Structural building fires

Structural fires mainly occur in a residential, commercial, or community-based building. The propagation rates of such fires vary depending on the types of materials used in building construction; in turn, the degree of flame and/or radiant heat generation differs. The building materials can be broadly classified into five categories based on the fire resistivity: (1) concrete and fire-resistive coated steel for high rise residential or commercial buildings, (2) steel (for wall) and steel rafters (for roof) for commercial buildings, (3) brick, mortar (for wall), and wood frame (for floors) for residential buildings, (4) heavy timber for community-based buildings, and (5) wood frame for residential buildings [46,47]. Here, it is clear that categories (1) and (2) comprise the fire-resistant and noncombustible materials. The residential or commercial buildings constructed using such materials do not propagate the fire; therefore, flame behavior remains restricted [48]. However, the materials in categories (3), (4), and (5) are semicombustible and/or combustible; consequently, their flame generation rate is very high [49].

In addition to the building materials, the placement of windows (near or far away from the fire source), condition of windows (open or closed), and the methods of building construction play an important role in propagating the structural fires. In this context, an international fire consultant group attempted to graphically model the structural fires’ propagation through an improperly sealed wall. They observed that an improperly constructed building allows a significant wind flow inside the building that may considerably propagate structural fires [50]. Furthermore, many other combustible (eg, wood furniture, clothes, cooking gas, oil) and noncombustible (eg, metal furniture, ceramic appliances, water) substances may come in contact with structural fires, and could cause a significant amount of flame, radiant heat, hot surfaces, hot liquids, and vapors [51]. Any metal with a low melting temperature could easily melt in structural fires. The presence of flame, radiant heat, hot surfaces, hot liquids, vapors, and molten metal substances in structural fires make it dangerous for any living being. In this situation, a flashover condition may occur and the temperature can rise above 600°C with a heat flux range of 60-200 kW/m2 [52,53].

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