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This paper will report US Navy submarine philosophy and test experience with the emergency atmosphere control system. A vital aspect of emergency recovery within contained environments is the ability to maintain life while directing escape or awaiting rescue. Emergency atmosphere control differs from primary life support in several key areas. The primary atmosphere control system provides a habitable atmosphere so that the crew can live comfortably and work efficiently in an enclosed environment. Additionally the primary atmosphere control system controls chronic and acute toxicants to minimize both short and long term health consequences. For long duration missions, primary atmosphere control is generally regenerative and may include redundant components for reliability. The emergency life support system replaces the primary system in the event of a catastrophic failure.

The US Navy is currently conducting a new round of atmosphere control sea trials on operational submarines. Atmosphere trials have been conducted over the past four decades. Traditionally each trial builds upon the prior one. For this next round of atmosphere control trials, the US Navy started with a bottom up approach to the entire trial. A team of engineers, chemists, industrial hygiene scientists and medical experts was assembled to develop the test protocol and then execute the trial. The team established a methodology to identify the monitoring requirements, sampling location and periodicity. Two underway atmosphere trials are currently scheduled. The first trial will be held onboard a submarine designed in the 1970's and commissioned in the mid 1990's. The second trial will be conducted on a newly designed submarine soon entering operational service.

Since the 1950's US submarines have employed a heated catalytic oxidizer to remove trace contaminants and hydrogen from their atmosphere. A copper oxide-manganese oxide catalyst, Hopcalite® [1], is the traditional material for this application. In the late 1990's the United States supplier ceased production of this catalyst. This paper describes the Navy's efforts to qualify new catalyst and to establish a new performance based specification. Results of land based and shipboard testing are summarized.

The replacement of refrigerant CFC-12 (dichlorodifluoromethane) with ozone-friendly HFC-134a (1,1,1,2 tetrafluroethane) in submarines has not only required changes in the refrigeration system but the life support equipment as well. Modifications to the refrigeration systems, catalytic oxidizer used for air purification and atmosphere analyzer were required to implement the conversion. Each of these modifications required careful laboratory and full scale testing to assure no adverse impact on the submarine equipment or crew.

The Navy uses both real time and retrospective methods to analyze the air in submarines. The methods are described in detail. The reasons for the selection of the methods and their capabilities and limitations are presented. A few recent results are shown to demonstrate these methods.

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.

Alternate refrigerant HFC-134a has been found to be substantially more reactive than CFC-12 in the US Navy submarine catalytic burner. The burner operates at 316°C and uses a manganese dioxide/copper monoxide catalyst, Hopcalite. The reaction of HFC-134a produced hazardous quantities of HF in the outlet air in excess of the established submarine exposure limits. No other hazardous products, such as carbonyl fluoride, were detected.