The determination of natural gas content in coal seams is essential to safe mining activities and to estimate gas resources. It is used to estimate methane emissions into workings, which is very important when using preventive measures of methane ignition and explosion. Methane content in a coal seam is mostly determined using a direct method. However, a problem with estimation of gas loss during collecting a sample in a mine occurs in each method. That gas loss is estimated using different procedures. In the Polish mining industry, methane content in a coal seam is mostly determined during roadway advancing faces in coal seams. The differences in procedures for determining methane content in coal in various laboratories gave rise to starting research into developing a new method. This article presents results of study of gas loss unification for the determination of methane content in coal seams. The research focused mainly on determining a uniform method for estimating gas loss using the early adsorption diffusion process. The method of coal sample saturation with methane was used to measure gas desorption rate. Saturation pressures of samples were determined for coal seams in the Upper-Silesian Coal Basin. The analysis of desorption results allowed to determine the dependence between methane content in a coal sample and the initial methane content in a coal seam. It was concluded that the desorption rate was highest within two minutes. For the procedure of coal sampling, gas loss was determined at 12% of both desorbed and residual gases. The presented research results gave rise to developing a uniform method for determining gas content used in Polish coal mining. The method was accepted as the national standard. Methodology using a new gas loss estimation procedure allows for achieving relatively fast results of the determination of methane content in coal seams, which is very important, especially in gassy mines.

An overlap auxiliary ventilation system is very often used for driving roadways in methane-rich coal seams. An overlap zone between the outlets of the forcing duct ends with a whirl flow air-duct (WFAD) and the exhaust duct ends with a dust scrubber that is created by applying the overlap system. This study examines the distribution of methane concentrations at various distances in the overlap zone. Maintaining a long overlap zone could increase the advance of the face. Therefore, the impact of overlap zone length on the methane concentration distribution, in and beyond the overlap zone, is investigated. The evaluation of methane concentrations is performed utilizing a well-established computational fluid dynamics (CFD) approach. The mathematical model of methane emissions into the roadway is adopted. Moreover, the CFD model is validated. A vortex of the return air, caused by the free airstream flowing out of the dust scrubber, is found. This air vortex is responsible for higher methane concentrations at the end of the overlap zone. Therefore, the conclusion can be drawn that maintaining the length of the overlap zone at 5 m to 10 m should be done to control permissible methane concentrations.

The determination of methane content of coal seams is conducted in hard coal mines in order to assess the state of methane hazard but also to evaluate gas resources in the deposit. In the world’s mining industry, natural gas content in coal determination is usually based on direct methods. It remains the basic method in Poland as well. An important element in the determination procedure is the gas loss that occurs while collecting a sample for testing in underground conditions. In the method developed by the authors, which is a Polish standard, based on taking a sample in the form of drill cuttings, this loss was established at a level of 12%. Among researchers dealing with the methane content of coal, there are doubts related to the procedures adopted for coal sampling and the time which passes from taking a sample to enclosing it in a sealed container. Therefore, the studies were designed to evaluate the degree of degassing of the sample taken in the form of drill cuttings according to the standard procedure and in the form of the drill core from a coal mine roadway. The results show that the determinations made for the core coincide with the determinations made for the drill cutting samples, with the loss of gas taken into account.

Methane has a bad influence on safety in underground mines as it is emitted to the air during mining works. Appropriate identification of methane hazard is essential to determining methane hazard prevention methods, ventilation systems and methane drainage systems. Methane hazard is identified while roadways are driven and boreholes are drilled. Coalbed methane content is one of the parameters which is used to assess this threat. This is a requirement according to the Decree of the Minister of Economy dated 28 June 2002 on work safety and hygiene, operation and special firefighting protection in underground mines. For this purpose a new method for determining coalbed methane content in underground coal mines has been developed. This method consists of two stages - collecting samples in a mine and testing the sample in the laboratory. The stage of determining methane content in a coal sample in a laboratory is essential. This article presents the estimation of measurement uncertainty of determining methane content in a coal sample according to this methodology.