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The behaviour of different gases (He, N 2 and CH 4 ) in coal was analyzed using a device for treating raw coal, designed for taking samples in the mine. This device was subsequently used to transport the samples and inject them with the gases under study. Experiments were conducted under different pressures, and a clear relationship was found between the drop in pressure and the occupation of different storage levels. On analysing the pressure evolution it was found that helium rapidly stabilised due to the characteristics of this gas. As for the other gases, N 2 showed a percentage fall much lower than that of CH 4 . In order to compare the storage capacity of different materials with respect to these gases, experiments were performed with different materials which form the mine's ceiling and walls. It was shown that the fall in pressure is very inferior. A fitting equation relating the evolution of pressure with time is proposed which may be used to define the time needed for the gas to stabilize in the coal. A normalized equation, very similar to that proposed by Langmuir, is likewise obtained to characterize the adsorption and desorption processes.

Underground coal mines have always had to control the presence of different gases in the mining environment. Among these gases, methane is the most important one, since it is inherent to coal. Despite of the technical developments in recent decades, methane hazards have not yet been fully avoided. This is partly due to the increasing depths of modern mines, where methane emissions are higher, and also to other mining-related circumstances, such as the increase in production rates and its consequences: difficulties in controlling the increasing methane levels, increasing mechanization, the use of explosives and not paying close attention to methane control systems. The main purposes of this paper are to establish site measurements using some critical parameters that are not part of the standard mining-control methods for risk assessment and to analyze the gas behavior of subvertical coal seams in deep mines in order to prevent gas incidents from occurring. The ultimate goal is the improvement in mining conditions and therefore in safety conditions. For this purpose, two different mines were instrumented for mine control and monitoring. Both mines belong to the Riosa–Olloniego coalfield, in the Asturias Central Basin, Spain and the areas instrumented are mined via subhorizontal sublevels at an actual depth of around 1000 m under the overburden of Mount Lusorio. During this research, a property favoring gas outbursts was site measured for the first time in an outburst-prone coal (8th Coalbed), gas pressure and its variations, which contributed to complete the data available from previous characterizations and to set some guidelines for assessing the potential outburst-prone areas. A gas-measurement-tube set has been designed for measuring gas pressure as well as its variation over time as a result of nearby workings and to calculate permeability. The paper establishes the effect of overlapping of works, but it also shows the efficacy of two preventive measures to be applied: high pressure water infusion and the exploitation of a protective coal seam (7th Coalbed), that must be mined preferably two complete sublevels before commencing the advance in the outburst-prone coalbed. Both measures constitute an improvement in the mining sequence and therefore in safety, and should be completed with a systematic measurement to control the risk: gas pressure in the 8th Coalbed in the area of influence of other workings, to establish the most suitable moment to renew the advance. Further researches could focus on ascertaining the permeability, not only in mined areas but also in areas of the mine that are still not affected by mining work and on tuning more finely the ranges of influence of overstress time and overlap distance of the workings of the 7th Coalbed in the 8th Coalbed.