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Respirable Crystalline Silica Dust, Occupational Hazards 

28/11/2022by minal.metkari0Read: 7 minutes

Respirable crystalline silica dust produced from processes done on products in the manufacturing and construction industries is a serious concern for organisations in Australia. It is harmful to the workers exposed to it and can cause life-threatening illnesses.

This blog will discuss respirable crystalline silica dust, products and processes that produce it, precautions that need to be taken, laws and standards, Workplace Exposure standards (WES), and its key changes.

What is Respirable Crystalline Silica Dust?

Respirable crystalline silica (RCS) refers to particles of crystalline silica that is less than four microns in size, or particulate matter 4 (PM4). PM4-sized particles can penetrate deep into the lungs, where the most critical effects of RCS– silicosis and cancer – are thought to occur

Respirable crystalline silica is also known as silica dust. Silica dust is made up of small particles that become airborne during processing with materials that contain crystalline silica. Activities include cutting, sawing, crushing, drilling, and grinding. Other work activities like construction, quarrying, or tunnelling can also generate silica dust.

Natural stones such as granite and sandstone consist of silica dust. It is also utilised in the manufacturing of products like tiles.

It is also generated as a waste residue released during the processing of silica-containing goods; and sand-based products.

Sand, concrete, stone, and mortar can contain crystalline silica. It’s also used to create engineered stone for bathroom and kitchen benchtops, as well as tiles and bricks.

Identification of products and processes releasing silica dust

Silicon dioxide is referred to as Silica, a naturally occurring and abundant mineral on earth that forms the major component of most rocks and soils. There are non-crystalline and crystalline forms of silicon dioxide. The most common type of crystalline silica is quartz (CAS 14808-60-7).

Identification of silica dust released at a workplace is the first step towards its prevention. Airborne silica dust is harmful, and workers, when exposed to it, can inhale it, which can lead to occupational diseases such as silicosis.

Different types of rock and its products can contain different amounts of silica.

Common silica-containing materials and products are as listed below:

  • Natural and engineered stone products
  • manufactured timber
  • composite dental fillings
  • bricks, asphalt, cement
  • plasterboards and drywall
  • tiles, grout, tiles, and mortar
  • certain plastic material.

Crushing, cutting, drilling, grinding, sanding, sawing, or polishing of natural stone or man-made silica-containing products generates respirable silica dust. Silica dust can be produced and found in manufacturing and road construction, mining and tunnelling, waste or sand-based products, and materials brought to your workplace.

Other activities that release silica dust into the air include:

  • engineered stone countertop fabrication, installation, maintenance, and removal
  • plant excavation, earth moving, and drilling rig
  • clay and stone processing machine operations
  • surfacing and paving
  • mineral ore treating procedures and quarrying
  • demolition and labouring during construction
  • concrete, brick, or stone cutting, especially using dry methods
  • blasting of abrasives
  • foundry casting
  • jackhammering, angle grinding, and masonry or chiselling of concrete
  • hydraulic fracturing of oil and gas wells
  • pottery
  • loading, crushing, dumping or muck, or rock and hauling.

Workplace Activities that cause Exposure to harmful Silica dust

Some of the workplace activities that release silica dust into the air are as follows:

1) Quarrying, mining, extractive minerals, and tunnelling

Silica dust exposure is a well-known problem, with significant risks of occupational exposure during stone crushing activities.

2) Manufacturing of products consisting of silica

Over the last 10-15 years, the use of materials containing engineered stone to granite counters in residential and commercial buildings has increased exponentially. When stone items are manufactured, dust exposure can occur.

3) Fabricating, installing, maintaining, and removing silica-containing products

Silica dust can be produced during industrial processes like trimming, grinding, cutting, or blasting silica-containing products or when depositing or discarding dusty waste from these procedures.

Engineered stone products can comprise up to 97 percent silica content. Given the high silica content, there is a very large probability of workers developing respiratory issues and Silicosis only when they breathe in the harmful silica dust present in these products. Working with engineered stone has been interconnected to a rise in the number of industrial workers diagnosed with diseases like Silicosis and progressive massive fibrosis.

