Assessment of the relationship between isocyanate exposure levels and occupational asthma

As part of a previous study, we identified Ontario cases of isocyanate-induced occupational asthma (OA) and the companies at which they worked. The Ontario Ministry of Labour maintained a computerized database including isocyanate air sampling determinations conducted by the Ministry. Within this database, we compared levels of isocyanate concentrations measured at 20 case companies [with compensated isocyanate asthma (OA) claims] with 203 noncase companies, based on air samples collected during the same 4-year period during which the OA claims arose. The proportion of case companies that were ever recorded as having a measured ambient isocyanate concentration of > or = 0.005 ppm was greater than that for noncase companies, for TDI users (43% vs 22%), and for MDI users (40% vs 27%). This reached conventional significance when combined across companies and isocyanate types (50% vs 25%; P < 0.05). This provides some evidence that facilities having OA claims have higher isocyanate exposures than do those without claims.