Laboratory Investigation of Fire Transfer from Exterior Wood Decks to Buildings in the Wildland–Urban Interface

Abstract In the wildland-urban interface, wood decks are a target for wildfire and may be ignited by firebrands or flaming debris. Wood decks also present a potential source for ignition of structures in the wildland-urban interface. However, their role in ignition of the adjacent structure is unclear and current regulation is based in part on anecdotal evidence. This paper examines the results of a set of preliminary laboratory experiments used to determine how experimental variables affect the thermal exposure from a burning wood deck to an attached structure. The experimental setup consists of a test deck of 609 mm by 711 mm (24 inches by 28 inches) on a stand with an attached back wall equipped with two heat flux sensors and twelve thermocouples. Two ignition sources were considered: a below deck flame test using a propane burner and an above deck test using a Class A burning brand. The initial tests study the effect of wind and burner size and were all conducted on redwood decking. The experimental data from these tests showed that wind speeds of 2.9 m/s (6.5 mph) and 5.4 m/s (12 mph) had the highest temperature and heat flux on the wall. These winds were then further tested on three different species; redwood and inert deck boards. The test methods developed herein and the data obtained can be used to gain insight into how a burning wood deck contributes to structural ignition.