The world of mining safety has come a long way since the canary alarm system. Unfortunately, even with all the advances in mining techniques, disasters can still happen. Having the latest designs for mining safety is especially important to my community here in West Virginia. After the 2006 Sago mining disaster took twelve lives, engineers and mine owners in the state have worked to produce mining chambers or shelters, to save the lives of trapped miners until they can be rescued. These shelters are an engineering feat, capable of sustaining the lives of several miners for up to ninety-six hours. The shelters, which are now found in most underground mines, are the product of endless hours of work from a collaboration of almost every type of engineer.
Several factors had to be taken into account when designing these chambers. They have to provide a stable environment, with sufficient levels of oxygen. The miners also require levels of carbon dioxide and monoxide to be kept at low levels. In addition, the chambers have to keep humidity levels and temperature from rising to an unbearable height. Aside from providing a suitable environment, the miners sufficient food and water, along with first aid supplies and some sort of toilet system. Monitors for gas levels and communication with the surface are also requisite. The challenge is that all of these things must be provided in a small underground cell which would have no access to fresh air.
Two possibilities arise for sustaining oxygen levels of at least 19.5%. One possibility is compressed oxygen tanks. Another less voluminous option would be to generate oxygen from chemical compounds. Oxygen can be thermally decomposed from chlorate compounds, super oxides, or per chlorates. While this option takes less space, it does generate extra heat. As for keeping carbon dioxide levels below two percent, there are also two options for chemically “scrubbing” carbon dioxide out of the air in the chamber. This can be done with lithium monoxide curtains, or canisters of soda lime. Both use carbon dioxide from the air in a reaction that produces other harmless byproducts. Because the curtains “passively” draw carbon dioxide out of the air, they are often used instead of the soda lime canisters, which require fans, and therefore a power source.
Carbon monoxide levels are often dangerously high in mines when a disaster such as an explosion, fire, or collapse occurs. Carbon monoxide levels need to be kept lower than 50 PPM to prevent harm to the miners. For this reason, most mining chambers have an anterior chamber, or air lock, which miners initially enter from the outside. In this chamber, carbon monoxide is purged with air tanks until it reaches a suitable level. Then, when the miners enter the interior chamber where they will live, the air will have only trace amounts of carbon monoxide. Monitors for the gasses allow miners and above ground rescue teams to ensure the rates of oxygen, carbon dioxide, and carbon monoxide remain at suitable levels in the chamber until rescue can occur.
One of the main problems engineers faced in designing these chambers was keeping heat levels at a survivable temperature. MSHA states that temperatures must not go above 95 degrees in the chambers. With heat coming from the miners themselves, the carbon dioxide scrubbing chemicals, and possibly oxygen-generating chemicals, this was a real trial. If the temperature outside the mine is low enough, then heat can be dissipated outside the cell. However, a fire or explosion causes ambient temperatures to rise above 90 degrees, requiring that the cell be air conditioned in some way. This is done with a split system air conditioning unit, utilizing a heat pump. However, by solving the heat problem, another issue is created: power.
Power can be supplied primarily in two ways. One is with a battery system, requiring an invert to convert the DC power to AC to run the air conditioning unit. However, because this option requires much space and maintenance, a diesel generator is usually opted for. The generator requires a small oxygen and fuel supply to operate for four days, but is a viable option. The air conditioning unit also removes some moisture from the air, helping to control humidity levels. The rest of the humidity control falls in most cases to a desiccant, such as silica gel, which would be stored in the chamber. Through these systems, temperature and humidity are kept in check.
One last aspect had to be considered by the engineers designing the chambers. They have to be made of a material which can withstand an explosion and extreme outside temperatures for at least a short amount of time. Also, the material has to have a high thermal conductivity, so it will be able to dissipate heat to the outside if there is no air conditioning system. If there is an air conditioning system, the chamber has to be made of a material which keeps out the heat. A basic steel framework is used in almost all cells for strength. Nylon is commonly used because of its heat-dissipating capabilities. Lastly, some engineering companies have used carbon foam because it is strong yet lightweight, and can withstand temperatures of up to 450 degrees Celsius. Carbon foam also has a low thermal conductivity, making it the perfect material for mining chambers with air conditioning systems.
Aside from the more technical aspects of the chambers, food and water also have to be provided. Each miner needs 2000 calories per twenty-four hours. This is usually provided with military issue food, which has a small volume and long shelf life. One gallon of water a day per miner is stored in a tank kept in the cell. For a toilet, either waste disposal bags or a chemical toilet is used. Chambers are often designed with the toilet in the airlock for privacy. First aid supplies, blankets, and some sort of entertainment are also stored in these cells. Through much design and study, engineers have produced mining chambers which will undoubtedly save the lives of many miners over the years until they can be rescued.
Several types of engineers were involved in producing these mining chambers. Materials engineers were involved in producing the carbon foam and other structural materials of the chambers, along with the desiccant to control humidity. Chemical engineers developed the lithium hydroxide curtains and soda lime canisters which scrub carbon dioxide. They would also have contributed to chemical toilets, if used, and chemicals such as chlorate compounds which produce oxygen. Mechanical engineers have a hand in the airlock entry system to purge carbon monoxide, and also would help design the air conditioning system, including the diesel generator if used. Electrical engineers would be involved in providing power for the air conditioning system through the battery and inverter.
Civil and mining engineers also have a hand in the design of the mining chambers. They provide input as to the position of the chamber in the mine and the number of chambers needed per mine. This would ensure every miner could get to a cell in case of emergency. Computer engineers design programs which are used to design and “test” the mining chambers. Through these programs, disasters and conditions of every kind can be simulated to make sure the cell will stand up to any accident which should occur in the mine.
Chambers such as these are not beneficial for mining emergencies alone. With a few adaptations, they can be used to help people survive many disasters. In our world today, terrorism, even of the nuclear kind, is one of the first applications to come to mind. The main change made would be to have a lead lining encompassing the entire cell, to keep out radiation. Also, the shelter could be designed to hold fewer people so they could stay inside longer, and it could be buried at a shallower level under the ground. Another situation the chamber could potentially be modified to assist in would be in chemical leaks or explosions at the many chemical plants across the country. The main change in the shelter’s structure to suit this purpose would be to have a more thorough air filter and cleansing system in the initial airlock antechamber, preventing the inner chamber from being infiltrated.
Since its beginnings, the safety measures of the mining industry have increased exponentially. However, no matter how many regulations are put into place, disasters inevitably occur at some point. Engineers have designed so many innovative technologies to alleviate the damage of these catastrophes. The prevalence of mining chambers is on the rise today, and will no doubt save many lives in the future. From the coal mine chambers and levees to defibrillators and emergency generators, engineers are certainly revolutionizing the world of safety. Because of men and women who dedicate their lives to protecting ours, we are able to maintain a feeling of security even in this volatile world.
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