Performance of a human inhalation challenge exposure system. I. Gases

The purpose of this study was to characterize and evaluate the performance of a whole-body human exposure chamber for controlled test atmospheres of gases and particulates. This article is a report on the performance of the system with gas phase agents. Results of the performance of the system with particulate phase agents will be presented in a separate report. The chamber was constructed from Plexiglas with a volume of 2.13 m(3) (75 ft(3)) and operating at a flow rate about 1.0 m(3)/min (34 cfm). Both the makeup and exhaust air were HEPA-filtered. CO(2) was used as a tracer gas and its concentration was measured using Metrosonics aq-5000 instruments. The CO(2) concentrations used in this study ranged from about 5000 to 12,000 ppm. Observed and predicted concentrations at equilibrium of test material were in agreement within 1.7%. Concentration of CO(2) was found to be even horizontally throughout the chamber, with a small initial lag of about 30 sec between the maximum concentration at the top and the bottom of the chamber. The system can thus be reliably used for inhalation challenge procedures for gases.