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Guide · Respirable crystalline silica
Respirable crystalline silica is the dust behind silicosis and lung cancer - and, because of engineered-stone worktops, it is harming workers faster and younger than it used to. This guide explains what RCS is, what the law requires, where the risk hides, and how to control and test for it.
The short version
Respirable crystalline silica is invisible, it is everywhere stone and concrete are worked, and it causes diseases that cannot be undone. For most of the last century the harm showed up slowly, over decades. Engineered-stone worktops have changed that - the dust is now disabling and killing workers within a few years of starting the job.
This guide is written for employers, managers and anyone responsible for people who cut, grind, drill, sand or polish stone, concrete, brick or manufactured stone. It covers what RCS actually is, the harm it does, what COSHH requires of you, where the risk is highest, and - the practical part - how to control the dust and prove your controls are working. It is general guidance; your own COSHH assessment, and the current HSE guidance, come first for your site.
What it is
Crystalline silica is one of the most common minerals on earth. It is a major part of sand, sandstone, granite, slate, flint and quartz, and it is built into the concrete, mortar, brick, tile and manufactured stone we work with every day. In solid form it is harmless. The danger appears the moment it is broken up.
Cutting, grinding, drilling, polishing or crushing these materials shatters the silica into dust across a whole range of particle sizes. Most of that dust is coarse enough to settle or to be trapped in the nose and throat. But a portion is respirable - fine enough, generally below about 4 to 5 micrometres, to be drawn past the body's defences and deep into the gas-exchange regions of the lung. That fine fraction is respirable crystalline silica, RCS, and it is what does the damage. It is invisible in ordinary lighting, so a bench, a cab or a workshop can look perfectly clean while the air is loaded with it.
The health risk
Once in the deep lung, RCS particles trigger inflammation and scarring that the body cannot clear or repair. The results are a group of serious, progressive and largely irreversible conditions:
Historically the harm was slow: decades of exposure before symptoms showed, often in men near or past retirement. Engineered stone has rewritten that timeline, producing accelerated silicosis in fabricators in their twenties and thirties. HSE describes silica as one of the biggest risks to construction workers' health after asbestos.
The law
Respirable crystalline silica is a substance hazardous to health, so it falls squarely under the Control of Substances Hazardous to Health Regulations (COSHH). In plain terms, the law requires you to:
The 0.1 mg/m3 figure is worth dwelling on. It is the point the law will not let you exceed - but HSE has estimated that significant numbers of workers exposed at that level across a working life could still develop silicosis, which is why the duty is to go as low as reasonably practicable, and why the limit is kept under review. Treat 0.1 as a line you stay well clear of, not one you aim for.
Where the risk is
The risk tracks two things: how much crystalline silica the material contains, and how much dust the task throws up. The silica content varies enormously between materials - which is why the same cutting task is far more dangerous on one material than another. The figures below are approximate and vary by source, but the pattern is what matters:
| Material | Approximate crystalline silica content |
|---|---|
| Engineered / artificial stone (quartz worktop) | up to ~95% |
| Sandstone, gritstone, flint | ~70-90%+ |
| Concrete and mortar | ~25-70% (variable) |
| Granite | ~20-45% (often cited ~30%) |
| Slate | ~20-40% |
| Brick | ~5-30% |
| Marble, limestone | ~2% (low) |
So the highest-risk activities are the ones that combine a high-silica material with a high-energy, dust-making process: cutting engineered-stone and sandstone, dry grinding and polishing, abrasive cutting of concrete and paving, demolition, and sanding of silica-bearing fillers and plasters. The industries that live with this daily are construction and demolition, stonemasonry and worktop fabrication, quarrying, brick and tile manufacture, pottery and ceramics, and foundries.
The emerging crisis
Engineered stone - the quartz composite sold for kitchen and bathroom worktops - is the reason silica is back at the top of the occupational-health agenda. Because it can be up to about 95% crystalline silica, fabricating it (cutting to size, mitreing, cutting sink holes, edge-polishing) releases RCS in quantities that dwarf natural stone. The consequence has been a wave of accelerated silicosis in young fabricators, and deaths, including of workers in their twenties and thirties.
HSE has responded with specific action. Its guidance Working engineered stone: control silica risk is a dedicated COSHH sheet for the sector, and its central message is blunt: no dry cutting. Dry fabrication can expose workers to five to ten times more RCS than wet methods using the same tools, so HSE's controls effectively rule dry cutting out unless a business can demonstrate an equally effective or better control. Alongside the guidance, HSE is running a nationwide programme of inspections of fabricators, with enforcement action for those who fall short. Internationally, the concern has gone further still - Australia banned the manufacture, supply and installation of engineered stone in 2024.
Controlling it
COSHH expects you to control exposure by working down a hierarchy, not by jumping straight to masks. In order of priority:
RPE matters, but it protects only the person wearing it, only while it is worn correctly, and only if it fits. The controls above it protect everyone in the area and do not depend on individual behaviour - which is why the law puts them first.
