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Case study · Stone fabrication · Respirable silica
Three CNC machines cut engineered-stone worktops for dental surgeries. The dust they produce is respirable crystalline silica - one of the most dangerous substances in British industry right now, and the subject of a live HSE crackdown. This examination did not pass the system. Here is why, and what had to change.
The site
The factory fabricates worktops and surfaces for dental and clinical settings, where a hard, non-porous, hygienic finish is the whole point. The material is engineered stone - quartz and resin composite - cut and profiled on three CNC machines. It is exactly the product, and exactly the process, that the HSE has spent the last two years warning about.
Engineered stone looks and behaves like a premium natural material, but it carries a hidden hazard: it can be more than 90% crystalline silica, far higher than granite or most natural stone. When it is cut, ground or polished, it releases respirable crystalline silica (RCS) - the fine dust fraction that reaches deep into the lung and causes silicosis, lung cancer and other irreversible disease. Young fabricators abroad have developed advanced, life-shortening silicosis after only a few years of dry cutting this material.
The three CNC machines were fitted with water suppression, and the business brought us in to examine the LEV that backs it up. The brief was straightforward on paper and serious in practice: confirm that the extraction controlling residual silica dust actually works, against a limit that leaves almost no margin for error.
The hazard and the law
The workplace exposure limit for RCS is 0.1 mg/m³ as an 8-hour average - one of the lowest limits in the regulations, set that low because the dust is so damaging. Dry cutting of engineered stone can blow past it many times over; HSE research found dry fabrication produces exposures five to ten times higher than wet methods using the same tools.
This is not a quiet corner of health and safety. In May 2026 the HSE published its first dedicated COSHH guidance for engineered stone, sheet ST3A, which in effect rules out dry cutting unless an employer can prove an equally effective or better control. The regulator is running more than a thousand inspections of stone fabricators across Great Britain and has already issued prohibition notices for dry cutting without on-tool water suppression, inadequate mist control, missing respiratory protection and failures in health surveillance. For a fabricator, the expected standard is now wet cutting plus working LEV, enclosure, good housekeeping, RPE and health surveillance - all of it, not some of it.
What we tested
Water suppression and LEV are complementary, not interchangeable. The water knocks dust down at the cutting edge; the LEV is there to capture the respirable dust that water never catches - from dry handling, chipping, edge dressing, blade changes and clean-down. So our examination focused on the extraction: capture velocity at each machine's hoods and enclosure, the condition of ducting and filters, the discharge arrangement, and whether any airflow indication existed to warn operators if extraction dropped.
We also assessed the process as a whole, because an LEV examination on a silica job that ignored housekeeping and dry handling would be missing the point. Settled silica dust is not inert - it becomes airborne again every time it is disturbed, swept or walked through - so how the factory dealt with accumulated dust was directly relevant to the exposure the LEV was supposed to control.
What we found
| Check | Finding | Result |
|---|---|---|
| On-tool water suppression | Operating at the cutting point | OK |
| LEV capture at CNC enclosures | Weak - dust escaping during dry edge work and handling | Fail |
| Housekeeping / settled dust | Dry dust built up on surfaces and floor; swept, not vacuumed | Fail |
| Airflow indication | None fitted - no warning if extraction drops | Fail |
| Discharge / filtration | Filtration stage requiring attention | Fail |
The water suppression did its job, but the system around it did not add up to control. Capture at the machines was too weak to catch the silica released during dry handling and edge work; accumulated dust was being swept rather than vacuumed, putting RCS straight back into the air; there was no airflow indication to flag a drop in extraction; and the filtration stage needed attention. Against a 0.1 mg/m³ limit, that combination is not a near miss - it is a system that cannot be relied on to protect the people working on it. The outcome was not compliant, with urgent remedial works required.
The remedial actions
With silica, remedials are not a wish-list - they are the price of continuing to operate the process lawfully. The priority actions were:
The outcome and the wider point
The examination gave the business a clear, prioritised path from "not compliant" to a controlled, defensible process - and, just as importantly, an honest picture of how far short a busy-looking system can fall. The water suppression had created a false sense of safety; the measurements showed the residual dust was not being controlled.
Engineered stone is the asbestos story of our time, and regulators here and abroad are treating it that way - Australia has banned the material outright. If you cut, grind or polish it, the expectation is now unambiguous: wet-cut everything, never dry-cut, keep the LEV examined and tested every 14 months and actually working, vacuum rather than sweep, provide fit-tested RPE, and put your people under health surveillance. A thorough examination is the instrument that tells you whether your controls are real or just reassuring - and with inspectors actively visiting this sector, finding out from a test is far better than finding out from a notice, or from a silicosis diagnosis years down the line.
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
Respirable crystalline silica (RCS) is the fine fraction of silica dust small enough to reach deep into the lungs. Breathing it causes silicosis - irreversible scarring of the lung - as well as lung cancer and other disease. Engineered or 'artificial' stone is especially hazardous because it can be more than 90% silica, far higher than most natural stone, and cutting it dry releases enormous quantities of RCS.
The workplace exposure limit for respirable crystalline silica is 0.1 mg/m³ as an 8-hour time-weighted average. It is a very low limit precisely because the dust is so harmful, and dry cutting of engineered stone can exceed it many times over. HSE's own research found dry fabrication gives exposures five to ten times higher than wet methods.
In practice, no. In May 2026 the HSE published COSHH guidance (sheet ST3A) that effectively rules out dry cutting of engineered stone unless an employer can demonstrate a control that is equally effective or better - which is a very high bar. HSE is carrying out over a thousand inspections of fabricators and has issued prohibition notices for dry cutting without on-tool water suppression. Water suppression plus LEV, enclosure and RPE is the expected standard.
Because water suppression and LEV do different jobs and neither is complete on its own. Water knocks down dust at the cutting point, but handling, dry edges, chipping, dressing and clean-down still release RCS, and LEV is what captures what the water misses. The examination checks that the extraction is genuinely controlling that residual dust - and in this case it was not.
It can look busy and still fail. Here the water suppression was working but the LEV capture at the machines was weak, dust was escaping during dry handling and edge work, housekeeping had let settled dust build up (which becomes airborne again when disturbed), and there was no reliable airflow indication. Against a 0.1 mg/m³ limit, those gaps matter enormously.
Treat silica as the serious carcinogen it is: wet-cut everything, keep engineered stone dry-cutting off the table, make sure LEV capture is examined and tested every 14 months and actually works, enforce housekeeping with H-class vacuums rather than sweeping, provide proper RPE, and put workers under health surveillance. With HSE actively inspecting this sector, getting the LEV examined and the gaps closed is both a legal duty and a sensible move.
Tell us your capture points and the process they control, and we will quote the thorough examination and test to COSHH and HSG258.
