Crystalline Silica in Stone
What do you need to know about crystalline silica?
Crystalline silica is a natural mineral that forms part of most rocks, including natural stones like Granite, Marble, Limestone, and Sandstone, as well as artificial products like engineered stone and tiles.
It’s important to note that crystalline silica is not harmful when solid. The dust generated when you cut, grind, drill, polish or saw these materials can cause serious health problems if the dust is inhaled.
If you’re working with natural stone, it’s essential that you understand what crystalline silica is, what levels are typical in different stone products, how to control the dust and how to protect yourself and your workers from the risks.
Scientific evidence suggests that natural stone, regardless of the crystalline silica content by weight, is safer to cut and handle than engineered stone. (Ramkissoon, C, et al. 2022) (Carrieri, et al. 2020) (Hall, et al. 2022) (Thompson and Qi 2023).
What is crystalline silica?
Crystalline silica is the crystalline form of silicon dioxide, a common mineral that makes up about 12% of the earth’s crust. It has different forms, such as quartz, cristobalite and tridymite.
Quartz is the most common form, found in many types of rocks and soils. Engineered benchtops typically comprise 95% natural quartz aggregates bound together with polymer resins and pigments. The high contents of quartz, and therefore crystalline silica, within engineered stone, is why Safe Work Australia is currently questioning the overall safety of the products.
Crystalline silica is very hard and resistant to chemical and physical weathering. These physical characteristics make it ideal for many purposes, such as making glass, ceramics, concrete, bricks and mortar.
Why is crystalline silica dangerous?
Crystalline silica is not harmful when it is in solid form. However, when broken down into microscopic particles, called respirable crystalline silica (RCS), it can become airborne and enter your lungs when you breathe.
RCS particles are so tiny that they can reach the deepest parts of your lungs, where they can cause inflammation, scarring and fibrosis, potentially leading to serious lung diseases, such as silicosis, chronic obstructive pulmonary disease (COPD) and lung cancer. RCS can also affect other organs, such as the kidneys and the immune system.
Silicosis is a progressive and irreversible lung disease that causes shortness of breath, coughing, chest pain and fatigue. It can also increase the risk of tuberculosis and other infections.
There are three types of silicosis: chronic, accelerated and acute. Chronic silicosis develops after long-term exposure (more than ten years) to low or moderate levels of RCS. Accelerated silicosis develops after shorter exposure (5 to 10 years) to higher levels of RCS. Acute silicosis develops after very short exposure (weeks or months) to extremely high levels of RCS. Acute silicosis can be fatal.
What are the typical levels of crystalline silica?
The amount of crystalline silica in different products varies depending on the type and source of the material. The graph below shows the maximum typical levels of crystalline silica by weight found in various products. Stone is a natural product, and these numbers are guidelines only.
Marble and Limestone generally contain less than 3% crystalline silica, putting them in the lower range for natural stone. Close behind is Bluestone (or Basalt), typically comprised of less than 10% crystalline silica.
Granite has a broader range and varies from as little as 5% and up to 50% crystalline silica by weight. On the higher end of the spectrum are Sandstone and Quartzite, with a range of 20% to 95% crystalline silica by weight.
Engineered stone, made by mixing quartz or other minerals with resin and pigments, can contain up to 97% of crystalline silica by weight.
- Bluestone/Basalt: Typically less than 10%
- Marble: Typically less than 5%
- Limestone: Typically less than 5%
- Granite: 5% to 50%
- Sandstone: 20% to 95%
- Engineered Stone: 40% to 95%
- Concrete: Less than 30%
- Bricks: Less than 30%
- Ceramic Tile: 5% to 45%
- Quartzite: 20% to 95%
How is Natural Stone safer than Engineered Stone?
The available scientific literature shows that processing engineered stone products with a high crystalline silica content generates much higher RCS compared to natural stone (Ramkissoon, C, et al. 2022) (Carrieri, et al. 2020) (Hall, et al. 2022) (Thompson and Qi 2023).
Cutting engineered stone generates high concentrations of RCS, and personal air monitoring has shown common tasks involved in engineered stone fabrication can expose workers to RCS at levels well above the current WES (0.05 mg/m3 8-hour TWA) if effective controls are not in place. High levels of airborne RCS have been detected in all areas of an engineered stone fabrication workshop, including areas that were not used for processing of engineered stone (Jennings 2021).
What’s the best way to control the dust from stone products?
The best way to prevent exposure to RCS is to eliminate or minimise the generation of dust from stone products, either using alternatives, such as non-silica-containing materials or wet methods of cutting or polishing.
If this is not possible or practicable, you should use engineering controls, such as local exhaust ventilation (LEV), water suppression or dust extraction systems, to capture or reduce the dust at the source. You should also use appropriate work practices, such as isolating the work area, cleaning up regularly with a vacuum or wet method (not sweeping or blowing), and disposing of waste safely.
How to protect yourself, your workers and your customers from RCS?
In addition to the above control measures, you must still provide personal protective equipment (PPE), such as respirators (generally a minimum of a P2 efficiency half-face respirator), gloves, goggles and protective clothing, to yourself and your workers.
You should also provide information, training and supervision on how to use the PPE and the control measures. You should also monitor the exposure levels of RCS in the workplace and conduct health surveillance for yourself and your workers to detect signs of silicosis or other diseases.