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SAFETY
from the smoke and fumes generated; toxic gas that can easily, and quickly, prove fatal to anyone who is unprotected. As with day-to-day house fires in residen- tial communities, it is invariably the smoke that kills: the fatalities at the Sunshine mine in 1972 resulted from smoke or carbon monoxide inhalation. Recent coal-mine tragedies have pro- vided the spur for mine safety organiza- tions world-wide to place an increasing focus on fire risk as a significant poten- tial hazard throughout the industry as a whole. In response, mining companies are investigating new ways of providing safe havens for miners in the event of fire, while a growing number of suppliers are now offering equipment that can help people escape by themselves, and give them shelter, if the worst comes to the worst.
Understanding the Mechanics of Fires
Diesel fuel and hydraulic oil may have revolutionized underground mining tech- nology, but their combustibility remains a well-recognized hazard. The replacement of the early, mineral-based hydraulic flu- ids used in the coal-mining industry by emulsions and water-based materials was not mere chance: it was a clear response to the potential danger they posed. Hard rock mining differs in a number of respects, not least of which is that the equipment that uses flammable fluids is invariably mobile. LHDs, drill rigs, mine trucks and service vehicles are used for their flexibility, in contrast to an essen- tially static longwall face set-up. There are also significant differences in terms of the volumes of fluids needed. The fluid capacity of a longwall installation represents a major fuel source should a fire ever occur, although an individual mine truck can also carry enough diesel and hydraulic fluid to make life more than uncomfortable for any fire crew hav- ing to deal with it. As an example, a 50 t-capacity mine truck from one of the leading manufactures carries an 844- liter (220 gallon) fuel tank and 238 liters (63 gallons) of hydraulic fluid. Aside from these, other potential sources of smoke and fumes include electrical failures, such as overheated fan or pump motors, jammed belt drives on equipment, and conveyor belts. The use of modern materials has reduced the flammability potential of belt conveyors,
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Fire is not the only potential hazard for which personal gas detection may be needed. Chemicals can also pose a risk, and MSA's Altair 4X detector can be equipped with a sampling probe to check confined spaces or containers.
yet they still represent a significant risk in that the belt can continue to travel considerable distances when alight. Either smoldering or open fires will produce both smoke and toxic gas, with the ability to spread along haulages and through raise systems at a truly alarming rate. In addition, there is never any guar- antee that combustion products will behave in a predictable way, even in rela- tion to clearly defined ventilation flows; smoke and gas have been shown to flow back against the airstream if other condi- tions allow it.
A fire needs three components to sur- vive: fuel, heat and oxygen. A hot exhaust system, a leaking hydraulic hose and a good ventilation flow provide all of these without any difficulty, which is one good reason why today's mobile equipment
OEMs invariably fit extinguisher systems on their machines as standard. Yet the risk remains, and the next part of this article looks at some of the equip- ment and systems that can be put in place to protect and rescue people in the event that underground fires get out of control.
Security and Shelter While the
priority for any under-
ground fire incident is to put it out as quickly as possible, the reality is that peo- ple who are in the immediate vicinity when it starts may not be the best equipped to react, or may have no opportunity to do so because of the intensity. In this case, and the decision-making time may be a matter of seconds, the
priority is to
ensure their safety, and that of anyone else in the mine at the time. Since smoke and
FEBRUARY 2012 • E&MJ; 43
initial absolute
