The article presents the results of research into the influence of the location of auxiliary ventilation devices on the distribution of methane concentrations at the outlet of the longwall in an underground mine. Since this area is crucial from the point of view of explosion risk, the existence of an optimal arrangement of these devices could lead to improved safety of the crew working in the area. The aim of conducted study was to examine if the impact of this devices placement is significant. The research was carried out with the use of computational fluid dynamics (CFD) modeling—Ansys Fluent. The analyses took into account the location of the two most commonly used devices: a brattice and an auxiliary air-duct. The numerical model has been prepared and validated based on in situ measurements. Thirty-two cases of device configurations were analysed. The length and position of the brattice, as well as the height and position air-duct outlet along tailgate, were modified. It has been shown that although the presented solutions are an effective risk mitigation method, contrary to the common opinion of many practitioners, the impact of their exact placement, provided it is compliant with the regulations, is not significant for the registered methane concentration distribution at a longwall outlet.

The article addresses a significant aspect of ventilation in excavated workings with the influx of hazardous gases. The selection of appropriate ventilation affects worker safety and helps avoid localized accumulation of gases at dangerous concentrations. Polish mining regulations allow methane accumulation in roadways of up to 3%, which provides a safety margin relative to the methane explosibility limits of 5–15% CH₄. The methane concentrations obtained in the study ranged from 0.3% to 1.39%. The presented studies focused on the impact of air velocity on the formation of methane concentration fields. For this purpose, a numerical model was created based on an underground measurement results obtained in the active roadway with confirmed methane influx. The analysis of methane concentration distribution in the excavation was conducted using Ansys Fluent 2024 R1 for three different air velocities in the whirl flow airduct. It was shown that within 30 m from the face, the methane–air mixture is heterogeneous. Beyond this distance, it becomes a homogeneous mixture, regardless of the air velocity supplied by the auxiliary ventilation. Additionally, the occurrence of air recirculation was observed, resulting from the typical arrangement of equipment in the excavation space. The presence of elevated methane concentrations in the zone between the whirl flow airduct and the adjacent excavation floor is a notable phenomenon.

A range of preventive works has been presented based on the example of one of the exploited longwalls and the costs borne by the coal mine have been exhibited. Further, the paper presents the costs of preventive aerological practices conducted for the improvement of work safety, borne by one of the coal mining companies. The paper also includes the calculation of cost indices. Based on these cost indices, an analysis of costs of the applied aerological preventive practices was conducted for the longwalls driven in years 2014-2015 by one of the coal mining companies.

Aim: The article aims to present and evaluate the costs of preventive works carried out in 16 selected longwall panels in the mines of two coal mining com- panies. The article is based on the analysis of data made available by the companies, which the author has properly prepared to enable their comparison. Introduction: Fires occurring in coal mines are one of the more frequent technical hazards. Consequently, the mine’s ventilation departments are re- sponsible for carrying out preventive measures to limit and minimise the fire risk. The danger of a fire in mine workings is connected not only with the possibility of exogenic fire, which is influenced by external factors such as machine and equipment failures, short-circuits in electrical installations or the possibility of a fire on transport routes, but also with endogenic fire, which the low-temperature oxidation of coal may cause with the remains left in long- wall caving. The costs of prevention depend on the method of ventilation of the longwall faces and the coal’s susceptibility to spontaneous combustion. Methodology: The costs of coal mining are very high. They are related to the increasingly difficult mining conditions, which are influenced mainly by the increasing depth of exploitation and the increase in natural and technical hazards during mining work. The costs of mining within a longwall area are usually divided into the costs of starting up the longwall, its exploitation and liquidation. Within this division, more detailed cost analyses are rarely conducted. As part of the research conducted since 2015, ways of cost assessment were developed on the basis of appropriately prepared cost tables for various natural and technical hazards occurring within the ventilation hazards presented in the example discussed in the article. Based on the analyses of unit costs of fire hazard prevention elements obtained in coal companies and the developed cost tables, the costs of prevention works were compiled. The costs of prevention works were evaluated and compared for 16 longwall faces using the elaborated indices. Conclusions: Correctly applied fire hazard prevention in hard coal mines is one of the main elements of maintaining functional safety. Costs of hazard prevention in mines were usually compared together with the costs of exploitation, longwall equipment, media and crew working days. Cost tables were developed as part of the research to allow for cost assessment and determination of fire prevention cost indices. Keywords: coal mining, fire hazard, preventive work, cost of preventive work Type of article: review article

This paper presents the characteristics of methane hazard and prevention undertaken in the N-6 longwall of seam 330/2 in "Krupiński" coal mine. On the basis of methane concentration measurements conducted with the use of telemetric system, time series of the average and maximum methane concentration at the outlet of the longwall area were generated. It was ascertained that they exhibit a strong autocorrelation. Based on a series of the average methane concentration, a time series of ventilation methane content was created and a total methane content was calculated with the use of methane flow rate measurements in the demethanization system. It was ascertained that dependence between methane concentration and output on the examined day and on the previous day is weak and also that the dependence between methane concentration and air flow rate is very weak. Dependencies between ventilation methane content, total methane content and demethanization efficiency were also investigated. Based on forecasting models [1] developed earlier by H. Badura, forecasts have been made to predict the average and maximum methane concentrations. The measured values f methane concentration show a high level of accordance with forecasted ones.