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The determination of explosibility is critical for mine rescues or controlling the severity of a mine accident, especially for the gas explosion event. After a severe coal mine fire or an explosion event, a common practice for minimizing the risk is to seal the related area, and then to inject the inert gas (N2 and/or CO2) into the sealed area to e...
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... to a mine fire event that happened in a mine gob of a Chinese coal mine, the longwall panel was sealed immediately, and mine operators carried out a mitiga- tion measure which was N 2 injection to control the mine fire. Table 3 lists the main events during this mine fire event. Table 4 shows raw data for the total of 27 gas samples recorded from the mine atmosphere monitoring system after the accident happened. ...
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... According to the report of China's Health Commission (Commission, 2019), more than 20,000 new cases of occupational disease cases were reported annually in China from 2010 to 2018, of which more than 80% of these cases are pneumoconiosis. Second, high coal dust concentration is prone to explosion, which may result in catastrophe, economic losses, and casualties (Cheng et al., 2013;Azam and Mishra, 2019). Third, studies show that the coal dust shortens the equipment's service life, reduces the visibility of the working face, and pollutes the underground working environment (Strzemecka et al., 2019;Liu R. et al., 2020;Song et al., 2020). ...
Coal dust pollution in fully mechanized excavation faces not only affects the safety production of the coal mine but also threatens the health of workers. In order to reduce coal dust pollution and improve work conditions in mines, the layout of the dedusting-air duct in the dry dust collector and the influence of the duct position on the dust-producing area were studied. In addition, the effects of different cutting positions on dust removal efficiency were also studied. A full-scale model of mine roadway is established by CFD, and the influence of the position of the dedusting-air duct on dust diffusion and the distance between the tunneling head and the dedusting air duct on dust removal efficiency are studied. The results show that the higher the cutting position, the higher the dust concentration, and the longer the dust diffusion time in the coal roadway. When the distance between the dedusting-air duct and the tunneling head is set to 4 or 5 m, the dust removal efficiency is the highest. Moreover, the dust removal efficiency of the dry dust collector with the dedusting air duct arranged on the opposite side of the roadway is higher than that of the collector with the duct in the middle of the roadway.
... These accidents resulted in 7,567 deaths, which accounted for 66% of the total fatalities during this period [7]. Gas explosion is also known as the most dangerous hazard in U. S. coal mining history [8]. In recent years, due to the constant demand for coal resources, the mining depth has increased at a rate of 10-20 m/a, and even up to 50 m/a in some regions. ...
Underground gassy longwall mining goafs may suffer potential gas explosions during the mining process because of the irregularity of gas emissions in the goaf and poor ventilation of the working face, which are risks difficult to control. In this work, the 3235 working face of the Xutuan Colliery in Suzhou City, China, was researched as a case study. The effects of air quantity and gas emission on the three-dimensional distribution of oxygen and methane concentration in the longwall goaf were studied. Based on the revised Coward’s triangle and linear coupling region formula, the coupled methane-oxygen explosive hazard zones (CEHZs) were drawn. Furthermore, a simple practical index was proposed to quantitatively determine the gas explosion risk in the longwall goaf. The results showed that the CEHZs mainly focus on the intake side where the risk of gas explosion is greatest. The CEHZ is reduced with increasing air quantity. Moreover, the higher the gas emission, the larger the CEHZ, which moves towards the intake side at low goaf heights and shifts to the deeper parts of the goaf at high heights. In addition, the risk of gas explosion is reduced as air quantities increase, but when gas emissions increase to a higher level (greater than 50 m³/min), the volume of the CEHZ does not decrease with the increase of air quantity, and the risk of gas explosion no longer shows a linear downward trend. This study is of significance as it seeks to reduce gas explosion accidents and improve mine production safety.
... Conditional probability tables have been established by expert investigation with fuzzy Bayesian networks [13][14]. In addition, some assessment methods are applied during the mine gas disaster research process [15][16][17][18]. The causes of gas tunnel disasters are not only natural factors, but also human factors, and the management level is critical to ensure the safe construction of gas tunnels. ...
