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APPENDIX A SURVIVAL SUBSYSTEM Two life support systems are required for the proposed coal mine rescue and survival system: a lightweight individual emer- gency breathing device that can be carried continuously by a coal miner and a life support system capable of supporting 15 men for up to two weeks for a small refuge chamber. Emergency Breathing Device The present emergency breathing device for individual miners is the self-rescuer. This device uses the catalyst hopcalite to con- vert carbon monoxide to carbon dioxide as the mine atmosphere is breathed through the self-rescuer. The name hopcalite refers to various mixtures of the oxides of manganese, copper, cobalt, and silver. In "four-component hopcalite" all of these oxides are pres- ent, and the catalyst is precipitated as hydrous oxide. In the two- component catalyst only oxides of manganese and copper are present; the copper is precipitated as a carbonate. Both of these hopcalite catalysts are very effective for low-temperature oxidation of carbon monoxide, although the four-component catalyst rapidly loses its activity at elevated temperatures. Hopcalite is relatively immune to the effects of water vapor at elevated temperatures, but at lower temperatures the catalyst must be protected from water vapor by the addition of a drying agent. It must also be protected from organic materials that can poison the catalyst. In a 1 1/2 percent carbon monoxide atmosphere, temperatures at the mouthpiece of the self-rescuer may reach 185°F because of the exothermic reaction of the conversion of carbon monoxide in the catalyst. At concentrations higher than about 11/2 percent, the temperature of the inhaled air becomes greater than can be tolerated by the man wearing the self-rescuer. In addition to the disadvantage of the high temperature of the inhaled air, the percentage of carbon dioxide in the air breathed by the wearer is increased by three factors. First, following a mine fire or explosion, the concentration of carbon dioxide in the air is substantially increased. Second, the carbon monoxide is converted to an equal percentage of carbon dioxide by the action of the self-rescuer. - 15 -
- 16 - Third, some of the wearer's exhaled breath, which contains carbon dioxide as a body waste product, is rebreathed. Carbon dioxide is a powerful respiratory stimulant causing an involuntary increase in the minute volume (the volume of air inhaled each minute) even though there is no change in the work rate. Thus, although a few percent of carbon dioxide would not of itself be harmful, the effect of the gas is to increase the breathing rate of the wearer (possibly causing fatigue), reducing the lifetime of the self-rescuer. Two models of the self-rescuer are now currently available. One is rated by the Bureau for 30-minutes duration and the second is rated for a 1-hour duration in an atmosphere containing carbon monoxide. The 1-hour device has a heat exchanger built into the mouthpiece to reduce the temperature of inhaled air. For either device there is no way the wearer can determine whether the catalyst is functioning properly. In many instances following an explosion, the miners must pass through heavy smoke and dust concentrations to egress from the mine or to reach an area where barricades can be erected safely. Occasionally the smoke and dust concentrations are so heavy that the miners cannot see each other and can communicate only by touch or by voice. An emergency escape device should take this into consideration and should provide the capability for intermittent voice communication. Following is a description of two concepts that the Committee believes might overcome the disadvantages of the self-rescuer in providing emergency respiratory protection. Although these two approaches appear promising, there are no doubt many other concepts that should be considered. A relatively short- duration study (three to six months) would bring many of these to light. Both concepts considered here use a plastic hood to completely enclose the head of the wearer. The preferred material is polyimide, which was used in the FAA development of a proposed protective pas- senger smoke hood for aircraft. Polyimide was selected because of its nonmelting property when exposed to extreme heat and because it is transparent and nonflammable. It reportedly does not begin to char until temperatures exceed 1472°F. Other desirable features include high tensile strength, folding endurance, low shrinkage, insolubility in inorganic solvents, and inertness to fungi. It is conceivable that a coal miner wearing this hood could pass quickly through a relatively high temperature flame without suffering severe burns.
