1. What is mine air? What is the difference between mine air and ground air?

Mine air refers to a mixture of fresh air from the ground and harmful gases and floating dust generated underground.

The source of mine air is surface air. After surface air enters the mine, the composition, temperature, humidity, and pressure of the air change. These changes are mainly manifested in the following four aspects:

(1) The oxygen concentration decreases while the carbon dioxide concentration increases.

(2) Mixed with various harmful gases, mainly toxic and explosive gases such as carbon monoxide, hydrogen sulfide, sulfur dioxide, carbon dioxide, and biogas.

(3) Mixed with coal dust and rock dust.

(4) The temperature, humidity, and pressure of the air change. Under normal circumstances, the temperature increases in winter and decreases in summer; Absolute humidity increases, relative humidity increases; In a pressurized ventilation mine, the pressure increases; In extraction ventilation mines, the pressure decreases.

 

2. What is the density of air? What is the weight ratio of air? What is the relationship between density and weight ratio?

The mass of air contained per unit volume is called air density. The density of air under standard conditions is 1.293kg/m3.

The weight of air contained per unit volume is called air weight ratio, and the weight ratio of dry air is N/m3.

The relationship between air density and weight rate is: ρ=γ/g ρ - density, γ - weight rate, g - gravitational acceleration (m/s2)

What is the source of underground carbon dioxide (CO2)?

The main sources of underground carbon dioxide are as follows:

(1) The main sources are the decay and deterioration of pit wood, slow oxidation of coal and carbon bearing rock layers.

(2) The carbon dioxide content in coal seams is high, and sometimes coal (rock) and carbon dioxide outbursts occur. In a very short period of time, carbon dioxide suddenly protrudes in large quantities along with coal (rock).

(3) Blasting operations at the mining face. After blasting, a large amount of carbon dioxide will be generated. According to measurements, each kilogram of ammonium nitrate explosive can produce 150L of carbon dioxide.

(4) Human respiration. In general, when working underground, the amount of carbon dioxide exhaled by a person is 0.75-0.85L/min.

(5) When gas, coal dust explosions, and fire accidents occur underground, a large amount of carbon dioxide is also produced.

 

3. What are the hazards of carbon dioxide (CO2) to human health? How does the Coal Mine Safety Regulations regulate the concentration of carbon dioxide?

Carbon dioxide poses a significant threat to human health. Trace amounts of carbon dioxide can accelerate breathing and increase respiratory volume. When the concentration of carbon dioxide in the air reaches 1%, human breathing becomes rapid; When the concentration of carbon dioxide reaches 5%, people feel difficulty breathing. Accompanied by tinnitus and increased blood flow sensation; When the concentration of carbon dioxide reaches 10% -20%, a person's breathing will come to a standstill and lose consciousness, which can be life-threatening if left for a longer period of time; When the concentration of carbon dioxide reaches 20% -25%, people will suffocate and die.

The Coal Mine Safety Regulations stipulate that the concentration of carbon dioxide in the intake air of the mining face shall not exceed 0.5%. When the concentration of carbon dioxide in the total return airway or one wing return airway of the mine exceeds 0.75%, the cause must be immediately identified and dealt with.

 

4. What are the properties of carbon monoxide (CO)?

Carbon monoxide is a colorless, odorless, and tasteless gas; Relative density 0.97, absolute density 1.25kg/m3; Slightly soluble in water; Under normal temperature and pressure conditions, the chemical properties are not active. When the concentration of carbon monoxide in the air reaches 13% -75%, it can cause combustion and explosion.

 

5. What are the hazards of carbon monoxide (CO) to human health? How does the Coal Mine Safety Regulations regulate the concentration of carbon monoxide?

Carbon monoxide is highly toxic, with an affinity for human hemoglobin that is 250-300 times greater than oxygen. Inhaling carbon monoxide into the human body quickly binds to hemoglobin, hindering the normal binding of oxygen and hemoglobin, resulting in a decrease in hemoglobin's ability to absorb oxygen, causing hypoxia in various tissues and cells of the body, leading to poisoning, suffocation, and even death. When the concentration of carbon monoxide in the air reaches 0.016%, people will feel mild headaches after a few hours; When the concentration of carbon monoxide reaches 0.048%, it will cause mild poisoning, such as tinnitus, dizziness, headache, and rapid heartbeat; When the concentration of carbon monoxide reaches 0.128%, it will cause severe poisoning, loss of mobility, and dull sensation in people; When the concentration of carbon monoxide reaches 0.4%, people will lose consciousness, experience spasms, and even die in a short period of time.

 

6. What are the hazards of hydrogen sulfide (H2S) to human health? How does the Coal Mine Safety Regulations regulate the concentration of hydrogen sulfide?

Hydrogen sulfide has strong toxicity, stimulating the human eye membrane and respiratory system, hindering the body's oxidation process, and causing hypoxia. When the concentration of hydrogen sulfide in the air reaches 0.0001%, the human sense of smell can detect the odor; When the concentration of hydrogen sulfide reaches 0.0005%, mild poisoning occurs several hours later, with severe salivation, clear nose, and difficulty breathing; When the concentration of hydrogen sulfide reaches 0.02%, people will be severely poisoned, experiencing dizziness, headache, vomiting, and limb weakness; When the concentration of hydrogen sulfide reaches 0.05%, people will quickly lose consciousness and experience spasms. If not rescued in time, there is a risk of death; When the concentration of hydrogen sulfide reaches 0.1%, death occurs in a very short period of time.

The Coal Mine Safety Regulations stipulate that the maximum allowable concentration of hydrogen sulfide in mine air is 0.00066%.

 

7. What is air pressure? What are the ways to express stress?

Air pressure refers to the force exerted by air molecules on a unit area of the vessel wall. There are three ways to express stress:

(1) Expressed in terms of the force per unit area, Pa.

⑵ Expressed in terms of liquid column height, mmH2O or mmHg.

⑶ Expressed in atmospheric pressure, atm or at.

The relationship between the three is: 1atm=760mmHg=10332mmH2O; 1at=10000mmH2O.

 

8. What is ventilation total pressure difference? What is the role of total pressure difference in ventilation?

The difference in total ventilation pressure between any two sections in the underground airflow is called the total pressure difference between the two sections. The total pressure difference between two sections in the air flow in the well is the fundamental reason for the air flow between these two sections. The air flow in the mine shaft is achieved by the total pressure difference between the intake and return air shaft sections. The direction of air flow is from the section with higher total pressure to the section with lower total pressure.

 

9. What are the main factors related to natural wind pressure?

The natural wind pressure is related to the following three main factors:

⑴ The elevation difference between the inlet and outlet air shafts.

⑵ Changes in ground temperature.

⑶ Microclimate in the mining industrial square.

What is upward ventilation?

The ventilation method of airflow flowing from bottom to top along the coal mining face.

 

10. What is downward ventilation?

The ventilation method of airflow flowing from top to bottom along the coal mining face.

 

11. What are the two methods used for determining the ventilation capacity of mines?

The ventilation capacity of the mine is determined using the overall accounting method or the inside out accounting method.

The overall accounting method can be used in mines with a production capacity of less than 300000 t/a; The inside out accounting method can be used in mines with a production capacity of over 300000 tons per year.

 

12. What are the main contents of capacity assessment for mine ventilation systems?

(1) Verify the basic conditions of the coal mining face, excavation face, and independent underground air supply locations.

(2) Verify the operation status of the mine ventilation fan.

(3) Mines implementing gas drainage must verify the stable operation of the mine gas drainage system.

(4) When there are two or more ventilation systems in a mine, the ventilation capacity of each ventilation system should be evaluated separately, and the ventilation system capacity of the mine is the sum of the capacity of each ventilation system. Mines must organize production reasonably according to the capacity of each ventilation system.

 

13. Which aspects should be used to verify the ventilation capacity of mines?

The ventilation capacity of a mine should be verified from the performance of the main ventilation fans, the ventilation network, the effective air volume at the ventilation location, and the ability to dilute gas in the mine.

 

14. Under what conditions can the ventilation system capacity of coal mines be used as the basis for determining production capacity?

The capacity of the coal mine ventilation system must be determined based on the actual air supply volume, and the required air volume for each underground air consumption location must comply with regulatory requirements. The annual ventilation capacity of mines approved by the provincial coal industry management department can be used as the basis for determining production capacity.

 

15. What should be done if it is identified as an "incomplete and unreliable ventilation system"?

After being identified as' incomplete and unreliable ventilation system ', it should be immediately registered and documented, and a designated person should be responsible for tracking and monitoring, urging the enterprise to rectify seriously and eliminate hidden dangers. After the rectification is completed, the main person in charge of the coal mine shall organize self inspection. After passing the self inspection, submit an application report to the coal mine safety production supervision department of the government at or above the county level to resume production. Production can only resume after passing the acceptance inspection.

 

16. What is air volume regulation?

The adjustment work of the total or local air volume in the mine to meet the required air volume of the mining face and chamber.

