Coal mine rock burst early warning method

Abstract

The invention discloses a coal mine rock burst early warning method. The method comprises the following steps that the layer position of a main source area of impact energy of a coal mine is divided into a top plate layer position, a coal body layer position and a bottom plate layer position; microseismic signals of different layers are collected, and the danger source range is determined according to the microseismic signal strength of the different layers and the distance between the different layers; and / or collecting micro-seismic signals of different layers, establishing rock burst early warning models of the different layers according to the micro-seismic signal intensities and weights of the different layers, and determining danger levels of the different layers. According to the invention, layered and partitioned early warning can be realized, and the early warning accuracy is improved.

Description

Technical Field

[0001] This invention relates to the field of coal mining safety technology, specifically to a rockburst early warning method, which is particularly suitable for rockburst monitoring and early warning scenarios in deep mining shafts. Background Technology

[0002] As coal mining in my country extends deeper, rockbursts have become one of the major dynamic hazards restricting the safe and efficient mining of deep coal resources. Their sudden onset causes severe casualties, equipment damage, and disruption of underground engineering, posing a significant threat to coal mine safety. Therefore, accurate prediction and early warning of rockbursts are crucial for ensuring the safety of deep coal mining operations and are of great significance for reducing disaster losses and promoting the sustainable development of the coal industry.

[0003] During the process of coal and rock failure, various characteristic physical information such as sound, light, heat, and electromagnetic fields are generated. This physical information can directly reflect the changes in the internal mechanical state of coal and rock and the trend of failure evolution. Based on this characteristic, experts and scholars at home and abroad have conducted extensive research and proposed a series of rockburst monitoring and early warning methods. Typical methods include acoustic emission monitoring based on sound signals, microseismic monitoring based on vibration signals, and electromagnetic radiation monitoring based on electromagnetic signals, which provide a certain technical foundation for the prevention and control of rockburst disasters.

[0004] From a macroscopic perspective, rockbursts are closely related to various factors, including geological structural conditions (such as faults, folds, and facies changes in strata), roof strata fracturing, the influence of residual coal pillars, and disturbances caused by mining operations. Furthermore, the spatial distribution of rockburst hazard sources is significantly complex, potentially located in different underground areas and within different strata or coal seams. However, existing rockburst early warning technologies and methods generally suffer from key technical bottlenecks: on the one hand, they cannot achieve stratified early warning for different strata, making it difficult to accurately capture the evolutionary characteristics of hazard sources in specific strata; on the other hand, the early warning results are ambiguous, failing to effectively delineate the areas where hazard sources are located, resulting in insufficient guidance for precise on-site control and ultimately low early warning accuracy, making it difficult to meet the needs of precise rockburst control under complex mining conditions in deep coal mines. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a rockburst early warning method that can realize layered and zoned early warning and improve the accuracy of early warning.

[0006] To address the aforementioned technical problems, the present invention provides the following technical solution: A method for early warning of rockburst in coal mines includes the following steps: The stratigraphic layers of the main source area of ​​impact energy in coal mines are divided into roof strata, coal seam strata, and floor strata. Collect microseismic signals from different geological layers, and determine the hazard range based on the intensity of the microseismic signals at different layers and the distance between different layers; and / or, Microseismic signals from different layers are collected, and rockburst early warning models for different layers are established based on the intensity and weight of the microseismic signals from different layers to determine the hazard level of different layers.

[0007] In some embodiments of the present invention, determining the danger zone based on the microseismic signal intensity at different layers and the distance between different layers includes: When the distance between different layers is less than a first preset value and the intensity of the microseismic signal is greater than a first preset intensity, the range of the hazard source is determined to include the range covered by the layer whose distance is less than the first preset value.

[0008] In some embodiments of the present invention, the coal seam is divided horizontally into a first coal seam adjacent to the working face and a second coal seam away from the working face, wherein the thickness d of the first coal seam in the horizontal direction is 2m-5m.

[0009] In some embodiments of the present invention, the top plate layer is divided into at least two layers in the vertical direction from low to high, and the relationship between the thickness t of the layer adjacent to the coal body layer in the vertical direction and the thickness d of the first coal body layer in the horizontal direction is: t≤3d.

