Silica is a natural substance found in many types of stone, sand and clay – including bricks, concrete, slate and tiles – and occurs in both crystalline (including quartz, cristobalite and tridymite) and non-crystalline (or amorphous) forms. The approximate crystalline silica content within each material varies, with tiles containing 30-45%, slate 20-40%, brick up to 30% and concrete 25-70% (www.is.gd/jejubu).
Exposure to crystalline silica largely affects those working within the construction and engineering industries, where regular working activities such as cutting, drilling, grinding, crushing and polishing are known to produce dust. Respirable crystalline silica (RCS) may also be generated when these materials are fractured.
When working with slate and tiles, certain activities are known to produce high levels of crystalline silica dust that, if not monitored and controlled, can lead to chronic respiratory conditions. It is, therefore, imperative to understand the health risks associated with slate and tile cutting and how best to protect against the harmful effects of silica.
High levels of crystalline silica dust are released when cut-off saws are used to cut roof slate and tiles, and this applies regardless of the size of the material or the length of time that it is cut for. There is a considerable risk to workers who inhale excessive quantities of RCS over an extended period of time – for example, when packing and stacking slates after they have been split and dressed.
As well as being released through cutting, RCS can cause harm long after the work has been completed. Dust tends to settle on worktops and clothing and become airborne again following sudden movement, such as dry sweeping or brushing or as a result of a leak or spillage. This makes it all too easy to inhale crystalline silica via secondary exposure, as even if workers are located outside of the cutting area, they can still come to harm by inhaling newly disturbed airborne dust.
The health risks associated with exposure to crystalline silica were noted as long ago as the 1700s, when evidence of silicosis was first discovered in stone cutters. In the UK, now, it is estimated that 600,000 workers are exposed to silica dust each year, and there are an average of 600 silica-related deaths per annum (www.is.gd/jiqucu).
Silica dust is only dangerous if it is disturbed and subsequently inhaled. Then, it has the potential to cause life-threatening respiratory conditions, such as silicosis, lung cancer and chronic obstructive pulmonary disease. Many of these conditions do not show symptoms until many years after initial exposure and can even lead to fatality if lung capacity is compromised.
When crystalline silica dust is inhaled into the lungs, the body’s natural defence cells and immune system is attacked, reducing the ability of the lungs to transfer oxygen into the blood supply and causing inflammation and scar tissue formation. RCS can remain in the lungs for many years, and as it builds, increases the likelihood of a chronic respiratory condition.
While the current Workplace Exposure Limit (WEL) for RCS is currently 0.1 mg/m3 (www.is.gd/jejubu), a group of MPs have called for the WEL to be reduced from 0.1 mg/m3 to 0.05 mg/m3 over an eight-hour time weighted average (TWA), which would place it in line with the recommended exposure standards from the Scientific Committee on Occupational Exposure Limits (SCOEL). This is a result of increased health risks being seen at low levels of exposure, including at or below the current UK limit of 0.1 mg/m3.
CONTROLS & MONITORING
RCS was also recently classified as a carcinogen in the HSE’s Updates to EH40/2005 Workplace Exposure Limits guidance document, specifically in cases where it is generated as a result of a work process. This means that RCS is deemed capable of causing cancer and/or heritable genetic damage. As such, according to the Control of Substances Hazardous to Health (COSHH) Regulations, exposure to RCS must now be reduced to as low as reasonably practicable. So, what control measures can be implemented to protect from RCS exposure?
There are a variety of preventative measures and procedures that can be implemented to protect against RCS. Here is a breakdown summary:
|- Use engineering controls such as enclosures, hoods and other types of Local Exhaust Ventilation (LEV)|
- Apply wet methods of cutting, chipping, drilling, sawing and grinding to eliminate or minimise dust creation
- Use a handheld cut-off saw with a water suppression attachment connected to a pressurised water container
- Douse equipment with water during the clean-up process and debris removal
- Avoid high pressure spraying, brushing and sweeping that could disturb silica dust
- Where engineering controls are not reasonably practicable, wear, store and maintain the correct Respiratory Protective Equipment (RPE) – an FFP3 disposable dust mask or half mask with P3 filters, all of which must be face-fit tested
- Replace seals and worn cutting discs when necessary
- Employ dust extraction equipment in dedicated workspaces
- Use covered chutes and skips/screening-off areas to prevent the spread of dust
- Create space for a dedicated, well-ventilated cutting area (control rooms, barriers and enclosures) and limit the number of people who can access the workspace
- Substitute silica-containing materials with a lower RCS content or eliminate silica-based substances completely
- Specify half or bespoke sized tile sizes from manufacturers at the building design stage as this may reduce the need for cutting.
According to the COSHH regulations, employers are legally required to prevent or, where not reasonably practicable, adequately control exposure to substances hazardous to health, which includes RCS. As a result, employers must implement effective control measures that are directly proportionate to the risk to health, all of which must be regularly monitored and maintained at all times. Employees who may come into contact with RCS must also be provided with sufficient training and information to ensure they are adequately protected against silica exposure.
Only a small amount of crystalline silica dust is required to contract respiratory conditions, which is why the HSE requires employers to monitor dust levels and ensure that exposures remain as low as reasonable practicable, while also being below the current WEL of 0.1 mg/m3 over an eight-hour TWA.
Employers are required to regularly monitor exposure levels in order to ensure that any control measures such as LEV or even RPE are working effectively. Exposure monitoring can be carried out with personal dust sampling equipment, and samples of respirable dust can then be further analysed for crystalline silica for the most accurate measure of exposure.
Where there is a risk that workers may develop silicosis and other respiratory conditions, employers are recommended to introduce health surveillance, which will allow for the early identification of occupational health effects and identification of appropriate control measures.