4) Construction, building, and demolition

On-site silica dust can be generated by cutting concrete and using power tools on stone.

Health effects of Respirable Crystalline Silica dust

It is not the particulate materials in solid form but the inhaling of the silica dust produced that causes silica-related diseases such as Silicosis.

A high amount of silica dust is found near worksite units that handle silica-based products, threatening the workers’ health.

Once tiny silica particulates become airborne, factory workers may inadvertently inhale them into their lungs, resulting in respiratory diseases such as lung cancer, Silicosis, and chronic bronchitis.

Inhaling in respirable crystalline silica (RCS) at concentrations above the workplace exposure standard (WES) for many months or years can cause Silicosis, a disease that leads to scar tissue forming in the lungs, resulting in loss of lung function and an increased risk of lung cancer. RCS may also be linked to the development of other diseases like COPD, kidney disease, and autoimmune disorders.

Procedure to Measure Exposure Silica Dust

Respirable crystalline silica (RCS) when inhaled deeply into the lungs poses a health risk. Exposure is thus determined by measuring the concentration of a specific size fraction in the air. It should be noted that state guidelines are available that detail how to manage the monitoring of workers’ RCS exposure and health surveillance.

One such example of the state guidelines is the Queensland Guideline for Management of Respirable Crystalline Silica in Queensland Mineral Mines and Quarries – QGL02 (Queensland DNRME, 2018)).

According to Safe Work Australia (SWA) (2013a), air monitoring should not be used as an alternative to controlling the exposure and is best done after control measures have been implemented. The sampling and analysis components of air monitoring can influence the accuracy and precision of RCS exposure measurement.

Air monitoring – Sampling

AS 2985 (2009) is the current method for sampling and gravimetric determination of respirable dust.

AS 2985 (2009) defines respirable dust as the proportion of airborne particulate matter that, when breathed, enters the unciliated air passages deep in the lung.

It is critical that any sampler utilised to collect respirable dust fulfils the requirements of ISO/CEN/ACGIH sampling efficiency curve requirements. Difficulties with sampling, like poor flow rate control and sample duration, can lead to uncertainty in the exposure approximation.

Analysis of air monitoring samples collected crystalline silica is typically measured in respirable dust and identification of the dust through X-ray diffraction (XRD) in accordance with the NH&MRC method for measuring quartz in respirable dust using XRD calibrated against a known national quartz standard.

Health Surveillance for Crystalline silica exposure

Health surveillance is used to assess adverse health effects in RCS-exposed personnel by comparing results to a baseline medical assessment.

Where there is a long-term risk of exceeding 50% of the exposure standard, crystalline silica health monitoring should be conducted in accordance with ‘Health Monitoring for Exposure to Hazardous Chemicals – Guide for Medical Practitioners’ (SWA, 2013b) and ‘Crystalline silica health monitoring’ (SWA, 2013c)

Organisations in Australia should also follow the relevant state health surveillance guidelines, such as the Queensland WorkSafe (2018) ‘Guide to safe benchtop fabrication and installation.

Available Controls

A combination of regular medical surveillance, exposure reductions such as compliance with a regulatory exposure standard, the prohibition of specific tasks associated with high risk (such as sandblasting and the use of silica flour in foundry operations), and the use of adequate dust suppression systems such as ventilation and wetting down has historically resulted in a reduction in silicosis numbers.

Controls for both inhalable and respirable dust exposures will have an effect on RCS levels in the air. Thus, the RCS control principles are identical to the ones that adhere to all mechanically produced mineral dust exposures.

