## 3 Results and Discussion
Based on the tests and the results obtained, it was concluded that the zone with a particularly high risk of spontaneous combustion, for the longwall ventilated with the Y-type system, is formed immediately behind the longwall front, and reaches 100.0 m inside the goaves. Figure 17: The distribution of oxygen concentration 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. Figure 18: The zone with a particularly high risk of endogenous fires in the goaves formed by rocks with tensile strength equal to 3.06 MPa. Therefore, it can be assumed that the goaves with caving formed by roof rocks whose tensile strength amounts to 3.06 MPa have no cooling zone in which the air (behind the powered roof support along the entire length of the longwall) reaches a flow value higher than 0.02 m/s. This value was exceeded only in the upper and bottom corner of the longwall at the flow height of up to 8.0 m from the floor of the exploited seam. Behind the zone with a particularly high risk of spontaneous combustion, at a distance of more than 100.0 m from the longwall front to approximately 345.0 m, there forms a zone with insufficient air speed, yet with sufficient oxygen concentration in the air, in terms of the risk of spontaneous coal combustion. In order to determine the impact of the strength of the rocks forming the caving on the extent of the zone with a particularly high risk of spontaneous combustion for longwalls ventilated with the Y-type system with the air being discharged along the goaves and supplied along the tailgate, additional tests were conducted for different values of this strength (2, 4, 5, 6 and 7 MPa). Figures 19-30 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). Figures 19-21 present, respectively, the distributions of the air speed and the dangerous speed due to the risk of endogenous fires, as well as the oxygen concentration levels in the goaves with caving at a distance of 0.5 m from the floor of the exploited seam. Figure 22: The distribution of the air speed flowing through the goaves with caving at a distance of 2.0 m from the floor of the exploited seam. Figure 23: The distribution of the air speed within the range from 0.02 m/s to 0.0015 m/s flowing through the goaves with caving at a distance of 2.0 m from the floor of the exploited seam. Figure 24: The distribution of oxygen concentration in the air flowing through the goaves with caving at a distance of 2.0 m from the floor of the exploited seam. Figure 25: The distribution of the air speed flowing through the goaves with caving at a distance of 7.0 m from the floor of the exploited seam. Figure 28: The distribution of the air speed flowing through the goaves with caving at a distance of 10.5 m from the floor of the exploited seam. Figure 27: The distribution of oxygen concentration in the air flowing through the goaves with caving at a distance of 7.0 m from the floor of the exploited seam. Figure 31 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 6.0 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 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. At a distance of 25.0 m behind the longwall front to 160.0 m inside the goaves, the speed of the flowing air reaches the critical value due to the spontaneous combustion risk, i.e., the value from 0.0015 m/s to 0.02 m/s. After exceeding the distance of 160.0 m from the longwall front, the speed of the air flowing through goaves with caving reaches a value lower than 0.0015 m/s.