I. Examples of casualties caused by gas explosions in the fire zone According to incomplete statistics, from 2000 to 2004, there were 12 fire accidents in the Hegang mining area, resulting in 34 deaths and 25 injuries. The gas explosion accident occurred in the Donghai Coal Mine of Jixi Mining Group of Heilongjiang Province and the Baoxing Coal Mine of Fangzheng County. It was also caused by improper measures in dealing with fires. The gas explosion occurred in the closed fire zone, which caused the serious casualties of the disaster relief personnel. 1. On December 16, 2001, the Hegang Regional Mine Ambulance Brigade handled the fire accident at Linyuan Coal Mine in Hegang City. It has already been supported by Mufang when the construction of the plate is closed. The two dampers were opened for nearly an hour at the same time. The instability of the underground airflow caused a sudden gas explosion in the goaf. The shock wave destroyed the wood, causing 9 rescuers on the scene to fall, and 4 people were slightly poisoned by carbon monoxide. . 2. On April 8, 2002, when the Donghai Coal Mine of Jixi Mining Group handled the mine fire, dozens of operators were organized to close the fire zone. In the process of the firefighters closing the fire zone, a gas explosion suddenly occurred in the fire zone. Four people were killed and 19 were injured. 3. On January 11, 2003, the 5th section of the second section of Baoxing Coal Mine in Fangzheng County, Heilongjiang Province, was naturally ignited. More than 30 people in the mine organization were preparing to construct two permanent closed closed fire zones. When the second road was closed, a gas explosion occurred in the goaf. The 36 people working in the underground, except for 2 people, were all killed. The remaining 34 people were killed. 4. On January 1, 2004, a gas explosion occurred in the +20 elevation fire zone in the upper left section of the second level of the five-stone gate of Hegang Coal Mining Company, Hegang Coal Mining Company, destroying the closed wall. When the four squadrons of the rescue team went into the well to evacuate and inspect the gas survey site, a second gas explosion occurred in the fire zone, and the two team members were burned.
II. Causes of Gas Explosion in Fire Zone The cause of gas explosion in the fire zone should be analyzed according to the three elements of the explosion. Since the fire source always exists in the fire zone, the main trend of oxygen and gas concentration in the fire zone is analyzed. . According to the characteristics of the gas explosion in multiple fire zones, we can analyze the types of fire explosions into the following forms: 1. The reverse flow of the wind is shown in Figure 1. Under the normal conditions of the ventilation system, there is a certain After the wind flow, the wind direction is also stable. The upper wind flow does not accumulate gas conditions, and the gas and combustion products from the lower wind coal seams flow away with the wind flow. The lower air flow does not pass through the fire source even if there is gas accumulation condition, and the explosion cannot occur. If the network is complicated due to the change of the state of the equipment of the ventilation facility or the wind passage of the roadway, under the action of other wind pressures, the downhole airflow may be reversed, and the gas flow reverses to make the gas on the downwind side reach the explosion limit. The source, which causes the gas explosion, that is to say, if the wind direction is changed in the fire area, there is a possibility of gas explosion. Adopting a wind adjustment plan must be cautious. 2. The fire zone is closed as shown in Figure 2.
In the fire zone during and after the closure, due to the isolation of oxygen supply, the combustion in the fire zone also consumes residual oxygen, generates carbon dioxide, and infiltrates into the atmosphere of the fire zone together with the gushing gas, causing the oxygen concentration in the air of the fire zone to continue. decline. As the gas in the coal seam continues to rise, the gas concentration continues to increase and the gas concentration curve is on the rise. See the trend trend of O2 and CH4 in the fire zone. If the amount of gas in the enclosed area is large, the gas concentration will rise to the explosion limit before the oxygen concentration has dropped to 12%, and an explosion will occur. If the fire area is tightly closed, the gas in the area is still infiltrated by rocks and coal seams, and the pressure in the area increases, which can suppress the emission of CH4 and slow the rate of increase of CH4 concentration. When the O2 concentration is above 12%, the CH4 does not reach the explosive limit concentration, and no explosion will occur. When there is air leakage in the air, the fresh air flow increases the O2 concentration, and the gas concentration rises to within the explosion limit. The O2 concentration has not yet fallen, and there is an open flame in the fire area, which is prone to explosion. The order of closure is important when closing the fire zone in the high gas area. Due to the improper sequence of the fire zone closure, the wind flow in the fire zone may be reversed and other roadway gas may be supplied to the fire zone. 3. The oxygen supply from the wind flow has not been completely cured in the fire area as shown in Figure 3. However, after the closure, the oxygen supply is isolated. When the O2 concentration in the fire zone is less than 5%, the flame combustion will begin to gradually weaken or even extinguish. When the O2 concentration is below 1%, the flame combustion is completely extinguished. However, even under the condition that the concentration of O2 in the air is zero, the smoldering of the combustible material in the ignition zone can last for a long period of time, and the fire zone is in an oxygen-deficient and smoldering state. If the ventilation system is unintentionally changed due to artificial wind adjustment or construction of equipment, the fresh air containing enough O2 is supplied into the fire area, causing the fire to increase and the gas reaching the explosive limit concentration to pass. The source of fire can cause an explosion in the fire zone. If the fire zone does not fully reach the extinguishing condition, the wind supply will be vulnerable to explosion. 4. Gas supply type As shown in Fig. 4, in the case where there are many air leakage passages in the fire area, a small amount of airflow in the fire area passes through the gas-free or gas concentration, and even if the gas passes through the fire source, it cannot be exploded. The external gas enters the fire area under the action of wind pressure, or the gas accumulated in other roadways communicating with the fire area is brought into the fire area, which will cause gas explosion. Special attention should be paid when discharging gas after closing the fire zone.
