Fire risk assessment and fire control measures for steeply inclined cable tunnels used in pumped-storage power stations

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.