How do you control silica dust on a building site?
Respirable crystalline silica (RCS) is the fine dust made when you cut, drill, chase or grind concrete, brick, stone and similar materials. It causes silicosis, lung cancer and COPD, so HSE expects you to stop it reaching the air with water or extraction, and to add a mask on the dustiest jobs.
Where it comes from
Silica is in most rocks, sand and clay. HSE gives these rough shares: sandstone over 70%, concrete and mortar 25% to 70%, shale 40% to 60%, slate up to 40%, brick and granite up to 30%. Limestone, chalk and marble are low, up to 2%, though they can contain silica layers.
Cutting, drilling, grinding and polishing these materials makes dust. The part that does the harm is fine enough to get deep into your lungs and too fine to see in normal light, so a job can look clear and still be dusty. HSE's high-dust examples include cut-off saws on kerbs, blocks, paving and roof tiles, wall chasing and raking out mortar, scabbling, grinding, drilling and dry sweeping.
What it does to you
HSE links RCS to three main diseases.
- Silicosis. Scarring of the lung that causes severe breathlessness. It is irreversible and carries on developing after exposure stops.
- Lung cancer. HSE says heavy and prolonged exposure can cause it.
- COPD (chronic obstructive pulmonary disease). Chronic cough, phlegm and breathlessness, and a leading cause of death.
HSE says silica is the biggest risk to construction workers after asbestos, and estimates it may be responsible for the deaths of over 500 people a year who have worked in construction. Silicosis usually follows years of exposure, though very high exposure can cause acute silicosis more quickly.
The exposure limit
The workplace exposure limit for RCS is 0.1 mg/m3, averaged over 8 hours. COSHH is the law that covers it. It is a tiny amount of dust, and HSE's own measurements show how fast it can be passed: dry brushing concrete dust gave short peaks of around 1 to 2 mg/m3, and uncontrolled chasing gave peaks of around 5 mg/m3.
Controls, in HSE order
COSHH requires you to assess the risk, control it and review the controls. HSE guidance sets out how:
- Cut the dust at source. Order the right size of material, use a block splitter instead of a cut-off saw, or fix directly instead of drilling.
- Water. It has to be supplied properly for the whole time the work is done. Wetting the material beforehand does not work.
- On-tool extraction. Use an H or M class extraction unit, not a general-purpose vacuum cleaner.
- A mask as well, for high-risk tasks. HSE says a cut-off saw, grinder or wall chaser on silica-bearing material needs respiratory protective equipment (RPE) with an assigned protection factor of 20, such as an FFP3 disposable mask or half mask with a P3 filter. Tight-fitting masks need a face-fit test and a clean-shaven face. HSE says RPE is the last line of protection, so if you rely on it alone, be ready to justify why.
HSE also says to check extraction every week and to have it thoroughly examined and tested at least every 14 months.
Cleaning up
Dry sweeping puts settled silica dust back in the air, so HSE says to avoid it. For small amounts, damp down and use a brush, shovel and bucket. For regular site cleaning use a water spray, or vacuum attachments on an H or M class unit. HSE says to wear RPE with a protection factor of 20 where the location, duration and type of work call for it.
Health surveillance and training
HSE says health surveillance must be provided to workers who are regularly exposed to RCS where silicosis could reasonably develop, and that you should consider it for construction work. HSE suggests getting advice from an occupational health professional on the programme.
Train people on the dust risk, how to use and check the controls, and how to fit, use and look after their masks.