Under standard conditions, when the gas concentration is 5- 16% by volume, it will explode when it meets a high temperature fire source. The explosive force is the largest when the concentration is 9. 1-9.5%.
The boundary of gas explosion is not fixed, it is affected by temperature, pressure and the mixture of other combustible gases and inert gases in coal seam.
2. Ignition temperature: The ignition temperature of gas is generally 650℃-750℃, but it is affected by the gas concentration and the nature of fire source. ) The delay of gas initiation has practical significance for blasting work. When blasting, the instantaneous temperature of explosive can reach 2000℃, but the flame exists for a short time, only a few thousandths of a second, so it will not cause gas explosion. However, if the explosive deteriorates and the charge mud does not meet the requirements, it may prolong the flame existence time, or even ignite the charge to cause gas combustion or explosion accidents, so the underground blasting work should be paid great attention to. The existence of high temperature fire source is a necessary condition to cause gas explosion. Electric spark, illegal shooting, coal spontaneous combustion, open flame, etc. It is easy to cause gas explosion.
3. Adequate oxygen content:
Experiments show that when the oxygen concentration in the air decreases, the explosion limit of the gas becomes narrow, and when the oxygen concentration decreases below 12%, the gas will not explode.
New technology of coal mine safety: the first chapter is an overview
Mine ventilation is the basic guarantee of mine safety production. Mine ventilation refers to the operation that with the help of mechanical or natural wind pressure, an appropriate amount of fresh air is continuously transported to various underground wind points for people to breathe, dilute and discharge all kinds of harmful gases and floating dust, so as to reduce the environmental temperature and create good climatic conditions, and adjust and control the airflow route according to the needs of evacuation and disaster relief when disasters occur.
Since 1980s, with the improvement of coal mine mechanization level, the reform of coal mining method, roadway layout and support, and the development of electronic and computer technology, China's mine ventilation technology has made great progress, ventilation management has become increasingly standardized, serialized and institutionalized, and more and more new ventilation technologies and equipment have been put into use. Ventilation system optimization based on low consumption, high efficiency and safety has been implemented in many coal mines, which can better provide safety guarantee for intensive production with high yield, high efficiency and safety. Mine gas explosion is a thermal chain reaction (also known as chain reaction). When the explosive mixture absorbs a certain amount of energy (usually the heat energy given by the ignition source), the reaction molecular chain breaks and dissociates into two or more free radicals (also called free radicals). This kind of free radical has great chemical activity and becomes the activation center of continuous reaction. Under suitable conditions, each free radical can be further decomposed to produce two or more free radicals. In this way, there are more and more free radicals, the chemical reaction speed is faster and faster, and finally it can develop into combustion or explosive oxidation reaction. Therefore, in essence, gas explosion is a violent oxidation reaction of methane and air with a certain concentration under moderate action.
The high temperature and high pressure produced by gas explosion make the gas near the explosion source impact outward at a great speed, causing casualties, destroying roadway and equipment, raising a lot of coal dust, making it participate in the explosion and producing greater destructive power. In addition, a large number of harmful gases were produced after the explosion, resulting in poisoning and death.