[0010] In some embodiments of the present invention, the roof strata are divided into three layers vertically from low to high: the first roof strata, the second roof strata, and the third roof strata. The relationship between the thickness t1 of the first roof strata vertically and the thickness d of the first coal seam strata horizontally is: t1 ≤ 3d; the relationship between the thickness t2 of the second roof strata vertically and the thickness d of the first coal seam strata horizontally is: 3d < t2 ≤ 30d; and the relationship between the thickness t3 of the third roof strata vertically and the thickness d of the first coal seam strata horizontally is: t3 > 30d.

[0011] In some embodiments of the present invention, the bottom plate layer is divided into at least two layers in the vertical direction from high to low, and the thickness s of the layer adjacent to the coal body layer in the vertical direction is ≤5m.

[0012] In some embodiments of the present invention, the base plate layer is divided into a first base plate layer and a second base plate layer in the vertical direction from high to low. The thickness of the first base plate layer in the vertical direction is s≤5m, and the thickness of the second base plate layer in the vertical direction is 5m<s≤50m.

[0013] In some embodiments of the present invention, the step of establishing rockburst early warning models for different layers based on the microseismic signal intensities and weights at different layers, and determining the hazard levels of different layers, includes: The hazard warning index for different levels is obtained using the following formula. According to the risk warning index The size determines the level of danger;

[0014] in, E i The intensity of the microseismic signal in the i-th layer among the roof, coal seam, or floor layers is given. It is the weighting coefficient of the i-th stratum among the roof stratum, coal seam stratum, or floor stratum.

[0015] In some embodiments of the present invention, the weight coefficient of the first coal seam is 1, and the weight coefficients of the second coal seam, the roof seam, and the floor seam are less than 1; wherein, when the roof seam is multi-layered, the weight coefficients of the seams divided from low to high gradually decrease; the weight coefficients of the floor seams divided from high to low gradually decrease. More specifically, the weight coefficients of the first roof seam, the second roof seam, and the third roof seam are 0.5, 0.3, and 0.2, respectively; the weight coefficients of the first floor seam and the second floor seam are 0.7 and 0.3, respectively.

[0016] In some embodiments of the present invention, based on a risk warning index The size determines the hazard level, including: When 0 < If the value is ≤μ1, the hazard level is determined to be Level 1; μ1 < ≤μ2, the hazard level is determined to be Level II; μ2 < If μ1 is ≤1, the hazard level is determined to be Level 3; where μ1 is between 0.4 and 0.6, and μ2 is between 0.7 and 0.9.

[0017] The technical solution of the present invention has the following technical effects compared with the prior art: The coal mine rockburst early warning method provided by this invention divides the main source area of ​​coal mine rockburst energy into roof strata, coal seam strata, and floor strata, clarifying the differences in rockburst risk in different spatial areas and solving the problems of vague early warning results and lack of clear regional division in existing technologies. Simultaneously, through complementary verification of hazard source range identification and hazard level determination, combined with the quantitative differentiation of stratum risk using weighted coefficients, invalid signal interference is effectively filtered out, reducing the false positive and false negative rates. Attached Figure Description

[0018] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, which will help to understand the purpose and advantages of the present invention, wherein: Figure 1 This is a schematic diagram of the underground strata distribution of a coal mine. Figure 2 The flowchart is a method for early warning of rockburst in coal mines provided by the present invention. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0021] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] like Figure 2 The illustration shows a coal mine rockburst early warning method disclosed in this embodiment. This method is implemented based on existing geological exploration data, mining engineering layout plans, and actual on-site conditions. First, stratigraphic division and monitoring arrangements are completed. Then, early warning is achieved through microseismic signal acquisition and analysis, and two pathways (including hazard source range identification and hazard level judgment). The specific early warning implementation method is as follows: S1. Based on the geological structure characteristics of the coal mine, the physical and mechanical properties of the rock strata, and the distribution law of impact energy, the main source areas of impact energy are clearly divided into roof strata 10, coal body strata 20, and floor strata 30. The division process should focus on the occurrence state of the rock strata, the location of historical impact disasters, and the scope of mining impact to ensure that the boundaries of each stratum are clear and cover all potential impact energy release areas.

