The Dangers of Exposure to Isocyanates – Concept Edition 10

There is growing awareness of an increasing number of occupational asthma cases, which are associated in some way with exposure to isocyanates, particularly in occupations where paints and other coatings are applied by spray methods. Spraying 2-pack isocyanate paints is in fact the main cause of occupational asthma in the UK.

Isocyanates are a group of chemicals used in the manufacture of polyurethane plastics, synthetic rubbers, foams, paints, varnishes and adhesives. The use of isocyanates can be found in the following applications:

  • Chemical processing
  • Coating/spreading
  • Gluing/sealing
  • Mixing
  • Moulding/injecting
  • Painting (brush and roller)
  • Painting (spray)
  • Polyurethane spraying

Dusts from solid forms of isocyanates are a hazard and should not be inhaled. Burning or breaking down polyurethane materials by heating may lead to the production of free isocyanates and a number of toxic gases such as carbon monoxide and hydrogen cyanide.


The health effects of isocyanate inhalation are widely reported and may cause permanent asthmatic symptoms, but more worryingly, the most common adverse health outcome is respiratory sensitisation. It is believed that sensitisation may occur after a single peak exposure to isocyanates. After sensitisation, asthmatic attacks may occur even when exposed to very low levels of isocyanates, which may be much less than the relevant occupational exposure limit.  The severity of the asthmatic attacks which occur after re-exposure have been known to cause death in sensitised. The only effective remedy for the sensitised individual is complete cessation of isocyanate exposure.

Companies carrying out work with isocyanates should ensure they have the correct control measures in place. These control measures may include:

  • Mechanical ventilation storage area Isolation booths
  • Local Exhaust Ventilation (LEV) Systems
  • Respirators
  • Personal protective clothing (overalls, safety eyewear, and  gloves)


Companies need to perform regular checks on the various control measures they use, including:

  • Continuous monitoring of the airflows in ventilated rooms and booths
  • 14 Monthly examination and inspection of LEV Systems
  • Biological monitoring
  • Sampling and analysis of airborne isocyanates
  • Frequent checks on the condition of respirators and breathing apparatus
  • Ensuring an adequate supply of protective clothing.


Due to the inherent problems with the sampling and analysis of air samples for isocyanates, companies should use biological monitoring to demonstrate workers are being adequately protected.