COSHH Assessment: Identifying Hazardous Substances & Writing Risk Assessments for Trade Use

Summary

COSHH is one of the most important but least understood health and safety obligations for UK tradespeople. Many sole traders believe COSHH only applies to chemical factories or laboratories — in fact, it applies to any workplace where hazardous substances are used or generated, including domestic refurbishment, roofing, painting, and groundworks.

The consequences of ignoring COSHH are long-term and serious: silicosis (from silica dust), occupational asthma (from wood dust, isocyanates in spray paints), hand-arm vibration syndrome (HAVS), and dermatitis from cement contact are all common among tradespeople. HSE data consistently shows that construction workers have significantly elevated rates of occupational lung disease compared to other industries.

COSHH assessment is not primarily a paper exercise — it is a process of understanding exposure risks and putting controls in place. The paperwork is evidence that the process has been carried out. For most trades, a generic COSHH assessment per activity type (e.g., 'cutting concrete' or 'applying solvent-based adhesive') is sufficient, reviewed annually or when working methods change.

Key Facts

• Legal duty: COSHH Regulations 2002 (SI 2002/2677) — mandatory for any employer or self-employed person where hazardous substances are used or generated
• What counts as hazardous: Any substance with a hazard classification on its Safety Data Sheet (SDS), any substance with a Workplace Exposure Limit (WEL) in EH40, and any biological agent (mould, Legionella, sewage)
• Workplace Exposure Limits (WELs): Published in HSE document EH40. Key WELs for trades:
  • Respirable crystalline silica (RCS): 0.1 mg/m³ (8-hour TWA) — cutting stone, concrete, brick, fibre cement
  • Wood dust (hardwood): 1 mg/m³ (8-hour TWA) — routing, sawing, sanding hardwood
  • Wood dust (softwood/mixed): 5 mg/m³ (8-hour TWA)
  • Portland cement dust: 1 mg/m³ (respirable) — mixing, cutting, grinding
  • Bitumen fumes: 1 mg/m³ — hot bitumen roofing
• Safety Data Sheet (SDS): Manufacturers must supply an SDS (formerly MSDS) for all hazardous substances. Section 8 of the SDS gives the WEL and recommended PPE. Keep SDS on site for all hazardous substances in use
• Hierarchy of control (COSHH):
  1. Eliminate the hazardous substance (substitute with a safer alternative)
  2. Reduce exposure (use a less hazardous form — pellets instead of powder; pre-mixed instead of mixing on site)
  3. Engineering controls (LEV — local exhaust ventilation; on-tool extraction)
  4. Administrative controls (rotate workers to reduce individual exposure; wet methods to suppress dust)
  5. PPE (respiratory protection — last resort, not a substitute for engineering controls)
• Dust masks: FFP2 = adequate for wood dust and general dust; FFP3 (or full-face P3 with powered PAPR) required for silica dust. A simple dust mask (surgical mask) provides no COSHH-level protection — it filters particulate but not at a tested standard. Disposable FFP2/FFP3 must be worn correctly (sealed to face, no beard)
• Health surveillance: Required where exposure to specific substances is significant and health effects are predictable. For construction: lung function tests (spirometry) for workers regularly exposed to silica or isocyanates; skin checks for wet cement workers. Typically carried out by an occupational health provider

Quick Reference Table

Detailed Guidance

Writing a COSHH Assessment

A COSHH assessment does not need to be a lengthy document. For most trade activities, a single A4 sheet per activity or substance group is adequate. It must cover:

1. Substance or activity identified: Name the substance (or describe the activity that generates the hazard, e.g., 'cutting concrete blocks with angle grinder').

2. Who is exposed and how: List the workers involved, the duration of exposure (hours per day), and the route of exposure (inhalation, skin contact, ingestion).

3. What are the health effects: Refer to the SDS Section 2 (hazard identification) and Section 11 (toxicological information). State clearly what the health risk is: silicosis, occupational asthma, dermatitis, cancer.

4. Current controls: List the controls already in place: extraction, wet methods, PPE.

5. Residual risk: Is the residual risk acceptable? If controls are adequate, risk is low. If not, additional controls must be specified.

6. Actions required: Any additional controls, training, health surveillance, or equipment.

7. Review date: Typically annual, or when working methods change.

Template structure:

COSHH Assessment
Activity: [e.g., Cutting concrete blocks on site]
Substance/hazard: Respirable crystalline silica dust
Date: [date]  Assessed by: [name]

Exposure: Operatives cutting concrete blocks with angle grinder. 
Duration: up to 2 hours per day. Route: inhalation.

Health effects: Silicosis (irreversible lung scarring), lung cancer (Group 1 carcinogen). 
WEL: 0.1 mg/m³ (8-hour TWA).

Controls in place:
- Angle grinder fitted with shroud and dust extraction (H-class vacuum)
- Wet cutting where possible
- FFP3 disposable respirator worn at all times during cutting
- Work area cleared of non-essential personnel during cutting

Residual risk: LOW — controls meet COSHH regulation 7 requirements

Review date: [date + 12 months]
Signed: [signature]

Silica Dust — The Most Critical Trade COSHH Issue

Respirable crystalline silica (RCS) is present in most masonry, concrete, brick, natural stone, and fibre cement materials. When cut, drilled, or ground, RCS particles are generated that can reach the deepest parts of the lungs and cause silicosis — a progressive, irreversible, and potentially fatal lung disease with no cure.

The HSE's CONIAC (Construction Industry Advisory Committee) has designated silica dust as the highest priority dust hazard in construction. The WEL of 0.1 mg/m³ (8-hour TWA) is extremely low — uncontrolled cutting of concrete can generate levels 10–100× this WEL within seconds.

