The "three elements" of mine fires

The presence of a certain combustible substance. In the coal mine, coal itself is a large and ubiquitous combustible material. Secondly, a large amount of coal dust, gas and used pit wood, electromechanical equipment, explosives, oil and other substances exist in the process of production. Flammability, their presence is an essential element of a fire.

A heat source with sufficient heat. The heat source is a necessary factor for the fire in the coal mine. Only a heat source with sufficient heat can cause the combustion of combustible materials. In coal mines, coal self-ignition, gas, coal dust combustion and explosion, fire, mechanical friction of the owner of the heat; current short circuit, electrical equipment failure caused by overheating; smoking, welding and other open flames may cause fire.

There is a sufficient concentration of supply. Combustion is defined as a heat, luminescence, accompanied by a violent oxidation reaction of smoke. Any combustible material, although there is a heat source with sufficient heat, if the lack of sufficient concentration, the combustion is difficult to sustain, so the supply is an essential condition for the formation of combustion. Experiments have shown that in the air environment with a concentration of 3%, the combustion of any combustibles cannot be maintained; in the air with a concentration lower than 12%, the gas loses its explosiveness; if the concentration is below 14%, the candle cannot burn. Therefore, the source mentioned here is a normal amount of air.

Classification of coal mine fires

At present, there is no unified standard for the classification of fires in China, and there are many classifications. According to the following classification methods:

According to the different sources of fire, coal mine fires are usually divided into two categories, namely external fires and internal fires.

According to the different locations of fires, it can be divided into wellbore fire, roadway (ingress and return) fires, face fires, coal pillar fires, goaf fires and diverticulum fires.

According to the different classification of combustible materials, it can be divided into electromechanical equipment fire, gunpowder fire, oil fire, pit fire, gas fire, coal dust fire and coal fire caused by spontaneous combustion.

According to the influence of ventilation and wind flow in coal mines, it can be divided into inflow wind current fire and return air flow fire.

The essence analysis of coal mine fire

In essence, coal mine fires are also a kind of combustion phenomenon, and also a phenomenon of mutual conversion of energy and energy. According to relevant statistics, 90% of coal mine fires belong to internal fires, and all coal mine fires occur and develop. Finally, the stage of fire and the formation of hazards are reached.

In the coal mine, due to the "three elements" of the theory of combustion and explosion, the fire can be transformed into an explosion. The condition is: there is a large volume and a high temperature combustible gas mixture, and the concentration of the combustible gas mixture reaches the explosion limit; When the concentration of the mixed gas exceeds 14%, the mixed gas generates combustion when it is at a high temperature or its own temperature is high.

Mine fire hazard

Underground fires have the following major hazards to the safety of coal mines and the safety of miners:

The underground space is small and the activities are limited. The connection between the ventilation and the roadway of the mine is complicated, and the air supply is limited. When a fire occurs in the underground, the personnel evacuation and evacuation will be restricted by the complicated environment.

There is a large amount of combustibles in the coal mine. The fire is easy to produce and the speed of development and spread is fast. When the high temperature flame flows in the roadway and mixes into the fresh air flow, it will generate a new fire source of secondary combustion at the air mixing point, resulting in fire. The expansion of the area.

A large amount of toxic and harmful gases (mainly CO2 and CO) are generated during combustion accompanied by high temperature flames, causing casualties. These gases flow into the downhole operating point, causing poisoning and suffocation.

Fires generated underground can easily cause gas, coal dust or coal dust and gas to burn and explode. The fire in the underground not only provides an explosion source for gas and coal dust, but also causes the combustibles to release explosive gases such as H2 and various hydrocarbons due to the dry distillation of the high-temperature fire source. Therefore, fires can cause gas and coal dust explosions, further expanding the disaster and casualties.

Fire can burn equipment and cause spontaneous combustion of coal seams. If a fire breaks down in the well, if effective measures are not taken in time, then the opportunity to extinguish the fire will be lost, and the fire will be enlarged. This will burn a large amount of equipment and even cause coal seam combustion. Affect the normal production of mines.

After a fire in the mine, the downhole wind flow is reversed, resulting in the expansion of the disaster situation, the roadway through which the high temperature smoke flows, the air quality changes, and the temperature rises; on the other hand, the wind flow of the mine ventilation network changes, causing the mine ventilation system to be disordered. Further expand the scope of the disaster area, and at the same time bring great difficulties and harm to the evacuation of underground personnel, and increase the difficulty of accident loss and fire fighting work.

Coal mine fire prevention measures

External fire prevention measures

Characteristics of external fires: The fire is relatively sudden, the development speed is fast, and the fire is fierce. If it cannot be discovered and controlled in time, it will bring huge losses. According to relevant statistics: more than 90% of major fire accidents recorded in China belong to internal fires, while the proportion of fires in mines is small (only 4%-10%), but it can not be ignored. The prevention of external fires is very important. The specific measures are as follows:

It is strictly forbidden to bring pyrotechnics and flammable and explosive substances into the well; it is strictly forbidden to use electric furnace or bulb to heat in the underground, and it is not allowed to use electric welding, torch welding or cutting. If it must be used, it must be formulated with strict, scientific and reasonable safety technical measures and reported to the relevant departments for approval. Secondly, there must be no fireworks or fire for heating within 20 meters of the wellhead room and the ventilation room.