 

17. What are the measures for regulating mine air volume?

There are many measures that can be taken to regulate the airflow in mines:

(1) Adopt regulating equipment and facilities. Such as ventilation fans, jets, windshields, and air curtains.

(2) Add parallel well tunnels.

(3) Expand the ventilation section of the tunnel.

(4) Shorten the ventilation airflow path.

(5) Change the form of roadway support.

 

18. What are the regulations for measuring mine air volume?

According to the Coal Mine Safety Regulations:

(1) The mine must establish a wind measurement system and conduct a comprehensive wind measurement every 10 days.

(2) Wind measurement should be carried out at mining faces and other wind consuming locations as needed.

(3) Each wind measurement result should be recorded and placed on a record board at the wind measurement location.

 

19. What is the content of measuring mine air volume?

The measurement of mine air volume mainly involves measuring the wind speed and cross-sectional area in the roadway. The measured wind speed is multiplied by the area to obtain the air volume

Q=V × A × 60

In the formula, Q represents the airflow through the tunnel, m3/min.

V-average - average wind speed in the tunnel, m/s;

A - Tunnel cross-sectional area, m2.

 

20. What should be noted when measuring wind speed with an anemometer?

When using an anemometer to measure wind speed in tunnels, the following issues should be noted:

(1) The wing wheel of the wind gauge must be perpendicular to the direction of the airflow, especially when measuring wind in inclined tunnels, otherwise significant errors will occur.

(2) One side of the wind gauge dial should be backed by the airflow, otherwise the wind gauge pointer will reverse.

(3) The anemometer cannot be fixed in one position, but must constantly move along a moving path at a uniform speed, or use a fixed-point method, otherwise the measured wind speed is not the average speed.

(4) The number of wind measurements on the same section shall not be less than 3 times, and the error between each measurement result shall not exceed 5%. Then, the average of the 3 measurement results shall be taken, otherwise the measured wind speed will not be accurate.

(5) When measuring wind in a well, it is necessary to wait for the air flow in the tunnel to stabilize before proceeding. For example, the accuracy of wind measurement is affected by the passage of trains and personnel, and must be measured 3-5 minutes after the passage of trains and personnel.

 

21.What are the hazards of mine air leakage?

What are the main hazards of mine air leakage?

(1) Resulting in a decrease in effective air volume at the location where the wind is used, which may lead to the accumulation of toxic and harmful gases such as gas, as well as adverse weather conditions in the workplace.

(2) If there are many air leakage routes, it will complicate the ventilation system, affect the stability and reliability of mine ventilation, and increase the difficulty of air volume regulation.

(3) May cause spontaneous combustion of residual coal in goaf.

(4) There is a large amount of air leakage in the mine, which will inevitably reduce the effective air flow rate and increase the power consumption of mine ventilation.

 

22.What are the hazards of low or high wind speed underground?

Low or high wind speeds are not acceptable for tunnels and mining faces. When the wind speed is too low, sweat is not easily evaporated, and excess heat in the human body is not easily dissipated, making people feel stuffy and uncomfortable. At the same time, gas and coal dust may accumulate, which may cause gas and coal dust explosions or suffocation accidents; Excessive wind speed not only releases too much heat from the human body, making it prone to catching a cold, but also causes dust to fly, deteriorating the working environment and endangering personnel's health. It may also cause coal dust explosions.

 

23. What is mine and other accumulated holes?

The hypothetical thin-walled orifice area value used to measure the difficulty of ventilation in mines or tunnels.

Assuming there is a thin wall in infinite space, a hole with an area of A (m2) is opened on the thin wall. When the air volume passing through the orifice is equal to the mine air volume, and the air pressure difference on both sides of the orifice is equal to the mine ventilation resistance, then the orifice area A is called the equal area orifice of the mine.

 

24.What are the uses of accumulated holes in mines?

Mine equal area hole A=1.19/Rm

In the formula, Rm - total air resistance of the mine, m2.

From the above equation, it can be seen that A is a function of Rm. The larger Rm, the more difficult it is to ventilate the mine, and the smaller A obtained. Therefore, A can represent the difficulty level of mine ventilation. In China, the commonly used indicator for measuring the difficulty of ventilation in mines is the accumulation of holes in mines.

The difficulty level of mine ventilation is classified as follows:

Difficulty level of ventilation in mines with equal area holes A>2 m2: easy;

Difficulty level of ventilation in mines with equal pore size A1-2 m2: moderate;

Difficulty level of ventilation in mines with equal pore size A<1 m2: difficult.

However, there are still some problems in measuring the difficulty of mine ventilation using the method of measuring the size of the mine and other accumulated holes. For example, if there is a serious air leakage or short circuit in a well or alley, there may be a phenomenon where although the ventilation condition is poor, there are still considerable equal accumulation holes; In addition, due to the significant development and improvement in the scale, mining methods, mechanization level, and ventilation fan capacity of modern mines, there is still some reference value for the ventilation conditions of small mines; The indicators for measuring the difficulty of ventilation in large mines or mines with multiple fan ventilation systems still need further research. So, the concept of accumulated holes in mines can only be used as a reference to measure the difficulty of ventilation.

 

25. What is mine ventilation method? What are the main types of ventilation methods in mines?

The arrangement of the intake and exhaust shafts in a mine. According to the different arrangements of mine intake and return air shafts, mine ventilation methods can be divided into the following three basic types:

(1) Central ventilation. Central ventilation refers to the situation where the air shaft and return air shaft are roughly located in the center of the mine field. Central ventilation can be divided into two forms: central parallel ventilation and central boundary ventilation.

(2) Diagonal ventilation. Diagonal ventilation refers to the situation where the intake air is located in the center of the mine field, and the return air shafts are located in the center of the mining area along the two wings of the shallow part of the mine field. Diagonal ventilation can be divided into two forms: wing diagonal ventilation and partition diagonal ventilation..

(3) Mixed ventilation. Hybrid ventilation is a commonly used ventilation method for deep mining in large and old mines. Generally, the intake and return air shafts are composed of three or more shafts or inclined shafts combined in two ways: (1) and (2), and are divided into three forms: central split and diagonal mixed type, central parallel and diagonal mixed type, and central parallel and central split mixed type.

 

26.Why must the main ventilation fan for mining be installed on the ground?

The main ventilation fan in a mine is a reliable equipment to ensure effective ventilation and is also an important equipment to ensure mine safety. The main ventilation fan in the mine is installed on the ground, which can ensure a continuous supply of stable and sufficient fresh air flow to the underground, ensuring effective and reliable ventilation of the mine. It has the following benefits:

⑴ Fresh, dry, and dust-free ground air is beneficial for equipment maintenance and upkeep.

Some large auxiliary equipment does not need to use explosion-proof series, and the equipment selection is simple.

 

27.What are the basic parameters of a ventilation fan?

Ventilation fans have the following basic parameters:

(1) Air volume. Refers to the air volume passing through the ventilation fan per unit time, m3/s.

(2) Full wind pressure. Refers to the energy obtained by a unit volume of air passing through a ventilation fan, including fan static pressure and velocity pressure, Pa, mmH2O, or atm, etc.

(3) Power. Refers to the input power (obtained from the electric motor) and output power (external power) of the ventilation fan, kW.

(4) Efficiency. The ratio of the output power to the input power of a ventilation fan, expressed as a percentage.

(5) Speed. The speed at which the ventilation fan rotates per minute. Generally calculated based on the number of revolutions per unit time of the rotor of the ventilation fan motor, r/min.

 

28. What is forced ventilation? What are the advantages and disadvantages of forced ventilation? What are the applicable conditions?

The ventilation method of forcing air into the underground or air duct by a ventilator.

Advantages and disadvantages:

(1) Can use a portion of the return air to press harmful gases from adjacent small coal mine collapse areas to the ground.

(2) Due to the positive pressure of the underground airflow, when the main ventilation fan stops running for some reason, the pressure of the underground airflow decreases, which may increase the amount of gas emitted from the goaf.

(3) The air intake network has many air leaks, difficult management, high air resistance, and difficulty in adjusting air volume.

Applicable conditions: The application scope of the press in method is relatively small. When the ground of the small kiln connected to the mine collapses severely or there are many surface cracks, and the terrain is complex, it is not possible to set up a main ventilation fan in the return air shaft or the main return air roadway cannot be connected or maintained, this method can also be used.

 

29. What is extraction ventilation? What are the advantages and disadvantages of extraction ventilation? What are the applicable conditions?

The ventilation method of using a fan to extract polluted air from underground or local areas.

Advantages and disadvantages:

(1) Due to the negative pressure of the underground airflow, when the main ventilation fan stops running for some reason, the pressure of the underground airflow increases, which can reduce the gas emission in the goaf and is relatively safe.

(2) Low air leakage and simple ventilation management.

(3) When adjacent mines or mining areas are interconnected, harmful gases accumulated in adjacent mines or mining areas will be pumped into the mine, reducing the effective air volume of the mine.

Applicable conditions: Pull out ventilation is a widely used ventilation method in coal mines in China, especially suitable for high gas mines and mines with large mining areas.

