Exposures to 1,6-hexamethylene diisocyanate during polyurethane spray painting in the U.S. Air Force

1,6-Hexamethylene diisocyanate (HDI) exposures were measured during polyurethane enamel spray painting at four Air Force bases. Breathing zone samples were collected for HDI monomer and polyisocyanates (oligomers) using three sampling methods: NIOSH Method 5521, the Iso-Chek sampler, and the total aerosol mass method (TAMM). Exposures to HDI monomer are low when compared to current occupational exposure limits; the highest 8-hr time-weighted average (TWA) exposure found was 3.5 micrograms/m3, below the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 34 micrograms/m3. HDI oligomer levels were higher; mean task exposures indicated by either the Iso-Chek sampler or TAMM are above the Oregon ceiling limit of 1 mg/m3. Eight-hour TWA exposures, however, were much lower, with only one exceeding the Oregon standard of 0.5 mg/m3. Poor worker practices commonly observed during this study included: standing in downwind positions so paint overspray passed through breathing zones; spraying toward other painters; and using excessive paint spray gun air cap pressures. Workers should stand in upwind orientation relative to the aircraft being painted, causing overspray to move away from the painter's breathing zone; adjust their position to prevent spraying other painters or limit paint application to one worker at a time; and use air cap pressure gauges prior to spraying to limit spray gun air cap pressures and reduce paint overspray generation rates. These improved techniques will result in reduced worker exposures to isocyanates.