COSHH · Mandatory · Pre-Construction

COSHH Assessment — Paints and Solvents

This COSHH assessment addresses health risks from paints, varnishes, stains, thinners, and solvents used in construction. It covers inhalation of volatile organic compounds, skin absorption, and flammability risks. Substitution with water-based products should be considered first, with adequate ventilation and respiratory protection provided where solvent-based products are necessary.

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

Isocyanates	Respiratory sensitisers and Group 2A carcinogens. Found in two-pack (2K) polyurethane paints, lacquers, and coatings. WEL: 0.02 mg/m³ (8-hr TWA as NCO). Once sensitised, any subsequent exposure — even at very low levels — can trigger a severe asthma attack. Sensitisation is irreversible.
VOC solvents	Volatile organic compounds including xylene, toluene, white spirit, methyl ethyl ketone (MEK), acetone, and others. Cause CNS depression (dizziness, drowsiness, narcosis), liver and kidney damage from chronic exposure, and dermatitis from skin contact. Many have substance-specific WELs.
Spray painting	Generates a fine aerosol mist that is readily inhaled. For isocyanate-containing coatings, spray application requires local exhaust ventilation (LEV) or a spray booth, plus supplied-air RPE (air-fed visor or full-face airline BA). A simple dust mask or half-face respirator with organic vapour cartridge is not adequate for isocyanate spray.
Lead paint	Work involving disturbance of existing lead paint (removal, sanding, burning off) is regulated under the Control of Lead at Work Regulations 2002 (CLAW) in addition to COSHH. Lead paint on pre-1960s buildings requires specific controls, blood lead monitoring, and medical surveillance.
DSEAR	Solvent-based paints, thinners, and cleaning agents are flammable or highly flammable. The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) require a risk assessment for fire and explosion risk wherever flammable solvents are stored, used, or may accumulate as vapour in enclosed spaces.

1. The Isocyanate Hazard

Isocyanates are the single most significant COSHH hazard in painting and decorating work on construction sites. They are present in two-pack (2K) polyurethane paints, lacquers, varnishes, floor coatings, and spray-applied protective coatings. The two most common isocyanates encountered are methylene diphenyl diisocyanate (MDI) and hexamethylene diisocyanate (HDI). Isocyanates are respiratory sensitisers: once a worker becomes sensitised, any subsequent exposure — even at concentrations far below the WEL — can trigger a severe and potentially fatal asthma attack. Sensitisation is irreversible and effectively ends a worker’s career in any role involving isocyanate exposure.

The workplace exposure limit for isocyanates is 0.02 mg/m³ (8-hour TWA, measured as NCO). This is an extremely low concentration and is easily exceeded during spray application, even in well-ventilated conditions. Brush or roller application of two-pack products generates lower airborne concentrations but still requires adequate ventilation and appropriate RPE. The COSHH assessment must identify all products containing isocyanates, specify the application method, evaluate the likely exposure, and set out controls that are proportionate to the exposure route and duration.

Isocyanates can also cause occupational asthma through skin absorption, not just inhalation. Skin contact with uncured isocyanate products must be prevented by the use of appropriate chemical-resistant gloves (nitrile, minimum 0.4 mm), protective clothing, and face/eye protection. The COSHH assessment must address both inhalation and skin contact routes.

Isocyanate sensitisation is irreversible

Once a worker is sensitised to isocyanates, the condition is permanent. There is no treatment and no desensitisation therapy. Any future exposure — even at levels well below the WEL — can trigger a life-threatening asthma attack. Workers who become sensitised must be permanently removed from all work involving isocyanate exposure. This makes prevention through adequate control measures and health surveillance critical. Occupational asthma caused by isocyanates is the most commonly reported cause of occupational asthma in the UK and is a prescribed industrial disease (D7).

2. Solvents and Volatile Organic Compounds

Solvent-based paints, varnishes, stains, and coatings contain volatile organic compounds (VOCs) that evaporate during application and drying. Common solvents include xylene (WEL 220 mg/m³), toluene (WEL 191 mg/m³), white spirit (WEL 575 mg/m³), methyl ethyl ketone (MEK, WEL 600 mg/m³), and acetone (WEL 1210 mg/m³). Acute effects include headache, dizziness, drowsiness, nausea, and at high concentrations, narcosis and loss of consciousness. Chronic exposure can cause liver and kidney damage, peripheral neuropathy, and dermatitis. In enclosed or poorly ventilated spaces, solvent vapour concentrations can reach hazardous levels rapidly.

