This paper examines the characteristics of 261 work-related asthma (WRA) cases exposed to isocyanates reported to an occupational disease surveillance system in Michigan from 1988–1998, and reviews Michigan Occupational Safety and Health Act (OSHA) inspections at 42 of the facilities where they worked. After October of 1993 when the Michigan OSHA program implemented a newer sampling methodology for isocyanates, 42 inspections were conducted in relation to the WRA cases reported. Samples for isocyanates were not collected in one facility. Isocyanate air levels at 40 of the 41 companies where measurements were taken revealed exposures <0.005 parts per million (ppm), as a time-weighted average (TWA). Sampling for isocyanates at one company revealed a level of 0.005 ppm for TDI (TWA).
At 36 of the 42 inspections, similarly exposed co-workers as the index cases completed a breathing symptom questionnaire. Although non-significant, companies were more likely to have co-workers indicate breathing symptoms where the index case reported exposure to one or more isocyanate spills (11 of 13 companies with spills vs. 15 of 23 companies without spills; OR 2.93, 95% CL 0.43-34), and a higher average percent of symptomatic co-workers compared to the companies where the index case reported no spills (23% vs. 16%; OR 1.42, 95% CL 0.99-2.03). Again, although non-significant, there were more MDI-using companies in which at least one co-worker reported breathing problems than TDI or HDI-users (83% vs. 67% vs. 56%; chi-square 2.49, p=0.29). MDI-using companies had a higher average percentage of symptomatic coworkers than TDI-users and HDI-users (23% vs. 15% vs. 14%; chi-square 9.92, p=0.007).
Michigan workers are exposed to isocyanates below permissible exposure limits yet continue to develop WRA. Spills may account for some but not all of these cases. Despite the lower volatility of MDI, co-workers with exposure to MDI were more likely to have respiratory symptoms than co-workers exposed to TDI or HDI. The majority of these 42 isocyanate-using companies (72%) had no medical surveillance program to monitor for worker sensitization. Compliance with OSHA laws, or “being within permissible exposure limits” will not guarantee the prevention of WRA. Effective engineering controls, established spill clean-up procedures, a comprehensive hazard communication program, and a medical surveillance program to identify newly sensitized workers for prompt removal from exposure may help to prevent isocyanate-induced WRA. Further work is needed to determine the relative effectiveness of each of these components in preventing isocyanate-exposed workers from developing asthma.