[0023] S2. Based on the spatial distribution characteristics of each stratum, several microseismic sensors 40 are arranged. For example, as shown in the figure, when the coverage area of ​​the roof stratum 10, coal seam stratum 20, and floor stratum 30 is rectangular, four or more sets of microseismic sensors 40 can be arranged within the area covering the roof stratum 10 on the surface. Eight sets of microseismic sensors 40 (four at the top and four at the bottom) are placed in the mining area (i.e., the working face area) of the coal seam stratum. Additionally, four sets of microseismic sensors 40 can be arranged in the four corner areas of the lowest layer of the floor stratum 30 by drilling. The arrangement density of the microseismic sensors 40 must meet the requirements of signal acquisition continuity and integrity, ensuring that the microseismic signals generated at each stratum can be effectively captured without monitoring blind spots. Since each set of microseismic sensors 40 can obtain the microseismic signal intensity of different areas of the roof stratum 10, coal seam stratum 20, and floor stratum 30, the final microseismic signal intensity of each stratum can be the average value of each microseismic sensor 40.

[0024] S3. Microseismic signals at each layer are collected in real time using microseismic sensors 40, and the spatial distance relationship between different layers is recorded synchronously. The specific distribution range of the hazard source is located by combining the correlation characteristics between signal intensity and interlayer distance. And / or based on the difference in the contribution of each layer to the occurrence of rockburst, differentiated weights are set for different layers. Then, combined with the microseismic signal intensity of each layer, a layered early warning model is established, and the hazard level of each layer and the overall area is determined by the model calculation results.

[0025] By dividing the data into layers, the system can accurately focus on the targets for early warning, avoiding the ambiguity caused by mixed signals in the traditional non-layered mode. The two early warning paths can be used alone or in combination to adapt to the early warning needs of different mining scenarios and improve the practicality of the method.

[0026] Specifically, such as Figure 1 As shown, in one optional implementation, in step S1, based on the disturbance patterns of the mining operation, the coal seam 20 is horizontally divided into a first coal seam 21 and a second coal seam 22. The working face is the area where the current mining operation is located; the first coal seam 21 is the area adjacent to the working face and directly affected by mining disturbances; and the second coal seam 22 is the area far from the working face and less affected by mining disturbances. By horizontally dividing the coal seam 20, the degree of disturbance impact in different areas within the coal seam is refined, avoiding the problem of coarse early warning caused by making an overall judgment of the coal seam 20, and improving the accuracy of identifying hazards within the coal seam.

[0027] The thickness 'd' of the first coal seam stratum 21 along the horizontal direction is set to 2m-5m. This thickness range is determined based on both the transmission and attenuation law of mining disturbances in the coal seam and verification through actual microseismic testing. Specifically, microseismic testing devices are deployed horizontally at coal seam stratum 20. After continuous testing for a period of time, areas with microseismic signal intensity greater than the set value are screened out, and the specific value of 'd' is finally determined by combining the theoretically derived range. This setting can comprehensively cover the main disturbance areas and high signal intensity areas caused by mining operations to the coal seam, ensuring that no high-risk areas are missed.

[0028] Specifically, in one optional implementation, in step S1, the roof stratum 10 is divided into at least two layers vertically from low to high (i.e., from near the coal seam to far from the coal seam). The thickness t of the layer closest to the coal seam 20 in the vertical direction satisfies t≤3d with the thickness d of the first coal seam stratum 21 in the horizontal direction. This relationship is determined based on the transmission law of mining impacts in the roof, ensuring that this roof layer can cover the main impact area caused by mining disturbances, achieving precise focusing on high-risk sections of the roof. Through the vertical stratification and thickness constraints of the roof stratum 10, the area most significantly affected by mining in the roof stratum 10 is clearly identified, avoiding the ambiguity of high-risk areas caused by overall early warning of the roof stratum 10, and improving the targeting of hazard source identification in the roof stratum 10.

