Silica Dust: Exposure Limits, Masks and Controls

Summary

Respirable crystalline silica is the second-biggest cause of occupational lung disease in UK construction after asbestos. HSE estimates more than 500 construction workers die each year from silica-related disease — silicosis, lung cancer, COPD and accelerated kidney disease. Unlike asbestos, the risk is not historical: every brick cut, every chase chased into block, every kerb cropped on site produces RCS today.

Most tradespeople underestimate it because the visible dust cloud is not the danger. The respirable fraction — particles under 4 microns — is invisible. By the time you can see a haze around a cut-off saw, RCS levels are typically 10-100x the WEL. Symptoms can take 10-20 years to appear, which is why workers in their 20s and 30s feel invincible and workers in their 50s end up on long-term oxygen.

Anyone cutting, drilling, grinding, chasing or breaking silica-containing materials (concrete, mortar, brick, block, natural stone, sandstone, granite, slate, porcelain tile, fibre cement, engineered stone worktops) needs to know the WEL, the control hierarchy, and the right RPE. Engineered quartz worktops are the highest-risk material currently in widespread use — Australia banned them in 2024 and the UK is consulting on the same.

Key Facts

Exposure limit and the law

• Workplace Exposure Limit (WEL) — RCS is 0.1 mg/m³ as an 8-hour Time-Weighted Average, published in HSE's EH40 Workplace Exposure Limits document
• No safe level — the WEL is a legal maximum, not a "safe" target. HSE explicitly states exposure should be reduced "as low as reasonably practicable" (ALARP) below the WEL
• COSHH Regulations 2002 — make the employer legally responsible for assessing, controlling and monitoring exposure to RCS
• CLAW does not apply — Control of Asbestos Regulations 2012 cover asbestos, not silica. Silica sits under COSHH only
• RIDDOR reportable — silicosis is a reportable occupational disease under RIDDOR 2013 (Schedule 1) where a doctor diagnoses it in someone whose current job involves significant RCS exposure

Tasks that generate RCS

• Highest risk — dry cutting kerbs, paving slabs, blocks or engineered stone with a petrol saw; dry chasing walls; abrasive blasting; tunnelling/mining
• High risk — dry cutting tiles with an angle grinder, dry diamond drilling, demolition of masonry, breaking up concrete with a kango/breaker
• Medium risk — wet cutting without proper water flow, mixing dry mortar/render, sweeping up debris (resuspension)
• Lower risk — wet cutting with adequate water suppression, on-tool extraction with M-class vacuum, handling intact masonry

Control hierarchy (in order — try the top first)

• Eliminate — pre-cut materials off site; order purpose-made lintels rather than cutting on site; use mechanical breakers instead of cut-and-chase
• Substitute — silica-free abrasives for blasting (e.g. olivine, garnet, slag); polymer-modified mortars where appropriate
• Engineering controls — water suppression (wet cutting), on-tool LEV with M-class vacuum (must be CE-marked HEPA H13 for RCS), enclosed cabinets for stone-cutting workshops
• Administrative — rotate workers, restrict access, schedule dusty work when others are off site
• PPE/RPE — fit-tested FFP3 mask or powered air respirator, eye protection, washable overalls. RPE is the last line of defence, not the first

Respiratory Protective Equipment (RPE)

• FFP1 — APF (Assigned Protection Factor) 4. Not adequate for RCS under any circumstance
• FFP2 — APF 10. Inadequate for most cutting/grinding tasks. Only use where measured exposure is below 1 mg/m³
• FFP3 — APF 20. Minimum for cutting, grinding, drilling, chasing silica-containing materials. Disposable, must be changed at end of shift or when damp
• Half-mask reusable with P3 filter — APF 20. Suitable where FFP3 disposable would degrade rapidly (long shifts, hot conditions)
• Powered air-purifying respirator (PAPR) with TH3 hood — APF 40. Required for high-exposure tasks (engineered stone fabrication, demolition, abrasive blasting), or where face-fit cannot be achieved (beards)
• Face fit testing — legally required under HSE OC282/28 for all tight-fitting RPE (FFP3, half-mask, full-face). Must be repeated when the wearer's face changes (weight change, dental work) or the RPE model changes. Beards, stubble or even a day's growth will void the seal

