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The primary objectives of this study were (a) to measure potential exposures of applicators and assistants to airborne methylene diphenyl diisocyanate (MDI), (b) to measure airborne concentrations of MDI at various distances from the spray foam application, and (c) to measure airborne MDI concentrations as a function of time elapsed since application. Other study objectives were, (a) to compare the results from filter and impinger samples; (b) to determine the particle size distribution in the spray foam aerosol; (c) to determine potential exposures to dichlorofluoroethane; and (d) to measure any off-gassing of MDI after the foam had fully cured. This study was conducted during application of spray polyurethane foam inside five single-family homes under construction in the United States and Canada. Spray foam applicators and assistants may be exposed to airborne MDI concentrations above the OSHA permissible exposure limit. At these concentrations, OSHA recommends appropriate respiratory protection during spray foam application to prevent airborne MDI exposures above established limits and to protect against exposure to dichlorofluoroethane (HCFC-141b). Airborne MDI concentrations decrease rapidly after foam application ceases. The highest airborne concentrations measured after 15 min and 45 min were 0.019 mg/m3 and 0.003 mg/m3, respectively. After 45 min, airborne concentrations were below the limit of quantitation (LOQ) of 0.036-microg per sample. For samples taken 24 hours after completion of foaming, results were also below the LOQ. Approximately two-thirds of the total mass of the airborne particles in the spray foam aerosol was greater than 3.5 microns in diameter. Airborne MDI concentrations determined by filter sampling methods were 6% to 40% lower than those determined by impinger methods.

Isocyanates can cause occupational asthma. By using available HPLC-UVF methods, isocyanates can be quantified only at levels above 1% of the Permissible Exposure Limits (PEL). Once sensitized, workers can react to concentrations below these limits of detection (LOD) making these methods insufficiently sensitive to adequately evaluate trace amounts of isocyanates present in air or in materials at safe levels for sensitized workers. This article describes a novel method for isocyanate analysis allowing the quantification of 2,4TDI and 2,6TDI monomers at very low concentrations using HPLC-CIS-MS-MS. The method's sensitivity increases with a decrease in the alkali radius. The LOD is 0.039 ng mL(-1) for 2,4TDI and 0.100 ng mL(-1) for 2,6TDI in solution when lithium is the alkali adduct, which is 20 times more sensitive than HPLC-UVF method. This new method allows determination in foam at levels of 0.078 ng g(-1) for 2,4TDI and 0.200 ng g(-1) for 2,6TDI respectively, for a 0.5 g foam sample. This is more than 100 times more sensitive than other methods for determining free monomers in solid materials. Analytical reproducibility and precision are better than 92% and 93% for both diisocyanate monomers. The use of HPLC-UVF conventional method failed to detect unreacted isocyanates in foam samples, but TDI monomers were quantified by HPLC-CIS-MS-MS.

A model of exposure to isocyanates, based on knowledge of industrial processes and starting materials and the results of industrial hygiene surveys, is proposed. This model of exposure suggests the concentration and physical form of airborne isocyanate monomers and oligomers. A new sampling and analytical system was developed that is capable of determining the physical and chemical characteristics of occupational exposure to a variety of aliphatic and aromatic isocyanates as required by the exposure model. The sampling system consisted of a dual-filter 37-mm cassette, in which the first filter captured aerosol phase contaminants and the second captured vapor phase isocyanates through derivatization with 9-(N-methylaminomethyl) anthracene (MAMA). Urea derivative recovery by the sampling system, isocyanate-MAMA reactivity, and linearity of the calibration curve were evaluated in the laboratory. The practicality of the system was evaluated during field trials. Sampling times are reduced to 15 min, and the detection limit for TDI, HDI, and MDI was 1.0 micrograms/m3. A partial validation of the new sampling system was performed for HDI vapor by comparison to a standard method in field trials and for TDI vapor in a controlled test atmosphere. The analytical system may also be used to measure the concentration of oligomeric isocyanates. Airborne concentrations of isocyanates were measured in two foam plants, nine paint shops, and two foundries to verify the usefulness of the model. Exposure in foam plants was predominantly to gaseous monomeric isocyanates. Exposure to oligomer isocyanates was higher than expected in paint shops. Both monomer and oligomer isocyanates were undetectable in foundries.