[0029] More specifically, such as Figure 1 As shown, the roof stratum 10 is further subdivided vertically from low to high into a first roof stratum 11, a second roof stratum 12, and a third roof stratum 13. The first roof stratum 11 is the segment immediately adjacent to the coal seam stratum 20, the second roof stratum 12 is the segment above the first roof stratum 11, and the third roof stratum 13 is the segment above the second roof stratum 12.

[0030] Among them, the thickness t1 of the first roof stratum 11 and the thickness d of the first coal seam stratum 21 satisfy t1≤3d. This stratum is most directly affected by mining and is the main potential area for roof impact energy release. The thickness t2 of the second roof stratum 12 and the thickness d of the first coal seam stratum 21 satisfy 3d<t2≤30d. This stratum is less affected by mining and has a lower impact risk than the first roof stratum 11. The thickness t3 of the third roof stratum 13 and the thickness d of the first coal seam stratum 21 satisfy t3>30d. This stratum is only slightly affected by mining and has an extremely low impact risk. Through the three-layer refined division of roof stratum 10, the differences in impact risk among different roof strata can be accurately distinguished, enabling key monitoring and early warning of high-risk roof strata, further improving the accuracy of roof early warning, and avoiding the waste of resources on excessive monitoring in low-risk areas.

[0031] Specifically, in one optional implementation, in step S1, the floor strata 30 is divided into at least two layers vertically from high to low (i.e., from near the coal seam 20 to far from the coal seam 20). The layer closest to the coal seam 20 has a vertical thickness s ≤ 5m. This thickness is determined based on the depth of mining impact transmission in the floor strata, ensuring comprehensive coverage of the main areas of the floor strata affected by mining disturbances and preventing the omission of high-risk sections. Through the vertical stratification and thickness constraints of the floor strata 30, areas with higher impact risk within the floor strata 30 are clearly identified.

[0032] More specifically, as shown in the figure, the bottom plate layer 30 is divided into two layers vertically from high to low (i.e. from the layer closest to the coal body 20 to the layer furthest from the coal body 20), namely the first bottom plate layer 31 and the second bottom plate layer 32; wherein, the thickness of the first bottom plate layer 31 in the vertical direction is s1≤5m, and the thickness of the second bottom plate layer 32 in the vertical direction is 5m<s2≤50m.

[0033] The following section details the specific implementation method for locating the range of hazard sources based on the intensity of microseismic signals at different layers and the interlayer distance.

[0034] First, based on the specific geological conditions and mining intensity of the coal mine, a first preset value (i.e., the critical value of inter-layer distance) and a first preset intensity (i.e., the critical intensity of microseismic signal danger) are set. The first preset value needs to be determined according to the law of rock strata disturbance transmission to ensure the critical range of mutual influence between overburden layers; the first preset intensity needs to refer to the microseismic signal characteristics before historical shock disasters to ensure that normal disturbances and dangerous disturbances can be effectively distinguished.

[0035] Real-time monitoring of the spatial distance between different layers and the intensity of microseismic signals at each layer is performed. When the distance between any two or more layers is less than a first preset value, and the intensity of the microseismic signals at these layers is greater than a first preset value, the hazard source range is determined to be the spatial area covered by all layers whose distance is less than the first preset value. Through the dual constraints of inter-layer distance and signal intensity, the hazard source range can be accurately located, avoiding misjudgments caused by a single signal indicator. This solves the problem that traditional methods cannot clearly define the spatial distribution of hazard sources, providing a clear target area for precise on-site prevention and control. For example, when the microseismic sensor 40 detects that the intensity of the microseismic signal generated by the first coal seam 21, the first roof 11, and the first floor 31 is greater than the first preset intensity, since the distance between the three seams is less than the first preset value (e.g., 10m), it indicates that the spatial area covered by these three seams is within the range of the hazard source and there is a possibility of rockburst. Work needs to be stopped and support strengthened. If the microseismic sensor 40 detects that the third roof 13 and the second floor 32 have microseismic signals and the intensity of the microseismic signal is less than the first preset intensity, since the distance between them is greater than the first preset value (e.g., 10m), it indicates that there is no risk of rockburst.