III. Suggestions for Preventing Control of Fire Zone Explosion Measures in Mine Fires It can be seen from the above analysis that fire zone explosions generally occur in unstable ventilation systems or in old roads connected to fire zones, and the wind roads are complicated; It does not leak tightly; it is only when people adjust the wind path; if the fire area is closed in an improper order. In order to avoid the above phenomenon, special measures for preventing and controlling the explosion of fire areas are proposed. (1) To fully understand the situation of the fire zone. 1. Further investigate the location of the fire source, clarify the scope of the fire zone, and identify the waste roadways leading to the outside or the ground in the fire zone, geological drilling, grouting holes, and goafs and fires. The lanes and wind roads in the district must be closed in a timely manner. 2. Understand the mining situation of the coal seam in the fire zone, the lost coal pillars, the gas emission situation and the changing law, and the concentration of other gases in the fire zone. Grasp the geological structures in the fire zone and its vicinity (such as folds, faults, fracture zones, etc.) to prevent gas from entering the fire zone during closure or causing air leakage. 3. Understand the roadway layout, ventilation system, ventilation facilities, section and support form of the roadway, air volume, wind direction, smoke and temperature of the roadway. All roadways must be clearly contrasted (interlayer relationship, mining relationship, roadway relationship, and temporary relationship). 4. The ambulance team's reconnaissance work strives to be meticulous and serious, try to find out the fire, and do a reconnaissance. The command department should study the fire in detail, analyze the possibility of gas explosion and the complexity of the fire fighting work, and formulate a thorough fire fighting plan and safety measures to ensure the safety of the disaster relief personnel. (2) Controlling air volume and reducing fires During mine fires, wind flow control is one of the most important measures in disaster relief. Wind flow control includes air volume control and wind direction control. In the normal production period, the air volume is mainly controlled, and in the catastrophic period, the wind direction is mainly controlled to prevent the wind flow disorder. Generally, under the premise of ensuring that gas does not accumulate, the wind is reduced to reduce the fire, and a certain amount of air is flowed into the fire zone, so that the inflammables generated by the fire and the gas that flows out continuously flow out of the fire zone to maintain the wind direction consistency. In the case of dealing with fires caused by gas combustion and gas explosion, wind current short-circuit measures can be used in the absence of personnel in the well. The personnel then observe at a safe location. (3) After ensuring the stable control of the ventilation system, it is necessary to ensure the stability of the underground ventilation system, ensure that the wind flow continuously flows forward, and there is no phenomenon of wind flow reversal and gas supply into the fire zone. The following measures should be taken: 1. Look at the main fan to ensure the normal operation of the fan. 2. The local ventilator should remain in its original state and should not be stopped at will. 3. Special personnel look at the damper to ensure that the underground ventilation system and ventilation network maintain the original state. 4. If there is a reversal of the wind current, the phenomenon that the wind pressure (wind volume) changes frequently or the smoke flow rolls off frequently or the wind speed entering the fire area is less than the minimum wind speed to prevent the smoke from rolling off, all personnel must retreat. (4) Monitoring the gas and observing the sound. To deal with explosion accidents in fire areas, monitoring gas is an effective and important means. The combination of timed manual detection and chromatographic analysis and analysis is used to accurately reflect the gas data in the fire zone, establish observation records, and draw gas curve curves. To measure the air volume, set up an observatory at a safe location that is not threatened by an explosion shock wave, and grasp the changes in the fire zone to guide the implementation of various disaster relief work. When the gas in the fire area changes abnormally and is in an unstable state, it is strictly forbidden to enter the well. (5) Closure of the fire zone According to the actual conditions of the underground and the characteristics of the fire, the closed sequence should be selected. The influence of each roadway on the wind path of the entire fire zone and the change of wind pressure must be carefully considered. When multiple lanes need to be closed, the roadway that has no major influence on the system airway should be closed first. 1. When closing a fire area with explosive danger, first consider the problem of controlled explosion. Generally, the air side is sealed first, and the sand bag is used or sandblasting method is used, and a ventilation window is reserved to ensure a certain air volume is supplied to the fire area. After the explosion-proof work is completed, the ventilation window is tightly closed, and after 24 hours of observation, the construction is returned to the air return side. 2. When the fire zone is closed, special personnel should be arranged to closely monitor the change of the return air in the fire zone. The fire zone sampling should be taken at the top, middle and bottom of the roadway to accurately reflect the air composition of the fire zone. in this way. The best way is to install the beam tube once and perform beam tube monitoring to avoid multiple entry. 3. When the fire area is closed, it is necessary to pay attention to monitoring the change of atmospheric pressure. The rise of atmospheric pressure is the best time to build a firewall, which helps to avoid the spillage of fire gas from the enclosed area and threatens disaster relief personnel. 4. Only when the sealing condition of the fire area is good, and the air leakage can be ensured, the simultaneous sealing method can be considered, the sealing time can be shortened as much as possible, the temporary board can be quickly closed, and the oxygen supply condition can be quickly cut off, but the sealing should be ensured at the same time. Sex, the door hole is reserved when the construction plate is closed to ensure the ventilation of the fire area before the door hole is blocked. When the door hole is closed, the command is unified to ensure that it is closed at the same time as scheduled. If it can inject inert gas such as CO2 and N2 before closing at the same time, it is more conducive to ensuring the safety of the fire zone.
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