 

30. What is a mine ventilation network? What are its main basic forms?

The structural system in a ventilation system that represents the connection form and direction of air ducts (branches), that is, the route through which all air flows composed of interconnected shafts, tunnels, yards, chambers, working faces, etc., is commonly referred to as an air network.

There are three basic forms:

(1) Series wind path

A series air path refers to an air path in which the return air from the underground return air location enters other air consuming locations again without branching in between.

(2) Parallel wind path

Parallel air duct refers to the air duct formed by two or more ventilation tunnels that separate at one point and converge at another point without intersecting tunnels in between.

(3) Jiaolian Wind Road

Corner connected air duct refers to the addition of one or more air ducts connected to parallel air ducts.

 

31. What is the characteristic curve of mine ventilation network? What is its purpose?

Mine air resistance is related to wind pressure and air volume:

In the formula, R represents the mine air resistance, N · S2/m6.

H - Mine wind pressure, Pa.

Q - Mine air volume, m3/S.

If wind pressure is used as the vertical axis and air volume is used as the horizontal axis to draw the wind resistance curve, it is the characteristic curve of the mine network.

The characteristic curve of mine ventilation network can reflect the difficulty level of mine ventilation. The steeper the characteristic curve, the more difficult the mine ventilation is; On the contrary, the gentler the characteristic curve, the easier it is to ventilate the mine.

 

32.What are the differences in ventilation performance between series and parallel air ducts?

If the wind resistance of two air ducts is equal, forming series and parallel connected air ducts respectively, the total wind resistance of parallel air ducts is 1/8 of the total wind resistance of series air ducts. When the total air volume through series and parallel air ducts is equal, the total air pressure in parallel air ducts is 1/8 of the total air pressure in series air ducts. So, parallel ventilation is much more economical than series ventilation.

In addition, each air duct in the parallel air duct is independent fresh air, which is conducive to the control and regulation of air flow. The ventilation is good, and accidents are less likely to occur. Even if accidents occur, they will not affect other air ducts, and it is also convenient to isolate and handle accident air ducts. So, parallel air ducts are much safer and more reliable than series air ducts.

 

33.How does the Coal Mine Safety Regulations stipulate the measurement of ventilation resistance in mines? How to calculate the ventilation resistance of a mine?

According to the Coal Mine Safety Regulations, a ventilation resistance measurement must be conducted once before the new well is put into operation, and at least once every three years thereafter. After the mine enters a new level of production or changes one wing ventilation system, it is necessary to re measure the ventilation resistance of the mine.

Organize the measured data, calibrate them one by one according to the coefficients of the calibration instrument, and then calculate according to the following formula.

(1) When using the differential pressure gauge method, the ventilation resistance between the two measuring points is

H1~2=kh measurement+υ 21 ρ 1/2- υ 22 ρ 2/2

In the formula, H1~2- ventilation resistance between measuring points 1 and 2, Pa;

K - Accuracy correction coefficient for differential pressure gauge readings;

H-measurement - counting of differential pressure gauge, i.e. pressure difference between measuring points 1 and 2, Pa;

υ 1, υ 2- the average wind speed at the cross-sections of measuring points 1 and 2, m/s;

ρ 1 and ρ 2- the average air flow density at measuring points 1 and 2, in kg/m3.

(2) When using the barometer method, the ventilation resistance between the two measuring points is

In the formula, H1~2- ventilation resistance between measuring points 1 and 2, Pa;

K. K - Accuracy correction coefficient for barometer readings;

H-test 1, h-test 2- calibrate the count of the barometer during h-test 1 and h-test 2, Pa;

Z1, Z2- elevation of front and rear measuring points, m.

The total resistance of the measurement route is the sum of the ventilation resistance between each measuring point.

 

34. What is local ventilation fan forced ventilation? What are the advantages and disadvantages of forced ventilation?

Local ventilation fan press in ventilation refers to the use of local ventilation fans and air ducts to press fresh air into the excavation working face, while exhaust air is discharged through the roadway.

The advantage of forced ventilation is that the airflow is directed from the end of the air duct towards the working face, and the effective range of the airflow is relatively long, generally up to 7-8m. Therefore, it is easy to eliminate the lack of air and dust in the working face, and the ventilation effect is good. At the same time, the local ventilation fan is installed in fresh air flow, which has good safety performance.

The disadvantage of forced ventilation is that the exhaust air and dust emitted from the excavation face need to pass through the roadway where someone is working, and the exhaust speed of blasting smoke is slow and takes a long time during blasting.

Pressure ventilation is the most important way for local ventilation fans to ventilate.

 

35.What does the wind power lockout of local ventilation fans refer to? Why is it necessary to implement wind power locking for local ventilation fans?

The so-called wind power interlocking refers to the mutual interlocking between the air supply of the local ventilation fan and the power supply of the excavation tunnel. When the local ventilation fan stops running, it can immediately automatically cut off the power supply of all electrical equipment in the ventilation tunnel, and cannot connect all power sources in the tunnel before the local ventilation fan starts ventilation. According to the Coal Mine Safety Regulations, the location where local ventilation fans are used for air supply must implement wind power interlocking. If two local ventilation fans are used for air supply, both of them must achieve wind power interlocking simultaneously.

When the local ventilation fan stops for some reason, the gas in the excavation roadway cannot be effectively diluted and discharged, often causing the gas accumulation concentration to exceed the limit; Meanwhile, non essential safety electrical equipment, if not managed properly, is prone to electrical sparks. When electric sparks combine with gas that reaches explosive concentration, a gas explosion accident occurs. If the wind stops and the power can be cut off but not connected, it reduces the risk of generating electric sparks. After the power outage, workers were unable to work in the excavation tunnel, which also reduced the generation of other sources of fire and controlled windless operations on site. Therefore, implementing wind power lockout is an important measure to prevent gas explosions.

 

36. What is the effective range of local ventilation fan airflow? How to calculate the effective range of airflow?

When using a local ventilation fan for forced ventilation, the maximum distance from the outlet of the air duct to the exit of the airflow is called the effective range of the local ventilation fan airflow, measured in meters.

The formula for estimating the effective range of wind flow is as follows:

LS=（4-5） ，（m）

In the formula, LS - effective range of airflow, m;

A - cross-sectional area of the roadway, m2;

(4-5) - Effective range coefficient of airflow. When the outlet wind speed of the wind duct is low, select 4; When the wind speed at the outlet of the duct is high, select 5.

 

37.What factors are related to the gas content in coal seams?

The influence of gas content in coal seams is related to the following factors:

(1) The burial concentration of coal seams. The deeper the coal seam is buried, the higher the gas content. When the relative gas emission increases by 1m3/t, the corresponding vertical depth of mining varies depending on the natural conditions of the mine, generally ranging from 6-27m.

(2) The lithology of the roof and floor of the coal seam. If the top and bottom of the coal seam are sandstone with good permeability, gas is easily released and the gas content in the coal seam is relatively low; If the roof and floor of the coal seam are mudstone or shale with poor permeability, gas is not easily released and the gas content in the coal seam is relatively high.

(3) Coal seam dip angle. When the inclination angle of coal is large, gas will be released upwards along some rock layers with good permeability, making it easy to be isolated by some rock layers with poor permeability, resulting in a high gas content in the coal seam.

(4) Coal seam outcrop. When there is an outcrop in the coal seam, gas can be directly discharged to the ground along the coal seam. The longer the outcrop exists, the lower the gas content in the coal seam. If there is no outcrop on the ground, the gas content in the coal seam will be higher.

(5) Geological structure. Geological structure is an important factor affecting the gas content in coal seams. The gas content in the coal seam of the closed and intact anticline axis is high; The locally thickened 'large coal lump' has a significantly higher gas content than the surrounding thin coal area; Open faults reduce the gas content in coal seams.

 

38.What factors are related to the content of free gas and adsorbed gas respectively?

The free gas content is related to the size of the space, gas pressure, and surrounding rock temperature in the coal body, usually accounting for 10% -20% of the existing gas content in the coal seam.

The adsorbed gas content is related to the structural characteristics and carbonization degree of coal, usually accounting for 80% -90% of the existing gas content in coal seams.

However, free gas and adsorbed gas are in an uninterrupted dynamic equilibrium state. When external pressure decreases, temperature increases, or coal structure is damaged, adsorbed gas will become free gas; When external pressure increases or temperature decreases, free gas will become adsorbed gas, and this phenomenon of partial gas content change is called desorption and adsorption, respectively.

 

39.Why is it necessary to assess the gas level of mines every year?

Because there are many factors that affect the amount of gas emitted from mines, and there are many factors that frequently change during the production process. So the amount of gas emitted from mines is also constantly changing, and the level of mine gas may also change. After identifying the gas level of the mine, the required air volume is supplied according to the actual gas level of the mine. Different mechanical and electrical equipment is selected, and different measures are taken for management. This can ensure safe production of the mine and avoid unnecessary waste of manpower and material resources. Therefore, the "Coal Mine Safety Regulations" stipulate that the identification of gas levels and carbon dioxide emissions in mines must be carried out annually.