[0036] The following section details the specific implementation methods for determining shock risks based on early warning models.

[0037] The rockburst early warning model for different layers can be established using the following formula based on the microseismic signal intensity and weights at different layers:

[0038] in, E i The intensity of the microseismic signal is the i-th layer among the roof layer 10, coal seam layer 20, or floor layer 30. The weighting coefficient for the i-th stratum among roof stratum 10, coal seam stratum 20, or floor stratum 30; Q i It is the early warning index for ground pressure impact hazard of the i-th layer among the roof layer 10, coal layer 20, or floor layer 30.

[0039] When the top stratum 10 includes three layers, the ground pressure impact hazard warning index for the first top stratum 11 is:

[0040] in, Q d1 The ground pressure impact hazard warning index for the first top slab layer 11; E d1 , E d2 , E d3 The values ​​represent the microseismic signal intensities at the first roof layer 11, the second roof layer 12, and the third roof layer 13, respectively. These are the weighting coefficients for the first roof layer 11, the second roof layer 12, and the third roof layer 13, respectively.

[0041] When the foundation slab layer 30 includes two layers, the ground pressure impact hazard warning index for the first foundation slab layer 31 is:

[0042] in, Q D1 The ground pressure impact hazard warning index for the first bottom slab layer 31; E D1 , E D2 These represent the microseismic signal intensities at the first base layer 31 and the second base layer 32, respectively. These are the weighting coefficients for the first base plate layer 31 and the second base plate layer 32, respectively.

[0043] The ground pressure impact hazard warning index of the first coal seam 21 in coal seam 20 is:

[0044] Q m1 The ground pressure impact hazard warning index for the first coal seam 21; E m1 , E m2 The values ​​represent the microseismic signal intensities of the first coal seam (seam 21) and the second coal seam (seam 22), respectively. These are the weighting coefficients for the first coal seam 21 and the second coal seam 22, respectively.

[0045] Weighting coefficient The weighting is based on the contribution of each stratum to the occurrence of rockburst. The stratum more directly affected by mining and closer to the working face, the higher the weighting coefficient, and vice versa. Specifically, the first coal seam stratum 21, as the most important energy source and risk area for rockburst, has a weighting coefficient of 1, the highest weight. The weighting coefficients of the second coal seam 22, the roof stratum 10, and the floor stratum 30 are all less than 1. The weighting coefficients of the roof stratum 10 gradually decrease from low to high (closest to the coal seam to farthest from the coal seam), specifically: the weighting coefficient of the first roof stratum 11 is 0.5, the weighting coefficient of the second roof stratum 12 is 0.3, and the weighting coefficient of the third roof stratum 13 is 0.2. The weighting coefficients of the floor stratum 30 gradually decrease from high to low (closest to the coal seam to farthest from the coal seam), specifically: the weighting coefficient of the first floor stratum 31 is 0.7, and the weighting coefficient of the second floor stratum 32 is 0.3. The weighting coefficient for the second coal seam, stratum 22, is 0.2. This differentiated weighting coefficient reflects the varying impact risks across different seams, enabling the early warning model to accurately match the risk distribution patterns under actual working conditions and improving the relevance and accuracy of the early warning results.

[0046] According to the ground pressure shock hazard warning index The size of the hazard level is determined using the following method: When 0 < If μ1 ≤ μ1, the hazard level is determined to be Level 1; if μ1 < ... If μ2 ≤ μ2, the hazard level is determined to be Level II; if μ2 < ... A value ≤1 indicates a hazard level of Level 3. Specifically, considering the coal mine's on-site conditions, historical shock disaster data, and safety management requirements, the hazard level judgment thresholds μ1 and μ2 are set between 0.4 and 0.6, and between 0.7 and 0.9, respectively. Through clear threshold divisions and level definitions, the quantified warning index is transformed into an intuitive hazard level, providing clear risk guidance for on-site workers and facilitating the rapid development and implementation of corresponding prevention and control measures. For example, Level 1 risk necessitates normal operation, Level 2 risk requires enhanced monitoring, and Level 3 risk necessitates work stoppage.