Health surveillance

• Statutory requirement — under COSHH Reg 11 where exposure to RCS is significant. Annual lung function test (spirometry) and respiratory questionnaire by an Occupational Health professional
• Chest X-ray — typically every 3 years for high-exposure workers; baseline on starting silica-exposed work
• Records — must be kept for 40 years from date of last entry

Quick Reference Table

Detailed Guidance

Water suppression

The cheapest and most effective control for cutting tasks. Water binds the dust at source before it becomes airborne. A 0.5 L/min flow rate at the blade is the HSE benchmark for floor saws and disc cutters. Below 0.3 L/min the dust break-through is significant.

Practicalities: many saws are sold with token water connections that produce a dribble. Retrofit a pump-fed reservoir (5 L pressure bottle from a hire shop, around £40-£70) or mains feed where available. Check the spray pattern hits the blade, not the ground beside it. In freezing conditions, add automotive screen wash to prevent the line freezing.

Water creates slurry, which must be cleaned up wet (squeegee + wet vacuum) — never let it dry and re-suspend. Dispose of slurry as construction waste, not down a drain (silica slurry blocks gullies and breaches Water UK trade-effluent rules).

On-tool extraction (LEV)

Required where water cutting is impractical (indoors, on finished surfaces, near electrics, in cold weather). Use a HSE-approved on-tool shroud matched to the tool, connected to an M-class dust extractor minimum (H-class for very high-risk work). L-class vacuums are not adequate for RCS — the filter does not retain the respirable fraction.

Key checks:

• M-class vacuum has an audible airflow alarm — listen for it
• Hose diameter matches the shroud (typically 32 mm or 35 mm)
• Filter is HEPA H13 or better
• Empty/change the pre-filter bag before it's full; flow drops dramatically when 75% full
• LEV system needs a thorough examination and test (TExT) every 14 months under COSHH Reg 9

Face fit testing

The single most common compliance failure. A FFP3 mask achieves an APF of 20 only if it seals to the wearer's face. Face fit testing — qualitative (Bitrex/saccharin spray hood) or quantitative (PortaCount) — is a legal requirement before the mask is first used.

Common failures:

• Beard, stubble or sideburns crossing the seal — even 24 hours' growth fails the test
• Wrong size mask (manufacturers offer S/M/L — most workers default to M when they need L)
• Strap configuration ignored — upper strap at crown of head, lower strap below ears, both tightened evenly
• Damaged or deformed mask reused from previous shift

Where face fit cannot be achieved (e.g. religious beard requirements, scarring, dental work), provide a powered air respirator (PAPR) with a loose-fitting hood — these do not need a face seal.

See also coshh assessment for the wider COSHH risk assessment template, and face fit testing for fit-test procedure.

Engineered stone (quartz worktops)

Engineered stone contains 90-95% crystalline silica, compared with 30% for granite and 5% for marble. Fabrication generates extreme RCS levels and has caused an epidemic of accelerated silicosis in young workers worldwide — workers in their 20s presenting with end-stage lung disease.

Australia banned engineered stone in 2024. The UK HSE is actively consulting on additional controls and has issued targeted enforcement campaigns against worktop fabrication workshops. If you fabricate engineered stone:

• Segregated, wet-only cutting area
• LEV at every workstation
• Powered TH3 hood RPE minimum
• 6-monthly health surveillance (not annual)
• Air monitoring records maintained

Domestic installers (who only template, deliver and fit pre-cut tops) have much lower exposure but should still wear FFP3 when making site cuts and use on-tool LEV.

