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Review of Submarine Escape Action Levels for Selected Chemicals Summary An event, such as a collision or explosion, that causes a submarine to become disabled can cause on-board fires, potentially exposing crew members to toxic concentrations of combustion products. The product gases include ammonia, carbon monoxide, hydrogen chloride, hydrogen cyanide, hydrogen sulfide, nitrogen dioxide, and sulfur dioxide. Chlorine can also be produced as a result of contact between seawater and submarine batteries. Exposure to any of those gases at high concentrations can cause toxic effects, particularly to the respiratory and central nervous systems, and can result in death. Exposures can also impair crew members’ ability to escape from the submarine. To protect crew members on disabled submarines, scientists at the U.S. Navy Health Research Center’s Toxicology Detachment have proposed two exposure levels, called submarine escape action level (SEAL) 1 and SEAL 2, for each gas. SEAL 1 is defined as the maximum concentration of a gas in a disabled submarine below which healthy submariners can be exposed for up to 10 days without experiencing irreversible health effects. SEAL 2 is defined as the maximum concentration of a gas in a disabled submarine below which healthy submariners can be exposed for up to 24 hours without experiencing irreversible health effects. Exposures at SEAL 1 and SEAL 2 might produce moderate, reversible effects, such as irritation of the skin, eyes, and respiratory tract, but they will not impair the functions of the respiratory system and central nervous system to the extent of impairing the ability of crew members in a disabled submarine to escape or be rescued or perform specific tasks, such as shutting off a valve and using a fire extinguisher.
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Review of Submarine Escape Action Levels for Selected Chemicals The primary objective of establishing SEALs is to protect crew members from adverse health effects—particularly to the respiratory and central nervous systems—from exposures to the combustion gases and chlorine. The Navy will use SEALs as one of many parameters in its Submarine Escape and Rescue Expert System model. That model takes into account several additional parameters, such as geographical position and depth of the submarine, number and medical condition of the crew members, ability to communicate with search and rescue forces, and compartment temperature, and is used by the senior officer to assist in making a decision on whether to escape from the disabled submarine. STATEMENT OF TASK Seeking to protect the safety of submariners, the chief of the Bureau of Medicine and Surgery requested that the National Research Council (NRC review the available toxicologic and epidemiologic data on eight gases that are likely to be produced in a disabled submarine and to evaluate independently the scientific validity of the Navy’s proposed SEALs for those gases. The NRC assigned this project to the Committee on Toxicology (COT) and assembled the Subcommittee on Submarine Escape Action Levels, which prepared this report. The specific task of the subcommittee was to review the toxicologic, epidemiologic, and related data on ammonia, carbon monoxide, chlorine, hydrogen chloride, hydrogen cyanide, hydrogen sulfide, nitrogen dioxide, and sulfur dioxide to determine the scientific validity of the Navy’s proposed SEALs. The subcommittee was also asked to consider the implications of exposures at hyperbaric conditions and potential interactions between the eight gases, identify deficiencies in the database relevant to setting SEALs for the eight gases, and recommend further research. THE SUBCOMMITTEE’S APPROACH TO ITS CHARGE The subcommittee evaluated human data from experimental, occupational, and epidemiologic studies; data from accident reports; and experimental-animal data (single and repeated exposures). The evaluations focused primarily on high-concentration inhalation exposure studies. The subcommittee’s recommended SEALs are based solely on scientific data relevant to health effects. In general, the subcommittee’s approach was to recommend SEALs based on human data to avoid the need for incorporating an interspecies uncertainty factor commonly used in the derivation of exposure guidance levels from animal data. In its derivation of SEALs, the subcommittee did not incorporate an
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Review of Submarine Escape Action Levels for Selected Chemicals intraspecies uncertainty factor for hypersusceptible individuals, because only healthy men are selected as submariners. Asthma is a disqualifying condition for submarine duty. However, some submariners might be hypersusceptible to the effects of the irritant gases and require the use of emergency air breathing devices (EABs). When a large number of crew members use EABs, expired air increases the pressure inside the submarine; this can increase the chance of decompression sickness. Because only a small number of crew members would be expected to use EABs due to hypersusceptibility to the gases, the expired air should not significantly increase the air pressure inside the submarine. The subcommittee believes that for the irritant gases (i.e., ammonia, chlorine, hydrogen chloride, hydrogen sulfide, nitrogen dioxide, and sulfur dioxide), the concentration of the gases to which crew members are exposed is more important than the exposure duration for determining toxicity. Additionally, for several of the irritant gases, an acclimation phenomenon has been well established. In a disabled submarine, atmospheric pressure will likely be higher and temperature will likely be colder than the conditions used in most of the available studies from which SEALs were developed. The subcommittee emphasizes that its recommended SEALs are for normal atmospheric conditions (an atmospheric pressure of 1 and a temperature of 25°C). However, if the pressure increases in the disabled submarine, the SEAL values