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Due to a gradual increase in mining depths in northern China, the water inrush problem there has become increasingly complex. In the present study, a physical model was developed of a syncline-axis structural fractured zone above confined water, using measured parameters from the Baizhuang coal mine. Using the similarity theory, water inrush from a fractured floor was simulated with different water heads and different structural zones. The mechanism of a delayed water inrush from the floor under the combined action of confined water and a fractured zone was also studied. The results demonstrated that: (1) Water inflow under different pressures; (2) Sand inrush discharges gradually increased under various pressurized water pressures and then decreased; and (3) Based on water and sand inrush discharges, the changes in the Reynolds number and porosity were analyzed, and a "void flow-fissured flow-pipeline flow" transition was proposed. This research provides a basis for developing methods to prevent floor water inrush during deep mining. [ABSTRACT FROM AUTHOR]

Coal mine fires continuously attract the attention of researchers recently. Firefighting is the most important activities for protecting the mining safety and coal resources at the same time. Among them, liquid nitrogen is usually employed as emergency treatment for sudden fire accidents. However, it as a normalized fire prevention technology is still in the blank. Subsequently, a new system called ground fixed liquid nitrogen station has been developed for normalizing fire prevention. It took 5 months to build such total flooding fire extinguishing systems in JF colliery, with a maximum flow rate: 5000 Nm3/h, pressure: 1.0 ± 0.05 MPa, high purity: ≥ 99.99%, and outlet temperature of CGN is 10°C lower than the atmospheric temperature. Field observations showed that it only took 3 days for the concentration of CO to decrease by 95.36%. The main fire extinguishing mechanism of the system is the nitrogen inertization, and the cooling effect is supplemented. By using the presented technique, there was no waste left behind. Thus, it is concluded that the newly developed firefighting system can be put into practice, especially its broad application prospects in large capacity collieries. [ABSTRACT FROM AUTHOR]

Subsurface fires are a common threat for coal mining, since spontaneous coal combustion can easily result in gas combustion and explosion. In this paper, aiming to solve problems of the low efficiency, the line clogging, and some other related field issues in liquid nitrogen perfusion, a fire extinguishing application by using immediate liquid nitrogen infusion was presented. The presented technique is efficient in absorbing heat, and consequently, displacing oxygen and combustible gases. Field tests justified the efficiency of the technique. Only 12 days were taken to unseal the coal mine, which provides a quick and efficient management of the fire zone. Furthermore, by using the presented technique, there was no waste left behind which may impede the subsequent production. The presented technique is of great benefit from the social, economic, and environmental aspects, which indicates its broad application in fire prevention for large-scale coal mines. [ABSTRACT FROM AUTHOR]

Out of the thermal balance method, a method of presenting mine fire data is proposed in this work. By grouping fuels into a pseudo fuel, grouping nitrogen and oxygen into a pseudo air, and using carbon dioxide as the diluent, a diluted flammability diagram is reconstructed for this oxygen-modified environment. The flammability envelop is controlled by oxygen availability, while the operation point is controlled by fuel/diluent availability. The relative position between the envelop and the operation point shows the flammable state of this mixture. Coward's explosive triangle is also applied using the limiting oxygen concentration derived from the diagram. Both are most useful in guiding the suppression operation for an underground coal mine fire. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article “Theoretical Flammability Diagram for Analyzing Mine Gas" by Tingguang Ma and Michael D. Larrañaga published in the August 08, 2013 issue.

Coal mine fire is a serious problem in Jharia coal field, India. The coal mine fire can be detected with different techniques such as borehole temperature measurement, thermo-compositional analysis, remote sensing techniques, thermo-graphic measurement and geophysical methods. In this study, various geophysical methods were used to detect the surface and subsurface coal mine fires. Geophysical techniques used in the present study are apparent resistivity, self-potential (SP), magnetic method and thermography. Geophysical anomalies such as low SP value of -60mV, high negative magnetic response and low apparent resistivity value helped us to detect and delineate the fire and non-fire areas laterally as well as depthwise. Furthermore, the thermography survey was carried out in the coal field using thermal imaging camera in order to substantiate the geophysical methods. This integrated approach was found to be more advantageous for the detection and delineation of surface and subsurface fire with respect to use of any specific techniques. Moreover, the level of threat towards the locality, national railway line was also assessed unambiguously using the above techniques. Hence, proper planning and implementation towards the mitigation of hazard can be achieved on the basis of the reported results. [ABSTRACT FROM AUTHOR]