Calculation of exposure chamber leak rate with thermal correction: a measure of chamber integrity.

Abstract

A method for assessing inhalation exposure chamber integrity by calculation of leak rate was modified to account for temporal changes of temperature in the chamber. In a well-sealed chamber, accounting for thermal effect brought observed leak rates into better agreement with predicted values. Mean estimates of chamber leak rate without thermal correction ranged from 2.9 to 40.6 cm3/min whereas those with thermal correction ranged from 9.6 to 14.3 cm3/min. The average change in estimate of chamber leak rate brought about by correcting for thermal effect was 16.8 cm3/min per K change of temperature in the chamber. Accounting for thermal effect reduced the coefficient of variation for repeated estimates (n = 10) of chamber leak rate from 65 to 15%. The use of temperature-corrected calculation of chamber leak rate minimizes thermal artifact thereby improving decisions about chamber operation based on assessment of chamber integrity.