COSHH · Mandatory · Pre-Construction

COSHH Assessment — Silica Dust

This COSHH assessment addresses respirable crystalline silica (RCS) dust generated by cutting, drilling, and grinding concrete, stone, brick, and morite. Silica exposure can cause silicosis, lung cancer, and COPD. The workplace exposure limit is 0.1 mg/m3 and control measures must include water suppression, on-tool extraction, and RPE where limits may be exceeded.

Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. COSHH Regs 2002 / WEL remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.

RCS WEL	Respirable crystalline silica workplace exposure limit is 0.1 mg/m3 (8-hour TWA) — 40 times lower than the general respirable dust WEL of 4 mg/m3
High-risk tasks	Dry cutting concrete, block, stone or brick; scabbling; chasing; mixing dry cementitious products; drilling masonry; abrasive blasting with silica-containing media
Silicosis	Incurable, progressive and irreversible fibrotic lung disease caused by inhaling respirable crystalline silica. No effective treatment once established
HSE enforcement	Warmsworth Stone fined £18,000 for silica failures; Esken Ltd fined £160,000 after worker developed silicosis. HSE treats silica as a priority enforcement topic
Health surveillance	Required for all workers regularly exposed to RCS. Updated G404 guidance issued March 2025 sets out spirometry and respiratory questionnaire requirements
Enforcing authority	Health and Safety Executive (HSE)

1. What Is Respirable Crystalline Silica?

Respirable crystalline silica (RCS) is the fraction of airborne silica dust that is small enough to penetrate deep into the lungs and reach the gas-exchange region of the alveoli. Crystalline silica occurs naturally in most types of stone, rock, sand, gravel and clay. On construction sites, it is present in concrete, morite, brickwork, blockwork, natural stone, sandstone, granite, engineered stone, grout, render and many other common materials. When these materials are cut, ground, drilled, scabbled, blasted or otherwise mechanically disturbed, fine dust is generated — and a proportion of that dust is respirable crystalline silica.

The workplace exposure limit for RCS is 0.1 mg/m3 measured as an 8-hour time-weighted average. This is 40 times lower than the general respirable dust WEL of 4 mg/m3, reflecting the extreme toxicity of crystalline silica to lung tissue. At concentrations commonly generated by dry cutting, drilling or scabbling on construction sites, the WEL can be exceeded within minutes. This is not a marginal exposure — uncontrolled dry cutting of concrete or stone generates RCS concentrations that are typically 10 to 50 times the WEL.

Inhaling RCS over time causes silicosis — a progressive, incurable fibrotic disease of the lungs in which scar tissue replaces healthy lung tissue, progressively reducing lung capacity. Silicosis is irreversible: once the damage is done, it cannot be repaired, and in many cases the disease continues to progress even after exposure has ceased. Acute silicosis can develop after very high short-term exposure. Chronic silicosis typically develops after 10 to 30 years of exposure but can appear sooner at higher exposure levels. RCS exposure also increases the risk of lung cancer and has been classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC).

Silicosis has no cure — prevention is the only option

Once silicosis develops, there is no treatment that can reverse the fibrosis. The disease is progressive and can continue to worsen even after all exposure has stopped. Workers diagnosed with silicosis face a lifetime of declining lung function, increasing breathlessness, and significantly reduced life expectancy. The only effective intervention is to prevent exposure from occurring in the first place. This is why the HSE treats silica control failures with such seriousness — every failure is a potential future case of incurable disease.

Construction is the industry sector with the highest number of silicosis cases in the UK. The HSE estimates that around 500 construction workers die each year from silica-related diseases, including silicosis and lung cancer. Despite decades of awareness, enforcement data shows that control failures remain widespread. Common failings include dry cutting without water suppression or LEV, inadequate RPE selection, absence of health surveillance, and a persistent cultural attitude that visible dust clouds are a normal and acceptable part of construction work. They are not.

2. Control Hierarchy for Silica

COSHH Regulation 7 requires exposure to be prevented or, where prevention is not reasonably practicable, adequately controlled. For RCS, the hierarchy of control must be applied rigorously and in order. The following table sets out each level of the hierarchy with specific application to silica dust on construction sites.