Required controls for silica-generating activities:

1. On-tool extraction: Angle grinders, disc cutters, and chasing tools must be fitted with a dust shroud connected to an H-class (HEPA) vacuum. On-tool extraction is the most effective dust control for powered tools
2. Wet cutting: Water suppression at the cutting point dramatically reduces airborne dust. Diamond blade cutters with water feed are standard for external stone/paving cutting
3. Respiratory protection: FFP3 disposable respirator or a powered air-purifying respirator (PAPR) with P3 filter. FFP2 is NOT adequate for silica dust
4. Exclusion zone: Keep non-essential workers at least 10m from the cutting area during dry operations

Activities that generate silica dust (non-exhaustive):

• Cutting, grinding, or drilling concrete, brick, or stone with any power tool
• Scabbling or bush hammering concrete
• Repointing brickwork with a power grinder
• Drilling through concrete or masonry
• Cutting fibre cement (Eternit) sheets — very high silica content

Wood Dust — A Significant but Underestimated Hazard

Hardwood dust is classified as a Group 1 human carcinogen (nasal cancer). Softwood dust causes occupational asthma. The WEL for hardwood is 1 mg/m³ (lower than most tradespeople realise).

Sources: Routing, sawing, and sanding hardwood and MDF (MDF dust is particularly fine); cutting sheet materials; using orbital sanders without extraction.

Controls:

• On-tool extraction on all woodworking machines and hand-held sanders
• Workshop LEV (local exhaust ventilation) system for fixed woodworking machinery
• FFP2 disposable respirator where dust extraction is insufficient
• Regular cleaning of workshop with vacuum (not compressed air — compressed air re-disperses settled dust)

Cement and Wet Concrete — Skin Hazard

Portland cement contains chromium VI compounds that cause allergic contact dermatitis (cement burn). This is a delayed hypersensitivity reaction that develops over weeks or months of repeated exposure — the worker may not notice the damage occurring.

Controls:

• Waterproof nitrile gloves (Category III PPE — declared protection to EN 374) worn during all concrete, mortar, and plaster work
• Long sleeves to prevent skin contact on arms
• Change out of contaminated clothing before leaving the site
• Wash hands before breaks, before eating, and at end of shift — using skin-protective cream (barrier cream before work; skin repair cream after washing)

Note: Category I (general purpose) gloves provide no chemical protection. Disposable nitrile gloves (EN 374, Category III) are the minimum. Heavy-duty rubber gloves for prolonged contact.

Health Surveillance

COSHH requires health surveillance where:

• There is a risk of identifiable disease linked to exposure, and
• The disease can be detected by surveillance, and
• Surveillance is likely to benefit the worker

For tradespeople regularly exposed to:

• Silica: Lung function tests (spirometry) every 3 years minimum. Some contractors require annual tests for high-exposure workers
• Hardwood dust: Annual lung function test (sensitisation check)
• Isocyanates: Annual lung function — mandatory for spray painters using two-pack products
• Wet cement: Annual skin check (dermatitis monitoring)

Health surveillance is typically contracted to an occupational health provider. Costs are modest (£30–£80 per worker per test). Records must be kept for 40 years for substances causing long-term disease (silica, hardwood dust).

Frequently Asked Questions

Do I need a COSHH assessment for every product I use?

No — you can group similar substances. A single assessment for 'solvent-based adhesives' covers all similar products in that category. A single assessment for 'cutting concrete or masonry' covers all silica-generating cutting activities. Review the SDS for each product to confirm the hazard classification — if the hazards are substantially similar, a group assessment is appropriate.

Are dust masks adequate for cutting stone?

No — not for silica dust. A dust mask (surgical mask or FFP1) does not achieve the protection required for respirable crystalline silica. The minimum is FFP3 (assigned protection factor 20, meaning it reduces inhaled concentration to 1/20th of ambient). For prolonged or high-concentration exposure, a powered air-purifying respirator (PAPR) with P3 filter is more reliable (better seal, lower breathing resistance for long periods).

My employee says dust doesn't affect them. How do I respond?

Silicosis and occupational asthma develop silently over years of exposure — by the time symptoms appear, significant and irreversible damage has often occurred. The damage is cumulative — there is no safe lower threshold for RCS. The worker's perceived tolerance is not a reliable indicator of safety. Controls are required regardless of how the worker feels.

I work alone — do I still need COSHH assessments?

Yes. Self-employed workers are duty holders under COSHH for their own exposure. The Regulations apply to 'employees' but self-employed workers are treated the same for personal protective purposes. The assessment can be simpler for a sole trader — a generic one-page assessment per activity type is sufficient.

Regulations & Standards

• Control of Substances Hazardous to Health Regulations 2002 (SI 2002/2677) — Primary legislation

• EH40/2005 (4th edition, 2020) — HSE Workplace Exposure Limits — reference for all WELs

• COSHH ACOP (L5) — Approved Code of Practice for COSHH Regulations

• HSG258 — Controlling airborne contaminants at work (LEV specification)

• BS EN 529:2005 — Respiratory protective devices (for RPE selection)

• HSE COSHH guidance — COSHH essentials, assessment tools, and substance-specific guidance

• HSE — Silica and Your Lungs — Construction-specific silica dust guidance

• CONIAC — Dust Control Guidance for Construction — CONIAC dust control toolbox talks

• working at height — Working at height regulations

• scaffold inspection — Scaffold inspection requirements

• cdm regulations — CDM 2015 and health and safety plan requirements

• ppe selection — Selecting appropriate PPE for trade work