Hierarchy of Controls

The hierarchy of risk controls should be applied when determining the appropriate controls:

  • Create and implement processes and activities to reduce dust emission, release, and spread;
  • Position personnel so that they are either enclosed and filtered cabins with positive pressure (at least 50 Pa pressure differential) or working upwind of dust emission;
  • Use sharp cutting tools to reduce the generation of large amounts of fine dust;
  • Employ wet mechanisms to avoid dust generation, especially when working with freshly cut quartz surfaces;
  • To prevent dust spread, use water (or water with additive) suppression.
  • Reduce the fall distance of dust-producing materials;
  • To prevent dust release, use water curtains and rubber curtains, especially at conveyor transfer points and chute draw points;
  • To control dust spread and release, making use of appropriate ventilation, either dilution or, preferably, local extraction;
  • Guarantee that suppressed dust is seized by scrubbing or filtration so that it would not re-enter the worksite air;
  • Use good housekeeping practices to prevent dust accumulation, which is especially important inside vehicle dust-proof cabins;
  • To clean up dust spills, organisations should use a vacuum cleaner that has a suitable filter;
  • Offering training on the harmful health effects of RCS dust, its key sources, and control measures, as well as creating an awareness about the results of airborne monitoring and the assessed risk of exposure at the workplace;
  • Where adequate exposure control cannot be achieved through other means, provide suitable PPE in conjunction with other control measures. Most RCS exposures will require a P1 or P2 type filtering half-face respirator, though, for high RCS exposures, a P3 type filter, powered air purifying respirator (PAPR), or even an air-supplied respirator may be required.

Current applicable Legislation and Standards

As per the GESTIS International Limit Values website, the 8-hour TWA OEL for RCS differs from country to country, ranging from 0.03 to 0.15 mg/m3, with 0.05 and 0.1 mg/m3 being one of the most common.

According to the SWA (2016) Model Work Health and Safety Regulations, risks to health and safety must be eliminated or minimised to the greatest extent reasonably practicable, using the risk control hierarchy.

The Model Regulations stipulate nobody in a worksite be subjected to RCS at a concentration greater than the WES and that air monitoring be conducted to measure worker RCS exposure concentration(s) where:

  • It is unclear whether the RCS concentration exceeds; or
  • Monitoring will help determine the level of risk to workers’ health. Furthermore, where RCS exposure in the workplace might just have a negative impact on worker health, health monitoring (surveillance) should be offered.

Workplace Exposure Standards (WES)

Workplace Exposure Standards (WES) represent the amount of dangerous airborne substances, such as respirable crystalline silica, in a worker’s breathing zone, which won’t harm their health.

It is, therefore, mandatory for Australian businesses to have their workplaces in compliance with WES as made compulsory by WHS Legislation of the Commonwealth, state, and territory in Australia.

As per WES, your staff members should not be subjected to silica dust levels higher than 0.05 mg/m3 for an eight-hour work shift, five days a week.

Confirm with your regulatory body to find out if they have introduced and implemented any fresh silica dust regulations, which are an add-on to lowering the WES.

What are the legal obligations to manage Respirable crystalline silica risks?

An individual who runs a company or an organisation (for example, a small-business owner or an employer, might have to enforce extra control measures or implement modifications to your organisational procedures to prevent surpassing the WES for silica dust.

Australian businesses should practice the steps listed below to safeguard workers’ health from the dangers of crystalline silica dust:

  1. Assess the risk of silica dust at your workplace.
  2. Analyse the available controls to limit your employees’ exposure to silica dust.
  3. Arrange for air monitoring if you are unsure about the level of silica dust in your workplace.
  4. Inform your employees and any health and safety representatives (HSRs) about the reduced WES, how it may affect your workplace, and any new training your employees may require.
  5. If your workplace has silica dust, review your worker health monitoring program, including workers who generate silica dust or work near it.

How can Anitech Help?

Anitech’s expert Occupational Hygiene Consultants can help you develop monitoring strategies for your workplace and safeguard the health of your employees.

Feel free to enquire about our Occupational Hygiene Monitoring Services on our web page here

You can also ring us at 1300 802 163 or email us at info@anitechgroup.com.

Our Occupational Hygiene Consultants will be glad to help you!

For more industry updates and for services, blogs, and informative pieces, stay tuned to our website Anitech.

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