Mine gas is a general term for toxic and harmful gases mainly composed of methane CH4. It is a mixture of various gases. It contains methane, carbon dioxide, nitrogen and varying amounts of hydrocarbons and traces of rare gases, but the main component is methane. . Therefore, it is customary to say that mine gas refers to methane.
Accidents caused by gas are collectively referred to as gas accidents, including gas combustion, gas explosion, coal and gas outburst, anoxic asphyxiation, and toxic gas poisoning. In our city, the form of gas accidents is mainly caused by hypoxia and toxic gas poisoning.
Second, the mine underground hypoxia suffocation accident
Oxygen is a substance necessary to sustain human life, just as a fish cannot be separated from water. The average amount of oxygen required for each person at rest is 0.25 L/min. The well goes down and works at 1-3L/min. If the oxygen concentration in the air is lowered, it will affect human health. The hazard of oxygen concentration reduction on the human body is as follows:
Low oxygen concentration column for human body
Oxygen concentration in the air (%) | Human response |
17 | No effect at rest, causing wheezing and difficulty breathing during work |
15 | Shortness of breath, rapid pulse, rapid judgment, and weakened consciousness |
10-12 | Losing reason, life is a little longer |
6-9 | Lost consciousness, the heart can still beat in a few minutes, if not first aid, it will die |
The oxygen in the well is all supplied by the air on the ground by natural ventilation or mechanical ventilation. The main components of the surface air are nitrogen, oxygen, and carbon dioxide. According to the volume percentage, nitrogen accounts for 79%, oxygen accounts for 20.96%, and carbon dioxide accounts for 0.04.
The oxygen concentration will decrease after the surface air enters the well, because the operator's breathing, coal oxidation, pit wood decay, underground fire and gas dust explosion directly consume oxygen. In addition, the various gases continuously released after the coal rock layer is exposed and the harmful gases generated by the blasting and machine operation in the production process also reduce the concentration of oxygen in the air.
When a person enters a well-ventilated uphill, downhill, or single-head coal-rock tunnel, an oxygen-deficient suffocation accident may occur due to severe hypoxia.
The "Procedure" stipulates that in the inflow of the mining face, the oxygen concentration shall not be less than 20% by volume.
Third, the mine underground poisoning accident
The main toxic and harmful gases in the mine air are: carbon monoxide CO, carbon dioxide CO2, sulfur dioxide SO2, nitrogen dioxide NO2, ammonia NH3, methane CH4 and so on.
1. The nature, source and harm of carbon monoxide
Carbon monoxide is a colorless, odorless, odorless gas; the relative density is 0.97, which can spread evenly in the air; it is slightly soluble in water, can burn, but does not support combustion, and can explode when the concentration reaches 13% to 75%. ; has a strong toxicity.
The main sources of carbon monoxide in the well are: mine fire; coal spontaneous combustion; gas and coal dust explosion; blasting work and high temperature decomposition of lubricating oil.
Carbon monoxide is extremely harmful to the human body. When the volume concentration of carbon monoxide in the air reaches 1.28%, when people breathe in this air environment for 1-3 minutes, they will stop breathing and die. Carbon monoxide poisoning has red spots on the cheeks and pink lips. If you often work in an environment where carbon monoxide slightly exceeds the allowable concentration, although poisoning symptoms do not occur for a short period of time, chronic poisoning due to memory loss, insomnia, and bad mood can result from prolonged hypoxia in human tissues.
According to statistics, about 70% to 75% of the deaths in gas explosions, coal dust explosions and fire accidents in coal mines are caused by carbon monoxide poisoning. Most of the coal mine poisoning accidents in our city are caused by carbon monoxide.
The Regulations stipulate that the maximum allowable concentration of carbon monoxide is 0.0024%.
2. The nature, source and harm of nitrogen dioxide
Nitrogen dioxide has a pungent odor, is brownish red, has a relative density of 1.57, is highly soluble in water, does not self-ignite, and does not support combustion. It is a highly toxic gas.
The underground nitrogen dioxide is mainly from the work of shooting, and 1 liter of ammonium nitrate explosive can produce 10 liters of nitrogen dioxide gas after blasting. Nitrogen dioxide has a strong corrosive effect on human eyes, nasal cavity, respiratory tract and lung tissue, and can cause pulmonary edema. The characteristic of nitrogen dioxide poisoning is that it has no sensation at first. Even at dangerous concentrations, it only feels that the respiratory tract is stimulated and coughed. After 6-24 hours, the poisoning phenomenon occurs. The symptoms are severe bronchitis, difficulty in breathing, and fingertips. And the hair appears yellow spots, vomiting yellow sputum, pulmonary edema, headache, vomiting, resulting in death. Nitrogen dioxide poisoning is one of the most common types of gas poisoning accidents in coal mines in the city.