Hierarchy level	Application to silica	Practical examples
Eliminate	Remove the need to cut, drill, grind or scabble silica-containing materials on site	Use pre-cast, pre-cut or factory-finished components; specify off-site fabrication; design out the need for on-site cutting by using modular systems or accurate setting-out
Substitute	Replace high-silica materials with lower-silica alternatives where practicable	Use calcium silicate blocks instead of dense concrete blocks; specify diamond wire cutting instead of abrasive disc cutting; use non-silica abrasive blasting media
Enclose	Contain the dust at source so it cannot enter the worker's breathing zone	Enclosed cutting stations with integral extraction; enclosed scabbling equipment; sealed blasting cabinets for small components; use walk-behind saws with integral water and vacuum systems
Local exhaust ventilation (LEV)	Capture dust at the point of generation before it disperses into the air	On-tool extraction connected to an H-class vacuum; dedicated LEV hoods positioned at the cutting or drilling point; slot extraction at bench-mounted cutting stations. LEV must be examined and tested by a competent person at least every 14 months under COSHH Regulation 9
Water suppression	Wet the material at the point of cutting, drilling or grinding to prevent dust becoming airborne	Integrated water supply on disc cutters, floor saws, and wall saws; water-fed drilling systems; water misting at the point of scabbling or breaking. Water must reach the cutting point, not just the general area. Note: water suppression reduces but does not eliminate RCS — it must be used in combination with other controls
RPE (respiratory protective equipment)	Protect the individual worker when higher-level controls cannot reduce exposure below the WEL	Minimum FFP3 disposable mask (APF 20) for short-duration tasks with other controls in place; powered air-purifying respirator (APF 40) for extended tasks; full-face air-fed mask for abrasive blasting. RPE must be face-fit tested for the individual wearer. RPE is the last resort, not the first choice

Water suppression and LEV together — not one or the other

For tasks such as cutting concrete, block or stone with a disc cutter, the HSE expects to see water suppression AND on-tool extraction used together, not one as an alternative to the other. Water suppression alone reduces airborne dust significantly but does not eliminate it. On-tool LEV alone can be overwhelmed by the volume of dust generated by high-energy cutting. Used in combination, water suppression knocks down the bulk of the dust and LEV captures the residual fine fraction, achieving exposure levels that are consistently below the WEL. Specifying either control in isolation is unlikely to demonstrate adequate control under COSHH Regulation 7.

Health surveillance is a legal requirement under COSHH Regulation 11 for all workers who are regularly exposed to RCS. The updated G404 guidance (March 2025) sets out the requirements for health surveillance, which include a baseline respiratory questionnaire and spirometry before first exposure, followed by periodic reviews at intervals determined by the occupational health professional — typically annually. The purpose of health surveillance is early detection: identifying the first signs of silicosis or impaired lung function so that the worker can be removed from further exposure before irreversible damage progresses.

Air monitoring should be carried out to validate that controls are working and that exposure is below the WEL. The HSE recommends that air monitoring is carried out when a new process is introduced, when controls are changed, or when there is any reason to suspect that the WEL may be exceeded. Personal sampling using a Higgins-Dewell cyclone sampler worn in the worker’s breathing zone is the standard method. Samples are analysed for RCS content by X-ray diffraction. Results must be recorded and retained for 40 years.

3. Common Mistakes

Using FFP1 or FFP2 masks for silica exposure

FFP1 masks provide an assigned protection factor (APF) of 4, and FFP2 masks an APF of 10. Neither is adequate for RCS exposure, which requires a minimum of FFP3 (APF 20). Even FFP3 disposable masks are only suitable for short-duration tasks where other controls (water suppression, LEV) are also in place. For extended cutting, drilling or scabbling tasks, a powered air-purifying respirator (PAPR) with an APF of 40 or higher should be specified. Every RPE must be face-fit tested for the individual wearer — an untested FFP3 mask provides an unknown and potentially negligible level of protection.

Dry cutting concrete, block or stone with no water suppression or LEV

Dry cutting silica-containing materials with a disc cutter, angle grinder or chop saw generates RCS concentrations that are typically 10 to 50 times the workplace exposure limit within the first few minutes of cutting. This is the single most common silica control failure on UK construction sites and is treated as a serious breach by HSE inspectors. The HSE can and does serve prohibition notices on the spot for dry cutting without controls. There is no acceptable justification for dry cutting silica-containing materials without water suppression and on-tool extraction.

No health surveillance programme for silica-exposed workers

COSHH Regulation 11 requires health surveillance for all workers who are regularly exposed to substances with identifiable disease endpoints — and silicosis is a clearly identifiable disease caused by RCS exposure. Failure to provide health surveillance means that early signs of silicosis will not be detected, and workers will continue to be exposed until the disease has progressed to a stage where it produces symptoms — by which time irreversible damage has already occurred. Health surveillance must include baseline spirometry and a respiratory questionnaire before first exposure, with periodic reviews as specified in the updated G404 guidance.

