Underground Coal Mine Explosions Research Articles

Experimental Study on the Isolation Effect of an Active Flame-Proof Device on a Gas Explosion in an Underground Coal Mine

Passive explosion-isolation facilities in underground coal mines, such as explosion-proof water troughs and bags, face challenges aligned with current trends in intelligent and unmanned technologies, due to restricted applicability and structural features. Grounded in the propagation laws and disaster mechanisms of gas explosions, the device in this paper enables accurate identification of explosion flames and pressure information. Utilizing a high-speed processor for rapid logical processing enables judgments within 1 ms. Graded activation of the operating mechanism is enabled by the device. The tunnel flame-proof device’s flame-extinguishing agent has a continuous action time of 6075 ms. Experiments on the active flame-proof effect of a 100 m3 gas explosion were conducted using a cross-sectional 7.2 m2 large-tunnel test system. With a dosage of 5.6 kg/m2, the powder flame-extinguishing agent completely extinguished the explosion flame within a 20 m range behind the explosion isolator. Numerical calculations unveiled the gas-phase chemical suppression mechanism of the powder flame-extinguishing agent NH4H2PO4 in suppressing methane explosions. Building upon these findings, application technology for active flame-proofing was developed, offering technical support for intelligent prevention and control of gas explosions in underground coal mines.

A Scoring-Based Risk Assessment Method Proposal for Methane Explosions in Underground Coal Mines

Mining is one of the sectors with the highest number of fatal occupational accidents. According to statistics, the majority of these fatal accidents are caused by methane explosions. In order for the explosion to occur, methane needs to form a certain concentration, sufficient oxygen and igniting elements are required. One of the most important factors that can affect methane formation is the carbon content of coal. As the carbon content increases, the probability of formation of flammable hydrocarbon-derived gas increases. The porous structure is a factor that causes methane to accumulate and create instantaneous concentration. It is known that the formation of the ignition element is directly proportional to the quartz content of the wall rocks. In this study, a new risk assessment method is proposed by assigning scores to the linguistic expressions of all these side parameters. This proposed method enables a proactive approach regardless of exact measurements and forced ventilation principles. It is foreseen that unexpected results can be prevented with the measures to be taken in this direction.

Investigation of methane-air explosions and its destruction at longwall coalface in underground coalmines

ABSTRACT Methane-air explosions are the most fatal accidents in underground coalmines. To understand its destruction, a worst-case full-scale methane-air explosion at a longwall coalface was simulated and analyzed based on accident investigations. It was found the flame covers a short length with an expansion ratio of about 6.67 at the longwall coalface, and crosscuts reduce the ratio to 3.67. Bifurcation reduces the peak overpressure by 25%–32% and the peak velocity of blast waves by 18.5%–23.5%. Corners have a significant effect on mitigating the peak overpressure but have a negligible impact on the blast velocity. In a long straight tunnel, the peak overpressure and blast velocity decay slowly and linearly by just 18.5% and 17.3%. A high-speed blast wave with debris and toxic and anoxic airflows at a velocity higher than 100 m/s were obtained from the accident investigations and in most of the simulation domain, it is the biggest challenge to evacuation and the most destructive force at the far-field disaster areas of methane-air explosions in underground coalmines. Thus, crosscuts, corners and blast velocity retarding methods should be more adopted to mitigate explosions and improve the rescue and evacuation safety.

Workplace risk assessment and control of fires and explosions in underground coal mines

Workplace risk assessment and control of fires and explosions in underground coal mines

Workplace risk assessment and control of fires and explosions in underground coal mines

On 19 December 1984, the Wilberg mine fire resulted in 27 deaths, and on 5 April 2010, the Upper Big Branch Mine explosion caused an additional 29 fatalities. Investigations of these events suggested that they may have been prevented if the hazard-associated risks had been correctly identified to comply with existing standards and control measures. These investigations - comprised of reports and published papers - were reviewed to identify contributing factors that resulted in the disasters. This study applied the workplace risk assessment and control (WRAC) risk tool to identify contributing hazards and rank the corresponding risks. This study included major contributing hazards that led to the Wilberg mine fire and Upper Big Branch explosion, and also proposed new controls that could have prevented their occurrence. The outcome of this study provides a framework for applying WRAC in coal mines to improve miner safety and health.

