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Crystalline silica is found in most rocks, sand and clay. It is also found in manufactured products including bricks, concrete, tiles and composite stone.
Also known as quartz, crystalline silica dust is harmful when inhaled and can lead to silicosis. This disease can be fatal within five to ten years – sometimes for people as young as 20 or 30.
The NSW Work health and safety roadmap has a target of a 30% reduction in serious injuries and illnesses by 2022, which comprises a reduction in exposures to hazardous chemicals and materials. An initial list of 100 priority chemicals was developed based on national and international sources. This list was further refined using the following criteria: toxicity rating, exposure potential, estimated quantities used and potential number of workers using these chemicals. Crystalline silica ranked the second highest based on these criteria. Crystalline silica is a very common mineral used in manufactured building products and in construction materials. Applying adequate controls such as minimising the generation of airborne dust can reduce hazardous exposures and prevent illness in the workplace.
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Sources of exposure Materials and products containing crystalline silica include shale, sandstone, concrete, bricks and manufactured stone. Workers can come across crystalline silica during excavation or tunnelling through quartz containing rock such as shale or sandstone. A health hazard is created when the very fine particles of crystalline silica can be inhaled. The size fraction of airborne dust that can reach the lungs where air exchange takes place is known as the 'respirable fraction'. Once particles become larger than about seven microns (1 micron = 1/1000 mm) in diameter, they are no longer respirable.
Significant levels of airborne dust are most likely to occur when materials or products in the workplace are cut, sanded, drilled or during any other activities which create fine dust. Exposures in workplaces can also occur through dry sweeping or using compressed air (rather than wet cleaning or using a vacuum with HEPA filter) and re-suspension of settled dust from clothing or fabric materials.
Health effects Respirable crystalline silica (RCS), depending on factors such as how much dust a worker breathes in and for how long, can cause silicosis. Silicosis is a fibrosis (scarring) of the lung resulting in loss of lung function. This fibrosis is incurable and continues to develop after exposure has stopped. Persons with advanced silicosis suffer severe shortness of breath and may suffer complications such as heart failure.
Silicosis can be further classed into:
chronic (or classic) silicosis, typically observed in workers after 15 years or more since they were first exposed
accelerated silicosis, appearing in workers after high exposure over a shorter period of time (five to ten years)
acute silicosis, observed in workers within a few months to two years after exposed to silica at very high concentrations (acute silicosis can cause very serious health effects and is life threatening).
Significant long term exposure to crystalline silica has also been associated with an increased risk of developing lung cancer.
Labelling and safety data sheets Manufacturers and importers of products containing crystalline silica (a hazardous chemical) need to determine if workers can be exposed to the respirable fraction of airborne dust when working with these products eg when cutting. Where exposure to RCS can occur, products must be labelled and safety data sheets (SDS) provided (see clauses 330 and 335 of the Work Health and Safety Regulation 2017 (WHS Regulation).
Suppliers of a hazardous chemical to a workplace must provide current safety data sheets. A person conducting a business or undertaking (PCBU) must also obtain a copy of the SDS and make it readily accessible to workers involved in using, handling or storing the hazardous chemical at the workplace (cl 344).
Workplace exposure standards and air monitoring Respirable crystalline silica has a workplace exposure standard of 0.05 mg/m3 averaged over eight hours. Risks to health and safety from exposures to hazardous chemicals must, so far as is reasonably practicable, be eliminated. PCBU’s must ensure that no person at the workplace is exposed to a substance above its exposure standard and must reduce exposures so far as is reasonably practicable.
PCBU’s must undertake personal exposure (air) monitoring for substances with an exposure standard if they are not certain (on reasonable grounds) as to whether or not the exposure standard is exceeded.
Adjustments to the exposure standards are made for extended work shifts, taking into account the longer daily exposure. Air monitoring results must be readily available to workers and records of results kept for 30 years (cl 50).