should be reduced in inverse proportion to the pressure increase. The Navy should be aware that the altered atmospheric conditions on a disabled submarine would affect the toxicity of the gases. For example, cold temperatures will cause crew members to shiver; this will increase the rate of respiration because of an increase in metabolic rate. Lower air temperature might also result in the crew’s breathing unconditioned air, which is a risk factor for lower-airway disease and airway hyperactivity. However, data are lacking on the precise magnitude of effects; therefore, the Navy should conduct research to determine the nature and magnitude of the effects from altered submarine atmospheric conditions. Other parameters that should be taken into consideration are the distribution of the gases throughout the submarine; whether particular gases can be metabolized, absorbed, or neutralized by the crew; and whether the crew can acclimate to the gases at the concentrations present. Because of the lack of data on the effects of such parameters on toxicity of the gases, the subcommittee did not consider them in recommending SEALs. The senior officer on a disabled submarine should be aware of this limitation of the SEALs. The subcommittee did not find information on the effects of hyperbaric conditions on Dräeger-tube (tubes that measure concentrations of specific gases) measurements and recommends that research be conducted to determine the effect of increased pressure on Dräeger-tube measurements. The results of that
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Review of Submarine Escape Action Levels for Selected Chemicals research might show that values obtained for the gases using Dräeger tubes in a disabled submarine need to be corrected to an atmospheric pressure of 1 and 25°C. THE SUBCOMMITTEE’S RECOMMENDED SUBMARINE ESCAPE ACTION LEVELS After reviewing the available data on ammonia, carbon monoxide, chlorine, hydrogen chloride, hydrogen cyanide, hydrogen sulfide, nitrogen dioxide, and sulfur dioxide, the subcommittee concludes that the Navy’s proposed SEALs for all gases, with the exception of SEALs for chlorine, would be protective of the health of personnel in a disabled submarine. In addition, the subcommittee concludes that SEALs for all the gases except chlorine could be set at levels higher than the Navy’s proposed levels and still be protective of the health of crew members in a disabled submarine; at the subcommittee’s recommended higher levels, eye or respiratory-tract irritation or central-nervous-system effects would not be intolerable or impair the performance of specific tasks, including the ability to escape. A comparison of the subcommittee’s recommended SEALs with the Navy’s proposed SEALs is presented in Table S-1. ADDITIONAL RESEARCH RECOMMENDATIONS There are virtually no data on the effects of exposure to a mixture of the eight toxic gases likely to be generated in a disabled submarine from fires and other conditions. The subcommittee recommends that research be conducted on potential health effects caused by exposure to mixtures of those gases. In particular, research should be conducted on the effects of exposure to a mixture of the six irritant gases—ammonia, chlorine, hydrogen chloride, hydrogen sulfide, nitrogen dioxide, and sulfur dioxide. In addition, research should be conducted on the effects caused by the interaction of hydrogen cyanide, carbon monoxide, and hydrogen sulfide—gases that produce hypoxia. As described in Chapter 1, the Navy has developed an approach for the management of mixtures of toxic gases in disabled submarines. That approach uses a cumulative exposure index (CEI), which assumes that the effects of exposure to mixtures of the irritant gases are additive but not synergistic. The subcommittee concludes that the use of the CEI approach is appropriate in protecting the health of the crew. That conclusion is consistent with the conclusions regarding the effects of exposure to mixtures of chemicals in other NRC
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Review of Submarine Escape Action Levels for Selected Chemicals TABLE S-1 Comparison of the Navy’s Proposed SEALs with the Subcommittee’s Recommended SEALs Navy’s Proposed SEALs (ppm)a Subcommittee’s Recommended SEALs (ppm)b Gas SEAL 1 SEAL 2 SEAL 1 SEAL 2 Ammonia 25 75 75 125 Carbon monoxide 75 85 125 150 Chlorine 2 5 1 2.5 Hydrogen chloride 2.5 25 20 35 Hydrogen cyanide 1 4.5 10 15 Hydrogen sulfide 10 20 15 30 Nitrogen dioxide 0.5 1 5 10 Sulfur dioxide 3 6 20 30 appm, parts per million bThe subcommittee’s recommended SEALs are for an atmospheric pressure of 1 at 25°C Values obtained for the gases using Dräeger tubes or other measurement devices in a disabled submarine might need to be corrected to an atmospheric pressure of 1 and 25°C. reports. The subcommittee recommends that hydrogen sulfide be added to the CEI for irritant gases. The subcommittee also recommends that a separate CEI be established for carbon monoxide and hydrogen cyanide, because the effects of exposure to these gases could be additive as well. The use of the CEI approach results in effectively lowering the SEALs when the toxicity of mixtures of gases is being assessed. The subcommittee recommends that the effects of altered environmental conditions (e.g., pressure, temperature, and humidity) on the toxicity of the gases on a disabled submarine be studied. Because fires on a disabled submarine will generate a large amount of particulate matter, research should be conducted on the effects of particles on the toxicity of gases. The subcommittee recommends that the Navy give high priority to the development of battery-operated instruments that are more accurate than Dräeger tubes for measuring concentrations of the gaseous contaminants. In addition to the general research recommendations presented above, the subcommittee recommends further research specific for each gas. Those recommendations are presented in the individual chapters that address each of the gases.
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