## 3 Results and Discussion
Figure 32 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 16:0 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. Figure 16:1 The distribution of oxygen concentration in the air flowing through the goaves with caving at a distance of 10.5 m from the floor of the exploited seam. Based on the determined speed characteristics, it can be concluded that the concentration of oxygen in goaves with caring decreases along with the increasing distance from the longwall front. At a distance of up to 440.0 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 33). Based on the tests and the results obtained, it was concluded that the zone with a particularly high risk of spontaneous combustion is formed immediately behind the longwall front, and reaches 160.0 m inside the goaves. Figure 16:2 The zone with a particularly high risk of endogenous fires in the goaves formed by rocks with tensile strength equal to 6.0 MPa. Figure 16:3 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 6.0 MPa. In the goaves with caving formed by roof rocks whose tensile strength amounts to 6.0 MPa, the cooling zone in which this air (behind the powered roof support along the entire length of the longwall) reaches a flow value higher than 0.02 m/s occurs at a distance of up to 25.0 m from the longwall front. Behind the zone of a particularly high risk of spontaneous combustion, at a distance of over 160.0 m from the longwall front to approximately 460.0 m, there forms a zone with insufficient air speed, yet with sufficient oxygen concentration in the air (due to the risk of spontaneous combustion). The tests conducted made it possible to demarcate the zone with a particularly high risk of spontaneous combustion in the goaves with caving formed by rocks whose tensile strength was equal to 2, 3.06, 4, 5, 6 and 7 MPa. Table 2 summarises the extents of these zones for the actual conditions of the longwall in question as well as for the additional ones obtained from the analyses conducted. The results obtained unambiguously indicate that the type of roof rocks (defined by their tensile strength) has a significant impact on the value of the air speed flowing through the goaves with caving, and on the value of oxygen concentration in this air. The more resistant the rocks, the greater the extent of the zones in which the air speed and oxygen concentration reach critical values due to the risk of spontaneous coal combustion. The greater extent of the zone with a particularly high risk of endogenous fires in the caving goaves of the longwall ventilated with the Y-type system (compared, for example, to the U-type system) arises out of the necessity to maintain a tailgate along the goaves, through which the air can flow. Part of the ventilation air stream flowing through this tailgate migrates to the goaves through the sidewalls, thereby increasing the extent of this zone in the goaves.