A numerical model for urban fire spread is developed. Proposed model is distinct from existing models in that it explicitly describes fire spread phenomena with physics-based knowledge achieved in the field of fire safety engineering. In the model, urban fire is described as an ensemble of multiple building fires, i.e., fire spread is simulated by predicting behaviors of individual building fires under thermal influence of neighboring building fires. Adopted numerical technique for the prediction of individual building fire is based on the one-layer zone modeling. Governing equations of mass, energy, and chemical species for component rooms are solved simultaneously, to give development of temperature, concentration of chemical species, and other properties. As for the building-to-building fire spread, three phenomena are considered as contributing factors: (i) thermal radiation from fire involved buildings; (ii) temperature rise due to wind-blown fire plumes; and (iii) firebrand spotting. As for the model verification, fire spread simulations were carried out in a virtual urban area, where 2,500 buildings of identical configuration were aligned at constant separations. Calculated fire spread rates were then compared with that of the Hamada-model, and reasonable agreements were obtained.
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