Coal seam gas content method, stipulated by China's Coal and Gas Outburst Prevention Regulations, is one of the most important ways for regional prediction of outburst occurrence in Chinese coal mines. This paper presents a method to obtain the critical value step by step based on two case studies at the №.8 coal seam in Xieqiao Coal Mine, and the Xinzhuangzi Coal Mine of Huainan Mining Group. The first step is to collect and analyze all related data on all outburst cases with emphasis on outburst type, scale and gas geological conditions such as geological structures, gas contents, gas pressures and mining depths. Followed up is a combined underground onsite study including three integrated parts, namely, observation of outburst phenomena, measurements of both outburst prediction indices and gas contents, by which a relationship was established between outburst potential and gas content. The relationship then was validated in laboratory by experiments on gas emission rates from coal particles under different gas pressures. It is possible, and also a practice, to calculate outburst prediction indices with the experimental results so as to assess outburst potential under different gas contents or pressures. A comprehensive analysis of all previous study results was conducted to determine the critical value of gas content. Study results show that the critical values for Xieqiao and Xinzhuangzi mines are 7.0m3/t and 11.0m3/t respectively.
China is rich in coal resource, at the same time, the number one coal producing country in the world. In the constitution of energy in China, coal is the main energy source, which is 76% of primary energy output and 69% of primary energy consumption in China [1–2]. Therefore, as a primary industry in China, coal industry's sustained and steady development has profound impact on national energy safety. However, the overwhelming majority of China's coal resources are deeply buried with complicated geological conditions, imposing unaffordable challenges for coal mines to mine safely and efficiently. Gas related disasters in coal mine are widespread, and coal and gas outbursts, here after referred as outbursts, are extremely serious in coal mines of China. In recent years, with more emphasis on gas management and control, gas explosion accidents have decreased dramatically, nevertheless, disasters induced by outbursts have been experienced much more frequently than ever before in coal mines with thick overburdens and high gas contents. The situation will become worse than ever with the mining of deeper coal seams at higher production rates in a more complex underground mining environment, in order to meet the huge national demand for coal energy. In the year 2008, 754 out of 12,722 coal mines were identified as coal/rock and gas outburst mines, accounting for 5.9% of the total, and approximately 20% of the state owned coal mines[3]. Nineteen outburst accidents with three or more casualties killed 226 people in the year of 2009[4]. Reliable regional prediction of coal and gas outburst is the decisive task that guarantees safe and efficient production in coal seams with outburst potential.
