Complying with Workplace Exposure Limits in Australia
The Relevance and Importance of Workplace Exposure Limits in Australia
Without the proper monitoring instrumentation, airborne contaminants will often go undetected, posing a significant threat to both the short and long-term health of workers. This has necessitated the imposition of workplace exposure limits (WELs) which specify the maximum atmospheric concentration of certain hazardous airborne contaminants that a person can be exposed to without experiencing adverse effects.
In Australia, the Workplace Exposure Standards (WES) prescribe exposure limits for a large range of airborne contaminants. The WES is relevant in Australian states that have implemented the model Work Health and Safety Laws. In these jurisdictions, a person conducting a business or undertaking (PCBUs) must ensure that no person in the workplace is exposed to an airborne contaminant at a concentration exceeding the WES. The WES are therefore relevant in any industry where workers are exposed to a listed airborne contaminant.
Many of Australia’s largest industries often involve exposure to airborne contaminants such as gas or dust including:
Mining
Construction
Manufacturing
Defence
Oil and Gas
Food and Agriculture
Research and Laboratories
To ensure that your workplace is compliant with the WES, it is essential to understand the types of workplace exposure standards, the terminology used to describe exposure limits, and the role of environmental monitoring in ensuring workplace exposure limits are not exceeded.
Understanding the Various Types of Workplace Exposure Standards
The type of limit applied to a hazardous airborne substance depends on the critical effect of the contaminant. The ‘critical effect’ of an airborne contaminant is the lowest atmospheric concentration to which exposure will not generally cause an adverse effect. Of course, the point of critical effect is also dependent on the physiological characteristics of the individual being exposed. Therefore, the WHS Act imposes an obligation for businesses to not just meet the standards but eliminate the hazard, and if elimination is not possible, strive to minimise worker exposure to any listed airborne contaminant as far as is reasonably practicable.
The three types of exposure standards used in Australia are:
Time Weighted Average (TWA) – The average airborne exposure over any 8-hour shift of a 40-hour week. TWA is used if the critical effect on a worker is chronic (long-term) or sub-chronic (medium term).
Short Term Exposure Limit (STEL) – STEL focuses on short-duration exposure periods, typically 15 minutes time weighted average. STEL is used if the critical effect of a substance is acute (short term) providing an additional layer of protection beyond the TWA.
Peak Limitation (PL) – Maximum concentration over the shortest possible time frame that can be measured, to a maximum of 15 minutes. This limitation is particularly relevant in occupational health and safety contexts where workers may encounter short-term, high-intensity exposures to certain contaminants.
Complying with the Workplace Exposure Standards through Environmental Monitoring
Where monitoring is required, it must be done in the ‘breathing zone’ which is a 30cm hemisphere radius from front of a person’s face and midpoint between the ears.
Air sampling, dust monitoring and gas detection equipment all have options for instruments designed to be worn within the breathing zone that may be used to assess whether exposure limits are being complied with.
To be sure that WES are being complied with, environmental monitoring of airborne contaminants should be undertaken. The types of instrumentation required will vary depending on what airborne contaminants workers may be exposed to and the type of exposure limit prescribed. For example, monitoring for dust will often require different instruments to those used for gas detection.
Monitoring Airborne Contaminants with Personal Air Sampling
Air sampling can be conducted in a variety of ways depending on the airborne contaminant being measured and the type of workplace exposure standard that must be complied with. A standard ‘sample train’ set up involves a sample pump drawing air through a collection device (mounted in the breathing zone) with the two connected by tubing.
The sampling pump is worn by the user, collecting air quality data which when analysed in a lab, reflects the user’s exposure to airborne contaminants. Sampling pumps may be designed for a narrow flow range, low flow (20-500ml/min) or high flow (1000+ml/min). However, some sampling pumps like the SKC AirCHEK Essential+ are more versatile and can exert either a low or high flow to measure particulates and fumes, or gases and vapours, depending on the sample medium used.
When sampling particulates, a high flow is required alongside a particulate sampler such as a cyclone, impactor, cassette, sampler or filter which is chosen depending on the airborne contaminant being sampled.
In contrast, a low flow sampling pump such as the SKC PocketPump TOUCH is ideal to allow the filter medium to adequately adsorb or collect gas or vapour. This can be done by using a specific low flow sampling pump or by using a medium flow pump with a low flow adapter. Gas or vapour samples are generally collected in a sorbent tube or sample bag.
Collected samples are taken back to the lab for analysis meaning results are not known in real-time but do provide an accurate representation of worker exposure to atmospheric contaminants over the period sampling was undertaken. Due to the necessity of lab analysis, it is important that the right sampling pump and medium for the job are chosen before sampling is conducted. Through lab analysis, air sampling can be used to determine whether all three, TWAs, STELs and PLs have been complied with over the sampling period.
Using Personal Gas Detectors to Comply with Workplace Exposure Standards
Worn in the breathing zone, personal gas detectors provide precise atmospheric concentration measurements of one or multiple types of gas in real-time. Unlike most air sampling pumps, personal gas detectors generally provide instantaneous, on-the-spot real-time gas concentration measurements rather than collecting samples for later lab analysis, however, they are limited as to how many gases they can monitor simultaneously. For example, the Industrial Scientific Ventis Pro5 Confined Space Multi Gas Detector can monitor up to 5 gases.
To comply with WES, PCBUs must first identify the hazardous gases workers may be exposed to, which may be done through spot testing, and provide gas detectors with the relevant sensors. These detectors can then be used to monitor worker exposure to hazardous gases throughout the workday.
Almost all portable gas detectors currently on the market such as the Ventis Pro5 or Industrial Scientific MX6 feature some sort of datalogging capacity. Data can be downloaded directly from the detector itself or accessed remotely through online monitoring portals such as the iNet Control platform. Most portable gas detectors also allow concentration thresholds to be set which if exceeded will alert the worker through an alarm. These features make it easier for safety supervisors and workers to assess compliance to the WES.
Measuring Particulates with Personal Dust Monitoring
Personal dust monitors are designed to measure particulate matter in real-time, offering immediate insights into air quality levels and facilitating compliance through data logging. These devices are also equipped with alarms which can be set to adhere to WES, ensuring that exposure limits are not exceeded.
There are two primary types of dust monitors commonly used in Australia. These monitors are optical particle counters and nephelometers. Although both instruments assess airborne particles using light scattering, they do so in distinct ways. Nephelometers gauge light scattering by airborne particles to quantify suspended particulate matter (aerosols) in the atmosphere, providing users with total mass concentration data. Conversely, optical particle counters such as the Nanozen DustCount 9000, uses a light source to shine through a sample of air containing the particles. As particles pass through the beam of light, they scatter the light, and the scattered light is detected by sensors. By analysing the intensity and timing of the scattered light, an OPC can determine the concentration and size distribution of particles in the air.
While both these instruments can be used to monitor dust and comply with workplace exposure standards, their applications differ. OPCs are commonly used in air quality monitoring, air quality assessments, and particle research studies while nephelometers are commonly used in atmospheric research, studying visibility, air pollution monitoring (especially for particulate matter), and climate studies.
Broadly, complying with the WES comes down to accurately identifying airborne contaminants which may pose a risk to the workplace, assessing airborne contaminant levels by utilising monitoring instruments most suited to those contaminants, and implementing mitigation measures to minimise worker exposure to hazardous airborne contaminants.