No flammable oils are allowed to be stored underground.

Intrinsically safe electrical equipment must be used in the underground to strengthen management, regular inspection and maintenance, to ensure the performance of the equipment is intact; to prevent accidents caused by electric sparks, arcs and friction.

Strengthen blasting management; when carrying out blasting operations, it must use the permitted mineral explosives of the national standard; do not use expired or inferior explosives, do not allow the release of open guns or open flames, and put guns; The length of the mud and the sealing material must be sealed in accordance with the relevant requirements of the “Safety Regulations for Coal Mines” (2006 edition), and the shooting shall be carried out to avoid causing fire.

Cables, conveyor belts and air ducts that are not flame retardant or non-flammable are strictly prohibited from entering the well.

Buildings within 20m of wellheads, derricks and wellheads, as well as main entrance and return airways, main flats, joints of main roadways, main diverticulum and mechanical and electrical equipment, etc., shall be constructed or supported by non-combustible materials. The guard is preferably placed in the rock formation.

Wellhead should be set up iron fire doors, fire prevention wellhead or near ground fire spread underground, into the wind and roadway intersection of each production level should be set fireproof steel door, fireproof steel doors and regularly check the quality and reliability of flexible .

The mine must be equipped with a fire-fighting material library within 100m of the wellhead. A fire-fighting material warehouse should be set up in each of the main transport lanes of the production level, and a sufficient amount of fire-fighting equipment should be reserved, and a fire-fighting vehicle should be provided. Fire-fighting materials and tools must meet the needs of mine fire-fighting, and are not allowed to be used for other purposes. The explosives store, winch room or winch chamber, electromechanical chamber, pump house and mining substation, central substation Have enough fire-fighting equipment and keep it intact.

The mine must establish a fire-fighting pool with a capacity of not less than 200m3 on the ground. Two-way (1趟 work, 1趟 reserve) special fire-fighting pipeline should be laid in all the main roadways, and the two pipelines should be sensitively interchangeable. Set a set of fire hydrants every 30m - 50m distance.

Internal fire prevention measures

The internal fire refers to the damaged original coal seam, which has the spontaneous combustion coal seam; there is a certain amount of air supply, and it spontaneously oxidizes to generate a certain amount of heat accumulation, which leads to the fire formed by the fire.

The characteristics of internal fires: mainly difficult to extinguish fires, high technical content, large manpower and material resources, fire sources are hidden and not easy to be discovered, even burning time is long, and some can last for several months, several years, resulting in a large number The coal resources were frozen. According to statistics from 1985, the amount of coal resources frozen due to spontaneous combustion has reached nearly 60 million tons.

According to relevant statistics, among the national distribution and key coal mines, mines with spontaneous combustion hazard account for 46%-49% of the total number of mines in the country; self-ignition coal seams account for 60% of the total recoverable coal seams, 1953-1984 Statistics show that the number of internal fires accounted for 94% of the number of mine fires. Therefore, the internal fire has received attention and research. However, measures to prevent internal fires in coal mines involve various production links in coal mines, so research and discussion should be strengthened in terms of preventive measures.

In mining mines with coal seam spontaneous combustion hazard, it is necessary to correctly select the mine development method, coal mining method and mining sequence; improve the mine fire prevention capability; optimize the mine ventilation system, eliminate the air leakage in the goaf, and adopt the fire prevention measures of pressure equalization ventilation. Strengthen fire prevention management and other measures to prevent spontaneous combustion of coal, reduce or eliminate the hidden dangers of spontaneous combustion of coal.

Strengthen the training of management personnel and employees to grasp the relevant signs of coal spontaneous combustion in the early stage of fire, timely discover the signs of fire, bring time for fire fighting work, carry out forecasting and forecasting work to prevent fire, start the mine fire emergency plan, and deal with it Budding state.

Strengthen the management of abandoned roadways and goafs, and timely fill the abandoned coal roads in order to timely deal with various fire hazards left over from the mining production process.

Strengthen the quality of the airtight and daily inspection and management work to avoid spontaneous combustion of coal caused by air leakage.

Utilize the development of new technologies and new equipment to improve the mine's own ability to prevent fires

With the development of science and technology and the in-depth study of mine fires, a batch of new fire prevention technologies and fire prevention equipment have been developed and utilized. For example, the automatic fire alarm device can accurately detect the abnormal situation of the fire hazard, and feedback to the management personnel through the processing of the data information to make the fire hazard deal with the bud.

In short, it is necessary to actively carry out the research and exploration of the occurrence, development and formation mechanism of mine fires, and develop advanced automatic fire alarm systems, fire extinguishing equipment and underground escape equipment suitable for mines; , monitoring and fighting to achieve comprehensive prevention and control measures for three-dimensional space to ensure the safe production of mines.

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