Respirable Crystalline Silica – Understanding Your Risks, Obligations & Controls

In Australia, occupational diseases are 8 times more deadly than safety-related incidents. Each year, roughly 2000 workers die from a work-related illness or disease (e.g. cancers, lung diseases).

Silicosis – an aggressive and debilitating respiratory disease, which is often fatal – has become a focus within the Australian legislative framework in recent years following an increase in the number of workers within the engineered stone industry diagnosed with the disease, and other RCS related health impacts.

The problem is widespread. Safework Australia estimates that 38 per cent of workers in the construction industry are exposed to silica. Of these workers – 67 per cent are working in environments that are above the exposure standard (WES).

In manufacturing, 5 per cent of workers are exposed to silica. Of these workers – 64 per cent are over the WES. In agriculture, the numbers are 29 per cent of workers and 11 per cent respectively.

What is respirable crystalline silica (RCS)?

Silica, or silicon dioxide, is present in quartz, stone, soil, granite, bricks, cement, grout, mortar, bitumen, and also in engineered stone products. It is the crystalline form of silica in these materials that has raised concern in recent years. Materials such as drywall, fibre cement products, some paints, roofing tiles and pavers and stone such as granite, quartzite, sandstone, shale and limestones have potential to contain the crystalline form of silica.

Work processes generating RCS

The primary exposure route for crystalline silica is inhalation of dust in the respirable fraction. The respirable dust fraction are the particles that are so small that they pass to the unciliated lower regions of the lung airways, the alveoli, where they are deposited. These particles are generally less than 5-7 µm in diameter.

There are numerous work processes that have the potential to release RCS dust either directly or indirectly by disturbing settled materials. Respirable crystalline dust is also present in numerous construction materials and can become respirable in some of the following example processes.

• Cutting of stone
• Abrasive blasting
• Demolition of structures, building and refurbishment
• Drilling
• Chasing
• Grinding
• Commination processes (Including rock crushing and milling mineral samples)
• Jackhammering
• Road works and earth works
• Polishing and dry sanding
• Concrete grinding, sanding and polishing
• Sanding
• Scabbling, scarifying and scrapping
• Cleaning processes (e.g. sweeping)

Any activity where a high revolution, impact or crushing/breaking type activity is occurring, has a greater potential to release respirable crystalline silica dust into the atmosphere, which when inhaled, can have irreversible health consequences if exposed to the lungs.

Regulatory landscape

Whilst RCS is regulated as a hazardous chemical under the Model WHS Regulations and relevant OHS Regulations, industry-specific Codes of Practice are now coming into force within the various states and territories.

For some states and industries, such engineered stone in Queensland, these codes are legally enforceable, whereas other recently published codes (such as the Victorian Compliance Code for Engineered Stone) currently only represent guidance.

The increased legislative focus on the engineered stone industry does, however, highlight the importance of proactive identification, assessment and management of the risks associated with RCS within the construction, infrastructure and resources sectors where there can be high potential for silica exposure.

Specifically, all states have regulatory requirements for crystalline silica including the banning of ‘sand blasting’. As well as personal exposure monitoring, health surveillance is required in most states where potential exposure to respirable crystalline silica is an exposure risk.

Some states have specific regulatory requirements for assessment of personal exposure to crystalline silica in WHS regulations and/or specific mining regulations.

Exposure standards

Safe Work Australia has published workplace exposure standards (WES) for crystalline silica on its website in the Hazardous Chemical Information System (HCIS), as well as within the guidance document, Workplace Exposure Standards for Airborne Contaminants – 16 Dec 2019.

The current exposure standard for quartz, cristobalite and tridymite as respirable dust is 0.05mg/m3 measured as a time weighted average (TWA) for an 8-hour work shift, which was reduced from 0.1mg/m3 in the December 2019 update; however, this updated WES will only have effect in a jurisdiction when it is ratified by that jurisdiction, with further guidance provided on the SafeWork Australia website.

It is important to note that extended shifts will generally require a shift adjustment factor to be applied to the WES.

Health effects

The primary exposure route for crystalline silica is inhalation of dust in the respirable fraction. The respirable dust fraction are the particles that are so small that they pass to the unciliated lower regions of the lung airways, the alveoli, where they are deposited. These particles are generally less than 5-7 µm in diameter.

Exposure to crystalline silica can lead to irreversible health effects and death from both acute (short term) exposures and chronic (longer-term) exposure.

• Acute silicosis can develop quickly after heavy exposure to crystalline silica. The lungs fill with a protein containing fluid which can lead to severe shortness of breath and can lead to death.
• Accelerated silicosis is associated with high exposure where there is a rapid increase of scarring of the lung (fibrosis) within the first 10-years of exposure.
• Chronic, or more typical, silicosis where the fibrosis occurs more slowly can take up to 30 years after the first exposure.

Silicosis affects the immune system and increases the potential for lung diseases such as tuberculosis. Treatment options for individuals in advanced stages is generally poor, with the provision of oxygen and potential lung transplants.

Controls

Occupational safety and health legislation require employers, in consultation with workers, to identify hazards, assess risks and implement practical controls to protect workers’ health and safety.

Silica can be identified by considering the types of materials used in the task and the way they are used. More information is available in material safety data sheets where these are available and from material suppliers.

There are more specific controls required within Queensland and Victoria, as described within their respective Codes of Practice.

Examples of controls for crystalline silica:

• Choosing materials (e.g. abrasive blasting agents) that are silica free or have the lowest silica content
• Designing buildings with recesses for services to reduce the amount of chasing required
• Providing vehicles with enclosed cabs fitted with high efficiency air filters, for dusty earthworks or mining
• Using wet work methods to reduce dust (e.g. wet cutting or polishing, water sprays during earthworks)
• Using water spray or rubber curtains around conveyor transfer points
• Using local extraction ventilation, either fixed or on-tool (e.g. for mixing, crushing, milling, drilling or chasing)
• Shadow vacuuming (e.g. during drilling)
• Vacuum clean-up rather than sweeping
• Not blowing dust with compressed air

In addition to other controls, PPE such as an appropriate respirator (selected in accordance with Australian/New Zealand Standard AS/NZS 1715: Selection use and maintenance of respiratory protective equipment) may be required, depending on the task and the effectiveness of the other controls.

Recent publications have indicated that wet cutting is not sufficient to control exposure in some circumstances. Furthermore, a recent RCS monitoring of road crew workers who were working with concrete (cutting and grinding revealed TWA levels that easily exceeded the proposed new standard of 0.02mg/m3.

Workers must be given information and training on:

• Possible health effects of crystalline silica exposure
• Control measures and how to use them (including PPE)
• Any requirement for health surveillance under regulation 5.21 of the OSH regulations

The employer should keep records of:

• The risk assessment
• Air monitoring results
• Health surveillance reports
• Training records