Cause and prevention of misfire accident in mining

Cause and prevention of misfire accident in coal mining operation

underground blasting in coal mine is the process of loading special safety explosives and electric detonators for coal mine into the drilled blast hole, connecting one end with the foot line of electric detonator with non fixed line (blasting bus), connecting the other end with the blaster, and inducing explosives by supplying electric energy to electric detonators to break coal and rock mass. For various reasons, the detonator and explosive will not explode or the detonator will explode but the explosive will not explode after being energized and fired. This not only reduces the blasting efficiency, increases the consumption of blasting equipment, but also threatens the safety of operators. Therefore, it is necessary to analyze the causes of misfire and put forward preventive measures

1 cause analysis of misfire

1.1 problem of explosive materials at present, the explosive materials used in coal mines are mainly coal mine permitted electric detonators and explosives

1) the problems related to detonators mainly include: ① the quality defects of detonators (such as false welding of bridge wire, unqualified resistance, etc.) cause excessive resistance or instability, or even open circuit, so the power on is poor or does not conduct; ② Improper storage or use will damp and deteriorate the detonator head, rust the bridge wire, etc., resulting in a sharp decline in the sensitivity of the detonator and failure to detonate; ③ Detonators of different manufacturers, specifications and materials are mixed. Because the resistance values of electric detonators used in hybrid are quite different, according to Lenz Joule law, in the series electric explosion network, as long as the bridge wire resistance is different, the ignition heat cannot be completely consistent. Even if its resistance is the same or similar, the electric ignition characteristics will not be the same, so it is easy to cause misfire

2) the main problems of explosives are as follows: ① the damp, hardened and deteriorated explosives are used, which reduces the detonation sensitivity and detonation stability, resulting in the non detonation of the roll when the shape is exquisite; ② When using ordinary ammonium nitrate explosives, due to on-site construction reasons, it is easy to make the blast hole spacing of the mining face too small, and the detonator initiation time difference is too large, which is easy to cause the first blast hole to squeeze the explosives in the adjacent blast hole; ③ In wet and watery operation conditions, non water resistant explosives are used, or water resistant explosives are used without waterproof jackets, or the waterproof jackets are water leakage and wetting failure, and there are pulverized coal and rock powder between the cartridges, resulting in explosive misfire

1.2 operation process problems

1) in the blasting network, the wiring between the foot line and the foot line, the foot line and the connecting line, and the connecting line and the blasting bus are falsely connected, which increases the joint resistance and affects the joint conduction, so that the ignition impulse of the detonator is too small, and it is not easy to detonate, resulting in explosion rejection. At the same time, due to negligence of work, it may also cause leakage of wiring in some parts of the road, resulting in open circuit

2) the exposed joint or damaged part in the road contacts with external conductors and wet objects to cause electric leakage, resulting in the detonator not exploding

3) when charging and filling gun mud, the operation is not carried out according to the regulations. When charging, the gun rod is used to send the medicine too hard, and the explosive is compacted, reducing its sensitivity

4) the detonator pin wire is broken or the insulating skin is damaged, resulting in open circuit or electric leakage so that the detonator does not explode, and the exposed joints of the detonator pin wire contact each other, resulting in a short circuit and the detonator does not explode

5) due to improper operation, the detonator in the detonator is placed unreasonably or the detonator in the detonator is separated from the original position during charging, resulting in non explosion of explosives

6) the design of blasting circuit is unreasonable, and the number of detonators connected exceeds the initiating capacity of the detonator

1.3 blasting power supply problem the blaster malfunctions and the power is insufficient, so that the current in the local network is less than the quasi blasting current of the detonator, causing the detonator not to explode

2 prevention of misfire

2.1 shooting tools should maintain good performance. Before use, the blaster and the blasting bus shall be checked and maintained, and unqualified blasting tools shall not be issued and used. It shall be collected on duty to prevent collision and beating, and the battery shall be replaced in time. It is strictly forbidden to check the residual current by short circuit and spark of terminal posts; The initiating capacity of the detonator is slightly greater than the number of shots fired at a time

2.2 strictly enforce the storage management system of explosive materials and the detonator test and acceptance system of explosives. Do not issue and use deteriorated explosives and unqualified detonators. Detonators of different manufacturers and specifications shall not be mixed and used. Instantaneous detonators shall not be used as one millisecond detonators. 45% of them are caused by improper selection of materials and poor specifications

2.3 charge and connect according to the regulations. During charging, the shooter should straighten the detonator foot line with one hand and gently feed the roll into the blast hole with a wooden gun stick with the other hand to prevent the foot line from being broken or the insulating layer of the foot line from being broken. At the same time, the roll in the blast hole should be in close contact to ensure good explosive transmission. During the connection between the detonator and the bus, the bus and the foot wire, and the foot wire and the foot wire, the blaster's hand should be cleaned and wiped dry, and then the wiring head should be screwed and tightened. The road joint shall be connected without beard and knots, the rust on the connection end of the foot line shall be scraped off, and the joint shall be suspended. If the bus is not long enough, the bus of the same specification should be extended. The connecting line should use the pin line with the same specification as the detonator pin line in the road. The connection method should not be changed at will. After the connection, it should be carefully checked to avoid wrong connection, missing connection, and the total resistance of the network should be measured after the connection

2.4 do a good job in the management of on-site blasting equipment. The blasting equipment box should be stored in a dry and safe place without dripping water. It is not allowed to open and tear off the explosive skin package without charging and blasting

3 handling of misfire

in practical work, if you encounter misfire, you should carefully analyze it, find out the cause, and take effective measures to eliminate it. Handle the misfire on duty, and do a good job of shift handover. The following methods should be adopted when dealing with misfire

3.1 misfire caused by poor connection can be connected again

3.2 if the reconnection shooting does not sound, another new hole parallel to the misfire can be drilled at least 0.3m away from the misfire, and the blasting can be reloaded

3.3 after re drilling and charging, the shooter must carefully check the coal and gangue of the explosive and collect the unexploded electric detonators

it is strictly prohibited to dig with a pick or take out the originally placed explosives and detonators from the hole of the gun. It is strictly prohibited to continue deepening the residual hole of the gun hole. It is strictly prohibited to dig out the medicine by drilling. It is strictly prohibited to blow these car upholstery strips and Silver lower guard holes with compressed air. This is because detonators and explosives are relatively stable chemicals for a time. Under the action of the outside world, their own stability is destroyed, and they carry out chemical reactions quickly, leading to explosions. Therefore, detonators and explosives are sensitive to impact, friction, sparks, stray current and high temperature. If you dig with a pick or take out the originally placed lead wire from the hole of the gun and pull out the detonator from the medicine, it will be impacted, and the high-sensitivity initiation in the detonator will rub against the inner wall of the tube and catch fire, resulting in the explosion of the detonator. Pulling out the electric detonator will detonate due to the stray current of the mining face. The same is true of collecting unexploded detonators in the blasted coal and gangue after blasting. It is strictly forbidden to dig out the explosive by drilling. Blowing the blast hole with compressed air is because it will cause the explosive to self explode due to high temperature caused by extrusion and friction. Therefore, at any place in the coal mine, every time the blasting smoke is dissipated, the blaster must first go to the blasting site to check whether there is misfire under the safe condition that the roadway top sample holds the solid plate and the support does not collapse. If a misfire is found, it should be dealt with in time under the guidance of the monitor. Before the treatment is completed, it is strictly prohibited to carry out work unrelated to the treatment of misfire at the site to ensure personal safety