Control area	Requirement	Common failure	Consequence
Ventilation	Natural ventilation adequate for brush/roller application of conventional solvent paints in open or well-ventilated areas. Mechanical ventilation or LEV required for spray application, large-area application in enclosed spaces, or use of high-VOC products.	No ventilation assessment. Windows opened as the sole ventilation measure in enclosed rooms. No monitoring of air quality during application.	Solvent vapour accumulation causing CNS depression, dizziness, and loss of consciousness. Narcosis can occur without warning in poorly ventilated spaces.
Skin contact	Chemical-resistant gloves appropriate to the solvent (check SDS for glove material compatibility). Nitrile gloves are suitable for most solvents but not all. Protective clothing to prevent skin contact. Barrier cream is not a substitute for gloves.	Latex or vinyl gloves used. No gloves used for "just a quick job." Solvents used to clean paint from skin.	Solvent dermatitis. Skin absorption of solvents contributing to systemic exposure. Using solvents to wash hands removes the skin’s protective oils and accelerates dermatitis.
RPE	Half-face respirator with A2 (organic vapour) cartridge for brush/roller application of solvent paints in enclosed spaces. Full-face or air-fed RPE for spray application. Cartridge change-out schedule based on manufacturer’s guidance and exposure conditions.	Simple dust mask (FFP2/FFP3) used for solvent exposure. Cartridges not changed within their service life. No face-fit testing.	Dust masks provide no protection against solvent vapour. Exhausted cartridges provide no protection. Ill-fitting RPE leaks contaminated air around the seal.
Flammable / DSEAR	DSEAR assessment required for storage and use of flammable solvents. Eliminate ignition sources. Earthing and bonding for decanting. ATEX-rated equipment in areas where explosive atmospheres may form. Appropriate fire extinguishers (CO2 or dry powder, not water).	Solvent-based paints stored near heat sources or in direct sunlight. Hot works carried out in areas where solvent vapour may be present. No DSEAR assessment.	Fire or explosion. Solvent vapour is heavier than air and accumulates at low level, creating an explosive atmosphere that can be ignited by sparks, hot surfaces, or electrical equipment.

3. Common Mistakes

Using a simple dust mask for spray painting

A disposable dust mask (FFP2 or FFP3) provides no protection against solvent vapour or isocyanate aerosol. Dust masks are particulate filters only. Spray painting with solvent-based products requires, as a minimum, a half-face respirator with an A2P3 combination cartridge (organic vapour plus particulate). For isocyanate-containing (2K) spray paints, supplied-air RPE (air-fed visor or full-face airline breathing apparatus) is required because the WEL is too low for filter-type RPE to provide adequate protection. This is one of the most dangerous and most common mistakes in construction painting.

Not identifying two-pack products as isocyanate hazards

Two-pack (2K) products are those supplied as two separate components that are mixed immediately before use. The hardener or catalyst component in polyurethane 2K products almost always contains isocyanates. Many operatives and supervisors do not realise that the product they are using contains isocyanates because the product name does not mention them. The COSHH assessment must check the SDS for every two-pack product to identify whether the hardener contains isocyanates (look for MDI, HDI, TDI, IPDI, or the general term "diisocyanate" in the ingredients section).

Insufficient ventilation in confined or enclosed spaces

Applying solvent-based paints, varnishes, or coatings in enclosed rooms, stairwells, lift shafts, or other poorly ventilated spaces can cause rapid accumulation of solvent vapour to hazardous concentrations. Opening a window is not a ventilation assessment and may not provide adequate air change rates. The COSHH assessment must evaluate the ventilation in the actual work space and specify mechanical ventilation where natural ventilation is insufficient. In confined spaces (as defined by the Confined Spaces Regulations 1997), additional requirements apply including a confined space entry permit.

No health surveillance for isocyanate-exposed workers

Health surveillance is mandatory under COSHH Regulation 11 for workers exposed to isocyanates. This must include a baseline respiratory questionnaire and lung function test (spirometry) before first exposure, followed by periodic reviews (typically every 6-12 months). The purpose is to detect early signs of respiratory sensitisation before it becomes irreversible occupational asthma. Many painting subcontractors do not have health surveillance arrangements in place, which is a direct breach of COSHH and a common HSE enforcement finding.

