Study On The Secondary Explosion Rule In Disaster Area And Emergency Decision-making Model Of Coal Mine Gas Explosion

Gas explosion seriously affect the safety production of underground coal mine and often cause serious damage,the effective emergency rescue is the important way to reduce casualties and property loss.The disaster area environment of mine gas explosion is complicated and changeable.Factors like the limited space,the high temperature,the darkness,the toxic and harmful gas,the unstable rock formations and the falling areas,are interacting with each other and constantly evolving,which make the emergency rescue extremely risky and challenging.An inadequate emergency response would most likely result in mine resuce casualties.Many cases indicate that the orrcurrence of mine rescue casualties have important relationship with the insufficient understanding of the disaster situation and the bad emergency decision-making.An effective approach to contain mine rescue casualties is to strengthen the research on emergency decision-making of coal mine gas explosion.Therefore,this work studies the influence factors of rescue casualties in the disaster area and the secondary explosion rule in the disaster area,and further studies the emergency decision-making of coal mine gas explosion accident from aspects of decision-making mechanism and decision-making model.Methods like accident statistics,theoretical research,numerical simulation,case analysis and mathematical modeling are used in this work.The research contents include five aspects:(1)Influence factors of rescue casualties in the disaster areaIn order to put forward measures for avoiding the emergency decision-making error,the influence factors of rescue casualties in the disaster area are studied by accident statistical analysis.According to the relevant literatures and field survey,81 cases of mine rescue team casualties(MRTC)are obtained during the years 1953-2013.The cases are recorded in the light of occurrence time,influence factor,rescue work type and death toll.And it studies the characteristics of rescue casualty incidents in the disaster areas,the influence factors of rescue casualties in the disaster area and the effect of influence factors of rescue casualties on the emergency decision-making of gas explosion.The study shows that fire and explosion accident rescue bear the greatest risk of mine rescue casualties and this feature is more obvious in recent years.Moreover,that gas explodes during fire rescue has become a major characteristic of MRTC.MRTC's influence factors can be divided into 6 categories:organizational and personal factors,rescue technology and equipment problem,illegal command and disposal,irrational emergency decision-making and command,improper rescue measures,and others.Thereinto,organizational and personal factors induced the most of MRTC,accounting for 41.98%,followed by rescue technology and equipment problem,accounting for 16.05%.And in recent years,the proportion of MRTC caused by decision-making and command factor and improper rescue measures factor increases.The average casualties caused by the illegal command and disposal factors and the irrational decision-making and command factors can reach the number of a mine rescue unit,which is the emphasis of preventing MRTC.The MRTC occurring in fire rescue is serious,the average death toll can reach three to four,followed by that occurring in gas explosion rescue whose average death toll is two to three.Six main injuries that caused death were blast injury,burns,poisoning,suffocation,blunt trauma and overwork injury.The main inducing bodies of the factors affecting the rescue casualties are the rescue headquarters,the mine rescue team commanders and the team members.Research on the factors affecting the rescue casualties will help the rescue headquarters,the mine rescue team commanders and the team members to make scientific emergency decisions and to avoid blind rescue.(2)Rule of environmental change and identification of secondary explosion disaster in gas explosion areaIn order to achieve scientific emergency decision-making,the rule of environmental change and identification of secondary explosion disaster in gas explosion area is studied with the help of the related theory(i.e.,explosion mechnics,fluid mechnics,etc.),the previous research and the accident cases.A new insight is found that the change of disaster area environment leads to the evolution of secondary gas explosion.It studies the change rule of disaster area environment firstly,the inducement of the evolution of secondary gas explosion secondly,the evolution process of secondary gas explosion and the evolution form of secondary gas explosion thirdly,and the procedure for the identification of secondary explosion hazard in gas explosion area finnaly.?The formation mechanism of disaster area environment is put forward,and the formation process can be divided into three stages which are the destruction of explosion shock wave and flame front,the redistribution of heat and harmful gas,and the disturbance of rescue measures on disaster area environment.?The inducement of secondary gas explosion is analyzed from aspects of gas accumulation and ignition source.Ventilation break,no wind and little wind,recirculating air,insufficient air quantity,unreasonable ventilation system are important factors for the formation of explosive gas mixture during the production.However gas discharging and sealing up the disaster area control the formation and movement of the explosive gas mixture in the disaster area.Electric spark,spark caused by blasting,impact friction sparks,smoking fire,open fire,spontaneous combustion of coal are the main ignition source of gas explosion during the production.While the open fire and the spontaneous combustion of coal are the main ignition source inducing the gas explosion during the emergency rescue.In addition,the electric equipment in the disaster area(such as the miner's lamp)may become the ignition source of an explosion.?The evolution process of secondary gas explosion is summarized into four modes:the first is the explosion mode that the explosive gas mixture formed in rescue encounters the concealed spontaneous combustion of coal,the second is the explosion mode that the explosive gas mixture formed in rescue encounters the electric equipment in the disaster area such as the miner's lamp,the third is the explosion mode that the explosive gas mixture moves to the open fire locating in the coal face,and the fourth is the explosion mode that the fire district ignites the explosive gas mixture locating in the up(down)corner of coal face.Taking effective measures to control those four modes is key routes for gas explosion prevention.?Three evolution forms of secondary gas explosion in emergency rescue are put forward.In the process of mine rescue,the disaster area has the condition for direct detonation and flame acceleration.The change of disaster area environment can lead to the transition of gas combustion to deflagration,the transition of deflagration with small scale to deflagration with large scale,even the transition of deflagration to detonation,which would cause greater damage effect.?The procedure for the identification of secondary explosion hazard in gas explosion area is established,which is helpful for the rescue workers to determine the risk of secondary explosion and make scientific emergency decision.