Replacing ozone depleting refrigerants on U.S. Navy submarines has created new design challenges as they interface with the atmosphere control machinery. The environmentally friendly nature of new HFC's and HCFC's is in part due to their higher reactivity. Unfortunately that reactivity causes excessive decomposition resulting in toxic gas production when processed in the catalytic oxidizer, the U.S. Navy Submarine CO and H2 Catalytic Burner. The catalyst/air stream is heated to induce the decomposition of H2, CO and trace organics. An effort is underway to lower the burner temperature to minimize refrigerant decomposition. This paper discusses test results of varying catalyst temperatures when trace contaminants, representative of the submarine atmosphere, are oxidized on the burner's catalyst. The effects of water vapor and catalyst age on oxidation efficiencies are also reported. Both bench scale and full scale burner test results are discussed.