Polyurethanes are produced by reacting diisocyanates with polyols. Other chemicals, such as catalysts, surfactants or flame retardants, may be included in the process. Atmospheric emissions of MDI and TDI during isocyanate production or other applications are low, as they are carried out in closed equipment with controls on all vents.

Large quantities of MDI and TDI are routinely transported in a variety of dedicated containers ranging from ships' tanks to plastic drums. Most is transported without a drop being spilled. However, in the unlikely event of a spillage to the aquatic or soil environments, the MDI or TDI reacts to form inert polyureas. Also, because MDI and TDI are hydrophobic, they react with water forming, predominantly, insoluble inert solid polyureas and releasing carbon dioxide. Of course, any spill should be addressed appropriately in compliance with U.S. environmental laws and in accordance with the manufacturers MSDS. 

Emissions from rigid foam processes have been measured to range from less than 0.001 to 0.04 g per metric ton of MDI used. Emissions from flexible foam molding processes were measured (Chapman, 2001) at 0.2 to 6 g per metric ton MDI used. TDI emissions from slabstock foam production have been measured many times and average about 25 grams per ton of TDI used (Chapman, 2000). Other uses of TDI, in elastomer or molded foam production, generally release similar or smaller amounts of TDI.

MDI and TDI present on soil as the result of an accident reacts with moisture and slowly forms solid polyureas, which can be expected to be essentially unreactive in the environment for millennia. Whether it’s MDI or TDI, the liquid material would flow or freeze depending on temperature before reaction.

» view Regulatory Compliance Assistance Program
» view Isocyanate Emissions Toolbox

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The polyurethane industry, working together through the American Chemistry Council's (ACC) Center for the Polyurethanes Industry (CPI) and the Spray Polyurethane Foam Alliance (SPFA), has launched an enhanced product stewardship program to support further understanding of the benefits of spray polyurethane foam and its continued safe use and handling. A part of this outreach, a new Spray Polyurethane Foam Health and Safety website, www.spraypolyurethane.com, has been launched by CPI and SPFA that contains new materials, literature and posters to increase understanding of spray polyurethane foam (SPF) product stewardship information.

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