LEV and testing
Where you rely on local exhaust ventilation to control silica dust - on-tool extraction on a saw or grinder, a downdraught bench, a capture hood over a CNC machine - that LEV is a control measure under COSHH, and the law requires you to keep it working. In practice that means three things:
This is the point where a guide meets the real world. We have worked through exactly this on silica-cutting CNC machines - what the examination measures, what a pass and a fail look like, and what remedial actions follow - in a worked case study you can read alongside this guide.
Watching for harm
Controls can drift, and people can be exposed without any outward sign, so COSHH expects two kinds of checking where the risk is real:
Air (personal) monitoring measures the RCS in a worker's breathing zone over a shift and compares it with the 0.1 mg/m3 WEL. It tells you whether your controls are genuinely holding exposure down, and it is the evidence an inspector will look for. It is not a one-off: repeat it when the work, the materials or the controls change.
Health surveillance aims to catch the early effects of exposure while something can still be done. Following HSE guidance, it typically involves a respiratory questionnaire, lung-function testing (spirometry) and, where indicated, a chest assessment, carried out at suitable intervals by a competent provider. For higher-risk work - stone-worktop fabrication and installation in particular - HSE specifically expects health surveillance to be in place, and has updated its guidance to name those occupations.
What good looks like
If you want a quick test of whether silica is under control in your workplace, work through these:
If any of those is a "no", that is where your exposure - and your liability - is sitting right now.
In short
Silica dust is a solved problem in principle and an unsolved one in too many workplaces. The disease is terrible and permanent; the controls - substitution, water, extraction, RPE, monitoring and surveillance - are well understood and effective. What goes wrong is almost always a control that was never fitted, has quietly stopped working, or is trusted without being tested. Engineered stone has raised the stakes and HSE's patience with dry cutting has run out.
If your work involves cutting, grinding or polishing stone, concrete or manufactured stone, the two questions worth asking today are: do we actually know what our people are breathing, and can we prove our extraction works? Those are questions a COSHH assessment, air monitoring and a proper LEV examination answer - and they are a great deal easier to face now than after someone's lung-function test comes back wrong.
Sources and further reading
The duties, exposure limits and control standards described here come from the Health and Safety Executive. For your own process, always work from the current HSE guidance:
Questions
Crystalline silica is a natural mineral found in stone, sand, concrete, brick and many manufactured stone products. When those materials are cut, ground, drilled or polished, they release a fine dust. The respirable fraction - the particles small enough to be breathed deep into the lungs, generally under about 4 to 5 micrometres - is respirable crystalline silica, or RCS. It is far too fine to see in normal light, which is part of why it is so dangerous: a workplace can look clean while the air is full of it.
The workplace exposure limit (WEL) for respirable crystalline silica in Great Britain is 0.1 mg/m3 averaged over an 8-hour working day, set out in HSE guidance note EH40. That is a legal ceiling, not a target - COSHH requires exposure to be reduced so far below it as is reasonably practicable. HSE has estimated that even at the current limit a meaningful proportion of workers exposed over a working lifetime could develop silicosis, and the limit is periodically reviewed, so the sensible approach is to drive exposure as low as you reasonably can rather than aim for the number.
Construction and demolition (cutting paving, blocks, concrete and mortar), stonemasonry and stone-worktop fabrication, quarrying, brick and tile making, pottery and ceramics, foundries, and anyone sanding fillers or plaster. HSE describes silica as one of the biggest risks to construction workers' health after asbestos. The newest and sharpest concern is the fabrication and installation of engineered (artificial) stone worktops, where the silica content is extreme.
Engineered or artificial stone - the quartz composite used for kitchen worktops - can contain up to about 95% crystalline silica, against roughly 30% for granite and only a couple of per cent for marble. Cutting and polishing it releases enormous quantities of RCS, and dry cutting can produce five to ten times more than wet methods. The result has been accelerated silicosis in fabricators in their 20s and 30s, and deaths. HSE has issued specific COSHH guidance for engineered stone, is running a nationwide inspection campaign, and makes clear that dry cutting is effectively ruled out unless an equally effective control is proven.
Work down the hierarchy. First eliminate or substitute - choose a lower-silica material where you can. Then control the dust at source with water suppression and on-tool or fixed local exhaust ventilation (LEV). Keep the workplace clean without raising dust (no dry sweeping or compressed air). Only then rely on respiratory protective equipment (RPE) as the last line, with the right protection factor and face-fit testing. Back it all with a COSHH assessment, training and, where needed, air monitoring and health surveillance.
Where there is a real risk of exposure, yes to both in principle. Air (personal) sampling measures what workers actually breathe against the 0.1 mg/m3 limit and tells you whether your controls work - a visual check cannot. Health surveillance, following HSE guidance, typically involves a questionnaire, lung-function testing (spirometry) and sometimes a chest assessment, to catch early signs of harm while something can still be done. For higher-risk work such as stone-worktop fabrication, HSE specifically expects health surveillance.
Tell us your capture points and the process they control, and we will quote the thorough examination and test to COSHH and HSG258.
