Safety is vital in quarries and cement plants and dust inhalation can be a major problem. Responsible quarries are taking notice of HSE guidance and implementing dust suppression systems to reduce risks associated with Respirable Crystalline Silica (RCS). The European guidance document - "Good Practice Guide on Workers’ Health Protection through the Good Handling and use of Crystalline Silica and products containing it", made a significant impact on raising awareness of the issue of RCS and its impact on workers. Does your workplace comply with the exposure limits for RCS? What does it take for a dust reduction programme to be successful?
What is Respirable Crystalline Silica (RCS)?
RCS is found in varying proportions in stone, rocks, sands and clays. Exposure to RCS over time has been found to cause hardening of the lung tissue, leading to impairment of lung function. This is known as Silicosis, which is characterised by a severe shortness of breath causing sufferers to sometimes find it difficult even to walk short distances. The condition is so debilitating that it continues to worsen even after exposure has stopped - and it is irreversible. A link has also been proven between exposure to silica and the occurrence of lung cancer. Anyone with silicosis also has an increased risk of contracting a range of other diseases, including kidney inflammation, tuberculosis and arthritis.
Different types of stone contain varying levels of silica – ranging from sandstone, which is almost pure quartz at 70% to limestone and chalk at around 2%.
What are the exposure limits for RCS?
As well as being compliant with the EU guidance, quarries also need to operate within the specific requirements of the Control of Substances Hazardous to Health (COSHH) Regulations 2002.
In the UK, the workplace exposure limit (WEL) for RCS is 0.1 mg/m3 – which is expressed as an eight hour time weighted average (TWA). The Workplace Exposure Limit (WEL) applies only to the respirable fraction of the silica dust. This means the portion of dust that reaches the deepest parts of the lungs – which is said to be around 10-20% of the total inhalable dust. In industries such as limestone, where silica content is low, exposure levels to RCS may well be below the WEL. However, the quarry still needs to ensure that the amount of inhalable dust does not exceed 10 mg/m3 over an eight hour period and exposure to respirable dust should not exceed 4 mg/m3.
Anyone operating or managing a quarry is required, under guidance from the Health and Safety Executive to reduce the exposure of staff, contractors and those living close to a plant with silica dust generated by their operations.
Exposure to RCS is governed by the following factors:
- the proportion of silica in the material,
- the mechanical work involved in breaking up or processing the material,
- the work patterns influencing when and how individuals may be exposed.
Risk assessments should be carried out for each job or range of tasks. This includes:
- identifying the potential for exposure to RCS,
- measuring the effectiveness of existing dust control systems,
- ensuring use of respiratory protective equipment,
- maintaining and regularly inspecting any control systems in place to ensure effective operation.
Regulation 7 of COSHH requires that employers have a duty of care to prevent exposure of employees to RCS, or to ensure this is adequately controlled.
The smaller the dust particle size, the more hazardous.
Dust particle size is measured in microns and is typically of a size between 50-70 microns.There are, of course, dust particles larger than this (which tend to settle in the immediate vicinity of whatever is generating the dust), and dust particles smaller than this. It has been shown that dust particles of 20 microns or less can remain airborne for a very long time and can find their way onto and into machinery, into lungs, and also into areas outside of the mine itself.
Dust particles less than 10 microns in size are invisible to the naked eye and can remain suspended in the air indefinitely. Generally, the smaller the particle size, the more hazardous it is to health and equipment. Also the smaller the particle size the harder it is to remove from the atmosphere.