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.
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.