A calibrated delivery system for inhalation challenge of toluene di-isocyanate vapor

The vapor of TDI, a chemical commonly used in the plastics industry, may be associated with pulmonary symptoms at various concentrations. Because of the high volatility and adsorptivity of TDI, it has been difficult to deliver known, dilute concentrations of TDI to test subjects in inhalation challenge studies. A delivery system has been developed which can be calibrated to deliver an air-TDI mixture having a given flow rate and TDI concentration. The delivered gas stream is produced by diluting a gas stream having a low flow rate and a fixed concentration of TDI with a high-flow-rate stream of TDI-free air. A TDI detector continuously monitors the concentration of the resultant mixture, which is delivered to the subject by means of a face mask. For dilute mixtures, the output concentration is proportional to the ratio of the input flow rates; the proportionality factor depends on temperature and the geometry of the system. The flows for the described system could be regulated to produce concentrations in the range 0.0 to 0.08 ppm which remain stable to within +/- 10%.