The purpose of this research is to study how the natural gas transported by damaged distribution pipelines can migrate through the soil. If the gas emissions are not detected on time and the air vents are placed on inappropriate sites or are not maintained properly, gas can migrate directly throughout preferential pathways: bed sand pipes, sewer pipes, cable channels, channels for heating, then can enter the confined space and form explosive mixtures. As a proof of these phenomena, a series of events that occurred in industry and accidents suffered by civil citizens have occurred. The equipment used for emissions measurement is provided with 16 sensors to indicate the methane gas concentration. The sensors operate on the thermal conductivity principle being able to measure concentrations between 0% and 100% volume. A field version was adopted for tests to measure concentration of gases migrating through soil. For each location the soil permeability was determined using the running times distance between the source and the release detection heads. Also maps were drawn with time isolines for a particular concentration in order to characterize the dynamics of the natural gas migration, which helps improving the efficiency of solving technical expertise of the events due to natural gas explosions.

No abstract

Methane gas accompanying coal deposits was formed as a result of successive stages of the anaerobic process of vegetal material transformation into coal, at high temperatures and pressures, without external oxygen supply. During the metamorphism process, the content of C, H and O is modified, meaning an increase in carbon content, a decrease in hydrogen and oxygen, the nitrogen and sulphur content remaining constant. During this process, water and carbon dioxide is generated, the water being generated in the first transformation phases. Within the slow oxidation process, gas products result by using the oxygen content in plants, especially methane and carbon dioxide due to the fermentation stimulated by bacteria. Methane released into the atmosphere following the mining of coal have double ecological impact, participating in the destruction of the ozone layer and at the same time contributing to the enhancement of the greenhouse effect. At the same time, methane gas released into the atmosphere during coal mining may be used by mining operators as primary power resource for covering the power requirements of the mine or it can be used for commercial purposes.

Mining industry, by underground coal exploitations allows the release of important methane quantities in the atmosphere. Methane can be found stored both in coal deposits, as well as in sterile rocks from the proximity of coal beds. By carrying out the degassing process in advance of the exploitation, there can be obtained at least three benefits simultaneously: a new source of fuel for heating devices, methane emissions reduction and ventilation costs reduction. With the help of computer, simulations of the coal bed degassing process can show in safe conditions the differences between the situations that include this procedure and the situations in which the exploitation is performed without prior degassing of the coal beds.

The occurrence of spontaneous combustion phenomena in coal mines is generated by the reaction of mineral substance with atmospheric oxygen and favoured by the oxidation (self-ignition tendency) of coal, an oxidant environment and by the conditions in which heat exchange with the environment takes place. Preventing / Fighting against this phenomenon is regulated in the specific OHS requirements and in the General mining plan, comprising the technical and organisational measures for prevention and protection, as well as the costs related to this activity. However, despite all these measures, the combustion risk is reduced, but not totally removed. A series of methods are available, along with different types and schemes for preventing/fighting against the combustion phenomenon, which involve higher or lower costs depending on the chosen option: direct and indirect measurements (gaschromatographic analysis) of O2, CO2, CO, H2, CnHm, gases concentrations and temperature, treatments with chemical inhibitors, technologies for under-pressure water injection, inertisation technologies etc. Lately, monitoring production capacities through direct temperature means has been improved with portable thermal imaging cameras which simplify a lot the efforts and costs of the prevention activity. The applied procedure, advantages and disadvantages are analysed in the current paper.