Workplaces where two-part polyurethane paints are sprayed, most typically in the painting of motor vehicles. TDI evaporates most easily and is therefore the most harmful of these isocyanates. However, all isocyanates can pose a health risk during the spraying of paint or foam, when droplets containing unreacted isocyanates can be inhaled. Similarly, 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.
Isocyanates react slowly with water to produce carbon dioxide.
While this is not in itself a hazardous reaction, dangerous pressures can develop inside closed containers if an isocyanate becomes contaminated with water. As isocyanates can only be smelled at concentrations considered to be harmful, it is dangerous to rely on odour to detect the presence of an isocyanate. The purpose of training is to allow employees to work safely and to react appropriately if things go wrong. Workers must be informed of all identified hazards in the workplace. They must be given information, instruction, training and supervision in safe working procedures, including fitting, use and storage of personal protective equipment.