Treating fine dust as acceptable because it is not visibly thick

Respirable crystalline silica particles are typically between 1 and 5 micrometres in diameter. At this size, they are invisible to the naked eye and remain airborne for extended periods. A visible dust cloud consists predominantly of larger particles that are less hazardous because they are filtered out by the upper airways. The most dangerous fraction of silica dust is the fraction you cannot see. Judging exposure by the visible density of the dust cloud is not a valid method of assessing risk — air monitoring with personal samplers is the only reliable way to determine whether the WEL is being exceeded.

Not maintaining or testing LEV equipment

LEV systems, including on-tool extraction units and H-class vacuums, must be examined and tested by a competent person at least every 14 months under COSHH Regulation 9. Between formal examinations, the user must carry out routine checks to confirm that the equipment is functioning correctly — checking airflow indicators, inspecting hoses for damage or blockages, and confirming that filters are not saturated. An LEV system that is not maintained will lose extraction performance progressively, and workers will assume they are protected when they are not.

4. Related Documents

Document	Relationship
C1 — COSHH Assessment: General Site Substances	The general site COSHH assessment covers the overarching framework for substance hazard management on site. Silica dust requires a dedicated COSHH assessment because of its extremely low WEL, Group 1 carcinogen status, and the specific control requirements that go beyond the general COSHH framework.
C2 — COSHH Assessment: Cement and Concrete	Cement and concrete contain crystalline silica. The cement/concrete COSHH assessment addresses the alkaline burns and dermatitis risks of wet cement, while the silica COSHH assessment addresses the inhalation risk when these materials are cut, drilled or ground. Both assessments apply when workers are cutting or grinding concrete.
B3 — Excavations RAMS	Excavation in silica-containing ground (sandstone, sandy soils, granite) can generate RCS exposure. Breaking out rock or concrete foundations during excavation is a high-dust activity. The excavation RAMS must cross-reference the silica COSHH assessment where these materials are encountered.
B15 — Demolition RAMS	Demolition of concrete, blockwork and masonry structures generates significant quantities of silica dust. Mechanical breaking, crushing and scabbling during demolition are among the highest-exposure tasks for RCS. The demolition RAMS must incorporate the silica COSHH controls and specify water suppression, LEV or enclosed methods.

5. Frequently Asked Questions

Which common construction materials contain crystalline silica?▾

Concrete, mortar, cement, brickwork, blockwork, natural stone (sandstone, granite, slate, limestone), engineered stone (quartz worktops), sand, gravel, clay, render, screed, grout, roof tiles, paving slabs, and many aggregate materials all contain crystalline silica. The silica content varies by material — sandstone can be over 70% silica, concrete typically 25–40%, brick 5–25%. However, even materials with relatively low silica content generate hazardous RCS concentrations when cut, ground or drilled at high speed with power tools.

What is the difference between an H-class and M-class vacuum for dust extraction?▾

H-class vacuums are designed for hazardous dusts including RCS. They have a filtration efficiency of 99.995% for particles down to 0.3 micrometres and are tested to EN 60335-2-69 Class H. M-class vacuums have a lower filtration efficiency of 99.9% and are designed for medium-hazard dusts. For silica dust, only H-class vacuums are acceptable. Using an M-class vacuum for silica extraction means that a proportion of the fine RCS particles pass through the filter and are re-emitted into the workspace, exposing workers to the very dust the system was supposed to capture. This is a common compliance failure that the HSE specifically looks for during site inspections.

Does the silica WEL apply to outdoor work?▾

Yes. The workplace exposure limit of 0.1 mg/m3 applies equally to indoor and outdoor work. While natural air movement outdoors provides some dilution, dry cutting concrete or stone outdoors with a disc cutter still generates RCS concentrations that significantly exceed the WEL in the operator's breathing zone. The HSE has confirmed that outdoor work does not exempt the duty to control silica exposure. Water suppression and on-tool LEV are still required for outdoor cutting, drilling and grinding of silica-containing materials. RPE must still be worn where exposure cannot be reduced below the WEL by other means.

How often should air monitoring for silica be carried out?▾

Air monitoring should be carried out whenever a new cutting, drilling, grinding or scabbling process is introduced; whenever controls are changed or modified; whenever there is a reason to believe the WEL may be exceeded; and at periodic intervals to confirm that existing controls remain effective. The HSE does not prescribe a fixed frequency for routine monitoring, but as a practical standard, monitoring should be carried out at least annually for established processes and whenever a new material, tool or method is introduced. Personal exposure monitoring using a Higgins-Dewell cyclone sampler in the breathing zone, with laboratory analysis by X-ray diffraction, is the standard method. Results must be retained for 40 years as they constitute health records.

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