COSHH Assessment for Paints, Solvents and Thinners: UK Guide

Paints, solvents and thinners are among the most commonly used hazardous substances on construction sites and in workshops. Under the Control of Substances Hazardous to Health Regulations 2002 (COSHH), employers must assess the risks from these products and put controls in place before work begins.

This guide covers the key hazardous substances found in paint products, the workplace exposure limits (WELs) you need to know, and how to build a practical COSHH assessment that actually protects your team.

Common Hazardous Substances in Paint Products

Most solvent-based paints, varnishes and thinners contain a mix of volatile organic compounds. Here are the substances you will encounter most often, along with their UK workplace exposure limits from EH40.

White spirit (Stoddard solvent) is the backbone of most oil-based paints and brush cleaners. The 8-hour WEL is 575 mg/m³ (100 ppm), but research shows central nervous system (CNS) effects such as dizziness, headaches and impaired coordination can occur at concentrations well below the formal limit. Chronic exposure has been linked to "painters' syndrome," a form of chronic solvent encephalopathy.

Isocyanates (found in 2-pack paints and polyurethane coatings) are the most dangerous substances in this category. The 8-hour WEL for isocyanates is just 0.02 mg/m³. They are respiratory sensitisers, meaning that once a worker becomes sensitised, even trace exposure can trigger severe occupational asthma. Sensitisation is permanent. There is no "safe" level for a sensitised individual, and they will typically need to leave the trade entirely.

Toluene (WEL 191 mg/m³, 50 ppm) is found in some lacquers and specialty coatings. It is readily absorbed through the skin and causes CNS depression, liver damage, and reproductive harm with prolonged exposure.

Xylene (WEL 220 mg/m³, 50 ppm) appears in oil-based paints and industrial coatings. Health effects are similar to toluene, with the added risk of significant skin absorption.

Acetone (WEL 1210 mg/m³, 500 ppm) is used as a cleaning solvent and paint thinner. It has a relatively high WEL but can still cause irritation to the eyes, nose and throat in poorly ventilated spaces.

Methanol (WEL 266 mg/m³, 200 ppm) is present in some paint strippers and shellac-based products. It is toxic by all routes of exposure, including skin absorption, and can cause optic nerve damage.

Formaldehyde (WEL 2.5 mg/m³, 2 ppm) can be found in certain resins and preservatives used in paint formulations. It is classified as a Category 1 carcinogen under CLP, so any exposure must be reduced to as low as is reasonably practicable.

Who Needs This Assessment?

A COSHH assessment for paints and solvents is required for any employer or self-employed person whose workers handle these products. In practice, that includes:

• Painters and decorators using oil-based paints, stains, varnishes and white spirit for cleaning
• Spray painters (the highest-risk group), particularly those applying 2-pack isocyanate-based coatings in automotive, marine, or industrial settings
• Floor coating applicators working with epoxy and polyurethane floor coatings in enclosed spaces such as warehouses, kitchens and basements
• Anyone using 2-pack products, including adhesives, fillers and protective coatings that contain isocyanate hardeners

If your workers are only using water-based paints in well-ventilated areas, the risk is considerably lower, but you still need to document your assessment. Water-based products can contain biocides, preservatives, and small amounts of co-solvents that require consideration.

Step-by-Step COSHH Assessment

Follow this process to build a COSHH assessment that meets the requirements of the regulations and is genuinely useful on site.

1. Identify Every Product and Its Hazards

Start by listing every paint, primer, undercoat, varnish, thinner, cleaner and stripping product your team uses. Obtain the safety data sheet (SDS) for each one. The SDS is your primary source of information. Section 2 gives you the GHS hazard classifications, Section 3 lists the chemical composition, and Section 8 provides the relevant WELs and recommended PPE.

Pay close attention to GHS hazard statements. H225 (highly flammable liquid and vapour), H304 (may be fatal if swallowed and enters airways), H332 (harmful if inhaled), H334 (may cause allergy or asthma symptoms if inhaled), and H351 (suspected of causing cancer) are all common across paint products.