Currently, gas disasters in tunnels occur frequently and cause severe casualties and property losses.However, there are few studies on the risk assessment of gas tunnels, especially comprehensive analysis
of the safety risk of gas tunnels considering multiple factors. This paper presents a comprehensive assessment method for safety risk of gas tunnel construction based on fuzzy Bayesian network. The
results of safety risk assessment are determined by two aspects: risk probability and risk hazard. In the process of assessment, 12 risk indicators were extracted from 32 important factors by the principal
component analysis method, and a fuzzy interpretative structural modeling was established and converted into a fuzzy Bayesian network to evaluate the risk probability. The risk index weight was obtained through principal component analysis, and the risk hazard level was calculated by using the fuzzy comprehensive assessment method in combination with the hazard degree of the risk index. After
a comprehensive assessment of gas concentration and other field conditions, the relevant parameters such as the fuzzy interpretative structural modeling and fuzzy Bayesian network are determined. This
paper selects two construction segments of the Like tunnel as case studies to verify the feasibility and application prospects of this method. The method establishes a safety risk assessment model for gas tunnels, which can allow management personnel to fully evaluate gas tunnel risk and provides a safe construction environment.
... The limiting oxygen concentration and corresponding fractions of flammable gases were then used to draw an explosive triangle. Cheng et al. (Cheng et al., 2015, Cheng andLuo 2013;Cheng, Wang, Zhang 2012, J W andYang 2011) reported that the Coward explosive diagram can clearly identify the explosive status of mine gas and track its explosive trend upon changes to the mixture's components. ...
This work presents a comprehensive account of how adding C 3 H 8 impacts the possibility of explosion for CH 4-air mixtures. A series of experiments was carried out to determine the upper and lower flammability limits (UFL and LFL, respectively), and the explosive risk value for different mixtures of CH 4 and C 3 H 8. The critical oxygen concentration, the concentrations of CH 4 and N 2 at the point where the LFL and UFL merge, and the CH 4 explosive triangle were obtained for nitrogen-diluted mixtures. In addition, we used a detailed mechanism (GRI-Mech3.0) in the CHEMKIN software package to acquire the impacts of adding C 3 H 8 on the chemical kinetics of the explosion of CH 4. The flammable limits of CH 4 decrease linearly with the addition of C 3 H 8 while the flammable range increases slightly. The explosive risk value for CH 4 in air increases greatly upon adding C 3 H 8 following a parabolic relationship. Nitrogen dilution noticeably decreases the UFL and slightly increases the LFL, ultimately resulting in these points merging. The concentration of CH 4 and nitrogen at this merging point varies linearly when the C 3 H 8 concentration is varied between 0% and 2.0%. The addition of C 3 H 8 also expands and shifts leftwards and downwards CH 4 's explosive triangle. Numerical analysis reveals that the maximum temperature and pressure during the explosion, and the formation rates of CO and NO x , noticeably increase after adding C 3 H 8. Sensitivity coefficients of key dominant reactions show that overall more •H, •O, and •OH are consumed when C 3 H 8 is added. Furthermore, the time between ignition and maximum pressure (the burning time) is evidently shortened by the addition of C 3 H 8 , which also shortens the explosion duration.
... Dust explosions are also extremely dangerous. The most serious coal mine accidents are gas and coal dust explosions [5]. A coal dust explosion in West Virginia, USA in 2010, killed 29 people [6]. ...