Coal mines must strictly follow the standards of the "Code for Identification of Mine Gas Levels" (AQ1025-2006) to determine the amount of mine gas and carbon dioxide emissions, providing accurate basic data for the identification of coal mine gas levels.

 

40.When should the identification of mine gas levels be carried out?

The selection of time for mine gas level identification should meet the following requirements:

(1) The identification of mine gas levels should be carried out under normal production conditions of the mine.

(2) The identification of mine gas level should be carried out in the month with the highest absolute gas emission in the mine, generally in July.

(3) Take one day every 10 days in the first, middle, and second half of the month, such as the 5th, 15th, and 25th.

(4) Arrange three (or four) classes per day.

(5) In each testing class, normal production should be conducted at the same time.

 

41.What is the content of mine gas level identification and determination?

When conducting mine gas level identification, the measurement content mainly includes the following "four quantities":

(1) Air volume.

(2) The amount of gas and carbon dioxide emitted from the airflow.

(3) Gas extraction volume.

 

42.What are the advantages and disadvantages of optical methane detectors?

1. The main advantages of an optical methane detector are:

(1) Long lifespan, with no vulnerable or consumable parts except for the battery and light bulb.

(2) The water column pressure method can be used instead of the standard gas sample calibration instrument, eliminating the trouble of gas distribution.

2. The main drawbacks of optical methane detectors are:

(1) Poor selectivity. When there are other gases present in the measured gas, the different refractive indices of each gas can interfere with the measurement results.

(2) When the composition of the gas in the gas sample changes, the refractive index of the gas also changes, and the measurement accuracy is affected by humidity, gas composition, temperature, and pressure.

(3) The reading is not intuitive and cannot be automatically measured and alarmed.

 

43.How to use an optical methane detector to measure gas concentration?

The steps for measuring gas concentration using an optical methane detector are as follows:

(1) At the measurement site, install a carbon dioxide absorption tube on the intake pipe of the optical methane detector to absorb carbon dioxide, eliminate interference, and improve the accuracy of measurement data.

(2) Send the intake pipe of the optical methane detector to the testing location. If the position to be tested is too high or too far away, a long rubber tube can be connected to the intake pipe, and the rubber tube can be sent in place with a bamboo or wooden stick.

(3) Pinch and place the rubber suction balloon 5-10 times to allow the mixed gas containing gas to be sucked into the gas chamber.

(4) Press the light source button and observe the nearest integer value of the displacement of the black baseline through the telescope. This integer value is the percentage of the measured gas concentration integer.

(5) Rotate the fine adjustment screw clockwise to align the black baseline with the integer value scale. Observe the decimal value on the micro reading dial, which is the percentage of the measured gas concentration decimal.

(6) The sum of integers and decimals is the value used to measure gas concentration. For example, reading digit 1 from an integer, taking a micro reading of 0.5, and measuring a gas concentration of 1.5%.

 

44. How to calibrate the detection results of an optical methane detector?

The method for calibrating an optical methane detector is to multiply the measured gas or carbon dioxide concentration values by a calibration factor:

K′=365.8T/P

In the formula, K '- correction coefficient;

T - Absolute temperature at the measurement location, K.

T=t+273

In the formula, t - Celsius temperature at the measurement location, ℃;

P - atmospheric pressure at the measurement location, Pa.

For example, if the temperature at the measurement location is 27 ℃ and the atmospheric pressure is 86645Pa, and the gas concentration value is 2.0%, then T=27+273

K ′=345.8X300k/86645=1.197 After calibration, the gas concentration is 2.0% × 1.197=2.39%.

 

45. What is a coal mine safety monitoring system?

A coal mine safety monitoring system is a system that has functions such as analog, switch, cumulative acquisition, transmission, storage, processing, display, printing, sound and light alarm, control, etc., used to monitor methane concentration, carbon monoxide concentration, wind speed, wind pressure, temperature, smoke, power supply status, air door status, air duct status, local ventilation fan on/off, main ventilation fan on/off, and realize methane over limit sound and light alarm, power outage, and methane wind power blocking control. The system consists of a host, transmission interface, drilling, sensor, power outage controller, sound and light alarm, power box, lightning arrester, etc.

 

46.What is the sub station of the coal mine safety monitoring system? Where should the underground substation be located?

The device used in the coal mine safety monitoring system to receive sensor signals and transmit them over long distances to the transmission interface according to a pre agreed multiplexing method. At the same time, the device that receives multiplexed signals from the transmission interface is called a substation.

The underground substation should be set up in an air intake roadway or chamber that is easy for personnel to observe, debug, inspect, and has good support, no dripping, and no debris. During installation, it should be supported with brackets or hung in the roadway, so that it is not less than 300mm away from the roadway floor.

 

47. What are the main gas inspection locations on the mining face?

The main gas inspection locations for the mining face are as follows:

(1) The main inspection of the mining face includes the air inlet, air flow, coal side and upper corner, return air inlet, and tailgate.

(2) The excavation working face mainly inspects the working face air inlet, working face air flow, working face return air inlet, and partition return air at a distance of 30m from the connecting roadway.

(3) All blasting sites on the mining face must undergo "one shot, three inspections", which means checking for gas before loading, before blasting, and after blasting.

 

48. How to check the concentration of gas and carbon dioxide in blind alleys?

Gas usually accumulates in blind alleys, and some even reach high concentrations. When entering a blind alley to check gas and carbon dioxide concentrations, the following safety precautions must be taken:

(1) Firstly, check your own mining lamp, self rescue device, and methane detector to ensure they are intact and reliable before entering the blind alley.

(2) First, check the gas and carbon dioxide concentrations at the entrance of the blind alley. Only when their concentrations are both less than 3.0%, can the inspection be carried out section by section from the outside to the inside.

(3) When the concentration of gas and other toxic and harmful gases is high, two people must enter the blind alley at the same time, one in front and one behind, with one person measuring and the other monitoring.

(4) When the concentration of gas or carbon dioxide in a blind alley reaches 3.0% or above, the measurement must be stopped immediately and returned to fresh air.

(5) When entering a blind alley, attention should also be paid to the roof falling debris. If encountering roof collapse in the blind alley, the movement must be stopped.

(6) While measuring gas and carbon dioxide concentrations in blind alleys, oxygen and other toxic and harmful gas concentrations should also be checked to prevent suffocation or poisoning accidents.

 

49. Under what circumstances is it considered as "gas over limit operation"?

According to the "Measures for the Identification of Major Safety Production Hazards in Coal Mines (Trial)" formulated by the State Administration of Work Safety and the State Administration of Coal Mine Safety Supervision, any of the following situations shall be identified as "gas over limit operations":

(1) The number of gas inspection workers is insufficient.

(2) Failure to inspect gas according to regulations may result in missed or false detections.

(3) If no measures are taken to continue the operation after the underground gas exceeds the limit.

 

50.What are the measures to prevent gas explosions?

The main measures to prevent gas explosions include the following two aspects:

1. Prevent gas accumulation.

(1) Strengthen ventilation. Mine ventilation is a basic measure to prevent gas accumulation. Only when the air supply is stable, continuous, and reasonable can it ensure timely dilution and removal of gas.

(2) Drain gas. When the gas emission is large and normal ventilation cannot meet the requirements to solve the gas problem, the gas should be drained in advance.

(3) Strictly inspect. Strictly follow the "Coal Mine Safety Regulations" and relevant regulations to inspect gas, and strictly prohibit missed or false inspections.

(4) Timely processing. If gas accumulation is found, timely measures must be taken for discharge and treatment.

2. Eliminate ignition sources.

Strict management and control must be implemented for potential ignition sources that may occur during production

 

51. How to calculate gas accumulation based on gas emission?

The amount of gas accumulation is related to the amount and time of gas emission.

Q product=Q absolute x T stop

Q product in the formula - gas accumulation amount, m3;

Q Absolute gas emission rate, m3/min;

T stop - the duration of power and wind outage in the tunnel, in minutes.

 

52. How to calculate gas accumulation based on tunnel specifications?

The amount of gas accumulation in the roadway is related to the average gas concentration in the roadway and the specifications of the roadway.

Q Lane=C Mean × L × S

Q Lane in the formula - Gas accumulation in the roadway, m3;

C-average - average gas concentration in the roadway,%;

L - Lane length, m;

S - Lane area, m2.

 

53. What safety precautions should be taken when formulating, implementing, and carrying out gas emission measures?

The safety technical measures for gas emissions must comply with the following requirements:

(1) The gas emission safety technical measures that need to be formulated must be highly targeted, and the use of "universal" measures is strictly prohibited, let alone several locations sharing one measure.

(2) The safety technical measures for gas emissions should be formulated by the ventilation department. When the mine rescue team is responsible for implementation, an additional action plan needs to be developed.

(3) The safety technical measures for gas emissions must be reviewed and approved by the production, mechanical and electrical, and safety supervision departments, and approved by the mining technical leader or chief engineer.

(4) The approved gas emission safety technical measures must be implemented by relevant leaders, and all personnel participating in the implementation must personally sign.