Not managing RPE cartridge filter change-out schedules

Activated carbon cartridges in reusable respirators have a finite service life. They become saturated with solvent vapour over time and cease to provide protection. The breakthrough time depends on the solvent concentration, temperature, humidity, breathing rate, and cartridge type. The manufacturer’s guidance provides maximum service life data. In practice, many operatives use the same cartridge for weeks or months without replacement, meaning they are wearing RPE that provides little or no actual protection. The COSHH assessment must specify a cartridge change-out schedule and the supervisor must enforce it.

4. Related Documents

The paints and solvents COSHH assessment should be cross-referenced with the following related documents to ensure consistency and completeness across the project.

Document	Relationship
C1 — COSHH Assessment: General Site	The general site COSHH assessment provides the overarching framework. The paints and solvents assessment is a substance-specific assessment that sits underneath it and provides the detailed controls for paint, coating, and solvent exposure.
B16 — RAMS: Painting and Decorating	The painting and decorating RAMS addresses the activity-level hazards and controls for all painting work. The COSHH assessment provides the substance-specific detail on isocyanates, solvents, and VOCs that the RAMS must reference.
C9 — COSHH Assessment: Lead Paint	Where work involves disturbance of existing lead paint (pre-1960s buildings), the lead-specific COSHH assessment (C9) applies in addition to this assessment. Lead paint is also regulated under the Control of Lead at Work Regulations 2002 (CLAW).
C14 — SDS Register	Safety data sheets for all paint products, coatings, solvents, thinners, and cleaning agents used on site must be held in the SDS register and referenced in the COSHH assessment.
C13 — Hazardous Materials Register	All hazardous substances associated with painting work (including solvents, isocyanate-containing products, and flammable materials) must be recorded in the site hazardous materials register.

5. Frequently Asked Questions

How do I identify whether a paint product contains isocyanates?▾

Check the Safety Data Sheet (SDS), specifically Section 3 (Composition / information on ingredients). Look for any of the following chemical names: methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), or the general term "diisocyanate." Isocyanates are almost always found in the hardener/catalyst component of two-pack (2K) products, not the base component. Any product described as "two-pack," "2K," "two-component," or "catalysed" polyurethane should be assumed to contain isocyanates until the SDS confirms otherwise. The product label may carry the hazard statement H334 (May cause allergy or asthma symptoms or breathing difficulties if inhaled).

What RPE is required for spray application of 2K polyurethane coatings?▾

Supplied-air RPE is required. This means either an air-fed visor (positive pressure full-face visor with a clean air supply from a compressor with appropriate filtration) or full-face airline breathing apparatus. A half-face respirator with A2P3 cartridge is not adequate for isocyanate spray application because the WEL (0.02 mg/m³) is too low for filter-type RPE to provide a sufficient protection factor. In addition to supplied-air RPE, spray application of 2K products should ideally be carried out in a spray booth with dedicated extraction, or in a well-ventilated area with LEV to control overspray.

When does DSEAR apply to painting work?▾

DSEAR applies whenever flammable or highly flammable solvents are stored, used, or could give rise to an explosive atmosphere. This includes: storage of solvent-based paints and thinners; application of solvent-based products (particularly spray application, which generates a fine flammable mist); decanting of solvents; and any situation where solvent vapour could accumulate in an enclosed or poorly ventilated space. The DSEAR assessment must identify areas where explosive atmospheres may form, classify those areas into ATEX zones, eliminate or control ignition sources, and specify the precautions for safe storage and use. DSEAR requires a separate risk assessment from the COSHH health risk assessment, although both may be documented together.

How frequently should health surveillance be carried out for isocyanate-exposed workers?▾

Health surveillance for isocyanate exposure should include a baseline assessment before first exposure, comprising a respiratory symptoms questionnaire and lung function test (spirometry). Periodic reviews should be carried out every 6-12 months (HSE guidance recommends at least annually, with more frequent reviews in the first two years of exposure when the risk of sensitisation is highest). If a worker develops respiratory symptoms (cough, wheeze, chest tightness, breathlessness) between surveillance intervals, they should be referred for immediate assessment and removed from isocyanate exposure pending the outcome. Any decline in lung function or positive symptom questionnaire should trigger referral to an occupational health physician with experience in occupational asthma.

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