Dust containing crystalline silica in the extractive industry

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: 20% to 40%
• sandstone: 70% to 90%
• basalt/bluestone: less than 1%

Silica dust

Dust containing 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 become airborne when materials that contain crystalline silica are disturbed, such as when quarrying tasks are carried out.

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

Health risks

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 silica dust is inhaled it can cause silicosis, which is a type of pulmonary fibrosis (scarring of the lungs). Silicosis is a serious and incurable disease, and symptoms can include 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

Exposure standard

Safe Work Australia publishes exposure standards for airborne contaminants in the workplace.

The exposure standard for respirable crystalline silica (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 maximum average airborne concentration of a particular substance permitted over an 8-hour working day, for a 5-day working week.

The workplace exposure standard for respirable crystalline silica is based on the airborne concentration within 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.

The workplace exposure standard must be adjusted for non-standard work cycles typical in the extractive industry. An occupational hygienist with the requisite skills and knowledge can determine the time adjusted exposure standard for the employees based on their work cycles. There are a number of adjustment methods available which result in differences in adjusted exposure standards. An example of adjustment factors for differing work cycles using the Quebec model is given in the table below.

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

Crystalline silica processes

A crystalline silica process means one or more of the following processes carried out at a workplace:

• a quarrying process involving material containing crystalline silica
• the use of a power tool or other form of mechanical plant to cut, grind, polish, or crush material containing crystalline silica or to carry out any other activity involving material containing crystalline silica that generates crystalline silica dust
• the use of a roadheader on an excavated face if the material in the face contains crystalline silica
• a process that exposes a person to crystalline silica dust arising from the manufacture or handling of material that contains crystalline silica
• the mechanical screening of crushed material containing crystalline silica
• a tunnelling process involving material containing crystalline silica
• a process determined by WorkSafe to be a crystalline silica process

Extractive industry work can often involve a crystalline silica process. Specific duties apply for crystalline silica processes.

High risk crystalline silica work

High risk crystalline silica work (HRCSW) means work performed in connection with a crystalline silica process that is reasonably likely to result in:

• an airborne concentration of respirable crystalline silica that exceeds half the exposure standard for respirable crystalline silica, or
• a risk to the health of a person at the workplace

Identifying high risk crystalline silica work

Before undertaking a crystalline silica process, an employer or self-employed person must  identify whether the crystalline silica process (or processes) is HRCSW. This must be done by conducting a risk assessment or by choosing to identify the work as HRCSW without conducting a risk assessment.  

If conducting a risk assessment, the employer or self-employed person must take into account the following:

• the specific tasks or processes required to be undertaken with material containing crystalline silica
• the form of crystalline silica to be used (for example, granite, sandstone)
• the proportion of crystalline silica contained in the material
• previous atmospheric monitoring results
• the likely frequency and duration of exposure to crystalline silica dust, and
• any information about incidents, illnesses or diseases associated with exposure to crystalline silica dust at the workplace

Crystalline silica hazard control statement

An employer or a self-employed person must not perform HRCSW unless:

• a crystalline silica hazard control statement (hazard control statement) is prepared for the work before the work commences, and
• the work is performed in accordance with that hazard control statement

If the work is not performed in accordance with the hazard control statement, the employer or self-employed person must stop that work immediately or as soon as it is safe to do so. Work must not resume until the hazard control statement is complied with or reviewed and, if necessary, revised in accordance with the Occupational Health and Safety Regulations 2017 (OHS Regulations).

The hazard control statement must:

• state the hazards and risks to health associated with the HRCSW
• clearly detail the measures selected to control those risks in accordance with the hierarchy of controls (outlined below)
• describe how the risk control measures will be implemented, and
• be set out and expressed in a way that is readily accessible and comprehensible to the persons who use it

Additionally, if the HRCSW involves a quarrying or tunnelling process, an employer or a self-employed person must, before the work commences:

• collect samples of materials to be used in the quarrying or tunnelling process,
• arrange for analysis of those samples by a suitably competent person to identify the proportion of crystalline silica contained in each sample, and
• include the results of that analysis in the hazard control statement

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.

For more information about HRCSW, including how to prepare a hazard control statement, see Preparing a crystalline silica hazard control statement for high risk crystalline silica work guidance.

Selecting risk control measures

When selecting measures to control the risk to health from exposure to crystalline silica dust, the employer must apply the following hierarchy of controls.

An employer must, so far as is reasonably practicable, eliminate any risk associated with exposure to crystalline silica dust in their workplace.

If a risk cannot be eliminated, it must be reduced so far as is reasonably practicable, by implementing one (or a combination) of the following:

• substituting the crystalline silica substance with a substance that is less hazardous or a less hazardous form of crystalline silica
• isolating persons from exposure to crystalline silica dust, for example ensuring operator cabins are isolated from dust sources
• using engineering controls, for example wet suppression, positive pressure cabins, dry cyclone filtration systems

If a risk of exposure still remains after the above controls have been implemented, so far as is reasonably practicable, employers must reduce the remaining risk by using administrative controls.

