What Are Isocyanates?

A 2013 OSHA directive, which OSHA now presents as an archive document that may no longer represent OSHA policy, says isocyanates are widely used to make flexible and rigid foams, fibers, coatings such as paints and varnishes, and elastomers, and are increasingly used in the automobile industry, auto body repair and building insulation materials. A NIOSH report says spray polyurethane foam is a widely used insulation and air sealant, and that exposures to its key ingredient, isocyanate, and other spray foam chemicals during and after installation can cause asthma, sensitization, lung damage, and skin and eye irritation.

The OSHA directive says occupational isocyanate exposure can cause occupational asthma, skin and mucous membrane irritation, hypersensitivity pneumonitis and chest tightness, and that some isocyanates are classified as potential human carcinogens. It says skin contact is a significant cause of respiratory sensitization, which can occur at very low exposure levels and lead to asthma attacks with later exposures.

For methylene bisphenyl isocyanate, or MDI, the NIOSH Pocket Guide lists a recommended limit of 0.05 mg/m3 as a time-weighted average and a 10-minute ceiling of 0.2 mg/m3, with an OSHA ceiling of 0.2 mg/m3. For toluene-2,4-diisocyanate, it lists symptoms including bronchitis, bronchospasm, asthma and skin sensitization, and marks it as a potential occupational carcinogen.