(5) During the process of gas discharge, it is necessary to strictly implement gas discharge safety technical measures. Strictly prohibit 'blowing the wind'.

 

54. What should be included in the safety technical measures for gas emissions?

The safety technical measures for gas emissions should include the following aspects:

(1) The specific location and timing of gas emissions.

(2) Calculate the amount of gas emissions and estimate the time required for emissions.

(3) Clarify the gas concentration at the mixing point of the airflow and develop a method to control the airflow entering the single end roadway.

(4) Clearly define the route through which the emitted gas flows and indicate the location of ventilation facilities and electrical equipment.

(5) Clearly define the evacuation area and designate the location of the alert personnel.

(6) Clearly define the scope and location of power outages, as well as the executor of power interruption and restoration.

(7) Clearly identify the location for gas inspection and the person responsible for restoring power.

(8) Clarify the list of responsible persons and implementation personnel for gas emissions, as well as their respective roles and responsibilities.

(9) A schematic diagram of gas discharge must be attached. The diagram should indicate the ventilation facilities, electrical equipment, airflow routes, as well as the locations for warning, gas sensors, and gas inspection.

 

55. What is coalbed methane pressure? What are the types of coalbed methane pressure?

Coal seam gas pressure refers to the stress generated by the gas in the pores and fractures of the coal seam on the pore walls when the coal seam is buried at a certain depth, measured in Mpa.

Coal seam gas pressure can be divided into the following two categories:

(1) Original pressure of coalbed methane.

The original pressure of coalbed methane refers to the gas pressure inside the coal body that has not been affected by mining and drainage.

(2) Residual pressure of coalbed methane.

The residual pressure of coalbed methane refers to the existing gas pressure in the coal body affected by mining and drainage.

 

56.What are the basic characteristics of coal extrusion accompanied by gas outburst (extrusion)?

The basic characteristics of coal extrusion accompanied by gas outburst (extrusion) are as follows:

(1) What are the two forms of extrusion, namely the overall displacement of coal and the throwing of coal at a certain distance, but both the displacement and the throwing distance are relatively small.

(2) After extrusion, fine coal powder often remains in the cracks between the coal seam and the roof, and there are a large number of cracks on the coal body with overall displacement.

(3) The pressed coal is in block form without any sorting phenomenon.

(4) The amount of gas emitted from the tunnel increases.

(5) Squeeze out wedge-shaped or semi-circular holes that may have no holes or have a large mouth and small cavity.

 

57. What safety precautions should be taken when using blasting methods to deal with coal and gangue stuck in the coal (gangue) eye?

When dealing with coal and gangue stuck in the coal (gangue) hole, if there is no other method than blasting, blasting can be used, but the following regulations must be followed:

(1) Rigid explosives that meet the usage requirements must be used.

(2) Only one electric detonator and no more than 450g of explosives are allowed to be used for each firing.

(3) Water must be sprinkled before blasting.

(4) Before blasting, it is necessary to check the gas in the upper and lower spaces of the blocked parts in the coal (gangue) hole.

 

58. What types of coal mine explosives are commonly used underground?

According to whether it is allowed to be used in mining faces with gas and coal dust explosion hazards underground, it can be divided into two categories: coal mine permitted explosives and non coal mine permitted explosives.

The commonly used permitted explosives in coal mines underground include the following types:

(1) Coal mine ammonium ladder explosives (including water-resistant coal mine ammonium ladder explosives).

(2) Coal mine water gel explosive.

(3) Coal mine emulsified oil fryer.

(4) Ion exchange safety explosives.

(5) Charged with explosives.

 

59.What are the impacts of natural conditions in mines on the generation of mine dust?

The impact of natural conditions on the generation of mineral dust mainly includes the following aspects:

(1) Geological structure situation. The geological structure is complex, with developed faults and folds. In areas severely damaged by geological movements, the amount of mineral dust produced during mining is relatively large, while the amount of dust produced is relatively small.

(2) The occurrence conditions of coal seams. Under the same technological conditions, mining thin coal seams produces a larger amount of mineral dust than mining thick coal seams, because in the same dust producing environment, the space of thin coal seams is smaller than that of thick coal seams, which increases the concentration of mineral dust; Mining gently inclined coal seams produces less dust than mining steeply inclined mines.

(3) The physical properties of coal (rock). In general, when the joints of coal (rock) are developed, the structure is loose, and the moisture content is low, and the coal (rock) is hard and brittle, the amount of mineral dust produced during mining is relatively large, while the amount produced is relatively small.

 

60.How to classify mineral dust?

There are many classification methods for mineral dust, and currently in China's coal mines, there are mainly the following classification methods for mineral dust:

(1) Classified by the composition of mineral dust

① Coal dust: Coal particles with a diameter less than 1mm.

② Rock dust: Rock particles with a diameter less than 5 μ m.

(2) Classify according to the content of free SiO2 in mineral dust.

① Silicon dust: The free SiO2 content in mineral dust is above 10%.

② Non silica dust: The free SiO2 content in mineral dust is 10% or less.

(3) Classification based on the existence status of mineral dust

① Floating dust: Mineral dust suspended in the air of a mine.

② Dust accumulation: Mineral dust deposited around shafts, supports, equipment, and materials.

(4) Classified from a hygienic perspective

① Total dust: The sum of various particle sizes of mineral dust suspended in the mine air, also known as total dust. It refers to the mineral dust that can be inhaled through the nose and mouth during normal breathing.

② Non respiratory dust: Although it enters the body, it cannot enter the alveolar area due to the interception and retention effects of the nose, pharynx, trachea, bronchioles, and bronchioles.

③ Respiratory dust: dust that can be inhaled into the alveolar area of the human body. It is dust that causes lung disease. The aerodynamic diameter of respiratory dust is below 7.07 μ m, and the efficiency of an aerodynamic diameter of 5 μ m is 50%.

(5) Classified by explosiveness of mineral dust

① Explosive mineral dust: Mineral dust that is inherently explosive and can explode under certain conditions.

② Non explosive mineral dust: Mineral dust that is not explosive in itself and will not explode under any conditions.

 

61. What is the particle size of mineral dust? What is the relationship between granularity and human health?

The particle size of mineral dust refers to the size of mineral dust particles, also known as particle size. Due to the irregular shape of mineral dust, the particle size is generally represented by the average diameter of the dust particles or their projected length, with the unit being μ m (micrometers).

Generally speaking, the smaller the particle size of mineral dust, the greater the harm to human health. Respiratory dust with a particle size less than 5 μ m can be inhaled into the bronchioles and alveoli, causing pneumoconiosis.

 

62. What is the dispersion of mineral dust? What is the relationship between dispersion and mine safety and human health?

The dispersion of mineral dust refers to the degree to which a substance is broken, used to represent the composition of particle size in mineral dust. The dispersion of mineral dust usually refers to the percentage of a certain particle size of mineral dust to the total order of magnitude of mineral dust.

According to the percentage of different particle sizes of mineral dust in the total amount of mineral dust, the dispersion of mineral dust can be divided into high dispersion mineral dust and low dispersion mineral dust. High dispersion mineral dust contains a large proportion of fine dust particles, while low dispersion mineral dust contains a large proportion of coarse dust particles. The higher the dispersion of mineral dust, the greater the risk to mine safety and human health, and the more difficult it is to capture. Therefore, when formulating dust prevention measures, the dispersion of mineral dust must be considered to achieve the best effect.

 

63.What is the concentration of mineral dust? How to express the concentration of mineral dust?

The concentration of mine dust refers to the number of particles or mass of floating dust in the mine air per unit volume. There are two ways to represent it:

(1) Weighing method

The weighing method refers to the mass of floating dust contained in mine air per unit volume, measured in g/m3 or mg/m3. The weighing method represents the mass concentration of mineral dust.

(2) Counting method

The counting method refers to the number of floating dust particles contained in a unit volume of mine air, measured in particles/cm3. The counting method represents the quantity and concentration of mineral dust.

 

64. What is the charge of mineral dust? What are the hazards of electrical charge to human health?

Chargeability refers to the property in which mineral dust particles rub against each other during the crushing process, and the surface gains or loses electrons, causing the mineral dust to become charged. Mineral dust suspended in the air can also directly adsorb ions in the air and generate charges.

The electrical charge of mineral dust has a certain impact on its stability in the air. Same sex charges repel each other, increasing the movement of dust particles in the air; The attraction of opposite charges can cause dust particles to aggregate and settle upon collision. Some foreign countries use the method of charging the droplets to reduce dust by spray, and have achieved obvious results.

However, charged dust particles are easily trapped in the human body, and the charge of dust particles affects the phagocytic speed of cells. The higher the charge of mineral dust, the greater the harm to human health.

 

65.What is the essence of coal dust explosion?

The essence of coal dust explosion is the rapid chemical reaction process between oxygen in the air and coal dust under high temperature.

Coal dust suspended in the air is rapidly distilled or gasified to release flammable gases under the action of high-temperature heat sources. These combustible gases have a low ignition point, and when mixed with air, they burn under the action of a high-temperature heat source. The heat generated by the combustion heats up the coal dust and burns, producing more heat energy. These thermal energies propagate to nearby coal dust and repeat the above process. During this continuous process, the oxidation chemical reaction becomes faster, the temperature increases, and the range expands. When it reaches a certain level, it develops from ordinary combustion to a severe coal dust explosion.

