Steeply inclined cable tunnels are critical components of pumped storage power stations, and any fire incident within these components poses a severe threat to the operational safety of power stations. Unlike conventional horizontal tunnels, steeply inclined tunnels are characterized by unique characteristics, namely high drop, extended length, and large slopes. These unique geometric features create distinct fire dynamics, which render standard horizontal-tunnel assessment methods inadequate for evaluating specific risk profiles. Fire incidents in steeply inclined cable tunnels may be triggered by various factors, such as electrical short circuits, which can cause large-scale losses. Therefore, it is imperative to develop a specialized fire risk assessment framework for steeply inclined cable tunnels.

This study developed a risk-matrix-based fire-risk assessment method for steeply inclined cable tunnels. First, 19 basic events that may induce fires within steeply inclined cable tunnels were identified via literature review, historical case analysis, and field investigations. Based on these identified events, a fault tree was established to analyze fire probabilities under varying slopes, evaluate the significance of each basic event, and determine key basic events requiring prioritized prevention and control. Second, severity rating standards for fire consequences were formulated based on three technical criteria: ignition temperature of the cable, bearing capacity of the tunnel structure, and fire resistance performance of the fire compartment. Using computational fluid dynamics (CFD), the ceiling temperature and fire duration in the tunnel under fire scenarios were simulated, after which the severity ratings for fire consequences were determined. Finally, a comprehensive fire risk matrix was established, followed by the determination of the overall fire risk level for steeply inclined cable tunnels based on the integrated fire occurrence probability and fire consequence severity level.

Using the steeply inclined cable tunnel of the Jixi pumped storage power station in Anhui Province, China, as a case study, the fire risk levels were evaluated for four slopes (0°, 15°, 30°, and 45°). The results were as follows: 1) the fire risk ratings for slopes 0°, 15°, 30°, and 45° were found to be 3A, 3A, 2A, and 2A, respectively, all of which fall within the low risk range. 2) As the slope increased, the fire occurrence probability increased from 6.50×10^-5 to 8.88×10^-5. Meanwhile, as the slope increased, the ceiling temperature and fire duration within the tunnel decreased from 633℃ to 311℃ and from 0.65 h to 0.53 h, respectively, decreasing the fire consequence severity. 3) The importance indices of the fault tree revealed that X₁₃ (failure of the high-voltage grounding system), X₁₁ (decrease in the dielectric strength), and X₈ (aging of the insulating layer) represent the key basic events that exert the strongest impact on the fire-occurrence probability. Thus, the monitoring and control of the events must be prioritized.

By analyzing the data obtained from fault tree analysis and CFD simulations, this study quantified fire risk levels for steeply inclined cable tunnels across varying slopes. Furthermore, key basic fire-triggering events were identified. Accordingly, targeted prevention and control measures are proposed. Compared with conventional horizontal cable tunnel assessment methods, this framework accounts for the influence of slope changes on the fire occurrence probability and fire-consequence severity, providing results that are more suitable for steeply inclined cable tunnels of pumped storage power stations.

Forest fires can be triggered by the failure of overhead power lines, especially in forests that are prone to wildfires and have dense power transmission networks. The spread of such fires can, in turn, endanger the safety and stability of nearby power infrastructure. Understanding the evolution of forest fires and the mechanisms behind secondary and derivative accidents is essential for implementing risk control at key nodes within the disaster chain. This is crucial in reducing the likelihood of disaster occurrence and the severity of its consequences. However, research on secondary and derivative disaster chains related to forest fires remains limited, and no existing studies have addressed the coupling induction between forest fires and overhead line failures. This gap may lead to risk control measures that are inadequately targeted.

In this study, a secondary and derivative disaster chain network of overhead line failures and forest fires is built based on complex network theory, and the effect of the coupling induction of forest fires and overhead line failures on the formation mechanism of the disaster chain is investigated. First, indicators such as degree centrality and closeness centrality are calculated to evaluate the role and influence degree of each disaster node in the disaster chain network from multiple perspectives. Subsequently, the key nodes in the failure and secondary and derivative disaster chains between overhead lines and forest fires are determined. Second, the transmission probability of each evolution path in the disaster chain is used as the assessment criterion, and the Jaccard index is employed to identify the key evolution paths.

First, 92 related accident cases are analyzed, and experts are consulted to determine the inducing relationships among various disaster nodes. Based on this, a disaster chain evolution model is constructed to investigate the failure and secondary and derivative accident chains of the overhead lines and forest fires. This model has 21 disaster nodes, 46 edges, and 60 disaster evolution paths. Four indicators are calculated: degree centrality, closeness centrality, betweenness centrality, and disaster node hub count. The top five disaster nodes are forest fires, casualties, overhead line failure, forest resource destruction, and toxic gas leakage. The transmission probabilities of different disaster evolution paths are calculated based on the frequency of the disaster chain nodes in statistics and the Jaccard index. To confirm the validity of the model and its conclusions, a sensitivity analysis is conducted at the node of overhead line failures, which verifies the relevance of risk management for overhead lines in reducing the risk of the disaster chain.

Based on theory of chain-cutting disaster mitigation, how to cut off the evolution paths of the disaster chain or the control key disaster nodes and how to prevent the occurrence of secondary and derivative accidents are clarified in this paper to provide decision support for the actual prevention and control of forest fires and the operation and maintenance of forest power grids.