Numerical Simulation Studies on Effects of Explosion Impact Load on Underground Mine Seal

As the first barrier to prevent accidents caused by explosions in underground coal mines, the integrity and stability of mine seals have great effects on mine workers’ lives and underground production safety. In this paper, the mechanical responding performance of typical mine seals under the impact load are studied by using numerical simulation method. By such simulation studies, the safety of different seals subjected to the explosion load is evaluated. Seals’ stability are also investigated under effects caused by various influence factors including thickness of mine seal, cutting depth into surrounding rocks, rock type, and the roof-to-floor convergence under given the explosion load. The research results can provide theoretical basis and reasonable improvements for mine seal’s construction practices for improving its anti-explosion performance.

Effects of different factors on the minimum ignition temperature of the mixed dust cloud of coal and oil shale

The effects of particle size, oil shale content, dust concentration, dispersion pressure and inert dust on the minimum ignition temperature (MIT) of coal and oil shale mixed dust clouds (COSMD) were investigated in a dust cloud MIT testing system to understand the intrinsic mechanisms of these factors affecting the MIT of COSMD. The results demonstrated that 1) COSMD with larger particle size have higher MIT; with particle size increasing, MIT of COSMD with 50% oil shale content increases from 425 °C to 542 °C, 2) with the oil shale content increasing, MIT of COSMD exhibit the trend of increase, decrease and increase again with the two critical points at 50% and 80% oil shale content; 3) COSMD has an optimal ignition concentration and optimal ignition pressure to exhibit the lowest MIT; 4) the inhibitory effects of inert dusts NH4H2PO4, NaCl and CaCO3 on the MIT of COSMD show the order of NH4H2PO4>NaCl > CaCO3 with their critical concentrations at 30%, 40% and 60%, respectively; when the content of inert dust is 80%, all three inert dusts almost completely suppress the ignition and combustion of COSMD. The results and the underlying mechanism presented are extremely useful, not only in research and advancement of knowledge on the COSMDC ignition process, but also in taking necessary measures for preventing COSMDC explosions in underground coal mines.

Examination of classified rock dust (treated and untreated) performance in a 20-L explosion chamber

Mine explosions are caused by the ignition of excessive accumulations of combustible dust and/or flammable gas mixed with air in the presence of an ignition source. Rock dusting (limestone dust) is a primary measure to prevent propagating coal dust explosions in underground coal mines in the United States.Although rock dust is considered a nuisance dust, Continuous Personal Dust Monitors (CPDMs) do not distinguish between the coal dust and rock dust and assess the total dust exposure. During application, the <10 μm limestone particles and coal dust particles can become suspended and carried by the ventilating air for long distances and can be measured by the CPDMs. There is a concern in the mining industry that rock dust can be included in the CPDM measurements and make the samples noncompliant.Research conducted by the National Institute for Occupational Safety and Health (NIOSH) has found that all rock dust (RD) cakes after being wetted and then dried. To prevent rock dust from caking, several rock dust manufacturers have developed anti-caking rock dusts. The anti-caking additives used are typically fatty acids that make the rock dust hydrophobic and are added in very low quantities (<1%). While this development will add to the rock dust fluidity, an inevitable problem may be the increased airborne re-entrainment of rock dust due to vehicle movement and foot traffic in the area. Thus, one consideration to reduce such exposure from rock dust is to remove the respirable size fraction (<10 μm) of the applied rock dust. This paper presents the results of experiments that were conducted to determine if a rock dust can still inert a coal dust explosion when the respirable (<10 μm) or inhalable (<20 μm) component of the particle size distribution is removed. Three different untreated rock dusts (untreated A, B, and C) with their treated counterparts (treated A, B, and C) were classified using mechanical sieves into several different-sized fractions, including < 10, 10–20, 20–38, 38–53 and > 75 μm. The relative inerting effectiveness of these size fractions were determined using the United States Bureau of Mines (USBM) 20-L explosion chamber.

Factors Affecting the performance of trickle dusters for preventing explosive dust accumulations in return airways

Correctly applied rock dust can dilute, inert, and mitigate the explosive potential of float coal dust. Trickle dusters are one element of a comprehensive system to help prevent coal dust explosions in underground coal mines. Trickle dusters supply rock dust to inert fine float coal dust in areas where it is commonly deposited, such as the longwall tailgate returns, return airways, pillaring areas, and downwind of belt transfers. Dust deposition studies show that the effectiveness of trickle dusters depends on several key factors. Using multiple orifices, rock dust should be released near the mine roof in the direction of the airflow in order to spread the cloud cross the entry. The rock duster should have a mechanism to break up rock dust agglomerates as they leave the rock duster. The particle size distribution of the limestone rock dust and its airborne concentration should be proportional to the airborne size distribution and concentration of coal dust passing by the trickle duster. Specifically, rock dusts having a greater proportion of <74 μm material are more effective at minimizing downwind zones of explosible mixtures than mostly larger particles. In our testing, rock dusts having more than 95% of <74 μm sized particles were adequately dispersed by trickle dusters. Based on our results, the mass rate of rock dust discharge from the trickle duster should exceed the rate of float coal production by at least a factor of four in order to minimize accumulations of explosible dusts.

