Respirable Crystalline Silica (RCS) Dust Exposure Assessment at Quarries
DR SHARANN JOHNSON, AM, PhD, COH , FAIOH presented at the RCSD Management workshop.
The health and safety of your employees as well as compliance with the WorkSafe VIC Silica legislation, https://www. worksafe.vic.gov.au/high-risk-crystalline-silica-work-and-duties-manufacturers-and-suppliers, requires managers to assess their workers’ exposures to Respirable Crystalline Silica (RCS) and then implement controls to minimise exposures. The legislation has defined what is a silica process and this includes “quarrying process involving material containing crystalline silica.” The Victorian legislation is based on the workplace exposure standard of 0.05mg/m3, 8 hour time weighted average (TWA), as the criteria. This criteria is adjusted and reduced if the shifts are longer such as 12 hours. Furthermore, WorkSafe Victoria recommends that employees are not exposed to levels above 0.02 mg/m3 as an eight hour TWA.
The first step is to measure the personal exposures to airborne RCS in the dust at the quarry. Remember only a % of the respirable dust is RCS, dependant of the mineralogy. This involves a small pump attached to the workers belt and a cyclone to collect the respirable dust. There are certain protocols to follow to make sure the result is a true assessment of the exposure. This is important as the results will determine the level of controls you will need to implement and will be discussed by a WorkSafe VIC inspector visiting your site.
Selection of a Competent Person to do RCS Exposure Assessment?
RCS exposure assessments should be conducted onsite by a Trained Technician managed by a Certified Occupational Hygienist (COH) member of the Australian Institute of Occupational Hygienists (AIOH), https://www.aioh.org.au/ resources/consultants/. Make sure you ask the consultant how they plan to perform the work for you and their experience. Also, request that the % RCS in the respirable dust result is calculated. There should be consistency across the results and gives you information about the level of RCS in the general respirable dust.
Occupational Hygienists – Have developed techniques based on science and technology to measure worker exposures. This is the first step to assess worker risks and develop controls to improve the workplace environment. Occupational hygienists can provide advice on control strategies including hazard elimination, engineering modifications, administrative controls and finally personal protective equipment.
Quarry Managers – must complete a crystalline silica hazard control statement for High Risk Crystalline Silica Work (HRCSW). This risk assessment is important at identifying controls to eliminate or reduce exposures. The AIOH Breathe Freely site, dedicated to operations generating RCS, https://www. breathefreelyaustralia.org.au/quarries/ provides guidance on the Hierarchy of Controls. In many existing quarry plants, the opportunities to introduce engineering controls may be limited and it is more around administrative controls such as half the time of exposure, improve work operations through training and procedures. The last line of protection is RPE and this is discussed in more detail later in the article.
Monitoring Workers
Similar Exposure Groups (SEGs) – Quarry workers can be divided into at least two SEGs, the mobile equipment operators where the workers are in air conditioned cabins, and secondly, fixed plant operators working around the crushers and screens.
How Long do you Monitor For? – Monitoring is performed as a full shift sample to ensure the variety of exposures are captured over the shift. Mining regulations are now requiring full shift monitoring and not half shift.
How Many Samples? – To have confidence in the range of results, with high and low results depending on the day’s activities, it is best to have full shift results and over 8 samples to allow for a robust baseline. The mobile plant operators are the easiest group to do the statistics on, and depending on the numbers of mobile plant operators, after one or two days monitoring there are enough results to do the statistical analysis. Furthermore, this SEG is the easiest to control RCS exposures to below the criteria.
Mobile Plant Operators – Controls for Mobile Plant Operators to give exposures well below 0.05mg/m3:
• Windows closed for full shift;
• AC Filters cleaned regularly and AC operable;
• Clean cabin with vacuum but NOT the air gun;
• Door seals checked on prestart and repaired when damaged;
• Training and procedures covering the above.
The exposures of fixed plant operators can be more problematic to establish a baseline as it can take many more days of sampling and the variability in the tasks they do particularly around crushers and maintenance tasks. The variability in the results for the Fixed Plant Operators may cause the statistical analyses to exceed the 0.05mg/m3 criteria. An important control for the fixed plant operator is to have good respirator that has been fit – tested.
Respirator Fit Testing
The AIOH RESP-FIT program is a national respiratory protective equipment (RPE) fit testing training and accreditation scheme developed to improve the competency of fit testers against both the Australian and international ISO respirator standards for fit testing. RESP-FIT was developed by the AIOH through close collaboration with many stakeholders including RPE manufacturers and distributors, regulators and experts in the field. The goal is to protect worker’s health by ensuring the respirator, the last line of defence against dust is fitted properly and prevents leakages causing exposures to the contaminated air.
Both full and half face masks must (Refer to Prosecution Result Summaries and Enforceable Undertakings published on the WorkSafe Victoria website on Boral Resources https://www.worksafe.vic.gov.au/prosecution-result-summariesenforceable-undertakings) be fit tested , just like the P2 disposables. The aim is to get a good seal, and when workers wear them so tightly to mark their face, they may cause the moulded plastic to scrunch up and cause small gaps.
To find a Fit – Tester near you, check the website https://respfit.org.au/
Through professional risk assessments and the implementation of a range of pragmatic and effective controls will provide the basis for robust crystalline silica hazard control statement for High Risk Crystalline Silica Work and protect worker’s health.
Reference Publications
CMPA – https://cmpavic.asn.au/publications/support-sheets/
Concrete, Cement and Aggregate Australia
https://www.ccaa.com.au/CCAA/Docs/Industry/Workplace_Health_and_Safety_Guideline_Management_of_Respirable_Crystalline_Silica_in_Quarries.aspx
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