoring reports will give you a definitive answer about whether they’re being exceeded.
To make sure you’re complying with workplace exposure standards, call Airsafe on 1300 888 338.
