Evaluating the combustion and flame extension characteristics of cable fire in utility tunnels with spontaneous combustion scenarios: An experimental study

•The combustion characteristics of cable under spontaneous combustion are analyzed.•The flame extension characteristics of the cable fire are analyzed.•A model for predicting flame height was proposed.•A model for predicting flame spread rate was proposed. A cable fire in a utility tunnel can cause severe damage to the electric power supply in cities. This study aims to understand the combustion and flame spread characteristics of cable fires, which are mainly caused by overheating from the excessive current at the interconnections of the cables under spontaneous combustion. Fire experiments were conducted in a 1:6 scale model of a utility tunnel to analyse the flame spread characteristics under different heat release rates (HRRs), vertical distances, and transverse distances. The findings of this study show that the total burning time of the cable fire increases as the cable diameter increases, and the HRR also shows an increasing trend. Additionally, the spatial location of the cable fire has a significant impact on the flame spread. The terms Hc* and Dc* are defined to characterize the flame height and a general prediction model of the dimensionless flame height influenced by cable spontaneous combustion is proposed. A dimensionless model is also established to describe the flame spread rate. This research provides valuable guidance to aid in the development of fire safety measures in utility tunnels.