Silica is silicon dioxide, a naturally occurring widely abundant mineral that forms the major component of most rocks and soils. There are non-crystalline and crystalline forms of silica. Crystalline silica is also known as free silica. Crystalline silica dust particles that are small enough to penetrate deep into the lung are termed respirable. Respirable crystalline silica may cause lung damage and disease. The non-crystalline form of silica does not cause this kind of lung damage.
The most common form of crystalline silica is quartz (CAS 14808-60-7). Crystalline silica is found in varying proportions in aggregates, mortar, concrete and stone. Granite contains 25 per cent to 40 per cent quartz, shales average 22 per cent and sandstones average 67 per cent quartz. Quartz is the major component of sand in locations like stream beds, beaches and deserts. Other polymorphs of silicon dioxide, including cristobalite (CAS 14464-46-1) and tridymite (CAS 15468-32-3) are less common.
An increase in the number of workers diagnosed with silicosis and progressive massive fibrosis has been linked to working with engineered stone. Engineered stone products can contain up to 97 per cent silica. The high amount of silica means that there is a very high risk of workers developing breathing problems and silicosis if they breathe in dust made from these products.
Work activities that may represent a high risk exposure
Under the model Work Health and Safety (WHS) Regulations, free silica (crystalline silica dioxide) is listed as a restricted hazardous chemical and must not be used for abrasive blasting at concentrations greater than one per cent without authorisation from a relevant WHS regulator.
Examples of work activities involving crystalline silica that require special attention when assessing exposure include:
- fabrication, installation, maintenance and removal of engineered stone countertops
- excavation, earth moving and drilling plant operations
- clay and stone processing machine operations
- paving and surfacing
- mining, quarrying and mineral ore treating processes
- road construction and tunnelling
- construction labouring and demolition
- brick, concrete or stone cutting; especially using dry methods
- abrasive blasting (blasting agent must not contain greater than one per cent of crystalline silica)
- foundry casting
- angle grinding, jack hammering and chiselling of concrete or masonry
- hydraulic fracturing of gas and oil wells
- pottery and other ceramics industries
- crushing, loading, hauling and dumping of rock or muck, and
- clean-up activities such as sweeping or pressurised air blowing of dust.
Sources of non-occupational exposure
Silica is abundant in nature in multiple forms including quartz, cristobalite, tridymite and tripoli.
Non-occupational exposure to silica dust can occur around industrial sites (quartz crushing, agate grinding, ceramics, use of slate pencils, mining and milling of sand stones, silica flour milling) or from naturally occurring sources such as desert dust or sand.
Health monitoring required for crystalline silica under the model WHS Regulations
- Collection of demographic, medical and occupational history
- Records of personal exposure
- Standardised respiratory questionnaire to be completed
- Standardised respiratory function tests, for example, FEV1 (Forced expiratory volume in one second) , FVC (Forced vital capacity) and FEV1/FVC (Respiratory ratio, or Tiffeneau index)
- Chest X-Ray full PA view
Note: The term health monitoring is established under the model Work Health and Safety (WHS) laws. Health monitoring is a duty of a person conducting a business or undertaking (PCBU) when a significant risk to health or a significant risk of exposure is identified. It involves a registered medical practitioner with experience in health monitoring examining and monitoring the health of workers to see if exposure to hazardous chemicals at work is affecting worker’s health.
The term health screening, used recently in relation to accelerated silicosis, is in reference to the process of case finding and diagnosis. While this screening has recently been focussed on workers in the stone industry, it does not have the same purpose and intent as health monitoring under the model WHS laws.