Isocyanates in Spray Foam and Paints

Isocyanates are highly reactive chemicals used in spray foam insulation, two-pack paints, coatings, and polyurethane products.
Isocyanate exposure is the leading cause of occupational asthma in the UK, accounting for hundreds of new cases each year.
Once sensitised to isocyanates, a worker reacts to extremely low concentrations for life — the condition is permanent.
Exposure occurs through inhalation of spray mist and vapour, and through skin absorption during handling and application.
The COSHH workplace exposure limit for isocyanates is extremely low at 0.02 mg/m³ as an 8-hour time-weighted average.
Spray application creates the highest exposure risk because the product becomes a fine aerosol that fills the breathing zone.
RPE for isocyanate work must provide an assigned protection factor sufficient to reduce exposure below the WEL.
Health surveillance including lung function testing and questionnaires is mandatory for workers regularly exposed to isocyanates.
Isocyanate-containing products must be stored, mixed, and applied strictly according to the manufacturer's instructions and COSHH assessment.
Skin exposure must be prevented with chemical-resistant gloves, coveralls, and barrier cream — isocyanates penetrate skin rapidly.

Permanent asthma	Isocyanate-induced asthma is irreversible — once sensitised, any future exposure triggers severe breathing difficulty for life.
Career ending	A worker sensitised to isocyanates cannot work with them again, excluding them from spray painting, insulation, and coating trades.
Extremely low limit	The WEL is 0.02 mg/m³ — this concentration is exceeded within seconds of spraying without proper extraction and RPE.

Do

Don't

Read the COSHH assessment and safety data sheet before using any isocyanate product.
Wear RPE with adequate protection factor for the isocyanate concentration in use.
Ensure RPE is face-fit tested to your individual face before isocyanate work.
Wear chemical-resistant gloves and coveralls to prevent skin absorption.
Use local exhaust ventilation or spray booths during all isocyanate application.
Attend health surveillance including lung function testing at required intervals.
Mix products strictly according to the manufacturer's ratios and instructions.
Store isocyanate products in original containers in cool, ventilated areas.
Report any breathing difficulty, chest tightness, or wheezing to your supervisor.
Ensure adequate training on isocyanate hazards before handling any product.

DON'T use isocyanate products without reading the COSHH assessment first.
DON'T spray isocyanates without RPE rated for the specific exposure level.
DON'T wear RPE that has not been face-fit tested for isocyanate work.
DON'T handle isocyanates without chemical-resistant gloves and full skin protection.
DON'T spray isocyanates without extraction or in poorly ventilated areas.
DON'T skip health surveillance — it detects sensitisation before symptoms become severe.
DON'T alter mixing ratios — incorrect proportions increase free isocyanate levels.
DON'T store open or decanted isocyanate products in unventilated areas.
DON'T dismiss breathing symptoms — early reporting prevents permanent asthma.
DON'T allow untrained workers near isocyanate application without proper controls.

See also: COSHH Awareness | Respiratory Protective Equipment (RPE)

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