COSHH Assessment for Silica Dust: A Practical Guide for UK Tradespeople
Silica dust is one of the most serious occupational health hazards in the UK construction and trades sector. If you cut, grind, drill or sand materials containing crystalline silica — stone, concrete, brick, mortar, fibre cement board — you are generating respirable crystalline silica (RCS). A properly structured COSHH assessment for silica dust is not a paperwork exercise; it is the mechanism that keeps workers' lungs intact.
Why Silica Dust Demands Its Own COSHH Assessment
Under the Control of Substances Hazardous to Health Regulations 2002 (COSHH), employers and self-employed contractors must assess the risk from any substance hazardous to health before work begins. RCS qualifies as hazardous because prolonged inhalation causes silicosis — an irreversible, progressive and potentially fatal lung disease. It is also a cause of lung cancer and COPD.
The Workplace Exposure Limit (WEL) for RCS is 0.1 mg/m³ (8-hour TWA). This is a legal ceiling: you must not exceed it, and COSHH also requires you to reduce exposure as low as reasonably practicable below that limit.
Step-by-Step: Completing the COSHH Assessment
1. Identify the Substance and the Task
Start by listing the specific tasks that will generate RCS. Common examples:
- Angle grinding concrete or masonry
- Dry cutting kerb stones or paving flags
- Core drilling reinforced concrete
- Chasing brick or blockwork walls
- Scabbling or bush-hammering concrete surfaces
Note the material being worked, the duration of the task, and how often it is repeated. Frequency and duration directly affect cumulative dose.
2. Assess Who Is at Risk and How Badly
Consider not just the operative doing the cutting, but others in the vicinity — labourers clearing arisings, other trades working nearby, members of the public in adjacent areas. RCS is invisible to the naked eye, travels in air currents, and settles slowly. Bystander exposure is frequently underestimated.
3. Evaluate the Controls Using the Hierarchy
COSHH requires you to work through a genuine hierarchy of controls — not jump straight to a dust mask.
| Level | Example for silica dust tasks |
|---|---|
| Eliminate | Redesign the job so cutting is not needed — use pre-cut materials or off-site fabrication |
| Substitute | Switch to a lower-silica content material where technically feasible |
| Engineering controls | On-tool water suppression (wet cutting); on-tool Local Exhaust Ventilation (LEV) — H-class vacuum extraction attached to the tool |
| Administrative controls | Rotate workers to limit individual exposure time; restrict access to the work area; schedule dusty tasks when fewest people are present |
| PPE (last resort) | A correctly selected, fit-tested respiratory protective device (RPD) — minimum FFP3 disposable or P3 half-mask for high-exposure tasks |
Water suppression and H-class LEV are not optional extras — HSE guidance makes clear they are the primary engineering controls expected on site. PPE is a supplement to engineered controls, not a replacement for them.
4. Record Your Findings
Your COSHH assessment must be recorded in writing if you employ five or more people, but good practice (and the expectation of most principal contractors) means recording it regardless of business size. The record should cover:
- The substance (RCS from the named material)
- The task and its duration
- Who is exposed
- The controls selected and why
- Any monitoring or health surveillance required
- Review trigger points
This written record is the document an HSE inspector or principal contractor will ask to see.
5. Health Surveillance
Where a COSHH assessment shows that significant exposure to RCS cannot be ruled out despite controls, health surveillance is required under COSHH regulation 11. In practice, this means a baseline lung function test (spirometry) before or early in employment, with periodic repeats. Workers must be informed of the results. Keep records for 40 years — silicosis can develop decades after exposure.
Common Mistakes That Undermine a Silica Dust COSHH Assessment
- Treating the WEL as a target rather than a ceiling. You must drive exposure as low as reasonably practicable below 0.1 mg/m³.
- Relying on PPE alone. An FFP3 mask with no water suppression or LEV will not satisfy a COSHH assessment — nor will it adequately protect the worker.
- Generic assessments. "Dusty activities" is not specific enough. Name the task, the tool, the material.
- No fit-testing. An RPD only works if it seals against the wearer's face. Fit-testing is required for tight-fitting face pieces.
- Forgetting review. COSHH requires you to review the assessment if there is reason to suspect it is no longer valid — new tools, new materials, or a health surveillance result that raises concern.
What Inspectors Actually Look For
HSE's Construction Division targets RCS as a priority hazard. Inspectors on site will check that:
- Wet cutting or on-tool extraction is in use (not just available)
- The extraction unit is H-class rated and properly maintained
- RPE is appropriate, maintained, and fit-tested records exist
- Workers can articulate the risks and why controls matter
A COSHH assessment sitting in a folder back at the office, while a worker dry-cuts concrete with a bare angle grinder, will result in enforcement action. The assessment and the controls must match what is actually happening on site.
Quick Reference: Key Legal Basis
- COSHH Regulations 2002 — duty to assess, control, and monitor exposure to RCS
- WEL: 0.1 mg/m³ RCS (8-hr TWA) — set in EH40 (4th edition)
- Management of Health and Safety at Work Regulations 1999 reg 3 — overarching risk assessment duty
- Health surveillance — COSHH reg 11
Silica dust kills slowly and silently. A thorough, task-specific COSHH assessment — backed by real engineering controls — is the baseline standard, not a belt-and-braces extra.