Isocyanates COSHH assessment
Isocyanates are found in two-pack (2K) paints, lacquers and polyurethane foams. They are the leading cause of occupational asthma in the UK and need tight control, especially during spraying.
The hazards
- A leading cause of occupational asthma
- Sensitiser — once sensitised, tiny exposures trigger attacks
- Highest risk during spraying, which creates fine mist
- Also released when heating or cutting cured polyurethane
Who is at risk
Exposure routes
- Inhalation of mist and vapour
- Skin contact
Health effects
- Occupational asthma (often permanent once sensitised)
- Skin and eye irritation and sensitisation
- Chest tightness and breathing difficulty
Control measures (hierarchy of control)
Controls should be applied in order — eliminate or substitute first, then engineering controls, then PPE as the last line.
- Spray only in a properly ventilated spray booth or room with LEV
- Substitute for non-isocyanate products where possible
- Air-fed breathing apparatus for spraying — filters alone are not enough
- Restrict access during and after spraying (clearance time)
- Biological monitoring of urine to check exposure control
PPE & RPE
- Air-fed breathing apparatus for spraying
- Chemical-resistant gloves and coveralls
- Eye protection
First aid
- Move to fresh air immediately and monitor breathing
- Anyone with breathing symptoms should get urgent medical attention
- Health surveillance for asthma is required
Workplace exposure limit (WEL)
Relevant legislation & guidance
Isocyanates COSHH FAQs
Spraying two-pack paint creates a fine isocyanate mist. Isocyanates are potent asthma-causing sensitisers, and cartridge filters cannot be relied on for the whole spraying task — air-fed breathing apparatus and a booth with LEV are the standard controls.
Once sensitised, even tiny future exposures can trigger asthma attacks, often ending a spraying career. That is why control and health surveillance are so important — the goal is to prevent sensitisation happening in the first place.
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