Modelling smoke dynamics and hazards of smouldering fire in complex large space building

Abstract

Smouldering fires produce significant quantities of toxic smoke and gases that are responsible for severe casualties while rarely considered in building fire safety design. This work simulates smouldering smoke transport using a surrogate model with prescribed mass-loss rate, surface temperature, and CO/CO2 yields. It quantifies the hazards of low-buoyancy, CO-rich smoke from indoor smouldering fires by tracking the carbon monoxide concentration and smoke flow patterns. As the smouldering burning temperature increases, the smoke pattern changes from (1) the stagnation flow on the ground to (2) the boundary wall flow and finally to (3) two-zone structure, because a low temperature smouldering fuel induces a much weaker smoke buoyancy than a flame. Smoke stratification under a hot ceiling becomes easy to occur for a smouldering fire, preventing smoke flowing towards ceiling fire sensors and delaying the fire detection. The available safe egress time (ASET) of smouldering fire can be shorter than flaming fire under the same fuel-burning rate, showing a greater fire hazard. Building design features like roof shape, slab extension, and smoke extraction affect the smouldering smoke flow, where a sawtooth roof reduces ASET by 18% compared to a flat roof atrium. When a smouldering fire source is located under the slab extension, ASET may be reduced to less than a minute due to rapid smoke spread at floor level, while a mechanical extraction system can effectively remove low buoyancy smouldering fire smoke. This work improves our understanding of smouldering fire hazards in complex buildings and provides scientific guidelines for a more comprehensive design evaluation of building fire safety.