Ground air, also known as the atmosphere, is a mixture of gases. Except for the proportion of water vapor in the atmosphere that varies greatly by region and season, the remaining chemical components are relatively stable. The air that does not contain steam is generally called dry air. Its composition and volume percentage are oxygen (20.96%), nitrogen (79%) and carbon dioxide (0.04%).
Ground air from the wellbore into the well becomes mine air, and a series of changes will occur. Mainly include: reduction of oxygen content; increase of toxic and harmful gas content; increase of dust concentration; changes in physical conditions such as air temperature, humidity, and pressure. In mine ventilation, it is customary to divide the wind into fresh air (fresh air) and dirty wind (dust or lack of wind).
I. Main components of mine air and its basic properties
(a) Oxygen (O2)
Oxygen is a colorless, odorless, odorless gas with a relative density of 1.105 to the air. Oxygen is very active, it is easy to oxidize many elements and can help combustion.Oxygen is an indispensable gas for maintaining normal physiology of the human body. Under normal circumstances, the oxygen demand at rest is 0.2 to 0.4 L/min; at work, it is 1 to 3 L/min.
The relationship between human hypoxia symptoms and oxygen concentration in the air is shown in Table 1-1.
The relationship between the hypoxic symptoms of human body and the concentration of oxygen in the air. Oxygen concentration (volume)/% Main symptoms of the human body 17 15 10~12
6~9 No effect on rest state. Wheezing, difficulty breathing and strong heartbeat breathing and rapid heartbeat during work. Inability to work. Loss of consciousness, coma, and danger to life.
Loss of consciousness in a short time, respiratory arrest, may lead to the death of ground air into the underground, the oxygen concentration should be reduced, the main reasons for the decrease in oxygen concentration are: personnel breathing; slow oxidation of coal rock, pit wood and other organic matter; blasting work Underground fires and gas, coal dust explosions; coal and rock production and other harmful gases. In normally ventilated wells and working surfaces, the oxygen concentration generally does not change much compared with the ground, and does not cause much impact on the human body. However, in the case of blind alleys, poorly ventilated roadways, or fire and explosion accidents, special attention should be paid to the examination of oxygen concentrations to prevent suffocation accidents.
(b) Nitrogen (N2)
Nitrogen is a colorless, odorless, odorless inert gas with a relative density of 0.97. It is slightly soluble in water, does not support combustion, is nontoxic, and cannot be used for human respiration.
Nitrogen is not harmful to the human body under normal conditions, but when the concentration of nitrogen in the air increases, the oxygen concentration will decrease accordingly, and people will suffocate due to lack of oxygen. Nitrogen may accumulate in abandoned underground old lanes or enclosed gobs. For example, on September 7, 1982, a certain mine in China stopped the wind due to the main ventilators in the mine, and a large amount of nitrogen gas in the underground goafs blew out, resulting in the lack of oxygen and suffocation of the installers of coal mining face brackets, resulting in many casualties.
Nitrogen in the mine mainly comes from downhole blasting, decay of organic matter, and naturally occurring nitrogen gas gushing from coal and rock.
(iii) Carbon dioxide (CO2)
Carbon dioxide is a colorless, slightly sour gas with a relative density of 1.52. It does not support combustion and cannot be breathed by humans. It is slightly toxic and soluble in water.
Carbon dioxide has a stimulating effect on the human's breathing, so when oxygen is being given to people who are poisoned or suffocated, 5% of carbon dioxide is often added to oxygen to encourage the patient to breathe more. When the concentration of carbon dioxide in the air is too high, it can cause people to breathe faster, increase the amount of breathing, and in severe cases can also cause poisoning or suffocation. The degree of harm to the human body from the concentration of carbon dioxide in the air is shown in Table 1-2.
Carbon dioxide concentration (volume)/% Main symptoms of the human body 1 Respiratory deepening, shortness of breath
3 Shortness of breath, rapid heartbeat, headache, and rapid fatigue 5 Difficulty breathing, headache, nausea, tinnitus 10 Headache, dizziness, dyspnea, coma 10~20 Breathing pauses, loss of consciousness, a little longer time will lead to death
20~25 short-term poisoning death
Carbon dioxide is heavier than air, and it often accumulates in the floor of the tunnel under the coal mine, water tanks, coal eyes, the end of the mountain, blind lanes, goafs and poor ventilation.
The main sources of carbon dioxide in mines are: oxidation of coal and organic matter; personnel breathing; underground blasting; underground fires; gas, coal dust explosions. Sometimes it can also burst out of coal and rock, even with coal or rock, which can cause a major impact on production safety. For example, in one mine in China, there was a carbon dioxide and rock outburst accident in June 1975, which highlighted carbon dioxide 11000m3.
The asphyxiation of CO2 is one of the most important causes of casualties in mines, just like the lack of oxygen and asphyxiation.
II. Quality (concentration) of the main components of the air in the mine As the main components of the standard mine air, due to the great influence of oxygen and carbon dioxide on the physical health and safety of the people, the "Coal Mine Safety Regulations" (hereinafter referred to as the "Regulations") has its concentration. The standard makes explicit provisions. Mainly as follows:
When the mining work face enters the air stream, the oxygen concentration is not less than 20% by volume; the carbon dioxide concentration does not exceed 0.5%. When the carbon dioxide exceeds 0.75% in the total return air lane of the mine or the air flow of the one-wing return air lane, the cause must be immediately identified and handled. When the carbon dioxide in the airflow of the return air lane of the mining area and the working surface of the mining face exceeds 1.5%, when the concentration of carbon dioxide in the wind at the mining face reaches 1.5%, the work must be stopped and the personnel must be removed for disposal.
Third, the main components of the mine air detection method
The detection methods for the main components of the air in the mine can be divided into two major categories: the first is the sampling analysis method, and the second is the rapid determination method.
(a) Sampling analysis
Use sampling bottles or suction balloons to extract underground air patterns and send them to the ground laboratory for analysis. Analytical instruments mostly use gas chromatographs, which have high analysis accuracy, accuracy, and analysis speed. One injection can simultaneously complete the analysis of multiple gases; however, the required time is long, the operation is complicated, and the technical requirements are high. It is generally used in the detection of components in the downhole fire zone or where air components need to be accurately measured.
(B) Rapid assay
The use of portable instruments to detect on-site in the well and quickly determine the main gas composition is a commonly used measurement method.
Rapid Determination of Oxygen Concentration: There are many types of portable instruments that use oxygen detectors to detect downhole oxygen. It is recommended to use Andy's oxygen detectors and combustible gas detectors.
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