Silica in Mining: Preparing for the New WEL

The reduction of the workplace exposure limit for respirable crystalline silica from 0.05 to 0.025 mg/m3 represents a 50 per cent tightening that will affect virtually every mining operation in Australia. Silica is present in the host rock of most metalliferous ore bodies, in sandstone and granite quarry products, in coal mine roof and floor strata, and in the concrete and engineered materials used for underground infrastructure. Every activity that breaks, crushes, drills, or processes silica-bearing material generates respirable crystalline silica dust. At the current WES of 0.05 mg/m3, many mining operations already struggle to maintain compliance, particularly during drilling, blasting, crushing, and longwall operations. A 50 per cent reduction to 0.025 mg/m3 means that operations currently at or near the existing limit will immediately be non-compliant under the new WEL, and operations currently well below the limit may find that previously acceptable exposure levels now exceed the new threshold. Mining PCBUs should conduct baseline silica monitoring across all potentially exposed work groups now, before the December 2026 commencement date, to identify which operations require additional controls.

Dust suppression and ventilation are the primary engineering controls for silica in mining, and both will require upgrading at many operations to achieve compliance with the 0.025 mg/m3 WEL. For drilling operations, water injection through the drill string is the most effective source control, with water pressures and flow rates needing to match the drilling conditions — higher pressures for harder rock and larger diameter holes. Blast pattern design can influence post-blast dust generation through optimised fragmentation that reduces the proportion of fine material requiring secondary breakage. For crushing and screening operations, water spray suppression at feed points, crusher discharge, screen decks, and transfer points must be designed to achieve effective wetting without creating material handling problems. Enclosed crusher and screen installations with dust extraction and baghouse filtration provide the highest level of dust control but require significant capital investment. For underground operations, ventilation quantities in production and development areas must be sufficient to dilute airborne silica below the WEL at the worker breathing zone, and auxiliary ventilation design must account for dust generation rates from each activity. Where engineering controls alone cannot achieve compliance, they must be supplemented by respiratory protection programs.

Respiratory protective equipment is a critical supplementary control for silica exposure in mining, but it can only be relied upon as part of a compliant RPE program that includes fit testing, training, maintenance, and administrative controls. All RPE used for silica protection must be minimum P2 rated under AS/NZS 1716, and many mining operations will need to transition to powered air-purifying respirators for workers in high-exposure roles such as drillers, crusher operators, and underground development crews. Fit testing must be conducted for every worker using tight-fitting respirators, using either quantitative or qualitative fit testing methods, and the fit test must be repeated annually and whenever the worker's facial characteristics change. Workers with facial hair that prevents an effective seal cannot use tight-fitting respirators and must be provided with alternative protection such as powered loose-fitting air-purifying respirators. RPE maintenance including filter replacement, seal inspection, and valve function testing must be scheduled and documented. The assigned protection factor of the RPE must be sufficient to reduce the actual workplace exposure to below the WEL — this means the PCBU must know the actual exposure level to select appropriate RPE. An RPE program that simply provides respirators without fit testing, training, and maintenance does not provide a defence to prosecution for silica WEL exceedance.

Health surveillance for silica-exposed mining workers is required under WHS Regulation 2025 and state mining legislation, and the reduction in the WEL will likely expand the population of workers considered to be at significant risk who require monitoring. Health surveillance for silica exposure typically includes a baseline assessment before the worker commences exposure, regular periodic assessments at intervals determined by the exposure level, and exit assessments when the worker leaves the employer or transfers to a non-exposed role. The baseline and periodic assessments should include a standardised respiratory questionnaire, spirometry to measure lung function, and a chest X-ray or low-dose computed tomography scan interpreted by a B-reader or equivalent radiologist. Silicosis can develop years after exposure has ceased, and the latency period means that health surveillance must continue for workers who have had significant cumulative exposure even if they are no longer in exposed roles. Abnormal results must trigger a review of workplace exposure controls and may require the worker to be removed from further exposure. Health surveillance data across the workforce provides trend information that can identify exposure problems before they cause clinical disease, and this data should be integrated into the occupational hygiene program to inform control effectiveness assessments.