## 3 Case Study
### Dynamic Risk Reasoning and Analysis
#### 3.3.2 Dynamic Importance Analysis  
The networks (i.e., the risk evolution mechanism and DBN structure) presented in Figures 5 and 6 indicate that numerous risk factors may lead to cable fires in the distribution rooms. To pinpoint the critical basic factors that influence cable fires, we designated node Z (Fire) as the target node for the importance analysis of the root nodes. The significance of risk control was gauged using FV importance, while the importance of risk prevention was assessed via the BM's significance.  
During the ascending phase of risk, the pivotal imperative is the timely control of risk. Consequently, we focused on assessing the significance of risk control for the second phase of rapid risk escalation, as depicted in Figure 12. The FV importance of the root nodes in the second phase is calculated according to Equation (9), and the results are presented in Figure 13. It can be observed that the FV importance values of nodes X7, X8, and X2 are consistently significantly larger than those of other nodes, which means that improving the status of these nodes will reduce fire risks. Meanwhile, it is worth mentioning that the total FV importance value of the root nodes decreases from approximately 70% to approximately only 30% during this phase, which may be caused by the irreversible increase in the risks of intermediate nodes Y5 and Y7, which directly affect the fire risk (see Figure 11). Therefore, effectively reducing the risk level by controlling the risk factors of the root node is insufficient. As the risk exhibits an upward trend, the earlier prevention and control measures are taken, the lower the risk control effect. The power supply should be cut off as soon as possible to check for the pyrolysis of the cable, and the unqualified cable should be replaced in a timely manner.  
According to Equation (8), BM importance across multiple states is determined by assessing the influence of each individual state change on the target node. Consequently, we initially examined the impact of various states of each root node on target node Z (Fire). Assuming that all root nodes are in their optimal states (S0 = 1) at the initial time (t = 0), we employed DBN reasoning to observe the alteration in cable fire risk probability over 10 time slices when the root node changes to two different states, as illustrated in Figure 14. In the S1 state, nodes X1 and X7 have the greatest impact on the probability of cable fire risk, and the impact of X7 increases with time. In the S2 state, nodes X1, X5, X2, X7, and X6 have a significant influence on cable fire risk probability, and the fire risk probability reaches one at the tenth time slice.  
The BM importance values within 10 time slices of each root node were then obtained using Equation (8), as depicted in Figure 15. The order of the BM importance values from the largest to smallest at the 10 th time slice was X7 (0.887), X1 (0.75), X5 (0.6), X6 (0.549), X2 (0.498), X3 (0.271), X4 (0.03), and X8 (0), whereas the values of X7, X6, X2, and X3 increased over time. The greater the BM importance value, the higher the fire risk caused by the node. Therefore, the risk factors corresponding to nodes X7, X1, X5, X6, X2, and X3 in cable fire risk prevention should receive more attention.  
Figure 14: Change in cable fire probability with time under different states of the root nodes.  
Figure 13: Dynamic FV importance of the root nodes.