Design and Performance of an Inhalation Chamber for Exposing Laboratory Animals to Oxidant Air Pollutants

Abstract

A rectangular inhalation chamber with a volume of 0.27 m³ was designed to provide for continuous whole-body exposures of 10–40 small laboratory animals to oxidant gases. Instead of the more conventional top and bottom cones, this chamber is equipped with inlet and outlet manifolds. The inhalation chamber was found to be very suitable for performing animal exposures to ambient concentration profiles of oxidant gases for a duration of hours up to several weeks or months. Weighing and feeding of the animals and replacing cage boards of a chamber with a load of 20 animals can be carried out in less than 70 min. Two windows provide good observation of the animals and the interior of the chamber: All parts of the interior, window panes, and gaskets can easily be removed for cleaning purposes. Furthermore, the compact size of the inhalation chamber allowed an exposure facility of 27 chambers in piles of 3 in 2 rooms with a total floor space of 24 m². To characterize the inhalation chamber performance, a mathematical model used to describe flow and mixing characteristics of chemical reactors was applied. The model revealed an active mixing volume of 75%, a volume with piston flow of 20%, 5% dead space, and no short-circuiting. From the residence time distribution, axial dispersion was determined. The dispersion number ranged from 0.28 to 0.44, representing a large amount of turbulence. Measurement of concentration distributions revealed maximum spatial deviations of 8% at relatively low ozone concentrations and no detectable differences in nitrogen dioxide concentrations within the chamber.