2. Assess the Exposure Routes

For solvents and thinners, inhalation is the primary exposure route. Volatile organic compounds evaporate at room temperature, and concentrations build rapidly in enclosed or poorly ventilated spaces. Skin absorption is the second major route, particularly for toluene, xylene and methanol, which pass through intact skin and enter the bloodstream.

Consider the task, the duration of exposure, the size of the area, and available ventilation. A decorator using oil-based gloss in a large, open room faces a very different risk profile to someone applying 2-pack floor coating in a basement with no windows.

3. Apply the Control Hierarchy

COSHH requires you to apply controls in a specific order. Do not jump straight to PPE.

Elimination or substitution should be your first consideration. Can you switch to a water-based paint or low-VOC alternative? Modern water-based products have improved dramatically and often provide comparable performance. If the specification allows it, this single change can remove most of the solvent hazard.

Engineering controls come next. For enclosed spaces, provide mechanical ventilation to dilute and remove solvent vapours. Local exhaust ventilation (LEV) is essential for spray painting operations. Open windows and doors where possible, and use fans to create cross-ventilation. For large-scale work, air monitoring can confirm that your ventilation is adequate.

Administrative controls include limiting exposure time, rotating workers, scheduling solvent-heavy work during periods when fewer people are nearby, and ensuring all workers have received training on the hazards and controls.

Personal protective equipment (PPE) is the last line of defence. For general solvent use, this means chemical-resistant gloves (nitrile, not latex), safety goggles where splashing is possible, and an appropriate respirator. For organic vapours, an A-type filter (brown band) is the standard choice. For spray painting with isocyanates, a half-mask respirator is not sufficient. See the section below.

Spray Painting: The Highest Risk Activity

Spray painting deserves its own section because the risk profile is fundamentally different from brush or roller application. When paint is atomised, it creates a fine mist of droplets and vapour that is far more readily inhaled. These tiny particles bypass the upper airways and deposit deep in the lungs.

For isocyanate spray painting, the HSE is clear: a supplied-air respirator (airline fed or self-contained breathing apparatus) is required. Filtering facepiece respirators and cartridge-type respirators do not provide adequate protection against isocyanate aerosols. The worker must also wear a full body coverall, gloves, and eye protection.

Spray booths with local exhaust ventilation are the standard engineering control. The booth must provide sufficient airflow to capture overspray and prevent vapour build-up. Filters must be changed regularly, and the system needs to be examined and tested at least every 14 months under COSHH Regulation 9.

Health surveillance is mandatory for workers exposed to isocyanates. This typically includes a pre-employment respiratory questionnaire, baseline spirometry, and regular follow-up assessments. Any worker who develops symptoms of respiratory sensitisation must be referred for specialist assessment immediately.

Storage and DSEAR Considerations

Most paint solvents are highly flammable (GHS hazard statement H225 or H226). This means your COSHH assessment does not exist in isolation. You may also need a risk assessment under the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR).

Practical storage requirements include:

• Store solvents in a dedicated, fire-resistant cabinet or store, away from ignition sources, heat, and direct sunlight
• Ensure adequate ventilation in storage areas to prevent vapour accumulation
• Keep containers sealed when not in use to minimise vapour release and prevent spills
• Prohibit smoking, open flames, and hot work in or near solvent storage and use areas
• Provide appropriate fire extinguishers (CO2 or dry powder, not water) in the immediate area
• Use anti-static containers and grounding when transferring bulk solvents to prevent static discharge

Solvent-soaked rags are a particular fire hazard. They can self-ignite through spontaneous combustion, especially linseed oil-based products. Dispose of them in sealed metal containers and remove them from site regularly.

Generate Your COSHH Assessment with SwiftRMS

Writing a COSHH assessment from scratch takes time, especially when you are juggling multiple products across different jobs. SwiftRMS generates COSHH assessments tailored to your specific products and work activities, complete with the correct WELs, control measures, and PPE requirements.

Describe the work (for example, "spray painting steel beams with 2-pack polyurethane in a workshop"), and the system builds the assessment for you. You can edit every section, download a branded PDF, and share it with your team. Try it free and see how much time you save.

Related Guides

For a broader overview of the regulations, read our guide to COSHH regulations. If your team also works with construction materials, see our posts on silica dust COSHH assessments and cement dust exposure.