- 17 - The first system being considered uses a potassium superoxide canister to generate a 45-minute oxygen supply. The wearer would inhale air through the potassium superoxide from the hood or from the hood and a small supplementary breathing bag. If the circulation system can be so designed that there is no build-up of high carbon dioxide concentrations within the hood, the wearer can temporarily remove the mouthpiece and breath the air trapped in the hood while talking with other miners. Returning to breathing from the mouthpiece would flush the carbon dioxide from the hood, again permitting voice communication. It is believed that the physiological effects of the build-up of carbon dioxide when breathing directly from the hood would provide sufficient warning to the miner that he would resume breathing through the mouthpiece before becoming anoxic. This system could be carried on the miner's belt, and additional devices and potassium superoxide canisters could be stored in strategic locations within the mine; then should the miner be trapped in an irrespirable atmosphere for longer than 45 minutes, he would locate an additional device or replace his potassium superoxide canister. The second concept is quite similar, except that it uses a chlorate candle for the oxygen source. A 45-minute-duration candle is connected by a small tube to a mouthpiece inside the hood. The air exhaled by the wearer passes through a filter to remove the carbon dioxide and then into the hood. The filter might be built into the mouth- piece; however, sufficient filtering materials for a 45-minute duration might make this concept excessively cumbersome. Excess oxygen passes out the neck dam of the hood. Refuge Chambers If small refuge chambers are established near each working section and advanced or retreated as the mining advanced or retreated, it would not be economically feasible to provide a hole from the surface to the chambers. Therefore, the chambers must be equipped with self-contained oxygen-producing and carbon dioxide removal systems. In the concept under consideration, all life support equipment--oxygen supply, carbon dioxide removal agent, chemical light sources, food, water, blankets, oxygen level detectors, methane level detectors, carbon monoxide detectors, medical supplies, and perhaps a chemical toilet--would be mounted on a wheeled cart or "red wagon. " This wagon could easily be moved by a shuttle car as the refuge chamber was advanced or retreated.
- 18 - Three possible oxygen sources are being considered for the refuge chambers: potassium superoxide, chlorate candles, and high-pressure air or oxygen. Hydrogen peroxide also was considered, but was rejected because of its toxicity and the potential of its vapor becoming explosive in high enough concentrations. Potassium superoxide has the advantage of absorbing carbon dioxide in the production of oxygen. The systems using chlorate candles or compressed air or oxygen would require carbon dioxide scrubbers. Potassium superoxide will theoretically produce 33. 8 percent oxygen by weight with approximately 90 percent of the potassium superoxide actually available for conversion. The density of potassium superoxide is approximately 41 lb/cu ft, and it generates 415 BTU's per pound of oxygen produced. Potassium superoxide has been used in breathing systems for many years. Numerous long-term tests have been run: in l960 the Air Force ran a 1-man, 168-hour test using potassium superoxide ; in l960 the Navy ran a 6-man, 8-day test using potassium superoxide ; and in 1964 the Boeing Company, under contract to NASA, performed a 5-man, 30-day sodium superoxide test. Currently potassium superoxide is used for oxygen production and carbon dioxide removal in several small research submersibles. The crew could be expected to have an oxygen consumption of 2. 0 lb per man-day with a respiratory quotient of 0. 82, requiring a carbon dioxide removal rate of 2. 25 lb per man-day. This would require about 7 lb of potassium superoxide per man-day, which would absorb 0. 17 lb of water per man-day. Thus, for a 200 man-day system, 1,400 lb of potassium superoxide would be required. It might be possible to purchase potassium superoxide in these quantities for about $3 a pound, or about $4, 200 for a 200 man-day supply. Building this into a system might double this price. Chlorate candles theoretically produce 48 percent oxygen by weight with approximately 90 percent actual availability. The density of candles is 141 lb/cu ft, and they produce approximately 422 BTU's per pound of oxygen generated. Candles made of alkali metal chlorates have been used in submarine oxygen supplies for years and are currently planned for emergency oxygen systems in the C-5A military transport and the new generation of commercial jet liners. The standard submarine