The Regulations stipulate that the maximum allowable concentration of nitrogen dioxide is 0.00025%.
3. The nature, source and harm of carbon dioxide
Carbon dioxide is a colorless gas with a slight acid odor. The relative density is 1.52, which is heavier than air. It is accumulated in the lower part of the roadway. It is easily soluble in water, does not self-ignite, does not support combustion, is slightly toxic, and has a stimulating effect on some organs of the human body. Enhance human breathing.
The main sources of underground carbon dioxide are: from coal seams, rock formations, oxidation of coal, pits and other materials, blasting work, mine fires, gas, coal dust explosions, human breathing.
The Regulations stipulate that the concentration of carbon dioxide in the inlet airflow of the mining face shall not exceed 0.5%; the concentration of carbon dioxide in the total return or one-wind return of the mine shall not exceed 0.75%; the return airflow in the mining area and the mining face and the concentration of carbon dioxide in the wind in the mining face No more than 1.5%.
4. The nature, source and harm of hydrogen sulfide
Hydrogen sulfide is a colorless, rotten egg-like gas with a relative density of 1.19 for air, which is easily soluble in water and is highly toxic.
The source of underground hydrogen sulfide is mainly the decay of organic matter such as pit wood and the hydration of sulfur-containing minerals; the accumulation of hydrogen sulfide in the old empty area may be released when agitated; some hydrogen sulfide will also flow out in some coal bodies.
Hydrogen sulfide strongly stimulates the eyes and throat. When you are poisoned, you feel headache, vomiting, and when you are severe, you lose consciousness and cramps until you die. Hydrogen sulfide is flammable, and when the concentration of hydrogen sulfide in the air reaches 4.3% to 4.6%, it can explode in case of fire.
The Regulations stipulate that the maximum allowable concentration of hydrogen sulfide is 0.00066%.
4. Gas combustion accidents and gas explosion accidents
When the gas and the air are mixed to a certain concentration, the high temperature fire source can burn or explode. Once a disaster accident is formed, it will cause a lot of casualties of the underground workers, seriously affecting and threatening the safe production of the mine. The gas explosion accident is the first of the five natural disasters in the mine.
Gas explosion must have three conditions at the same time: (1) gas concentration is within the explosion range, generally considered to be 5% to 16%; (2) a certain ignition temperature, generally considered to be 650 ~ 750 ° C; (3) sufficient oxygen The content, oxygen concentration is greater than 12%, because the oxygen concentration in the underground working environment can not be lower than 12%, so effective measures to prevent gas explosion, mainly from controlling gas concentration and eliminating fire sources.
V. Division of mine gas rank
Mine gas rank is the basic indicator of mine gas emission and safety. Due to the different conditions of gas generation and occurrence in different coal fields, the amount of gas emission from different mines during mining varies greatly. In order to ensure safe production and to be economically reasonable, the selected ventilation equipment, ventilation requirements and related management systems should be different. Therefore, the mine gas is divided into different grades according to the amount of gas emission and the form of gush.
The Coal Mine Safety Regulations stipulates that as long as there is a coal (rock) layer in a mine, gas is discovered, and the mine is a gas mine. Gas mines must be managed according to mine gas levels.
The mine gas rank is divided according to the relative gas emission of the mine, the absolute gas emission of the mine and the gas emission.
1. Low gas mine: The relative gas emission of the mine is less than or equal to 10m3/t and the absolute gas emission of the mine is less than or equal to 40m3/min.
2. High gas mine: The relative gas emission of the mine is more than 10m3/t and the absolute gas emission of the mine is more than 40m3/min.
3. Coal (rock) and gas (carbon dioxide) stand out from the mine.
6. Measures to prevent hypoxia and suffocation and gas poisoning accidents
1. Strengthen ventilation to ensure that there is enough fresh air in each ventilation place under the well and dilute various harmful gases below the safe concentration. In order to achieve this goal, the mine should improve the ventilation system, eliminate the natural ventilation, and insist on using mechanical ventilation. If there is a condition to form a regular coal mining face, it is necessary to maintain a passage to the intake wind lane and a two safety exit to the return air alley. The coal mining face that cannot form the formal coal mining face and all the driving roadway sides should be equipped with sufficient power of the local fan and the corresponding wind, and strengthen the management of local ventilation, and the local fan should not be stopped at will.
2. The mine ventilation system should be completely independent and should not be shared with other mines. The goaf and the scrap roadway must be closed in time, which can effectively prevent other mine disasters from involving their own mines and improve ventilation efficiency. Closed and non-combustible materials are used for construction, tightly and without air leakage, and there are anti-pools or anti-water pipes in the air.
