What is an isocyanate?
Polyurethane is the reaction product of polyols and isocyanates, also known as an A and a B component. The B component is an isocyanate and consists of substances with a certain health risk.
After the A component (the polyol) and the B component (the isocyanate) have reacted, the isocyanate has reacted away and with it the health risk has disappeared.
Risks for the applicator
As indicated above, the B component (isocyanate) can cause health problems in its unreacted form. This will mainly happen through the airways. If the isocyanate is present in the form of gas, vapour or mist, the airways must be protected. For that reason the industry has decided that applicators of these products must use full-face masks during spray application (mist). During other forms of application such as pouring and rolling, the isocyanate is present in liquid form, so no health problems can arise through the airways. Health problems caused by skin penetration are theoretically possible as well, but the chance of this is many times smaller than through the airways and has never been proven. Protection of the skin by means of liquid-tight gloves is therefore more than sufficient.
Risks for the user
Mixing the A and B components forms a polyurethane. In that form there is no longer any health risk for the user, because the isocyanate has reacted away completely and no longer exists. Polyurethane is a very common plastic used in many materials, such as mattresses, cars, shoes and so on.
Conclusion
Isocyanates can carry a certain health risk in pure form, particularly as a gas, vapour or mist. Measures have been taken for applicators to minimise the risks.
After mixing and curing of the A and B components there is no longer any health risk. The resulting product, polyurethane, is safe in use for the end user and carries no health risks.