Gerald M. Fleming

A proposed standardized method for bronchoprovocation tests in toluene diisocyanate-induced asthma

Exposure to vapors of toluene diisocyanate (TDI), a chemical widely used in the plastics and rubber industry, can cause respiratory disease at low concentrations and can be a nonspecific respiratory irritant at high concentrations.‘. 2 While these clinical patterns have been known for some time, laboratory diagnosis has been a challenge because of several problems, including lack of methods for performing quantitative studies of the effect of inhaling precise TDI concentrations. For this to be possible, a delivery system must produce adjustable, stable concentrations of TDI that can be monitored accurately throughout the time of exposure to TDI fumes. Three major problems are encountered in the implementation of a suitable delivery system. First, TDI is an extremely volatile liquid at room temperature which readily produces a dense vapor (vapor density = 6.0; air = 1). Thus, exposed TDI liquid can create vapors of high concentration which vary with location, room size, and room ventilation characteristics. Second, TDI vapor readily adsorbs onto the surface of most materials, except glass and Teflon,” so that efficient transport of TDI test gases is difficult. Third, the present commercially available instruments for the continuous measurement of TDI concentration have an overall response time of 18 min. Therefore, unless the delivery system is stable throughout test procedures, it is impossible to determine the actual concentration of TDI the subject is inhaling because one is always measuring 18 min behind the event. Previous methods of controlling inhaled dosages of TDI for challenge-response studies have been based on reproducing a given environmental situation. Pepys et al.” had their subjects tested in a closed room, in which a polyurethane varnish containing