The chemical reaction equation for coal dust explosion is as follows:

(1) When coal dust is safely burned, C+O2====CO2+8140Kcal/kg。

(2) When coal dust is not completely burned, 2C+O2===2CO+2440 Kcal/kg.

 

66. What is the coal dust explosion induction period? What is the significance of the coal dust explosion induction period for mine safety production?

The induction period of coal dust explosion refers to the time required for coal dust to decompose into a sufficient amount of combustible gas and heat upon heating, leading to the formation of an explosion. The induction period of coal dust explosion depends on the level of volatile matter in the coal dust. The higher the volatile matter, the shorter the induction period. Generally, the induction period is 40-200ms.

Although the induction period of coal dust explosion is very short, it is of great significance for mine safety production. For example, when using safety explosives for underground blasting, although the high temperature generated by the explosion reaches 2000 ℃, the duration of this high temperature and the shock wave generated by the explosion is very short, not exceeding 10ms, far less than the induction period of coal dust explosion. Therefore, coal dust explosion will not occur during blasting. Similarly, the principle of coal dust explosion induction period is also applied in the design of underground explosion-proof electrical equipment, so it is safe to use explosion-proof electrical equipment in environments with coal dust explosion hazards.

 

67.What dust prevention measures are commonly used underground in coal mines?

The dust prevention measures commonly used underground in coal mines include the following:

(1) Coal seam water injection. Drill and inject water into the coal seam before mining, and pre wet the coal seam with pressure water to reduce dust production during mining.

(2) Wet punching. Use a water drill to drill holes to moisten the coal dust inside the eyes.

(3) Spray water. Spray and water each centralized dust producing point under the shaft to capture floating dust and wet accumulated dust.

(4) Ventilation and dust removal. Control reasonable wind speed, dilute and eliminate floating dust at the work site, and prevent excessive dust accumulation.

(5) Purifying airflow. Install facilities and equipment such as water curtains and water curtains in the tunnels where dusty air flows to capture coal dust and reduce floating dust.

(6) Water seal breaks coal. Seal the borehole with water cannon mud and use the gasification of water to reduce dust.

(7) Remove accumulated dust. Timely and regularly remove dust accumulation in tunnels, on supports, and on equipment and material surfaces.

 

68. How to choose the appropriate wind speed for ventilation and dust removal?

Excessive or insufficient wind speed in underground tunnels is not conducive to removing mineral dust. According to the Coal Mine Safety Regulations, the wind speed in rock tunnels during excavation should be controlled between 0.15-4.0m/s; The wind speed in coal mining faces, coal tunnels during excavation, and semi coal rock tunnels should be controlled between 0.25-4.0 m/s. According to relevant information, the optimal dust removal wind speed is generally 1.2-2 m/s in tunnels, and 2-2.5 m/s after dust prevention measures are taken in damp tunnels and coal mining faces.

 

69. How to choose the wind direction for ventilation and dust removal?

Reasonable selection of airflow direction has a certain impact on dust removal work. It can effectively reduce the concentration of mineral dust and alleviate the harm of mineral dust to human health. For example, in a coal mining face, if the direction of the airflow is consistent with the direction of coal transportation, the relative velocity between the airflow and coal transportation will decrease, and the amount of coal dust blown up will also be relatively reduced; At the same time, the coal dust raised during the transfer point and coal transportation will not be carried to the working face where personnel are concentrated, which will also reduce the concentration of mining dust on the working face, and the workers on the working face will not breathe more mining dust. If downward ventilation is adopted for the longwall coal mining face, the above effect can be achieved. So, from the perspective of ventilation and dust removal, downward ventilation should be adopted.

 

70. How to use purified airflow dust removal measures? What are the two purification methods?

The measures for purifying air flow and dust removal refer to the method of capturing mineral dust by passing dusty air in the mine through certain equipment or facilities, thereby reducing the concentration of mineral dust in the mine air flow.

Currently, it is commonly used to install purified water curtains and dust removal fans in tunnels. The purification water curtain should be based on the principle of covering the entire tunnel section with water mist, and should be arranged as close as possible to the dust producing point to expand the range of air flow purification. When setting up a water curtain, the direction of water mist spraying should be opposite to the direction of air flow to improve the dust removal effect.

 

71.What are the overall requirements for comprehensive dust prevention in excavation work face?

Comprehensive dust prevention measures should be taken for the excavation face to meet the following overall requirements:

(1) The total dust reduction efficiency of the excavator driver's work site and the return air side of the unit in high gas and outburst mines should be greater than or equal to 85%.

(2) The dust reduction efficiency of respiratory dust in high gas and outburst mines should be greater than or equal to 70%.

(3) The total dust reduction efficiency of the excavation driver's workplace and the return air side of the unit in low gas mines should be greater than or equal to 90%.

(4) The dust reduction efficiency of respiratory dust in low gas mines should be greater than or equal to 75%.

 

72.What dust prevention measures should be taken during the blasting of the excavation face?

The amount of coal dust generated by blasting in the excavation face is quite large, and the following dust prevention measures must be taken:

(1) Before blasting the excavation face, the surrounding area of the roadway within 30 meters of the working face should be washed.

(2) When blasting the heading face, a pressure spray or a high-pressure spray dust suppression system must be installed 10-15m away from the working face to implement blasting spray. The fog curtain shall cover the whole section and spray continuously for more than 5min after blasting. When high-pressure spray is used for dust suppression, the spray pressure shall not be less than 8.0 Mpa.

(3) After blasting the excavation face, it is necessary to sprinkle water around the roadway and the coal (gangue) pile within a range of 30 meters from the working face before loading coal (gangue). In the process of coal (gangue) loading, water is sprayed while loading. When bucket coal (gangue) loader is used, spray system with automatic or manual control water valve shall be installed on the coal (gangue) loader to implement coal (gangue) loading spray.

 

73. How to determine the flushing cycle of coal dust in the tunnel?

The flushing cycle of the roadway should be determined based on the sedimentation intensity, and the general principle is to strictly prohibit the accumulation of coal dust (dry coal dust with a thickness exceeding 2mm and a continuous length exceeding 5m in the roadway):

(1) The main intake and return air ducts of the mine should be flushed at least once a month;

(2) The mining area roadway and ground storage, loading, and transportation system should be flushed at least once every 10 days;

(3) Within 30 meters of the mining face, the roadway should be washed in shifts. Within 30-100 meters, it should be washed at least once a day. Outside 100 meters, it should be washed at least once a week. Within 30 meters of the blasting face, it should be washed before and after blasting. For locations with high coal dust such as mining faces, coal should be randomly cut and washed along;

(4) Wash the shift within 20 meters of the transfer, loading, and unloading points;

(5) The mine should conduct at least one brushing of the main air intake roadway every year.

 

74.How to prevent mechanical equipment friction, impact sparks underground?

Reasonably select and operate mechanical equipment and tools to reduce friction and impact sparks. The main measures are as follows:

(1) It is strictly prohibited to use mechanical equipment and tools that have not been certified as qualified.

(2) The distance between the aluminum alloy motor fan used underground and the fan cover, cover plate, and other fasteners shall not be less than 1% of the fan diameter, and the minimum spacing shall not be less than 1mm.

(3) Mechanical equipment and tools should be used and operated carefully underground, and small metal equipment and tools should be handled with care to avoid collisions and sparks.

(4) Mining machinery should avoid cutting rocks. When encountering gangue, it is necessary to loosen it by blasting and then use mining machinery.

(5) During inclined lane transportation, it is necessary to conduct a thorough inspection of the traction steel wire rope. Unqualified steel wire ropes cannot be used, and it is necessary to adhere to the principle of not lifting beyond the limit and setting up "one slope, three gears" safety facilities to prevent rope breakage and sparks from racing cars.

(6) When using a belt conveyor, it is necessary to prevent the belt from being buried by floating coal or rubbing against the bottom coal to avoid friction heating and ignition.

 

75.Why is it necessary to install explosion-proof sheds in underground coal mine tunnels?

Explosion proof shed is a safety facility that blocks and isolates explosions.

Due to the continuous explosion characteristics of coal dust explosions, a coal dust explosion occurred at a certain location underground, and the resulting shock wave and flame quickly spread to other locations, not only causing damage near the explosion source, but also causing casualties, mine damage, and property losses in its diffusion area; At the same time, due to the faster propagation speed of shock waves than flames, shock waves first raise the accumulated dust, causing the concentration of floating dust to reach the explosion limit. Then, high-temperature flames propagate to this point, causing another coal dust explosion, and the harm is even more serious. The purpose of setting up blast shelters in underground tunnels is to limit coal dust explosions to a smaller area, prevent their further spread and development, and minimize the impact of explosion accidents. According to the Coal Mine Safety Regulations, mines that mine coal seams with the risk of coal dust explosion must have measures to prevent and isolate explosions. Setting up explosion-proof sheds in underground tunnels is the main measure to isolate coal dust explosions.