(3)Numerical simulation of gas explosion based on environmental parameters of disaster areaIn order to further explore the rule of secondary gas explosion and avoid emergency decision-making error,the numerical simulation of gas explosion is carried out based on the environmental parameters of the disaster area.The disaster area is simplified into the premixed methane/air area in the tube,and the methane concentration in the premixed area is selected based on the disaster area parameter.A lm-long closed tube model with a diameter of 0.1m is established by Ansys Gambit 2.4,and the premixed methane/air explosion process(the length of the premixed area are 0.2m and 0.3m,respectively)were numerical simulated by Ansys Fluent 15.0 when the volume fraction of methane are 6%,8%,9.5%,11%and 14%,respectively.Through analyzing some indicators(i.e.,explosion overpressure,rate of pressure rise,temperature,chemical reaction rate,shock wave speed,flame propagation speed and the relative position of shock wave and flame wave),it studies the characteristics of partially premixed methane/air explosion in a small closed tube where the premixed area changes,and discusses the secondary explosion rule under the change of environmental parameters in the disaster area.?The secondary gas explosion shows a certain regularity when the environmental parameters of the disaster area change.For example when the premixed length increases and the concentration decreases,the overpressure of methane/air explosion will increase for the methane concentration close to the stoichiometric concentration.And the explosion overpressures will not increase even though the premixed length increases for the methane concentration close to the lower limit of explosion.As the premixed length increases,the chemical reaction time will increase accordingly.The application shows that the study results of numerical simulation can be used to guide practice.?The methane/air explosion overpressure reaches the maximum when the volume fraction of methane was near the upper explosive limit but not the chemical equivalent concentration.This is due to the propagation of the premixed combustible gas to the non-premixed area under the influence of the gas volume ratio between the premixed area and the non-premixed area.?The rate of explosion pressure rise(dp/dt)reaches a peak(i.e.,the(dp/dt)experienced rapid rise followed by rapid decline)within the first 50ms and continued to maintain a lower value.However,for methane with a volume fraction higher than the chemical equivalent concentration,partial methane will propagate to non-premixed zone after 50ms of explosion and whose volume fraction will be reduced to near the chemical equivalent concentration,resulting in an increase in the chemical reaction rate and a certain fluctuation in the rate of pressure rise.?The explosion form in the simulation is deflagration with a weak intensity,which is related to the small premixed area.The combustion process indicates that the partially premixed methane/air explosion in the small tube has a shorter distance of flame acceleration,and the continuous flame acceleration phenomenon is not obvious.The explosion duration increases a little when the length of premixed area rises.Explosion shock wave speed and flame propagation speed are relatively small.The shock wave speed is 300-400 m/s,and the flame propagation speed is 0-10 m/s.?The cloud map of methane/air explosion temperature at the chemical equivalent concentration and the temperature curve of monitoring points show that the temperature of the premixed area is higher than that of the non-premixed area when the ignition temperature is 2600K.Nevertheless,the temperature of the non-premixed area to which the explosion flame propagates can still cause serious burns.(4)Emergency decision-making and secondary explosion characteristics of typical gas explosionsIn order to seek the relationship between emergency decision-making and the evolution of secondary gas explosion,the gas explosion accidents of two coal mines in China in 2013 are taken as the research object to analyze the emergency decision-making and the secondary explosion characteristics.The relationship between emergency decision-making and the evolution of secondary gas explosion is constructed.The studies show that improper emergency decision-making could lead to the evolution of secondary gas explosion.Establishing rescue headquarters as soon as possible is an important guarantee for safety rescue for complex accidents.It is of great significance to construct an emergency decision-making mechanism for coal mine gas explosion accidents to standardize emergency disposal and reduce emergency decision-making errors.(5)Emergency decision-making mechanism of gas explosions and prospect theory emergency decision-making modelAccording to the multi-subject and multi-stage characteristics of coal mine gas explosion emergency rescue,the emergency decision-making mechanism and prospect theory emergency decision-making model are theoretically studied.?It studies the emergency decision-making mechanism based on mechanism design theory.Emergency rescue of coal mine gas explosion should be divided into 2 stages:early stage and middle and later stage,and each stage have corresponding emergency decision makers.Rescue headquarters is the core of emergency decision-making organization.The study suggests that it should set up a rescue headquarters under the guidance of government department for serious or especially serious mine accident or complicated mine disasters,such as the complicated fire disaster,even without a death.In view of the complexity of coal mine gas explosion,emergency decision-making mode should combine the decentralized decision-making mode with the hierarchy decision-making mode,giving a decision-making authority to rescuer operators under the unified command of rescue headquarters,and it helps to get a safe,effective and ordered emergency disposal.It expounds the emergency decision-making points of mine explosion,which contributes to guide the decision makers to make emergency decision.?It puts forward the prospect theory emergency decision-making model for mine gas explosion.The improvement of prospect theory can fit the feature of mine emergency rescue well.The application demonstrates the prospect theory emergency decision-making model can promote the scientific decision-making of mine gas explosion.