Isocyanates

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.

Controls

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.