Experimental study on cable combustion and smoke propagation in confined underground environments

Full-scale fire tests were conducted in a 331 m long urban underground cable tunnel to investigate how fire source area, cable layer number, and spatial arrangement jointly affect combustion, temperature evolution, and smoke toxicity. Eleven Case were designed by varying fuel tray area and volume, cable layers (0–5), and multilayer versus dense single-layer layouts. Enlarging the fire source significantly increased the mass loss rate and total fuel consumption, indicating stronger combustion. More cable layers raised ceiling peak temperature and prolonged high-temperature duration due to enhanced heat feedback. Stratified multilayer cables produced a stable high-temperature ceiling zone, whereas dense single-layer cables caused rapid heating but lower peaks and faster cooling because of local oxygen depletion. Higher cable load and denser layouts markedly reduced visibility and increased CO concentration and persistence. These findings deepen the understanding of fire behavior in urban underground cable tunnels and provide a scientific basis for optimizing safety design and emergency response strategies.