Fire Evolution Mechanisms and Protection Technologies in Urban Utility Tunnel Power Compartments: State-of-the-Art, Challenges, and Future Perspectives

As global urbanization transitions toward intensive underground space utilization, utility-tunnels have emerged as indispensable “urban lifelines.” Among their various compartments, the power compartment represents the most critical yet vulnerable zone, characterized by high-density fire loads and extreme confined boundary constraints. This review summarizes and critically discusses current research on the state-of-the-art in utility-tunnel fire safety, establishing a holistic framework that bridges fundamental physical mechanisms with advanced engineering applications. The review focuses on the fire dynamics specific to power compartments, including cable aging-induced ignition, multidirectional flame spread, heat release, and smoke propagation. Subsequently, the study critically evaluates the limitations of current fire codes and identifies the methodological gaps in reduced-scale experiments and CFD simulations when addressing complex heterogeneous topologies. As for fire safety protection, highlight transformative frontiers in smart prevention, including nano-enhanced intrinsically safe materials, AI-driven digital-twin frameworks for real-time situational awareness, and synergistic “gas–liquid–solid” extinguishing systems (e.g., liquid-nitrogen and fine water mist) were summarized and analyzed. Finally, a strategic roadmap for future research is proposed, advocating for a shift from “straight-segment” analysis to “network-wide” resilience assessment. This synthesis aims to guide the development of next-generation intelligent fire-protection systems for resilient underground urban infrastructures.