Wind-driven Fire Spread to a Structure from Firewood Piles
Erik L. Johnsson, Kathryn Butler, Marco G. Fernandez, Shonali Nazare, Alexander Maranghides
A series of field experiments was conducted to examine the effects on fire spread toward a structure for firewood piles under conditions that may be encountered in a wildland-urban interface (WUI) fire. The fire behavior of a variety of firewood types in multiple configurations was studied under various wind conditions. The 62 experiments conducted included long range firebrand travel and mitigation experiments. Wood types included kiln-dried oak, maple, pine, and undried oak. Configuration variations included woodpile height, orientation, and elevation on a rack. A wind machine provided a mean wind speed between 6 m/s and 14 m/s (13 mi/h to 31 mi/h). The woodpiles were ignited by a propane burner on the ground at the end farthest from a small structure located between 0 m and 7.32 m (0 ft to 24 ft) downwind of the woodpile. A target mulch bed at the base of the structure tested the ability of firebrands produced by the burning woodpile to ignite spot fires that threatened the structure. The experiments in this study demonstrated that firewood piles can be rapid sources of spot fire ignitions and can easily spread fire to nearby structures. Rapid fire growth on and substantial flames from the woodpiles were found for all wood types and configurations. Fire behavior was classified as mostly high with medium hazard for only the lowest wind condition. In all cases, spot fire generation was affected by the wind field; the structure created both upward flow (enhanced by buoyancy) and a vortex that deposited firebrands next to the structure. During all experiments, the burning woodpile produced firebrands that ignited spot fires in the target mulch bed. In long range experiments, firebrands from a woodpile caused ignitions over 26 m (85 ft) downwind. This study of the fire hazard of woodpiles is part of a series designed to better inform standards and codes regarding placement of landscape features around homes that are at risk of exposure to wildland-urban interface fires.
, Butler, K.
, Fernandez, M.
, Nazare, S.
and Maranghides, A.
Wind-driven Fire Spread to a Structure from Firewood Piles, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.TN.2251, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=935611
(Accessed September 26, 2023)