## 3 Results and Discussion  
The analyses conducted helped to determine a series of physical and chemical parameters of the air stream and methane flowing through the region under investigation. In order to illustrate the processes related to this flow, Figure 3 shows the trajectories of the mixture of air and methane flowing through the caving goaves of the longwall ventilated with the Y-type system with the air being discharged along the goaves. A preliminary analysis of the distribution obtained was enough to demonstrate its great difference from the distributions concerning, for instance, the U-type ventilation system. Figures 4-15 present the results of the analysis for the goaves with caving formed by roof rocks whose tensile strength is equal to 3.06 MPa (as is the case in a real-world system). Figure 3: The trajectories of the mixture of air and methane flowing through the goaves with caving for Y-type ventilation system (**a**) and U-type ventilation system (**b**). Based the results obtained, it may be concluded that the air speed value decreases along with an increase in the distance from the floor of the exploited seam. The air flowing through the goaves with caving reaches the highest speed value, irrespective of the flow height in the goaves, behind the caving line from the inlet side to the longwall, as well as along the tailgate maintained at the goaves. The highest speed value occurs at the flow height of 2.0 m from the floor of the exploited seam in the bottom corner of the longwall, and amounts to 0.36 m/s. The distribution of oxygen concentration for this ventilation system is also different than in the case of the U-type system [47]. It is clearly visible that the air stream moving along with tailgate leads to an increase in this concentration along this route. Figure 16 presents the distribution of air speed values in the goaves with caving as a function of distance from the longwall front for the actual values of the tensile strength of roof rocks amounting to 3.06 MPa. Red horizontal lines were used to mark the range of dangerous speed values due to the risk of endogenous fires in these goaves. Based on the determined speed characteristics, it can be concluded that the air speed in goaves with caving decreases along with the increasing distance from the longwall front. At a distance of up to 96.0 m from the caving line into the depths of the goaves, the speed of the flowing air reaches the critical value due to the risk of endogenous fires, i.e., the value from 0.0015 m/s to 0.02 m/s. After exceeding the distance of 96.0 m from the longwall front, the speed of the air flowing through goaves with caving reaches a value lower than 0.0015 m/s. Figure 17 presents the distribution of oxygen concentration in the air flowing through the goaves with caving as a function of distance from the longwall front. Figure 16: The distribution of air speed values in the goaves with caving as a function of distance from the longwall front for the actual values of the tensile strength of roof rocks amounting to 3.06 MPa. Based on the determined speed characteristics, it can be concluded that the concentration of oxygen in goaves with caving decreases along with the increasing distance from the longwall front. At a distance of up to 335.0 m from the caving line inside the goaves, the oxygen concentration in the air flowing through the goaves with caving falls within the critical range due to the risk of endogenous fires, i.e., reaches a value higher than or equal to 8%. The speed characteristics determined for the air flowing through the goaves with caving and for the oxygen concentration in this air served as the basis for demarcating the zone with a particularly high risk of spontaneous coal combustion (in which both of these conditions are met) (Figure 18).