 

76.What are the types of explosion-proof shelters?

There are many types of explosion-proof shelters, which can generally be classified as follows:

(1) Classified by the operating principle of the explosion-proof shed:

① Passive explosion-proof shed.

② Automatic explosion-proof shed.

(2) Classified by the function of explosion-proof shelters:

① The main barrier is the explosion shelter.

② Auxiliary explosion-proof shed.

(3) Classified by the material of the flamethrower in the explosion-proof shed:

① Rock powder shed.

② Water shed.

 

77.How to determine the number of sinks (bags) on each water shed?

The number of sinks (bags) on each water shed should meet the following requirements:

(1) When the cross-section of the roadway is less than 10m2, nB/L × 100% ≥ 35%.

(2) When the cross-section of the roadway is less than 12m2, nB/L × 100% ≥ 60%.

(3) When the cross-section of the roadway is greater than 12m2, nB/L × 100% ≥ 65%.

In the formula, n represents the number of sinks (bags) on each water shed;

B - Width of windward section of water shed, m;

L - width of the roadway where the water shed is located, m.

 

78. What is an explosion-proof water shed? What are the classification methods for explosion-proof water sheds?

Explosion proof water shed refers to a type of explosion-proof facility where a container filled with water is suspended from the top of a tunnel. When an explosion occurs, the shock wave flips over the container filled with water, causing the water to scatter and fill the tunnel space, forming a thick mist band that absorbs a large amount of heat from the explosion flame, thereby suppressing the spread of the explosion flame and limiting the expansion of the explosion range.

At present, there are several classification methods for explosion-proof water sheds in coal mines in China:

(1) Classification by material of water containers

According to the material of the water container, it can be divided into a sink shed and a water bag shed.

(2) Classified by usage scope

According to the scope of use, water shelters can be divided into main explosion-proof shelters and auxiliary explosion-proof shelters.

(3) Classify by layout method

According to the layout, water sheds can be divided into centralized water sheds and decentralized water sheds.

 

79. How to calculate the total water consumption of the explosion-proof water shed area?

The total water consumption of the explosion-proof water shed area can be calculated according to the following formula:

V=gs

Formula V - total water consumption, L;

G - the required water volume per unit tunnel section, L/m2. Calculated based on 400L/m2 for the main water shed and 200L/m2 for the auxiliary water shed;

S - cross-sectional area of the roadway, m2.

 

80.What are the types of mine fires?

Mine fires can be classified according to the type of combustible materials, the combustion state of the fire, and the different heat sources that cause the fire, as follows:

(1) Classification by combustible material type

① Class A fire refers to fires caused by ordinary combustibles such as wood, paper, sawdust, coal, and garbage.

② Class B fire refers to a fire that occurs on the surface of flammable liquids or in flammable gases.

③ Class C fire refers to a fire that occurs inside or near electrical equipment.

④ Class D fire refers to fires that occur in combustible metals.

(2) Classified by combustion state

① A smoldering fire, a fire without obvious flames.

② Open flame fire, a fire with longer flames.

(3) Classified by ignition heat source

① External fire, caused by external heat sources.

② Internal fire refers to the combustion of coal caused by the physical and chemical changes that occur within the coal itself.

 

81. Where do internal fires often occur underground?

The main locations where internal fires often occur underground in coal mines are as follows:

(1) The goaf, especially when there is a large amount of residual coal that has not been promptly or tightly sealed.

(2) Coal blocks damaged by ground pressure on both sides of the tunnel.

(3) Long term accumulation of floating coal in the roadway.

(4) In the high void after the roof collapse of the tunnel.

(5) Connected to the old kiln.

 

82.What are the factors that contribute to the spontaneous combustion of coal?

There are three main factors that contribute to the formation of coal spontaneous combustion:

(1) Spontaneous combustion tendency of coal

The spontaneous combustion tendency of coal is an inherent factor in the formation of coal spontaneous combustion. The higher the spontaneous combustion tendency of coal, the greater the possibility of spontaneous combustion and the shorter the spontaneous combustion period.

(2) Appropriate oxygen supply conditions

Air not only oxidizes coal, but also carries away the heat generated by coal oxidation. Insufficient oxygen supply results in less heat generation; Excessive oxygen supply prevents heat accumulation, so insufficient or excessive oxygen supply cannot form coal spontaneous combustion. Coal can only spontaneously ignite under appropriate oxygen supply conditions.

(3) Good thermal storage environment

Coal is a poor conductor of heat, and the thicker the coal seam, the easier it is to create favorable conditions for heat accumulation. At the same time, the formation of coal spontaneous combustion requires a time process, which occurs after a latent period and a self heating period.

 

83.What are the levels of danger for spontaneous combustion in mines?

All mines that extract coal seams that are prone to spontaneous combustion and spontaneous combustion are classified as spontaneous combustion mines, also known as spontaneous combustion mines.

The degree of danger of spontaneous combustion in mines is divided into the following four levels based on the million ton combustion rate and natural combustion period in the past 10 years:

(1) Level I natural fire hazard mine

(2) Level II natural fire hazard mine

(3) Level III natural fire hazard mine

(4) Grade IV natural fire hazard level mine

 

84. How to determine the hidden danger of spontaneous combustion?

When any of the following phenomena occur underground, it is determined to be a hidden danger of spontaneous combustion.

(1) Carbon monoxide appears in the goaf or roadway airflow, and its occurrence trend is increasing, but it has not reached the critical index for spontaneous combustion.

(2) CO2 appears in the airflow, and its occurrence is on the rise, but it has not yet reached the critical threshold for spontaneous combustion.

(3) The temperature of coal, surrounding rock, air, and water has risen and exceeded normal temperature, but has not yet reached 70 ℃.

(4) The oxygen concentration in the airflow decreases and shows a decreasing trend.

 

85. How does the human body feel about coal spontaneous combustion?

There are several ways for the human body to feel coal spontaneous combustion:

(1) Visual sensation

Coal generates moisture during the initial stages of oxidation and spontaneous combustion, which often increases the temperature inside the roadway, resulting in fog or parallel water droplets hanging on the walls of the roadway; During shallow mining, water vapor or melting of ice and snow may occur in ground boreholes or subsidence areas during winter; Mist may also appear at the confluence of two different temperature airflows underground.

(2) Smell sensation

During the process of self heating and spontaneous combustion of coal, there are various hydrocarbons in the oxidation products, which produce odors such as kerosene, gasoline, turpentine, or tar. On site experience has proven that when people smell the smell of tar, coal spontaneous combustion has already developed to a certain extent.

(3) Temperature sensation

During the process of coal oxidation to spontaneous combustion, heat is released, so the temperature of the water and air escaping from this area is higher than usual, and the temperature of the coal wall is also higher than that of other locations.

(4) Fatigue sensation

Coal oxidation, self heating, and spontaneous combustion all release gases such as carbon dioxide and carbon monoxide. These harmful gases can cause headaches, stuffiness, lack of energy, discomfort, and fatigue, especially when a group experiences the above feelings, it indicates that coal has already undergone spontaneous combustion.

 

86.How to predict the spontaneous combustion period of coal seams in newly built mines?

For newly built mines, in order to prevent mine fires during mine design, it is necessary to predict the natural combustion period of coal seams. At this point, statistical methods cannot determine it.

In this case, the analogy method must be used to predict the spontaneous combustion period of coal seams. Identification of spontaneous combustion tendency based on coal samples collected during geological exploration, and participation in adjacent and similar coal seams, geological conditions, occurrence conditions, and mining methods in mining areas or mines

 

87.How to choose a mine ventilation system when mining coal seams that are prone to spontaneous combustion and spontaneous combustion?

The mine ventilation system mainly includes central ventilation system, diagonal ventilation system, and central diagonal mixed ventilation system.

(1) Central ventilation system

The central ventilation system has long lines and high resistance, which can easily cause air leakage in underground tunnels and lead to spontaneous combustion of coal seams. Therefore, it is only suitable for small mines with limited mining areas.

(2) Diagonal ventilation system

The diagonal ventilation system has a short circuit and low resistance, which is conducive to reducing air leakage in underground tunnels and preventing coal seam spontaneous combustion. In addition, there are many safety exits in the mine, making it safer. Suitable for large and medium-sized mines, the ventilation system has adjustability within a certain range. When a fire occurs in an area, it can achieve local area air stoppage, reduced air flow or reverse air flow according to the needs of disaster relief, to avoid the accident scope affecting the entire mine.

Well, make analogies and predictions

 

88.What fire prevention measures should be taken at coal mine wellheads?

The fire at the coal mine wellhead not only affects the safety of the wellhead surface, but also seriously threatens the safety underground. The "Coal Mine Safety Regulations" stipulate that all fire prevention measures and systems at ground buildings, coal piles, gangue mountains, timber yards, etc. in the mine must comply with relevant national fire prevention regulations. The main fire prevention measures at the wellhead include the following:

(1) The location of this material yard, gangue hill, and furnace ash yard must be reasonable and safe.