Analysis of soma mine disaster using causal analysis based on systems theory (CAST)

Analyzing accidents of sociotechnical systems requires an understanding of the system safety structure. Among various methods proposed for accident analysis in complex sociotechnical systems the Systems-Theoretic Accident Model and Processes (STAMP) model is one of the most widely used model for predictive applications in the literature. The STAMP accident causality model with the accident analysis tool, called CAST (Causal Analysis based on Systems Theory) is an effective method for accident analysis. The Soma Mine Disaster (SMD), which occurred due to a fire in the underground coal mine and caused 301 fatalities in 2014, is one of the largest mine disasters in the last few decades. Although mine fires usually do not cause large number of casualties as compared to explosions in underground coal mines, the SMD has one of the highest number of deaths in the 21st century. In this paper, the CAST, which is based on STAMP is used for analyzing the SMD as it provides a system engineering perspective in accident analysis. Considering the complex nature of the SMD, a variety of factors were involved in the high number of casualties. Among them, socio-technical factors like unstructured organizational and human performance as well as inadequate safety culture, improper decision making and risk perception, which played a critical role in the SMD, are defined in an integrated system thinking framework. Finally, inadequate system control constraints are identified in each hierarchical level of the system and improvements are suggested, accordingly. It is also demonstrated that a CAST analysis is robust for the cases like the SMD, which involves high degree of uncertainty related to the occurrence of the accident. The analyses presented in this paper also show the design of prevention and mitigation measures against such disasters in different levels of the accident control hierarchy.

Experimental investigation on effects of particle size, dust concentration and dust-dispersion-air pressure on minimum ignition temperature and combustion process of coal dust clouds in a G-G furnace

The present study investigates the effects of three important parameters, namely, particle size, dust concentration and dust-dispersion-air pressure on Minimum Ignition Temperature (MIT) and explosion process of coal dust cloud using Godbert-Greenwald furnace. The coal sample collected from Jharia Coalfield, India was used for experimentation. The effects of particle size and concentration of coal dust on MIT of coal dust cloud were studied at five different particle size ranges, that is, <38 µm, 38 to <75 µm, 75 to <212 µm, 212 to <425 µm and 425 to <850 µm. However, the effect of dust-dispersion-air pressure was studied only with the initial three finer particle size ranges, because at coarser sizes it was not possible to maintain a dust cloud of sufficient concentration due to high particle settling velocity and the dust cloud became non-explosive beyond dust-dispersion-air pressure of 30–35 kPa, even at ignition temperature of 1000 °C, which is the limiting temperature of the apparatus. The results indicate that MIT of coal dust cloud increases exponentially from 420 to 730 °C with increase in coal dust particle size. MIT was also found to decrease with the coal dust concentration till a stoichiometric concentration was reached, beyond which MIT slightly increased for the three finer particle size ranges. Nevertheless, in the case of the coarser particle size ranges tested, initially a trivial decrease in MIT was observed only up to certain dust concentration, after which, the MIT increased faintly. The results and the underlying mechanism presented are extremely useful, not only in research and advancement of knowledge on the coal dust explosion process, but also in taking necessary measures for preventing coal dust explosions in underground coal mines.

Dynamic Error Correction of Methane Sensor

Abstract Coal mine methane is a term given to the methane gas produced or emitted in association with coal mining activities either from the coal seam itself or from other gassy formations underground. The primary reason for measuring methane is to improve the safety of the mines. In recent years, there have been many fatalities in underground coal mine explosions in which methane was a contributing factor. The rapid detection of methane is very important from the point of view of safety of mine workers. This paper presents a concept of fast methane detection by reconstituting its concentration in dynamic states.

Evaluation of load losses in the ventilation circuit by the use of fortification in coal mines, study case: Nechí Mine, Amagá, Antioquia

The research aims to identify the variables which influence on the increase of risk for explosions in underground coal mines, especially in the accumulation of coal dust on top of the fortification, as well as analyze how these affect the load losses in the ventilation circuit and the proper evacuation of coal dust. This analysis was carried out by a guide field visits to Nechí Mine (Municipality Amagá, Antioquia) where it was observed that the coal dust accumulated significantly in the wooden doors that in the steel arches, we proceeded to simulate different geometries of fortification and the amount of these for the purpose to determine which is the geometry that contributes to reducing the load losses. After analyzing the different scenarios, the geometry that optimizes the ventilation circuit has been called geometry Circular 2, which shows reduction in load losses of up to 14.67% compared to other geometries analyzed under the same conditions. Whit this, are proposed alternatives more efficient to optimize the ventilation circuit and ensure health and safety conditions for workers inside the mine.