Spray dust reduction is widely used in dust pollution control. The spray effect directly affects dust reduction efficiency, hence it is important to understand spray atomization and differential characteristics for typical water-based dust reduction media: tap water, magnetized water, surfactant solution, and magnetized surfactant solution. This study selected five measuring points 10, 15, 20, 25, and 40 cm from the nozzle to measure spray velocity and droplet size using a Phase Doppler Particle Analyzer at 1.5, 2.0, and 2.5 MPa. The results shown that the spray velocity of the other three media was generally larger than that of tap water. From 20 cm to 25 cm, the spray velocity of magnetized water and surfactant solution water decreased rapidly, with 35.53% and 49.78% reduction, respectively. The droplet size of tap water spray at 40 cm increased, whereas the sprays of other water-based media continuously decreased. The change amplitude of Sauter mean diameter (D32) was lower trend with pressure. Magnetized surfactant solution maintained the largest ratio of particles <60 μm at 2.0 MPa. This study provides significant guidance for spray dust reduction.
... Hence, a concept of explosibility safety factor (SF) has been proposed as one of the preliminary solutions to address such problems. 19 State-of-the-art engineering needs for underground firefighting works Due to coal spontaneous combustion problems, sealing a mined-out area in underground mines is very common to avoid any fire or explosion risks. A sealed atmosphere in an underground coal mine is simply a volume governed by some boundary conditions, 20 which can be understood by the following two aspects: Figure 1. ...
In the coal mining industry, explosions or mine fires present the most hazardous safety threats for coal miners or mine rescue members. Hence, the determination of the mine atmosphere explosibility and its evolution are critical for the success of mine rescues or controlling the severity of a mine accident. However, although there are numbers of methods which can be used to identify the explosibility, none of them could well indicate the change to the explosion risk time evolution. The reason is that the underground sealed atmospheric compositions are so complicated and their dynamical changes are also affected by various influence factors. There is no one method that could well handle all such considerations. Therefore, accurately knowing the mine atmospheric status is still a complicated problem for mining engineers. Method of analyzing the explosion safety margin for an underground sealed atmosphere is urgently desired. This article is going to propose a series of theoretical explosion risk assessment models to fully analyze the evolution of explosion risk in an underground mine atmosphere. Models are based on characteristics of the Coward explosibility diagram with combining mathematical analyzing approaches to address following problems: (1) for an “not-explosive” atmosphere, judging the evolution of explosion risk and estimating the change-of-state time span from “not-explosive” to “explosive” and (2) for an “explosive” atmosphere, estimating the “critical” time span of moving out of explosive zone and stating the best risk mitigation strategy. Such research efforts could not only help mine operators understand the explosibility risk of a sealed mine atmosphere but also provide a useful tool to wisely control explosive atmosphere away from any dangers. In order to demonstrate research findings, case studies for derived models are shown and are also used to instruct readers how to apply them. The results provide useful information for effectively controlling an explosive underground sealed atmosphere.
... Miners may be injured or unconscious, and may need external assistance to escape, hence a rescue has to be considered. This is only safe if methane levels are below the flammable range [29,30]. In turn this requires a working ventilation system, or the means to immediately re-establish ventilation. ...
The Pike River mine (PRM), an underground coal mine in New Zealand (NZ), exploded in 2010. This paper analyses the causes of the disaster, with a particular focus on the systems engineering and organisational contributions. Poor systems-engineering contributed via poorly designed ventilation, use of power-electronics underground, and placement of the main ventilation fan underground. Management rushed prematurely into production even though the technology development in the mine was incomplete. Investment in non-productive infrastructure was deprioritised resulting in inadequate ventilation, and the lack of a viable second emergency egress. The risk assessments were deficient, incomplete, or not actioned. Warnings and feedback from staff were ignored. Risk arises as a consequence of the complex interactions between the components of the sociotechnical system. Organisations will need to strengthen the integrity of their risk management processes at engineering, management, and board levels. The systems engineering perspective shows the interacting causality between the engineering challenges (ventilation, mining method, electrical power), project deliverables, management priorities, organisational culture, and workers’ behaviour. Use of the barrier method provides a new way to examine the risk-management strategies of the mine. The breakdowns in organisational safety management systems are explicitly identified.
... As the oil and gas in the pipelines were inflammable and explosive, the use of extinguisher may trigger explosion instead of putting out the fire. The firemen suggested that no actions should be made [1,2], just cordoned off the dangerous area, and waited until the oil and gas remained in the pipelines burned out and the fire extinguished itself. ...
