Multi-scale spatial-temporal principles of global evacuation safety based on Pareto Frontiers : a demonstration in tunnel

Abstract

Traditional design principle of fire safety evaluates an available safe egress time (ASET) in a whole, which ignoring spatial–temporal evolution of fires in complex structures such as high-rise buildings, complex tunnels and large underground spaces. This study introduces multi-scale spatial–temporal principles of evacuation safety to consider both the dynamic fire development and multi-scale flow of evacuees from individual zones to entire communities. We propose the use of local (L-ASET) and global (G-ASET) evacuation to capture the dynamic interactions of fire, building layout, and occupant behavior. A novel framework leveraging Pareto Frontiers is developed to optimize evacuation strategies by balancing conflicting objectives such as minimizing evacuation time, reducing congestion, and maximizing safety. The approach is demonstrated through a case study of tunnel fires, revealing significant variations in L-ASET and G-ASET across zones based on visibility, temperature, and Fractional Effective Dose (FED) criteria. 10 fire scenarios are studied, and in high HRR, Zone 1 becomes untenable within 20–30 s, while further zones remain tenable for up to 700 s based on visibility and temperature thresholds. FED-based assessment further confirms differentiated safety levels across regions. These findings demonstrate the limitations of uniform evacuation assumptions and highlight the need for spatially adaptive, phase-based evacuation strategies. It also provides insights into dynamic resource allocation for firefighting operations and enhancing fire safety design and intelligent evacuation systems with adaptive responses to complex fire scenarios for large infrastructures and underground spaces.