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- 3 - SURVIVAL, SUBSYSTEM The survival subsystem consists of a lightweight, portable emergency breathing device that a coal miner can carry on his person and two types of refuge chambers--large chambers centrally located and small chambers for individual sections. Emergency Breathing Device The present device for protection of individual miners in an emergency is the self-rescuer, which uses the catalyst hopcalite to convert carbon monoxide to carbon dioxide as the mine atmosphere is breathed through the self-rescuer. In a 1 1/2 percent carbon monoxide atmosphere, which is not unusual in areas close to a mine explosion, temperatures at the mouthpiece of the self-rescuer can reach 185°F due to the exothermic reaction of the conversion of carbon monoxide in the catalyst. The self-rescuers presently in use are rated by the Bureau of Mines for 30 minutes in a carbon monoxide atmosphere. A new model recently introduced has been rated for 1 hour. Most coal operators now provide self-rescuers for all men working underground. Although self-rescuers have saved the lives of many miners, they are only marginally adequate for the job for which they are intended. An emergency life support device for underground workers should provide a respirable atmosphere, regardless of the environ- ment, should permit intermittent voice communication to allow miners to communicate in areas of high dust and smoke concentrations, should be of the longest possible duration, and should be light and compact enough that miners will not object to carrying them continuously. The Committee believes that a device meeting the above criteria can be developed from existing technology to provide a 45-minute oxygen supply. With a market estimate of 50, 000 to 75, 000 units over a two-year period, such a device could be sold for under $50 per unit. This compares very favorably with the price of the improved model of the self-rescuer that provides substantially less protection at a slightly lower cost. Refuge Chambers When unable to escape following an explosion or fire, miners are trained to isolate themselves from poisonous gases by erecting barricades of wood, brattice cloth, and other materials.
- 4 - Many miners have been saved by well-sited and well-constructed barricades. However, analysis of the disaster reports from 1951 to 1968 shows that the majority of miners who erected barricades died behind them. This high fatality rate is not wholly attributed to poor barricad- ing methods or lack of materials. Many coal companies have placed barricading kits at strategic locations in their mines. Instructions have been given that these materials are not to be used for any other purpose. When materials have been available, fatalities have occurred for a variety of reasons; poor training in erecting barricades, failing to enclose sufficient air volume behind the barricade, or waiting until the air was contaminated with carbon monoxide before erecting the barricade. Some gas will leak past even a well-constructed barricade and delays in rescue have proved fatal. To overcome the weaknesses of barricades, two types of refuge chambers are being proposed; large central chambers that could support all of the men that might be in the mine and small chambers that would be located near each working section and would support the men employed in that section. Although there are many possible designs for both types of chambers, a typical large chamber might be a room cut into a coal pillar from a crosscut. The room would be lined with concrete blocks or bricks and would have substantial roof support. The chamber itself and both ends of the crosscut in which it was located should have masonry and steel doors that would with- stand the forces of a subsequent explosion. Communications and forced fresh-air ventilation would be through a 6- to 8-in. hole to the surface. A typical small chamber would be a crosscut with steel or inflatable bulkheads anchored to the coal at both ends and a self- contained life support and communications system inside. Holes to the surface from the small chambers would not be economically feasible. The bulkheads would be designed to withstand a 20-psi shock wave. When the chamber was not in use, doors in the bulk- heads would be left open to provide ventilation from the normal mine ventilation system. The bulkheads and the cart housing the life support and communication subsystems would be designed for portability. The chamber could be easily advanced or retreated in the section or moved to a new section.
- 5 - The choice between the two types of chambers should be based on a hazard analysis of the mine and on the duration of the emergency breathing devices available. Some mines may most efficiently and inexpensively provide protection by using chambers of both types. The Committee is considering computer simulation methods of hazard analysis to assist in determining the requirements for refuge chambers. For example, any mining crew should be able to reach a portal or refuge chamber without passing a potentially dangerous area such as the edge of a caved area that might contain explosive mixtures of methane or entries leading directly to another mining section that might be an ignition source. Possible oxygen sources for small chambers are chlorate candles, high-pressure oxygen, and potassium superoxide, which, in addition, removes carbon dioxide. Hydrogen peroxide was considered, but rejected because it is toxic and its vapor in high concentrations is explosive. Chlorate candles and high-pressure oxygen or air require carbon dioxide removal agents. Potential agents are lithium hydroxide, lithium peroxide, and baralyme (a mixture of calcium and barium hydroxide). Lithium hydroxide is very irritating but not toxic. Lithium peroxide has not been used extensively in life support systems, but has the advantage of evolving oxygen while removing carbon dioxide. Its use might be developed in one year, but it is primarily of interest for the longer term system. Thus baralyme looks most promising and is inexpensive. A 15-man, 14-day supply costs about $800. Any system 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. The small refuge chambers would be located in each working section and moved as mining advanced or retreated. Miners would never have to travel more than a few thousand feet to reach a chamber and receive immediate protection from the gases of an explosion or fire. The life support equipment includes--in addition to the oxygen-generating and carbon dioxide removal systems--food, water,