A fire accident occurred in an oil refinery in north China. The on-site investigations proved that the fire was triggered by the leakage of tail oil from one hole on the pipeline. The detailed analysis of the metallurgical microstructure of related pipelines indicated that some micro-cracks existed in the pipeline. Under the action of tensile stress induced by inner pressure, one of the micro-cracks kept propagating and evolved into macro-crack; under the action of cyclic circumferential tensile stress and stress concentration in the crack tip, the macro-crack was transformed to penetrated crack, finally the crack was torn open by inner pressure, and then the leakage hole on the pipeline was formed and fire accident occurred.
... Ma and Larranaga [3] construct a diluted flammability diagram to assess flammability of gases in a reduced oxygen atmosphere while in Letter to the Editor, the same authors [4] develop the concept of a heating/quenching ratio to explore the explosibility of gases in a sealed area. Cheng and Zhou [5] expand upon the Coward explosibility technique to develop methods for inertization of explosive atmospheres while Cheng, Luo and Zhou [6] derive an explosibility safety factor that is an extension and enhancement of Coward's work in order to improve safety in the recovery of sealed areas. Fu-bao et al. [7] describe the use of liquid nitrogen infusion to extinguish sub-surface coal fires and enhance mine recovery operations. ...
Fires in underground mines pose unique problems typically not encountered in other industries. The underground tunnels and entries may be lined with coal or heavily laden with wood for support providing an almost endless supply of fuel while the forced ventilation airflow provides a constant supply of oxygen to fuel the fires that occur while, at the same time, transporting smoke and toxic gases to distances far-removed from the affected fire area. Other fuels exist such as conveyor belts or liquid diesel fuel that may also contribute to the overall fire hazard if consumed as part of a spreading fire. Fires in mines may often be of spontaneous origin when coal is oxidized resulting in self-heating and a smoldering fire that is difficult to prevent and to control. To address these types of fires, Pandey et al. [1] describe the development of chemical retardants that can inhibit, if not prevent, the oxidation and subsequent self-heating of coal. Regardless of the type of fire or combusti ...
... Unsteady gas emission rate and potential gas leakages indicate that the calculation results only have reference values. A safety factor should be considered [4]. In addition, once the sealed area is reopened, mixing with more fresh air may dilute the concentration of combustibles back to the flammable range. ...
... The total underground sealed volume is 178,500 m 3 and the methane volumetric inflow rate in the sealed area is 0.4 m 3 /s. Analyze the mine atmosphere and estimate different mitigation measures used to inert the atmosphere.By using the Eqs.(1)(2)(3)(4)(5)(6)(7)(8), ...
Gas explosions or mine fires present the safety threats for coal miners or mine rescues members. For an explosive atmosphere in the underground mine, careful determination of its explosibility status and applying some mitigations to switch an explosive atmosphere into a non-explosive one are very important for any underground rescues or a mine fire extinguishment. However, due to the complicated compositions in an underground sealed atmosphere, accurate determination of the explosibility of such atmosphere status is always a knotty problem for mining engineers. Beside of that, a proper estimation method for the needed time span when an explosive atmosphere is artificially or naturally changed into a non-explosive is also urgently desired. In order to improve the mine safety, this paper is going to address such mentioned problems. The original Coward explosibility diagram is modified with handling the combination effects of different inert gases for more accurate determining the explosibility of an underground sealed atmosphere which consists of complex gas compositions. Then, based on the revised explosibility diagram, a set of mathematical equations are theoretically derived to estimate the inertisation time of a sealed mine atmosphere by using different inerting approaches. Such research efforts can help mine operators understand the risk and provide a tool to control such atmosphere away from dangerous conditions. In order to demonstrate the research findings, at the end of the paper, the explosibility of gas sample taken from a real mine has been analyzed by using the revised Coward diagram. Also, the different inertisation time durations of various mitigation measures for such underground atmosphere have also been calculated.
