Inhalation chamber with size discriminator for liquid aerosols.

To minimize data variation in inhalation toxicity testing and to evaluate human and animal hazards of inhaled chemicals, a practical inhalation chamber with a size discriminator for mists was developed to provide high concentration liquid aerosols of defined particle sizes. Liquid aerosols generated with an atomizer were separated by an impinging separator which was composed of aerosol jets directed upward against a flat plate. The principle of the separator eliminates particles larger than a calculated cutoff size in micrometer and submicrometer ranges by changing the orifice diameter of the jet nozzle under constant air flow. The mists thus separated are introduced into the space between two concentric cylinders just above the impaction plate. Ten rats can be positioned around the periphery of the chamber wall equidistant from the impaction plate, with their snouts thrust into the inhalation space. Preliminary testing with olive oil and water aerosols using particle cutoff sizes of 1, 3, and 3.3 micron showed that the obtained separation of particles was very clear, although the cutoff point seemed to shift somewhat to smaller values than calculated; the shift was especially evident with water aerosols. The concentrations obtained were more than 1 mg/liter when the cutoff point was selected at 1 micron. The mist at the inhalation space attained a steady concentration and particle size distribution within 2 min of the onset of mist injection, remained over a 4-hr period, and was cleared within 2 min of the cessation of mist generation.