Source of information: Article prepared for the 30th International Conference of Safety in Mines Research Institutes Caesars Gauteng Johonnesburg South Africa 5 - 9 October 2003
We suggest a new method and a new technique of fire extinguishing in drifts using a powder extinguishing installation "Vikhr". The ground of new technology application sphere is given.
Fire extinguishing in longwall faces of coal mines is an important scientific and production task. According to SRIMP data 15-20% of all mining fires occur in longwall faces every year . 70% of fires mostly occur all length long between upper and low niches and the rest 30%-directly in niches. Methane, coal, timber supports, rubber cables tubes, hoses, mineral oil etc. are on fire. As a rule it is impossible to extinguish drift fires at the initial stage and it results in a catastrophe. The fires starting in a working of extraction plots as a result of coal spontaneous heating and spontaneous combustion are extremely difficult. As a rule, such fires are accompanied by flashed and explosions of methane and air mixtures and they can be complicated with miners' deaths.
The attempts of fire extinguishing at the initial stage and other successful cases when the fires were put out by miners themselves with the help of manual fire extinguishers, inert dust, wet uniform and even water are known. For example, in 1997 the fires in drifts of Chapaev mine "Shakhtyorskugol" SHC and Glubokaya mine "Donugol" SHC were put out by mining rescue teams with the help of water and powder extinguishers in just 6 hours.
The same year in the drift of the 17th Partsyezd mine "Shakhtyorskugol" SHC mining rescue actions were carried out for 332 hours, labor costs accounted 2704 men hours from which 672 men hours while working in respirators. However, they failed and the fire spread into emptied face space.
In the mine "Kalinovskaya-Vostochnaya" "Makeevugol" SHC exogenic fire in the 4th western drift was isolated by stoppings.
In 1998 in the 9th Pyatiletka mine "Oktyabrugol" SHC the fire occurred in the second panel drift equipped with a mechanized KM-87 complex. Methane burning occurred in the distance of 56 m from the ventilating entry while striking of cutter-loader operating unit bits with seam roof which contained sandstone. Methane caught fire under the seam roof and spread from the cutter loader operating unit into the emptied face space. By that time primary main roof subsidence started, accompanied by intensive pressure on a coal seam and methane emission. After instant burning spreading to the ventilation entry miners started extinguishing the flame with water from spraying hose. Immediate use of three more powder and six foam fire extinguishers was not successful. Emissioning methane kept on burning along the longwall coal face. The mining rescue team and the miners brought 200 kg of inert dust from the belt entry. They started injecting it intensively at the air flow, the place of fire, the coal seam and its roof, which were enormously poured with water from the fire irrigating pipe line and they managed to put out the fire. The mining rescue teams arrived at the place of accident and under conditions of 8-hour main roof subsidence treated the face working and the emptied face space with fire extinguishing powder from UPSH 1000 and OPSH 1000 devices. Then the mining rescue teams increased air consumption up to 1000 nrVmin per a working and organized constant control over gas and temperature situation at the place of accident being afraid of fire reappearing. Samples analysis showed the absence of burning.
The given case is a demonstrative example of a successful use of primary fire extinguishing means to fight methane burning in mines.
The point of the suggested fire extinguishing technology is as follows. As a means of fire extinguishing in longwall face fire cases we suggest using powder fire extinguishing device "Vikhr". The "Vikhr" unit with a fan of local conditioning (SVN 6) and cassette pipeline (TGV with a diameter 600mm) is located in a mine buggy having upper cover and face hatches with a diameter 700 mm to prevent it from dust, soiling and damages. Another mine buggy with a powder supply amounting 2,5-3 t is located in 2 3 meter distance. Both mine buggies are located exactly in front of the drift distribution point. While approaching the drift mine, the cars with equipment and powder move together with the distribution point. In case of fire occurrence, fire extinguishing will be performed by giving finely dispersed P 2AP or superfinely dispersed P-4AP powder to the burning area along the ventilation pipes in the distance. Fire extinguishing concentration of powder in the air has to be about 130 g/m3 for finely dispersed powder and for superfinely dispersed powder not less then 70 g/m3.
While spreading air and powder mixture along the working, there occurs its sediment on the walls and soil of the working, and under the temperature of 190200 degrees there starts thermal decomposition of its particles. As a result of this, powder concentration in the mixture gradually decreases. That is why at the entry of a burning area the contents of powder in the air has to be 2 4 times more than pointed above fire extinguishing limit.
The "Vikhr" unit is intended for continuous and intensive giving of fire extinguishing powder in the place of fire from the side of coming ventilating current. It is applied for remote fire-extinguishing and localization of underground fires in horizontal and inclined workings aired by the mine air depression or by fans of local conditioning while burning of timber support, conveyer belt, electric equipment under voltage. Its technical characteristics is given below.
Technical of the "Vikhr" unit.
Fire-extinguishing powder (P2AP) consumption while supplying it along the ventilation pipeline with a diameter 600 mm kg/s is 0,1.
Fan:
type SBM-6m productivity, m3/min 200-460;
pressure, Pa 800-2000 ;
overall dimension (without a fan), mm 2245x985x720;
mass (without a fan), kg 40;
The operating principle is based on the use of air flow for airpowered mixture ejecting. This device can be attached both to the inlet and outlet pipe of local conditioning fan as BMN, SBM 6 m, BM 6 m.
The chamber is used to mix powder with the air which is fed by the fan and to supply air and powder flow into the fire area.
The chamber consists of a bunker, a confusion unit, a perforation tube and a diffusion unit. The confusion unit, the perforation tube and the defusing unit are "inserted" into the cowling.
The device operates in the following way. While connecting this device to the outlet pipe of the fan, air is divided into two flows, one of which is directed into the confusion unit and the other one is directed into the clearance between the cowling and the lowest part of the chamber. The part of the air flow coming into the confusion unit along the tubes gets into the bunker circle collector and makes the powder friable. The pressure is created in the collector exceeding the pressure in the perforation tube. This process provides the level powder feeding. The air and powder mixture coming through the fan gets into the ventilation pipeline and then into the fire area.
It is necessary that mining workers should be taught to do all kinds of mine rescue operations in order to put out fires at the initial stage.
That is why subsidiary mine rescue teams (SMRT) have been created in the sections of refining and preparation work and in the sections of ventilation and mine transport. These teams are completed from the most skillful and well trained workers and engineers.
SMRT size is appointed so that at each section there are 2 or 3 workers. Mine rescue equipment and apparatus have to be kept at each section of a mine.
SMRT members' actions in case of fire are the following :
connecting a suction nipple of the fan with a diffusion unit of the device, and fixing joint by the clamp;
inserting the net and the cutter with grating for polyethylene powder-bags cutting;
joining the cassette with the pipe-line outlet pipe of the local conditioning fan and directing it into the drift;
providing continuous powder supply into the drift after miners leaving.
The chart for range defining of efficient operating while two "Vikhr" devices are operating simultaneously.
The given technology will provide efficient range of powder supply to the distance up to 120 m and will allow to reduce considerably the number of developed fires in longwall faces at the expense of the active fire extinguishing at the early fire stage.