Polyurethanes, Isocyanates, and Asthma
Polyurethanes are a miracle of chemistry. They are used to make foams for packaging and insulation, paints and coatings, adhesives, sealants, elastomers, and fibers (think spandex!). What makes all of this possible are isocyanates.
Isocyanates are chemicals containing the highly reactive isocyanate group. When there are two or more isocyanate groups on a molecule (diisocyanates or polyisocyanates), they can link together with certain other molecules to form long chained polymers called polyurethanes.
Isocyanates are powerful sensitizers. Repeated inhalation of isocyanates, or a single large dose, can cause respiratory sensitization (asthma). If this happens, very low exposures can cause asthma attacks. Symptoms may develop immediately upon exposure or after a delay of several hours. Even if the sensitized worker is permanently removed from any isocyanate exposure, the asthma may persist. Repeated skin exposure can cause dermal sensitization. In addition, some studies suggest that skin absorption may cause respiratory sensitization.
Isocyanates are also very irritating to the skin, eyes, and respiratory system. They can cause coughing, chest pains, or difficulty in breathing even if a person is not sensitized.
Isocyanate aerosols created during spraying and foaming are an inhalation hazard. For some isocyanates (e.g., TDI and HDI), evaporation of the material can create enough vapors to be a hazard.
Polyurethanes come in one-component and two-component systems. The two-component systems always have hazardous isocyanate groups. In some one-component systems, all the isocyanate groups have been reacted and are no longer hazardous. Once fully cured, polyurethane products do not release isocyanates unless sufficiently heated (e.g., burning, welding, and hot-wire cutting).
Review your Material Safety Data Sheets (MSDS) if you might be using products containing isocyanates. The abbreviations of some commonly used isocyanates are TDI, MDI, HDI, and IPDI. Also, look for ingredients containing the words “isocyanate” or “diisocyanate” in them. The isocyanates may be in the form of monomers, oligomers, prepolymers, or polymers.
There are exposure limits in California for the TDI, MDI, HDI, IPDI, HMDI, and NDI monomers to limit how much of these chemicals employees may safely breathe. For guidance on airborne occupational exposure levels to other isocyanates, we can look to other states (Oregon), other countries (the United Kingdom), and manufacturers’ guidelines.
To protect workers from isocyanate aerosols and vapors, use local exhaust ventilation whenever possible. Respirators can also provide protection. Use airline respirators or air-purifying respirators with organic vapor cartridges and N-95 prefilters. If air-purifying respirators are worn, a change schedule for the cartridges must be implemented. Be sure to prevent skin and eye contact also. Consult the MSDS or contact the manufacturer for recommendations on gloves and protective clothing.
To learn more about isocyanates, look under I on the NIOSH web site at www.cdc.gov/niosh. If you need help identifying or controlling isocyanate hazards, request an industrial hygiene consultation through State Fund’s Loss Control Department or your broker/agent.
"Information or recommendations contained in these articles were obtained from sources believed to be reliable at the date of publication. Information is only advisory and does not presume to be exhaustive or inclusive of all workplace hazards or situations."
The above evaluations and/or recommendations are for general guidance only and should not be relied
upon for legal compliance purposes. They are based solely on the information provided to us and relate
only to those conditions specifically discussed. We do not make any warranty, expressed or implied, that your workplace is safe or healthful or that it complies with all laws, regulations or standards.
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