Premixed methane-air deflagrations in a completely adiabatic pipe and the effect of the condition of the pipe wall

A completely adiabatic pipe that is similar to a coal-mine coal or rock roadway was simulated using the computational software AutoReaGas. A partially adiabatic pipe was established using an experimental steel pipe with heat-insulating material installed in the inner wall, and a non-adiabatic pipe was also established using the experimental steel pipe without the heat-insulating material. Premixed methane/air deflagrations were studied in the three types of pipe to reveal the influence of the condition of the pipe wall on gas explosions. The results showed that in the completely adiabatic pipe, the maximum explosion overpressure was dynamic and decreased and increased with increasing distance; however, the flame-propagation speed increased gradually. In the partially adiabatic pipe and the non-adiabatic pipe, the maximum explosion overpressure and flame-propagation speed increased initially and then gradually decreased with increasing distance. The majority of explosion overpressure and flame-propagation speed values at each gauge in the completely adiabatic pipe were larger than those of the partially adiabatic pipe. Both measurements at each gauge in the partially adiabatic pipe were much greater than those of the non-adiabatic pipe. The condition of the pipe wall has a large influence on the maximum explosion overpressure and the flame-propagation speed. In future explosion experiments, heat insulating materials should be installed in the inner wall of steel pipes to obtain data for application to the prevention and control of gas explosions in underground coal mines.

Theoretical Analysis on the Attenuation Characteristics of Strong Shock Wave of Gas Explosion

In order to study the propagation characteristics of strong shock wave, a theoretical analysis is performed in this paper. Based on some assumptions, the relationships of the peak overpressure and the gas velocity during a gas explosion with the propagation distance were derived by using the explosion and aerodynamics theory. The results show that the peak overpressure of a strong shock wave is inversely proportional to the propagation distance and the cross-section area of the roadway, but directly proportional to the total energy of the gas explosion. However, the gas velocity is inversely proportional to the square root of the propagation distance and the cross-section area, but directly proportional to the square root of the total energy of the gas explosion. According to these results, some preventive measures can be taken to reduce the loss caused by the gas explosions in underground coal mines.

Effect of scale on the explosion of methane in air and its shockwave

Explosion experiments using premixed gas in a duct have become a significant method of investigating methane–air explosions in underground coal mines. The duct sizes are far less than that of an actual mine gallery. Whether the experimental results in a duct are applicable to analyze a methane–air explosion in a practical mine gallery needed to be investigated. This issue involves the effects of scale on a gas explosion and its shockwave in a constrained space. The commercial software package AutoReaGas, a finite element computational fluid dynamics (CFD) code suitable for gas explosions and blast problems, was used to carry out the numerical simulation for the explosion processes of a methane–air mixture in the gallery (or duct) at various scales. Based on the numerical simulation and its analysis, the effect of scale on the degree of correlation with the real situation was studied for a methane–air explosion and its shockwave in a square section gallery (or duct). This study shows that the explosion process of the methane–air mixture relates to the scales of the gallery or duct. The effect of scale decreases gradually with the distance from the space containing the methane–air mixture and the air shock wave propagation conforms approximately to the geometric similarity law in the far field where the scaled distance (ratio of the propagation distance and the height (or width) of the gallery section) is over 80.

From Scotia to Brookwood, fatal US underground coal mine explosions ignited in intake air courses

The National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, conducted a study of past mine explosions to identify the ignition locations and ignition sources responsible for the most severe explosion events resulting in death. Since the Scotia disaster of 1976, many fatalities from underground coal mine explosions have been linked to nonpermissible electrical equipment ignition sources located in intake air courses. With few exceptions, explosion protected equipment is generally not required in intake air courses of gassy underground coal mines in the US. Cigarette lighters were another prevalent ignition source for fatal explosions ignited in intake air courses. Several mine rescue/recovery teams have encountered electrical ignition hazards. The study provides evidence that intake air courses of gassy underground coal mines fit the description of certain Hazardous (classified) locations described in the US National Electrical Code ®. Class I Division 2 or Zone 2 explosion protection techniques may be used to design intake air equipment so that it does not present an ignition source under normal operation, before mine power is shut down in emergency situations. Nonpermissible circuits in intake air courses that are likely to remain energized during emergencies, e.g. battery powered equipment, should be protected by more stringent Class I Division 1, Zone 1, or Zone 0 techniques, to protect rescue/recovery personnel.