- 19 - candle is approximately 12 in. long and 7 in. in diameter, weighs 25 lb, and burns for 45 minutes liberating about 10. 2 lb of oxygen, an equivalent of 5 man-days. This candle is presently available for about $15. A 200 man-day supply, therefore, would cost $600. Chlorate candles, like superoxides, have essentially an infinite shelf-life. There are, however, disadvantages to the candles when used in a mine system. First, they decompose at 1300 to 1500°F and would ignite any methane that leaked into the candle container. Second, they are not self-regulating, as is potassium superoxide, and require frequent monitoring of the oxygen level to determine when an additional candle should be ignited. Third, chlorate candles would have to be supplemented with a carbon dioxide removal system. Another possibility for refuge chamber oxygen is compressed air or oxygen tanks. A 2, 400-psi tank containing 1, 500 cu ft of oxygen--sufficient for 60 man-days--costs approximately $225 when purchased in lots of 100 or more. Regulators and oxygen would slightly increase the total cost. One disadvantage is the difficulty of storing high-pressure gases for long periods of time without leakage. Leakage rates during long-duration storage would have to be determined, as would the effects of the shock waves generated by an explosion on the regulators, valves, and seals. A high-pressure oxygen system, like a chlorate candle system, would require a carbon dioxide scrubber. Potential carbon dioxide removal systems could use lithium hydroxide, baralyme, or lithium peroxide. Lithium hydroxide has the disadvantage of being very irritating, although it is not toxic. It would cost about $10 per man-day, or $2, 000 for a 15-man, 14-day supply. For a system to evolve from existing technology, baralyme is probably the most attractive carbon dioxide removal agent. Although on a weight basis twice as much baralyme is required as lithium hydroxide, it does not have irritating properties and thus is easier to handle. In addition, it is considerably cheaper at about $4 per man-day, or $800 for a 15-man, 14-day supply. Lithium peroxide has not been used extensively in life support systems; however, it has an obvious advantage over other carbon dioxide absorbers in that it evolves oxygen. Lithium peroxide is very promis- ing if its use could be developed in time for the near-term system.
- 20 - Any of the systems using a carbon dioxide removal agent and possibly even the potassium superoxide system would require a hand-cranked blower to circulate the air through the chemical bed. A chart would be provided with the system giving the length of time the blower should be operated each day as a function of the number of men in the chamber of the number of days they have been there. With this type of system, an activated charcoal bed could be added to aid in removing undesirable odors, although this would not be absolutely necessary. The small refuge chamber would be designed to be frequently reestablished as mining advanced or retreated in a given section. The bulkheads which would be used to enclose the crosscut forming the chamber would be made of sections capable of being loaded onto a shuttle car by 2 or 3 men. The life support system and all other equipment would be mounted on a cart that could easily be pulled by a shuttle car. The chamber should always be within a few.thousand feet of the working face so that miners in the section could travel rapidly to it and receive almost immediate protection from the gases generated by the explosion or fire. Depending on the type of system chosen, cost for the cart would range from $10, 000 to $15, 000. Trade-off studies should be conducted to select the optimum system, which should then be developed and tested.
- 21 - REFERENCES Emrnett, Paul H. , ed. , Catalysis, Vol. VII, Reinhold Publishing, New York, 1966.~ Office of Aviation Medicine, Department of Transportation, Federal Aviation Administration, A Protective Passenger Smoke Hood, April 1967. Fabuss, Bela M. , et al. , "Self-Contained Generator for Shelter Use, " Montsanto Research Corporation, 1964, AD 616 639. Keating, Donald A. and Konrad Weiswurm, "KO_ Passive Air Regeneration Studies for Manned Sealed Environments, " WADD TR 60-707, Wright Air Development Center, December l960. Mancinelli, D. A. and E. L. Michel, "Environmental Requirements of Sealed Cabins for Space and Orbital Flights," NAMC - ACEL - 418, May 24, l960. "Manned Environmental System Assessment, " The Boeing Company, NASA Contract NASw 658, May 1964, N65-12076. General Reference Charanion, T. R., A. J. Glueckert, R. G. Barile, and J. D. Zeff, "Environmental Control Systems for Closed Underground Shelters, " General American Transportation Corporation, Contract Report, Contract No. OCD-OS-62-56, April 1963, AD-413416.
