Residential Exterior Wall Reaction to Post-Flashover Compartment Fires

Large outdoor fires involving building-to-building fire spread are catastrophic, often resulting in significant loss of life and property. Previous research investigating ignition of buildings from exterior fires has focused on exposures from wildland fuels, which typically have shorter residence times compared to structure fires. This paper presents the details of full-scale building-to-building fire spread experiments conducted on residential exterior wall assemblies. Three wall assemblies sided with exterior plywood panels (hereafter referred to as T1–11), exterior insulation finishing system (EIFS), and fiber cement board were exposed to a post-flashover compartment fire at 1.8, 3.0, and 4.3 m separation distances to evaluate reaction-to-fire characteristics. All three wall assemblies tested ignited from the source exposure within this range of separation distances, which are common in residential areas with high structure density. Combustible siding (T1–11 and EIFS) ignited at the 3.0 and 4.3 m separation distances, whereas sheathing behind the noncombustible siding (fiber cement) wall assembly ignited at the 1.8 m separation distance. Compared to results from experiments with an identical protocol that examined the performance of double-pane window assemblies, the maximum heat load (time-integrated heat flux) at the time of ignition at the 3.0 m separation distance was consistently higher than the heat load at the time of cracking of the outer pane of plain (annealed) glass window assemblies but lower than that for cracking of both panes of a double-pane window assembly. Current codes, standards, and test methods should address fire penetration, as well as vertical and lateral flame propagation of exterior wall assemblies.