You're the flight surgeon. Isocyanates are the most common cause of occupational asthma.

Isocyanates are the most common cause of occupational asthma. They are used to produce polyurethanes for the manufacture of plastics, adhesives, surface coatings, and both flexible and rigid foams. Of the several types of isocyanates commonly used, toluene diisocyanate (TDI) is the most significant commercially and toxicologically. Asthma develops in approximately 5 to 10% of workers regularly exposed to TDI. Once sensitized, asthma can develop after exposure to extremely low concentrations of TDI. Although suggestive, an immunologic mechanism remains unclear since studies vary in their findings of positive skin tests and specific IgE. Once developed, isocyanate asthma persists with continued exposure and in some even after removal from exposure.