Isocyanates are chemicals used in:

  • the production of polyurethane foams : e.g. foam mattresses and rigid foams in chairs etc.
  • paint and lacquers in motor vehicle repair – in 2-pack paints in which isocyanate hardener or activator is added to a pigmented or clear base.
  • some adhesives.

What is the problem?

A single, high exposure to isocyanate vapour, aerosol or dust may cause immediate effects such as irritation to the eyes, nose and throat, resulting in coughing and a dry throat.

More severe effects can include chemical pneumonitis. Such a high exposure can cause immediate sensitisation, resulting in occupational asthma.

A series of smaller exposures over weeks, months and years may lead to wheezing, coughing, shortness of breath or a tight chest, symptoms of asthma.

Contact dermatitis may occur from skin contact with un-reacted isocyanates.

Exposure to isocyanates may occur via:

  • Inhalation of vapour – espe-cially from TDI class isocyan ates which are very volatile (TDI = toluene di-isocyanate)
  • Inhalation of airborne droplets from spraying or spray painting
  • Inhalation of dust while handling pure MDI (MDI = methylene bisphenyl isocyanate)

Isocyanates can react violently with alkalis and acids e.g. sodium hydroxide, ammonia. They also react (slowly) with water and this can result in a dangerous build up of pressure in closed containers.

Problem assessment

Employers should carry out air sampling to assess the risk. An exception is in spray booths where operators are wearing a full face airline respirator (as exposure outside the mask would be expected to be above the exposure standards).

Where a ventilated spray booth is being used, assessment of the airflow in the booth can be carried out and compared to New Zealand Standards. Pre-employment lung function testing is recommended and annual lung function testing and medical exam is required.


As always, the first steps in control should be substitution/elimination, isolation then minimisation. Minimisation controls include:

  • local exhaust ventilation for spray painting
  • use ventilated booths
  • spray-painters – do not remove visor or hood before ventilation clears the spray booth of mist and do not remove respirator before leaving the booth
  • safe cleaning practices e.g. of spray guns good housekeeping
  • appropriate PPE appropriate training

The Isocyanate Code of Practice requires air testing where TDI and MDI are being sprayed. Air monitoring should be discussed with a hygienist before being recommended or carried out.


DOL Approved Code of Practice for the Safe Use of Isocyanates.

New Zealand Standard for spray Booths AS/NZS 4114:2003.

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