What is crystalline silica?
Silica is an abundant mineral found within most rocks and soils. Silica can occur in either crystalline or non-crystalline (amorphous) forms. The crystalline form of silica poses the biggest risk to health, as it can damage your lungs when it is inhaled.
The most common form of crystalline silica occurs as the mineral quartz. The amount of silica found within different types of rocks and soils can vary, with some common examples listed below:
- granite: 25% to 60%
- shale: 22%
- sandstone: 70% to 90%
While geological surveys can give some indication of the potential silica content of a resource to be extracted, a petrographic analysis is more accurate in determining the crystalline silica content of a material and should be undertaken.
Dust containing respirable crystalline silica particles is commonly called silica dust. Silica dust is made up of particles of different sizes. The smallest particles are known as respirable crystalline silica, which can be released when you drill, blast, excavate, load, transport, crush, package, dump or simply disturb materials that contain crystalline silica.
Crystalline silica dust can be harmful when it's inhaled into your lungs over a long period of time at low to moderate levels, or short periods at high levels.
When crystalline silica dust is inhaled it can cause silicosis, a scarring of the lungs. Silicosis is a serious and incurable disease, with symptoms including shortness of breath, coughing, fatigue and weight loss. In severe cases, the damage caused to the lungs by silicosis can require a lung transplant or may lead to death.
Breathing in silica dust can also cause other serious diseases, such as:
- lung cancer
- kidney disease
- autoimmune disease, such as scleroderma
Safe Work Australia publishes exposure standards for airborne contaminants in the workplace.
The exposure standard for respirable crystalline silica dust (listed under Quartz (respirable dust)) is 0.05 mg/m3 as a TWA (time-weighted average) airborne concentration over 8 hours.
An 8-hour time-weighted average exposure standard is the average airborne concentration of a particular substance permitted over an 8-hour working day and 5-day working week.
The workplace exposure standard for respirable crystalline silica is based on the levels found in a person’s breathing zone, outside of any respiratory protective equipment that may be in use.
Employers are required to ensure employee exposure does not exceed this standard.
WorkSafe Victoria recommends that employees are not exposed to levels above 0.02 mg/m3 as an eight hour TWA. This is a precautionary measure to prevent silicosis, and to minimise the risk of lung cancer.
Exposure limits need to be adjusted for non-standard work cycles typical in the extractive industry. See the table below, adapted from one produced by the Queensland Department of Natural Resources.
Table 1 - Adjustment factor to respirable crystalline silica occupational exposure limit for typical non-standard work cycles in mining, assuming an exposure standard of 0.05 mg/m3 as a TWA
Extractive industry tasks and exposure
Exposure to crystalline silica can occur during common quarrying tasks where dust is generated, such as:
- drilling, blasting and rock breaking
- excavation, grading and site preparation
- crushing, screening and bulk handling
- maintenance and cleaning
- mobile plant movement on unsealed roads
- laboratory testing or product sampling
If employees are regularly exposed to material that contains crystalline silica without controls in place, it is likely that the exposure standard will be exceeded.
Controlling the risk of exposure
Employers must control the risk associated with exposure to crystalline silica by applying the hierarchy of control in Part 4.1 of the Occupational Health and Safety Regulations 2017 (OHS Regulations).
An employer must, so far as is reasonably practicable, eliminate the risk associated with exposure to crystalline silica in their workplace (for example by using non silica-containing products).
If it is not reasonably practicable to eliminate a risk associated with crystalline silica, the employer must reduce the risk so far as is reasonably practicable by:
- substitution (for example using materials which have a lower silica content)
- isolation (for example ensuring operator cabins are isolated from dust sources)
- engineering (eg wet suppression, positive pressure cabins, dry cyclone filtration systems)
- a combination of any of the above risk control measures
If the risk of exposure still remains, administrative controls (eg housekeeping, work practices) must be used to reduce the risk so far as is reasonably practicable. If a risk remains, personal protective equipment (such as respiratory protective equipment) must be used.
Controlling the generation of airborne respirable crystalline silica dust at the source is the most effective way to reduce exposure during the extractive process. It is much more effective than trying to control the exposure of employees after the dust has become airborne.
It may not be possible to completely eliminate crystalline silica from an extractive process, due to the presence of silica within the rock or soil itself. Employers must, so far as is reasonably practicable, apply controls at each stage in the process to reduce the risk of exposure. Examples of appropriate controls include:
- Drilling, blasting and secondary breaking (rock breaking)
- Wet suppression or dry cyclone filtration systems for drilling.
- Wetting down of access roads and work areas (where appropriate).
- Doors and windows of equipment are closed at all times.
- Well maintained cabins that are regularly cleaned to avoid dust accumulating during entry and exit.
- Air conditioning within equipment cabins is filtered with high capacity filters suitable for the dust loading of the operating environment.
- Excavation, grading and site preparation
- Crushing, screening and bulk handling
- Maintenance and cleaning
- Laboratory testing
- Respiratory protective equipment (RPE)
By law, employers must carry out air (atmospheric) monitoring for crystalline silica dust generated at their workplace where:
- there is uncertainty about whether the exposure standard is or may be exceeded, or
- air monitoring is necessary to determine whether there is a risk to employee health, and therefore if health monitoring is required.
Air monitoring and the interpretation of results (including comparison with the exposure standard) needs to be conducted by a competent person (such as an occupational hygienist) to determine employee exposure to crystalline silica. Results of air monitoring must be shared with employees who have been, or may have been, exposed. Where possible, air monitoring results should be shared with medical practitioners who are conducting health monitoring for employees.
Employers must provide health monitoring if exposure to crystalline silica is likely to have an adverse effect on employees’ health. This is particularly important where lower level control measures, such as RPE, are relied on to reduce exposure.
Health monitoring is required for employees who are exposed to silica dust at levels likely to exceed the exposure standard.
Health monitoring must be undertaken by a registered medical practitioner. It needs to be carried out by an occupational physician who is a fellow of the Australasian Faculty of Occupational and Environmental Medicine (AFOEM), with expertise in respiratory and silica exposure health monitoring. A list of practitioners can be found on the Royal Australasian College of Physicians website at (link below). Employers should speak to the occupational physician to ensure they have experience with silicosis and other silica dust diseases.
Where health monitoring is required, it should be completed when an employee is hired with a new employer (before they start work), regularly while they are in the job and when they finish working for that employer.
For more information on health monitoring see Crystalline silica health assessments.
Providing information to customers
Under the Occupational Health and Safety Act 2004 (OHS Act), operators extracting and supplying materials containing crystalline silica are required to provide information to customers about how to safely use the product they are supplying. For example, information should be provided in a safety data sheet (SDS), including the percentage of crystalline silica in the material being supplied, the hazardous properties and risks to health of respirable crystalline silica and risk controls that need to be used when processing the silica-containing material.
Queensland Department of Natural Resources, Mines and Energy, 2018: Guideline for management of Respirable Crystalline Silica in Queensland Mineral Mines and Quarries.
Crystalline silica: Safety basics
Crystalline silica health assessments
AIOH: Exposure Standards for Extended Work Shifts’External link
CCAA: SDS for products containing respirable crystalline silicaExternal link
CCAA: Respirable crystalline silica in quarriesExternal link
AIOH: Find an occupational hygienistExternal link
RACP: Find an AFOEM consultantExternal link