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.A steady flow of air must continuously move over the fire to carry off explosive gases, distillates, heat, and smoke away from the fire.The only way to keep the air flowing over the fire area is to leave one intake airway and one return airway unsealed while the other airways are being sealed.Then as a final step, the last intake and return can be sealed simultaneously.This method enables the ventilation to continue over the fire area until both seals are completed.Occasionally two teams are used to simultaneously seal the last intake and return.In such circumstances, the teams should be in constant communication between themselves or with a coordinator in order to synchronize the simultaneous construction.Usually fires are sealed far enough away from the fire in order to keep the heat and pressure in the sealed area from affecting the seals.In some cases though, the only site available for sealing a fire is close to the fire area where the heat and smoke are very intense in the returns.As a result, the mine rescue teams will not be able to work in the returns for very long.In this type of situation, the fire can be systematically sealed to protect the team as much as possible from the heat and smoke in the returns.When the intake seal is finished, the pressure will be reduced in the returns and the brattice curtain can be dropped immediately by the rescue teams, spadded to the ribs and weighted at the bottom-all within a few minutes.The teams then immediately leave the mine.If, for some reason, the seals do not hold because of the heat and pressure within the sealed area, the fire will have to be resealed further away from the fire.c) Explosion- If an explosion is likely to occur after the seals have been erected, arrangements should be made to close the last seals after all personnel are out of the mine.This can be done by leaving hinged doors (similar to drop doors) that will close automatically in one or more of the seals; usually it is the last intake seal to be erected.These doors can be temporarily held open with a counterbalance in the form of a perforated bucket filled with water.The holes in the bucket should be made to allow sufficient time to elapse before the water drains from the bucket.Using this device allows enough time for the personnel in the mine to reach the surface before the door or doors close to complete the seals.When fires are being sealed in gassy or dusty mines, it is essential to apply a thick coating of rock dust to the ribs, roof, and floor of entries, and to crosscuts for several hundred feet outby the seal, and if possible, inby the seal.In the event of an explosion around the fire, there will be less chance of propagating a coal-dust explosion.d) Isolation- It is important to isolate the sealed area from the mine in as many ways as possible.All power cables and water or air lines entering the sealed area should be removed or severed from the sealed area.Removing a section of rail from the track and a section from any other conductor leading into the sealed area is advised also.3.Permanent Seals- A mine cannot be returned to production until the sealed area of the mine has been closed off with permanent seals.After temporary seals are erected, the usual waiting period of 72 hours is recommended before beginning construction on the permanent seals.a) Types of Permanent Seals- Usually permanent seals are built with solid concrete blocks, although other material may be used.When building seals withconcrete blocks, mortar is used in between them, and the entire front of the seal is plastered over.Urethane foam can be put around the edges to seal any leaks.Urethane foam is an effective sealant around the perimeter of the seal, but should never be applied more than an inch thick because the potential for spontaneous combustion increases with greater thicknesses.All permanent seals should be well-hitched in the roof, floor, and ribs to make them as airtight as possible.The type of permanent seals used for sealing a mine fire depends on:lThe type of materials available;llThe length of time the materials are to be used; 0 The necessity for complete airtightness; andllThe strength required to withstand pressure or crushing.Permanent seals must be very well built to withstand the outward pressure on them, which can be very substantial.lb) Considerations While Building Permanent Seals1) Isolation- When erecting permanent seals, the area inby the seals is to be isolated from the rest of the mine.All cables, lines, and track which were removed or severed.For the temporary seal must also be removed or severed for the permanent seal.2) Air-Sampling Tubes- The permanent seals must have provisions for collecting air samples from within the sealed area.If air-sampling tubes were installed in the temporary seals, it will only be necessary to extend those tubes and valves to the permanent seals if they do not already reach.4.Taking Air Samples- After the fire area is sealed, it may be necessary to take air samples of the air behind the seal to assess the quality of the air.The best time to do so is when the sealed area is under positive pressure or "breathingout.Pressures within and without sealed areas will vary according to temperature and barometric pressure changes
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