[0047] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for early warning of rockburst in coal mines, characterized in that, Includes the following steps: The stratigraphic layers of the main source area of ​​impact energy in coal mines are divided into roof strata, coal seam strata, and floor strata. Collect microseismic signals from different layers, and determine the range of the hazard source based on the intensity of the microseismic signals from different layers and the distance between different layers; And / or, Microseismic signals from different layers are collected, and rockburst early warning models for different layers are established based on the intensity and weight of the microseismic signals from different layers to determine the hazard level of different layers.

2. The method for early warning of rockburst in coal mines according to claim 1, characterized in that, The determination of the danger zone based on the microseismic signal intensity at different layers and the distance between different layers includes: When the distance between different layers is less than a first preset value and the intensity of the microseismic signal is greater than a first preset intensity, the range of the hazard source is determined to include the range covered by the layers with a distance less than the first preset value.

3. The method for early warning of rockburst in coal mines according to claim 1, characterized in that, The coal seam is divided horizontally into a first coal seam adjacent to the working face and a second coal seam away from the working face. The thickness d of the first coal seam in the horizontal direction is 2m-5m.

4. The method for early warning of rockburst in coal mines according to claim 3, characterized in that, The top strata are divided into at least two layers vertically from low to high. The relationship between the thickness t of the layer adjacent to the coal seam in the vertical direction and the thickness d of the first coal seam in the horizontal direction is: t≤3d.

5. A method for early warning of rockburst in coal mines according to claim 4, characterized in that, The roof strata are divided into three layers vertically from low to high: the first roof strata, the second roof strata, and the third roof strata. The relationship between the thickness t1 of the first roof strata vertically and the thickness d of the first coal seam strata horizontally is: t1 ≤ 3d; the relationship between the thickness t2 of the second roof strata vertically and the thickness d of the first coal seam strata horizontally is: 3d < t2 ≤ 30d; and the relationship between the thickness t3 of the third roof strata vertically and the thickness d of the first coal seam strata horizontally is: t3 > 30d.

6. The method for early warning of rockburst in coal mines according to claim 1, characterized in that, The bottom plate layer is divided into at least two layers vertically from high to low, and the thickness s of the layer adjacent to the coal body layer in the vertical direction is ≤5m.

7. A method for early warning of rockburst in coal mines according to claim 6, characterized in that, The base plate layers are divided into a first base plate layer and a second base plate layer in the vertical direction from high to low. The thickness of the first base plate layer in the vertical direction is s≤5m, and the thickness of the second base plate layer in the vertical direction is 5m<s≤50m.

8. A method for early warning of rockburst in coal mines according to claim 1, characterized in that, The method of establishing rockburst early warning models for different layers based on the intensity and weight of microseismic signals at different layers, and determining the hazard level of different layers, includes: The hazard warning index for different levels is obtained using the following formula. According to the risk warning index The size determines the hazard level; in, E i The intensity of the microseismic signal in the i-th layer among the roof, coal seam, or floor layers is given. It is the weighting coefficient of the i-th stratum among the roof stratum, coal seam stratum, or floor stratum.

9. A method for early warning of rockburst in coal mines according to claim 8, characterized in that, The weighting coefficient for the first coal seam is 1, while the weighting coefficients for the second coal seam, roof seam, and floor seam are less than 1. When the roof seam is multi-layered, the weighting coefficients of the seams gradually decrease from low to high. Similarly, the weighting coefficients of the floor seams gradually decrease from high to low. More specifically, the weighting coefficients for the first, second, and third roof seams are 0.5, 0.3, and 0.2, respectively; and the weighting coefficients for the first and second floor seams are 0.7 and 0.3, respectively.

10. A method for early warning of rockburst in coal mines according to claim 1, characterized in that, According to the risk warning index The size determines the hazard level, including: When 0 < If the value is ≤μ1, the hazard level is determined to be Level 1; μ1 < ≤μ2, the hazard level is determined to be Level II; μ2 < If μ1 is ≤1, the hazard level is determined to be Level 3; where μ1 is between 0.4 and 0.6, and μ2 is between 0.7 and 0.9.

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