## 2 Materials and Methods
### Characteristics of the Database
#### 2.1.3 Mining Parameters  
A total of nine mining parameters related to the occurrence of rock bursts or preventing this phenomenon were selected. Six of them can be considered as unfavorable, in other words, the presence of the mining remnant, the vertical distance between the opening and mining remnant (in meters), the time since the remnant was left (in years), the neighborhood of goats in the same coal seam, excessive bed cutting, and other negative factors, relatively rare in the analyzed mine (e.g., change of mining direction during longwall mining, drilling the heading across the bedding of a seam, split or folding of coal seam etc.). The mining remnant, left due to an earlier extraction of another coal seam, causes a stress increase in the rock mass [1]. Three values of this parameter were assumed: none (63% of samples), edge of the coal seam (32.5% of samples), and residual coal pillar (4.5% of samples). The presence of additional stress in the coal seam is an important factor determining the occurrence of rock bursts. Therefore, the vertical distance of the mining remnant from the excavation is important. According to Polish mining regulations, the occurrence of the remnant in other coal seams must be considered when its vertical distance is between 160 m above and 60 m below the opening. Among the samples in the database, this distance ranged from about 316 m above and about 106 m below the opening (mean 103 m above the opening). The stress increase due to the presence of mining remnants should fade over time. However, the increase in stress due to remnants can persist for several decades [1]. The pressure of the rock layers above the boundary of goats may increase stress in the unmined coal body. An opening drilled in the vicinity of goats may be influenced by additional stress and thus may have a higher level of rock burst hazard. A neighborhood of goats was assumed when the distance between the excavation and boundary of goats did not exceed 50 m. A neighborhood of goats occurred in about 39% of the samples in the database. Another negative parameter is excessive bed cutting. Drilling several excavations at a short distance from each other causes weakening of the coal body and may lead to a rock burst. Samples with excessive bed cutting (i.e., where at least three excavations were next to each other) accounted for 6.5% of the database. The next three mining parameters were related to the earlier mining of the adjacent coal seam, which can significantly reduce the rock burst hazard. These parameters include the vertical distance to the extracted adjacent coal seam, the thickness of this seam, and the time since the mining of the adjacent coal seam was undertaken. In this article, such a previously extracted coal seam was referred to as a destressing coal seam, ignoring its vertical distance. According to Polish mining regulations, a coal seam is classified as a lower rock burst hazard degree if a destressing coal seam, deposited not more than 50 m below or 20 m above, is mined with caving. In the case of a thick coal seam, the destress effect is achieved by mining one of its layers. In general, the destress effect should be greater if the destressing seam is closer and thicker and a shorter time has elapsed since it was excavated. The parameters correlated with the so-called destressing seam were determined for about 71% of the samples in the database. The vertical distance between the excavation and the destressing seam for these samples ranged between 0 m (upper layer of thick coal seam) and about 309 m (mean 75 m). Therefore, the distance criterion of the destressing seam was met by only about 38.6% of these samples. The thickness of the destressing seam was between 1 m and about 4 m (mean 2.5 m), and the time elapsed since destressing mining ranged between 1 year and 34 years (mean 15 years).