Surviving home in the Village of Lytton, south Although the houses on both sides of the surviving house burned, the local ignition conditions of the surviving house did not meet the requirements for sustained ignition and thus, it did not burn. Inspection and Figure 17 showed no burning within the HIZ leading to the surviving structure, and, importantly, both adjacent burned houses had non-flammable stucco exterior walls (note the wall remnants) that acted as a radiation shield to their surroundings and confined flames to the burning interior. Thus, no structure-to-structure flame ignition occurred, as was particularly common with the high structure density in the Village of Lytton (Figs. 2, 17).
Figure 19: a, b) Adjacent burned houses to the south (left) and north (right) have non-flammable stucco exterior walls.
a
b
The south side burning house (Fig. 19a) did not thermally damage the surviving house (about 9 m separation), and there was no char on the wood fence panel (about 2 m separation). The north side burning house (Fig. 19b) was much closer (about 3m) to the surviving house. The top rail of the low wire fence was not charred, and the PVC vinyl siding had little thermal damage within 1 m of the ground. The thermal damage to the surviving house was likely radiation from the burning roof and attachments. As can be seen in Figure 19b, the vinyl siding melted off a portion of the exterior wall wood board sub-sheathing and eave enclosures. None of the exposed wood board sub-sheathing was significantly charred. The plate glass windows fractured but the small glass panes remained held in the vinyl sashes. For perspective, PVC softens to produce damage starting at 95 –100ºC; PVC liquefies starting at 180ºC; and PVC begins to decompose to produce flammable vapors starting at 140ºC. In contrast, wood surface temperature associated with flame ignition is about 325ºC. Thus, melted PVC siding is not indicative of the potential for wood wall ignition.
Key Finding (8): The non-flammable exterior walls remaining until structure collapse prevented flame radiation and contact sufficient for ignition at the adjacent surviving house. This indicates an opportunity to use common building materials that mitigate structure-to-structure community fire spread where there are densely overlapping HIZs.
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