Influence of Wall Collapse on Fire Dynamics and Spread in Informal Settlement Dwellings with Inert and Combustible Cladding Walls

Abstract Six full-scale ISO 9705 rooms, built with timber frames and clad with either inert (corrugated galvanized steel sheets) or combustible (wood) materials, were numerically modeled under multiple fire load conditions to investigate the changes in fire dynamics resulting from an idealized instantaneous collapse of the compartment’s front wall and its influence on nearby combustible materials. Fire Dynamics Simulator (FDS) was used to simulate the fire behavior and the potential fire spread resulting from the dwellings with both cladding materials. The results showed that the front wall collapse changed the fire regime in both dwellings due to the sudden change in ventilation, which increased the air inflow and smoke outflow. This change allowed more fuel to burn inside the structure, reducing the amount of fuel burning in the external environment. Although the radiative heat flux generally decreased with distance from the compartment, the wall collapse significantly altered its spatial distribution, redistributing thermal radiation across the frontal region and modifying peak flux locations depending on fire load and cladding material. Under high fire load conditions, the wall collapse partially modified this behavior, particularly for the combustible dwelling, where increased heat flux and a wider affected area were observed. By comparing the predicted radiative heat fluxes with critical heat flux thresholds reported in the literature, the results indicate that separation distances commonly considered critical in previous studies may be insufficient under medium and high fire load conditions, particularly when combustible cladding is present. Under the specific conditions analyzed, ignition potential at 2.1 m remained significant for medium and high fire loads, while at 3.1 m the predicted susceptibility was reduced, especially for inert cladding under low fire load conditions.