(2) The derrick and the joint building centered around the wellhead must be constructed with non combustible materials.

(3) Fire resistant iron doors should be installed at the inlet of the air intake shaft.

(4) Within a 20 meter radius of the wellhead room and ventilation fan, there shall be no fireworks or use of stoves for heating.

(5) A fire water tank should be set up near the mine shaft, and a water volume of over 200m3 should be regularly protected.

 

89. What is an electrical fire? What are the causes of underground electrical fires?

Electrical fire refers to a fire caused by the combustion of combustible materials such as coal and wood due to electric sparks, arcs, and high-temperature conductive parts when electricity is used underground.

The main reasons for electrical fires occurring underground are as follows:

(1) Long term overload operation of electrical equipment can cause overheating, burn electrical insulation, and result in short circuits or leakage, causing arcs or electric sparks.

(2) Electric sparks are generated due to wiring errors, poor contact, and live work.

(3) Electrical insulation is affected by moisture, and insulation performance is severely reduced, resulting in leakage and electric sparks.

(4) The deterioration of transformer oil quality or the infiltration of moisture or impurities into the oil can cause a phase to phase short circuit and arc, causing the oil in the tank to ignite and burn.

(5) The overhead electric locomotive generates electric sparks.

(6) Stray currents and static electricity can cause electric sparks.

(7) Explosion proof electrical equipment may cause electrical sparks or arcs when it fails to explode.

(8) Lightning strikes underground.

(9) Electrical equipment and circuits, various relay protection devices, and safety facilities do not meet the prescribed standards.

 

90.How to prevent electrical fires underground?

The basic methods for preventing electrical fires underground include the following:

(1) Design, select, install, debug, use, maintain, and repair electrical equipment and cable circuits correctly according to the allowable temperature rise conditions.

(2) Install relay protection devices and improve the electrical protection system to ensure sensitivity and reliability.

(3) Strengthen daily inspection and maintenance, and promptly deal with electrical faults and potential accidents.

(4) Transformer grease should be sampled, tested, and inspected regularly.

(5) Strictly implement the prescribed standards and regulations to ensure the normal operation of electrical equipment and cable lines.

 

91. What is fire pressure? What are the hazards of fire and wind pressure?

Fire wind pressure refers to the additional wind pressure generated when a high-temperature smoke stream passes through a well with a height difference during a fire underground.

The hazards of fire wind pressure mainly include the following aspects:

(1) May cause damage to the original ventilation system of the mine

(2) May increase or decrease the airflow in the mine

(3) May cause local airflow reversal

(4) May cause casualties

(5) May increase the difficulty of extinguishing fires

 

92. How to calculate the magnitude of fire wind pressure?

The magnitude of fire wind pressure can be calculated using the following two methods:

(1) Calculate using the height difference of the roadway:

H fire=Z (r0-r)

In the formula, h represents the fire air pressure value, mmH2O;

Z - The height difference between the starting and ending points of the tunnel through which the high-temperature smoke flows, m;

R 0- average air weight rate in the tunnel before the fire, kg/m3;

R - average air weight rate in the tunnel after a fire, kg/m3.

(2) Calculate using the temperature difference in the tunnel:

H fire=1.22 * △ t/T

In the formula, △ t represents the increase in temperature of the tunnel before and after the fire, in ℃;

T - Average absolute temperature in the tunnel after a fire, ℃.

 

93. Which locations underground should have fire-fighting equipment?

In order to extinguish mine fires in a timely and effective manner, fire extinguishing equipment should be available in locations where fires are prone to occur underground. These locations mainly include the following:

(1) Underground explosive material warehouse.

(2) Mechanical and electrical equipment chamber.

(3) Maintenance chamber.

(4) Material warehouse.

(5) Underground parking lot.

(6) Tunnels using belt conveyors or hydraulic couplings.

 

94.What safety precautions should be taken when a fire is discovered underground?

When a fire is discovered underground, the following safety precautions should be taken into account:

(1) When anyone discovers a fire underground, they should immediately take all possible measures to extinguish it directly based on the nature of the fire, ventilation and gas conditions in the disaster area, in order to control the fire.

(2) Quickly report to the mine dispatch room.

(3) The mine dispatch room or on-site team leader should evacuate all personnel in areas that may be threatened by fire according to the relevant provisions of the "Mine Disaster Prevention and Handling Plan", and organize personnel to carry out firefighting and rescue operations.

(4) When electrical equipment catches fire, its power supply should be cut off first. Before cutting off the power supply, only non-conductive fire extinguishing equipment is allowed to be used for extinguishing the fire.

(5) During the rescue and firefighting process, it is necessary to designate a dedicated person to inspect the ventilation and gas situation and develop safety technical measures to prevent explosions and personnel poisoning.

 

95.What are the basic requirements for the comprehensive management system of gas?

The basic requirements for "reliable ventilation" are: a reasonable system, intact facilities, sufficient air volume, and stable air flow.

The basic requirements for "reaching the standard of sampling" are: multiple measures should be taken simultaneously, sampling should be exhausted, sampling should be balanced, and the effect should meet the standard.

The basic requirements for "effective monitoring" are: complete equipment, accurate data, reliable power outage, and rapid disposal.

The basic requirements for "effective management" are: clear responsibilities, sound systems, strong execution, and strict supervision.

The above four links complement each other and jointly constitute the comprehensive management system of coal mine gas.

 

96.What are the basic requirements for "reliable ventilation" in the comprehensive management system of coal mine gas?

(1) The system is reasonable. Mines and mining faces must have independent and complete ventilation systems.

(2) The facilities are in good condition. The ventilation facilities in the mine are located reasonably and intact, and the ventilation tunnels have sufficient cross-sectional area.

(3) Adequate air volume. The air supply to mines, mining faces, and other places meets the requirements of safe production.

(4) Stable airflow. The wind direction, air volume, and wind speed at the location are continuously balanced and stable.

 

97.What are the basic requirements for achieving "extraction standards" in the comprehensive management system of coal mine gas?

(1) Take multiple measures simultaneously. Combining ground extraction with underground extraction. Adapting measures to local conditions and mines, we will comprehensively strengthen gas extraction work by combining measures such as pre extraction before the mine (mining area) is put into operation, extraction in the mining layer, extraction while mining, and extraction in the old goaf.

(2) It should be fully drawn. All coal seams that should be extracted must be extracted to maximize the extraction of gas and reduce the gas content in the coal seam.

(3) Extraction balance. The gas extraction capacity of the mine should be coordinated and balanced with the mining layout, so that mining production activities can always be carried out within the area where the extraction meets the standards.

(4) The effect meets the standard. By means of extraction, the gas content per ton of coal, the gas pressure in the coal seam, the gas extraction rate in the mine and working face, and the gas content before the coal mining face is extracted can meet the standards specified in the "Basic Indicators for Coal Mine Gas Extraction".

 

98.What are the specific requirements for "effective monitoring" in the comprehensive management system of coal mine gas?

(1) Fully equipped. The central station, sub stations, sensors and other equipment of the monitoring and control system are complete, the installation location meets the specified requirements, and the system operates continuously without missing reports.

(2) The data is accurate. Gas sensors must be calibrated on schedule, and their alarm values, power-off values, and restoration values should be accurate and reasonable. The monitoring center should be able to reflect the true state of gas in the monitoring area in a timely manner.

(3) Reliable power outage. When the gas exceeds the limit, the power supply to the workplace can be cut off in a timely manner, forcing the cessation of mining and other daily activities.

(4) Handle quickly. According to the emergency plan for gas accidents, when various abnormal phenomena occur due to gas exceeding the limit, correct measures can be taken quickly to effectively control the accident.

 

99.What are the specific requirements for "effective management" in the comprehensive management system of coal mine gas?

(1) Clear responsibility. Refine the responsibilities of gas control and safety production, decompose and implement them at all levels, links, and positions of the coal mine, from the chairman, general manager, and chief engineer to every employee at the work site, with their own clear and specific responsibilities.

(2) System improvement. Establish and improve regulations and systems for gas prevention and control, incorporating all work requirements for each link and position into a standardized and institutionalized track, ensuring that there are rules to follow, and continuously modifying, enriching, and improving regulations and systems according to changes in underground conditions and new situations and problems that may arise at any time. Continuously improve and strengthen various measures for gas control, so that management work is constantly updated, scientific, and effective.

(3) Powerful execution. Intensify the implementation efforts, put in great effort to ensure implementation, adhere to strict requirements, be meticulous, strictly enforce rules and regulations, and severely punish behaviors that violate commands, operations, and labor discipline. Implement job responsibilities and achieve collective prevention and control.

(4) Strict supervision. Establish a strong supervision mechanism and strengthen supervision and inspection. Cadres at all levels in coal mines must effectively fulfill their responsibilities for safety production. Coal management departments at all levels should strengthen industry management and guidance, and safety supervision and inspection agencies should increase supervision and inspection efforts to ensure that national safety production laws and regulations, as well as higher-level safety production instructions and directives, are effectively implemented in all types of coal mines.