The mine should have a complete independent ventilation system
3. Strengthen the management of ventilation facilities. Temporary stoppages must not stop the wind, otherwise the power supply must be cut off, fences should be set up, warning signs should be revealed, and personnel should be prohibited from entering. The damper, wind window and wind bridge that control the wind flow are set up reasonably. The wall is constructed with incombustible materials and is tightly airtight. The damper is not less than 2 channels and can be automatically closed.
4. The local ventilator should use the mining type. The press-in local ventilator and starter must be installed in the air inlet duct, no less than 10m from the return air inlet, no circulating wind, must be raised when placed, and the height from the ground (rail surface) is greater than 0.3m. The air volume at the exit of the wind and the distance to the working surface are in accordance with the provisions of the operating regulations, generally not more than 6 meters, and the hanging should be straight. The windshield is made of flame retardant material.
5. A large amount of toxic and harmful gases will be generated during the blasting process. After firing, the blasting must be continued for more than half an hour. After the toxic and harmful gas concentration drops to a safe concentration, the personnel can enter the blasting site.
6. In the place where the wind is stopped for a long time, a large amount of toxic and harmful gases are accumulated, and oxygen is seriously insufficient. In order to resume operations at these locations, special safety measures must be prepared in advance and reported to the technical person in charge of the mine for approval and strict implementation.
7. It is strictly forbidden to use more than 3 (including 3) local fans to supply air to one working surface at the same time. Do not use one local ventilator to supply air to two working surfaces at the same time.
8. Strengthen the wind measurement and gas measurement work, equip with sufficient full-time gas inspectors and gas detection instruments, implement the gas inspection system and the gas report review system of the mine manager and technical leader. The mine wind measurement record and gas inspection record must be filled in according to the regulations. The record must be “three pairs of ports†(ie, the board, the record book, and the report data should be consistent). The wind is measured once every ten days, and the gas concentration is measured at least twice per shift in the low gas mine. If an abnormal situation is found, the main person in charge of the mine must be immediately reported and appropriate safety measures such as evacuating the operator and powering off should be taken.
9. Mines with coal seams that are prone to spontaneous combustion should strengthen downhole CO detection. Once the CO concentration is exceeded, the cause should be identified and corresponding safety measures should be taken.
10. The unleashed goaf generally accumulates a large amount of toxic and harmful gases. When the coal mining face and the excavation face pass through the goaf, the operator should be evacuated immediately to enhance ventilation. After testing, the toxic and harmful gases are reduced to a safe concentration. You can re-enter the work location at the rear.
11. Gas poisoning and anoxic suffocation accidents occur in the underground. In the absence of effective safety measures, it is very dangerous to take risks and often cause accidents to expand. It is necessary to try to supply air to the accident site. The rescue personnel enter the accident site and check the concentration of oxygen and toxic gas on one side, and indeed meet the requirements of the Regulations before entering. When there is a self-rescuer or a respirator, after the test is completed in the fresh airflow, the group of 2 people can enter the accident site to quickly rescue. If you do not have the conditions for rescue, immediately contact the local coal management department or the nearest mine rescue team to request assistance.
One of the methods of wearing a self-rescuer
1. Undo the self-rescuer from the belt, use the thumb to open the wrench and open the lock band.
2. Hold the open wrench and pull open the sealing tape.
3. Uncover and throw away the upper casing.
4. Grab the mouthpiece, remove the filter from the lower casing, and discard the lower casing.
5. Remove the nose clip, bite the bite of the mouth with the teeth, and place the rubber piece between the lips.
6. Pull the nose clip open, hold the nose, and let it grip the nose after releasing the hand.
7. Remove the helmet and wear the headband from the top of the head.
8, all worn, and then wear a helmet.
7. First aid for poisoned or asphyxiated persons
1. Quickly lift the victims to a place where fresh airflow and surrounding brackets are in good condition. In the course of transportation, if you are still threatened by harmful gases, the first-aider must wear a self-rescuer and wear a self-rescuer to the rescued person.
2, remove the obstruction in the mouth of the poisoned person, such as mucus, blood clots, soil, broken coal, dentures, etc., and untie the tops and belts, take off the rubber shoes.
3. Cover the wounded with clothes to keep warm.
4, according to the characteristics of heartbeat, breathing, pupils and the mental condition of the wounded, preliminary judgment of the severity of the injury. The normal person beats 60 to 80 beats per minute and breathes 16 to 18 times. The pupils of the two eyes are equal and round, and the light can shrink rapidly and become conscious. The shocked two pupils are not the same size, and should be dull or not contracted. For those who have difficulty breathing or stop breathing, artificial respiration should be performed in time. When the phenomenon of cardiac arrest occurs, in addition to artificial respiration, the chest should be given the same amount of first aid.
5. The duration of artificial respiration is to restore spontaneous breathing or until the casualty actually dies.
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