How to Write a COSHH Assessment for Silica Dust: Complete UK Guide

What is Respirable Crystalline Silica (RCS)?

Respirable crystalline silica (RCS) is a fine dust created when materials containing silica are cut, ground, drilled, or broken. On construction sites, the most common sources are concrete, sandstone, brick, mortar, and engineered stone. The particles are so small (under 10 microns) that they penetrate deep into the lungs, where the body cannot clear them.

The health consequences are severe. Silicosis is an irreversible scarring of the lungs that progressively reduces breathing capacity. RCS is also classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC), meaning it is a confirmed cause of lung cancer. Long-term exposure is also linked to COPD and kidney disease.

The HSE estimates that around 500 construction workers in the UK die each year from diseases linked to silica dust exposure. It is not a theoretical risk. If your workers are cutting concrete or chasing walls without proper controls, they are being exposed.

UK Workplace Exposure Limit for Silica Dust

The workplace exposure limit (WEL) for respirable crystalline silica in the UK is 0.1 mg/m³ as an 8-hour time-weighted average (TWA). This is set out in the HSE’s EH40 table of workplace exposure limits.

To put that in perspective, 0.1 mg/m³ is one of the lowest WELs of any substance. For comparison, general inhalable dust has a WEL of 10 mg/m³, which is 100 times higher. The low limit reflects just how dangerous silica dust is at even small concentrations.

As a practical rule: any task that produces visible dust is almost certainly exceeding the WEL. If your workers can see dust in the air while cutting or grinding, exposure is too high and controls are inadequate.

Step-by-Step: Writing Your COSHH Assessment

A COSHH assessment for silica dust follows the same six-step structure as any COSHH assessment, but there are specific details you need to get right. Here is how to work through each step.

Step 1: Identify the Hazardous Substance

Start by recording the substance details. For silica dust generated from cutting or grinding site materials, use the following:

• Substance name: Respirable crystalline silica (quartz)

• CAS number: 14808-60-7

• GHS classifications: STOT RE 1 (causes damage to lungs through prolonged exposure), Carc. 1A (may cause cancer by inhalation)

• WEL: 0.1 mg/m³ (8-hour TWA)

If you are working with a specific product (e.g. a concrete mix or engineered stone), also reference the manufacturer’s safety data sheet (SDS) for the silica content percentage.

Step 2: Who is Exposed and How?

Identify every person who could be affected. This is not just the worker doing the cutting.

• Directly exposed workers: Operatives cutting, grinding, drilling, or breaking concrete, stone, brick, or mortar

• Bystanders: Other trades working nearby, labourers sweeping up dust, anyone in the same enclosed area

• Exposure route: Inhalation is the primary route. Skin and eye contact are secondary concerns from settled dust.

Silica dust stays airborne for a long time. Workers who enter an area after cutting has finished can still be exposed if the dust has not been suppressed or extracted.

Step 3: Assess the Risk

Consider the likelihood and severity of exposure based on the actual work being carried out. Key factors to record:

• Duration and frequency: How long does each task last? Is it a one-off or repeated daily?

• Quantity of dust: Cutting a single block creates far less dust than grinding a concrete floor for 4 hours.

• Location: Indoor work in an enclosed space is significantly higher risk than outdoor cutting with natural ventilation.

• Existing controls: Document what is already in place (water suppression, extraction, RPE) and whether it is adequate.

For silica dust, the severity is always high (irreversible lung damage, cancer). The risk level depends on how well you control the exposure.

Step 4: Control Measures (Hierarchy)

COSHH Regulation 7 requires you to prevent exposure where reasonably practicable, or adequately control it. Work through the hierarchy of controls from top to bottom.

• Elimination: Can you avoid the dust-generating task entirely? Use pre-cut or pre-formed materials. Design out the need for on-site cutting where possible.

• Substitution: Can you use a material with lower silica content? For example, some composite materials have reduced quartz levels compared to natural stone.

• Engineering controls: This is where most silica control happens in practice. Water suppression (wet cutting) reduces airborne dust by up to 90%. On-tool extraction with an H-class vacuum captures dust at the source. Enclosed cutting areas with local exhaust ventilation (LEV) contain the dust cloud.

• Administrative controls: Rotate workers to reduce individual exposure duration. Set up exclusion zones around cutting areas. Display warning signage. Monitor dust levels with personal samplers. Never dry sweep; use an H-class vacuum or damp methods.

• RPE (last resort): FFP3 disposable mask as a minimum (assigned protection factor of 20). Half-mask respirator with P3 filters for regular exposure. Powered air purifying respirator (PAPR) for prolonged or heavy exposure. All RPE must be face-fit tested under COSHH Regulation 7.

In practice, a good COSHH assessment for silica will specify a combination of engineering controls and RPE. Relying on RPE alone is not acceptable under COSHH.

Step 5: Health Surveillance

COSHH Regulation 11 requires health surveillance for workers with significant exposure to silica dust. In practice, this means anyone who regularly carries out tasks that generate RCS, even with controls in place.

Health surveillance for silica includes:

• A baseline health questionnaire and lung function test (spirometry) before the worker starts the role

• Periodic reviews, typically every 1 to 3 years depending on exposure level

• Referral to an occupational health professional if any abnormality is detected

Health surveillance records must be kept for at least 40 years. Your COSHH assessment should state that health surveillance is required and describe the programme in place.

Step 6: Review and Record

Your COSHH assessment is a living document. Review it:

• At least annually

• Whenever the work method, materials, or location change

• After any incident, near miss, or health surveillance finding

• If new information about silica risks becomes available

Record who carried out the assessment, the date, and the date of the next scheduled review. Keep the assessment accessible to all workers and supervisors on site.

Common Activities That Generate Silica Dust

If any of these tasks are happening on your site, a COSHH assessment for silica dust is required:

• Cutting concrete or paving slabs with a disc cutter or table saw

• Chasing walls for electrical cables or pipework

• Drilling into masonry, concrete, or brick

• Breaking out concrete with breakers or jackhammers

• Grinding or polishing concrete floors

• Mixing dry mortar, cement, or grout

• Demolition and refurbishment involving concrete or blockwork

• Tunnelling and earthmoving in sandstone or quartz-bearing ground

RPE Selection for Silica Dust

Choosing the right respiratory protective equipment (RPE) depends on the exposure level and task duration. Here is what the HSE guidance recommends for silica dust:

• FFP3 disposable mask: Assigned protection factor (APF) of 20. Suitable for short-duration, low-dust tasks. Must be fit tested.

• Half-mask respirator with P3 filters: APF of 20. More comfortable for regular or repeated exposure. Reusable with replaceable filters.

• Powered air purifying respirator (PAPR): APF of 40 or higher. Recommended for prolonged cutting or grinding sessions. Reduces breathing effort and heat stress.

All RPE must be face-fit tested in accordance with INDG479. A mask that does not seal properly provides almost no protection. Record all fit test results and retrain workers annually.

Remember: FFP2 masks are not adequate for silica dust. The minimum standard is FFP3.

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Related Guides

• COSHH Regulations UK: The Complete Guide

• COSHH Risk Assessment: What It Is and How to Write One

• Construction Phase Plan: Complete UK Guide (silica control is a CDM requirement)