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US Navy submarines have used Hopcalite catalyst (MnO2, CuO) for over 30 years to oxidize carbon monoxide, hydrogen, and many trace organic species. During that time, the material has been manufactured by the same company, and the performance of fresh Hopcalite has never shown significant variation. Recently, a new lot of Hopcalite was tested and found to be 300% more active toward one specific refrigerant than measured in previous lots. In life support applications, unexpectedly high activity can generate hazardous products that endanger crew and equipment. This paper will describe and interpret the tests performed by the Naval Research Laboratory and Naval Surface Warfare Center to investigate different Hopcalite samples.

The US Navy monitors atmospheric constituents aboard nuclear submarines with a ruggedized mass spectrometer called the Central Atmosphere Monitoring System (CAMS). The CAMS aboard each submarine is capable of sensing oxygen, nitrogen, carbon dioxide, carbon monoxide, water vapor and refrigerants in all regularly occupied spaces. This setup fulfills the majority of the Navy’s needs, however, the CAMS is not capable of “sniffing” enclosed spaces nor providing data after certain casualty situations. To meet these two critical needs and provide backup monitoring capability for the CAMS, the US Navy currently uses various gas-sensing colorimetric tubes. Aside from the traditional unpopularity of these tubes with the fleet, recent investigations have shown them to be inefficient, expensive and difficult to obtain. With that background, testing was funded to determine if the colorimetric tubes could be replaced with modern portable atmosphere monitoring equipment.