Wind-driven fire spread to a structure from fences and mulch

Abstract

A series of field experiments was conducted to examine the effects on fire spread toward a structure for combustible fences and mulch under conditions that may be encountered in a wildland-urban interface (WUI) fire. The fire behavior of a variety of materials, designs, and configurations were studied under various wind conditions. The 187 experiments were split into five categories: mulch only, fence only, fence plus mulch, parallel fences, and long range firebrand experiments. Fence materials included western redcedar, California redwood, pine, vinyl, and wood-plastic composites, and fence styles included privacy, lattice, and good neighbor (board on board). The tested mulch types were shredded hardwood, mini pine bark nuggets, pine straw, rubber, and artificial turf. A wind machine provided a mean wind speed between 6 m/s and 14 m/s (13 mi/h to 31 mi/h). The fence and/or mulch bed was ignited by a propane burner on the ground at the end farthest from the structure. A small structure was located between 0 m and 1.83 m (0 ft to 6 ft) downwind of the fence or mulch bed as a target for flames and firebrands. A target mulch bed at the base of the structure tested the ability of firebrands produced by the burning fence and mulch bed to ignite spot fires that threatened the structure.

Wind-driven fire spread to a structure from firewood piles

“…The firewood pile was located away from the wall of the structure by separation distances ranging from 0.91 m (3 ft) to 7.32 m (24 ft). This range was in contrast to the 0 m (0 ft) to 1.83 m (6 ft) range examined in the fence/mulch study [1]. To study the potential for firebrands to ignite the structure, a target pan of mixed hardwood mulch was positioned at the base of the structure wall.…”

“…Nevertheless, woodpiles do share the firebrand generation aspect of other landscape combustibles such as those mentioned above. The recent NIST study on fences [1] found that: 1. a combustible ground cover such as mulch can generate many firebrands that ignite downwind spot fires and 2. when combined with fences, firebrand production was enhanced. The report [1] listed prior studies of fences and mulch.…”

“…The recent NIST study on fences [1] found that: 1. a combustible ground cover such as mulch can generate many firebrands that ignite downwind spot fires and 2. when combined with fences, firebrand production was enhanced. The report [1] listed prior studies of fences and mulch. While much of the study's results were related to how fire spreads along these features, some also provided insight into how firebrands are generated and ignite downwind spot fires.…”

“…The fence/mulch report [1] provided an in-depth description of the wind field generated by the wind machine from both measurement/analysis and modeling perspectives. It explained the functionality and output of the software programs used to analyze and visualize the velocity measurements.…”

“…This report is the second in a series of NIST (The National Institute of Standards and Technology) experimental studies on fire spread from landscape combustibles to a structure. In the first report, we presented a study on fire spread via flames and firebrands from fences and mulch [1]. In this report, we describe the hazard to a structure due to flames and firebrands from woodpiles.…”