If a risk of exposure still remains after administrative controls have been implemented, so far as is reasonably practicable, employers must reduce the remaining risk by providing appropriate personal protective equipment (such as respiratory protective equipment).

Note: Employers must consult with their employees (including independent contractors), and any health and safety representatives, when identifying hazards and risks associated with crystalline silica exposure, and when deciding on how to control risks.

Controlling the generation of airborne 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

• Ensure operator cabins are isolated from dust sources (as above).
• Regular wetting down of work areas and operating faces.
• Watercarts and surfactants on roads.
• Planning activities around weather conditions.
• Minimise vehicle movements.
• Reduce onsite vehicle speeds, particularly in dry and windy conditions.

Crushing, screening and bulk handling

• Airborne dust suppression using water with water suppression nozzles appropriate to site conditions including air atomising, misting/fogging and high energy misting/fogging nozzles.
• Dust extraction ventilation.
• Enclose dust-generating sections of plant within purpose built enclosures.
• Isolate operators from generated dust.
• Minimise the fall height of material at stackers and transfer points.
• Install concertina type discharge chutes at the end of the screen.

Maintenance and cleaning

• Clean down equipment prior to performing maintenance work.
• Avoid accumulation of dust in work and administration areas.
• Ensure any vacuums in use are hazardous dust class M or H.
• Do not use compressed air for cleaning air filters.
• Do not use brooms for sweeping dust – use vacuums or wet methods.
• Provide boot washes at entrances to amenity or office areas.

Laboratory testing

• Employ wet cleaning methods when cleaning down equipment.
• Dust extraction ventilation for dust generating equipment.
• Provide a clean air supply through filtered ventilation.
• Isolation of the laboratory from adjacent dusty areas.

Respiratory protective equipment (RPE)

When higher order controls do not adequately control exposure to dust, respiratory protective equipment (RPE) may be required for employees exposed to silica dust.

RPE must be designed to protect the wearer from the inhalation of airborne contaminants and comply with AS/NZS 1716:2012 - Respiratory protective devices or requirements equivalent to those of that Standard. Check the product information to make sure RPE is compliant. If you are not sure, ask your supplier or contact the manufacturer.

RPE needs to have at least a P2 filter and be fit tested for each person to ensure it fits correctly. RPE that requires a facial seal, such as half-face respirators, should not be used by people with beards or even facial stubble. Where facial hair interferes with the fit of the RPE, a powered air purifying respirator (PAPR) that does not rely on a facial seal needs to be used.

RPE should be selected, used, maintained and stored in accordance with AS/NZS 1715 - Selection, use and maintenance of respiratory protective equipment or equivalent standard. If RPE is used to control risks associated with exposure to silica dust, employers must provide employees with information, instruction and training in RPE use, maintenance and storage.

Training

An employer must ensure that employees who are likely to be exposed to risks associated with HRCSW are given information, instruction and training in:

• the health risks associated with exposure to crystalline silica dust,
• the need for, and proper use of, control measures, and
• how the risk control measures are to be implemented

For example, training needs to be provided on:

• crystalline silica hazards and health risks
• how to properly and effectively use controls

Employers should provide information, instruction and training to employees on:

• the fit, use and maintenance of RPE
• how to dispose of waste
• methods for personal decontamination

The structure, content and delivery of the training needs to take into account any special requirements of the employees being trained. For example, information, instruction and training may need to be provided in a language other than English. Refresher training should be provided regularly.

Atmospheric monitoring

Employers must ensure that atmospheric monitoring is carried out in relation to crystalline silica dust generated at their workplace (including in relation to quarrying work) where:

• there is uncertainty about whether the crystalline silica exposure standard is or may be exceeded, or
• atmospheric monitoring is necessary to determine whether there is a risk to employee health (and therefore if health monitoring is required)

Atmospheric monitoring and the interpretation of results (including comparison with the exposure standard) should be conducted by a competent person (such as an occupational hygienist) to determine exposure levels to crystalline silica dust.

Results of atmospheric monitoring must be shared with employees who have been, or may have been, exposed as soon as reasonably possible.

Atmospheric monitoring results should also be shared with medical practitioners who are conducting health monitoring for employees.

Health monitoring

Employers must ensure that health monitoring is carried out for an employee if exposure to crystalline silica is likely to have an adverse effect on that employee’s health.

Health monitoring must be carried out under the supervision of a registered medical practitioner.

Health monitoring should be carried out by a specialist occupational and environmental physician or respiratory physician, 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 in line with the recommendations of the registered medical practitioner. This may include regular testing periods while they are in the job, when an employee is hired with a new employer (before they start work), and when they finish working for that employer.

Providing information to customers

Operators extracting and supplying materials containing crystalline silica are required to provide information to customers including about the proportion of crystalline silica contained in the product and how to safely use the product they are supplying.

References

Queensland Department of Natural Resources, Mines and Energy, 2020: QGL02: Guideline for management of respirable dust in Queensland mineral mines and quarries, Appendix 6, version 3 April 2020.