Common mistakes

• "It's only a few cuts" — RCS exposure is cumulative across the shift. Five 30-second cuts at 50 mg/m³ each equals 4.2 mg/m³ over the 8-hour TWA — 42x the WEL
• Using FFP2 because "FFP3 is uncomfortable" — FFP2 only filters 94% of particles; FFP3 filters 99%. The difference is one order of magnitude of dose
• Sweeping up at end of shift — re-suspends accumulated dust into the workers' breathing zone. Vacuum with M-class or wet sweep only
• Reusing FFP3 masks across multiple shifts — disposable means disposable. Filter loads up, seal deforms, mask becomes damp
• No face fit because "the boss said it's fine" — the boss is the duty holder, not a fit-test competence
• Sharing RPE between workers — hygienically poor and the fit will not be the same

Regional and contract notes

Tier 1 contractors (Skanska, Balfour, Mace, Wates) now require evidence of face-fit certification, COSHH RA and TExT certificate before allowing tools onto site. Many have moved to "no dust on site" policies that require water suppression as default, with on-tool LEV as the alternative. Domestic refurb work often has no such oversight — but the legal duty under COSHH still applies whether you have a site manager checking or not.

Frequently Asked Questions

Is FFP3 enough on its own without water or LEV?

No. RPE is the last line of defence under the COSHH hierarchy. HSE will issue improvement notices to anyone relying on RPE alone when water suppression or LEV is reasonably practicable. The legal test is whether you've controlled exposure ALARP — and a £40 water bottle on a cut-off saw is always ALARP.

Do I need a COSHH assessment for cutting one slab in a customer's garden?

Yes — COSHH applies regardless of job size. For very small, infrequent tasks the assessment can be a short generic document, but it must identify the substance (RCS), the exposure route, the control measures and the RPE. HSE has a free template at hse.gov.uk/coshh.

How do I get face fit tested?

Use a Fit2Fit accredited tester (search at fit2fit.org). Typical cost £25-£50 per person for qualitative test, £60-£100 for quantitative. Brings own tester to site for groups of 5+. Certificate valid for 2 years or until face changes.

Is silicosis curable?

No. Silicosis is permanent scarring of the lung tissue. Treatment can slow progression and manage symptoms but cannot reverse damage. This is why the entire regulatory framework focuses on prevention — by the time symptoms appear, the damage is done.

Does an L-class vacuum work for silica?

No. L-class is rated for "low hazard" dust only and the filter passes respirable particles. M-class is the legal minimum for silica. H-class is required for asbestos and some other high-toxicity dusts.

Regulations & Standards

• Control of Substances Hazardous to Health Regulations 2002 (COSHH) — duty to assess, control and monitor RCS exposure

• EH40/2005 Workplace Exposure Limits — sets the WEL of 0.1 mg/m³ for RCS (most recent revision; check HSE for current edition)

• HSG258 Controlling Airborne Contaminants at Work — HSE design guidance for LEV systems

• BS EN 149 — performance standard for FFP1/FFP2/FFP3 filtering facepieces

• BS EN 12942 — performance standard for powered respirators

• HSE OC282/28 — face-fit testing guidance

• Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 2013 (RIDDOR) — silicosis is reportable under Schedule 1

• Construction (Design and Management) Regulations 2015 (CDM) — silica control is a designer and principal contractor duty during planning, not just at site

• HSE: Construction dust — primary HSE silica hub

• HSE EH40/2005 Workplace Exposure Limits — current WEL publication

• HSE HSG258 Controlling Airborne Contaminants at Work — LEV design guidance

• Fit2Fit register of accredited face-fit testers — find a tester

• BOHS guidance on silica in construction — British Occupational Hygiene Society resources

• HSE Construction Dust Partnership — industry-led resources and toolbox talks

• coshh assessment — how to write a compliant COSHH risk assessment

• face fit testing — qualitative and quantitative fit-test procedure

• asbestos awareness — separate but related lung hazard

• render types — render mixing dust risks