A Comparison of Methods for the Microbiological Sampling of Compressed Gases

Abstract

A study was carried out to evaluate eight methods for microbiological sampling of compressed gases. The devices tested were: Koch exposed plate; exposed honeypot; exposed bottle; Hollaender & Dalla Valledevice;Portonimpinger; Multistage liquid impinger; ASBC. impinger: membranefiltration method.The devices were compared by presenting a constant number of organisms per unit volume of gas to each device. The organism used was Bacillus stearothermophilus which in its spore form represents the type of organism which is most difficult to entrap. Other aspectsof alternative sampling methods which were examined includedtestingofpotential desiccationeffectsinvolvingvegetativemicroorganismsonmembrane filters, and susceptibility of devices to external contamination. The method recommended was a modification of that of Hollaender & Dalla Valle. This method had the highest collection efficiency and greatest statistical reliability of all those tested. The recommended methods of analysis of the IOB.EBC and ASBC were found to be inferior in a number of respects including susceptibility to external contamination, poor collection efficiency and statistical variability.