Development of a new approach to characterize firebrand showers during Wildland-Urban Interface (WUI) fires:

Abstract

A new approach to characterize airborne firebrands during Wildland-Urban Interface (WUI) fires is detailed. The approach merges the following two imaging techniques in a single field-deployable diagnostic tool: (1) 3D Particle Tracking Velocimetry (3D-PTV), for timeresolved mapping of firebrand 3D trajectories, and (2) 3D Particle Shape Reconstruction (3D-PSR), to reconstruct 3D models of individual particles following the Visual Hull principle. This tool offers for the first time the possibility to simultaneously study time-resolved firebrand fluxes and firebrand size distribution to the full extent of their three-dimensional nature. Methodologies used in the present work are presented and their technical implementation are thoroughly discussed. Validation tests to confirm proper tracking/sizing of particles are detailed. The diagnostic tool is applied to a firebrand shower artificially generated at the NIST National Fire Research Laboratory. A novel graphic representation, that incorporates both the Cumulative Particle Count (CPC, particles m -2 ) and Particle Number Flux (PNF, particles m -2 s -1 ) as relevant exposure metrics, is presented and the exposure level is compared to that of an actual outdoor fire. Size distributions obtained for airborne firebrands are compared to those achieved through ground collection and strategies to improve the particle shape reconstruction method are discussed.

WUI structureparcelcommunity fire hazard mitigation methodology

“…Because the exposure intensity and duration cannot be controlled, or in many cases even predicted, ember hardening must address significant ember exposures and associated local ember accumulations. While scientific work is in progress to measure and quantify ember fluxes (e.g., [37][38][39]), visual observations and ignition occurrences are the best documentation at this time. The technical goal is to prevent ignition, not merely delay it.…”

Quantifying Firebrand Production and Transport Using the Acoustic Analysis of In-Fire Cameras

“…Similarly, studies utilizing aerial infrared imagery of active fires to identify spot fires ahead of the main fire front [2,24] quantify only those firebrands able to immediately ignite and accelerate to a new sizable fire, but may not capture firebrands with lesser energy that may be important in structure ignitions [25] or new ignitions on the forest floor. 3D particle tracking velocimetry had been shown as a powerful instrument to track firebrand count and other relevant metrics [26], but multiple deployments of such instruments would be challenging ahead of and within a crown fire. Simple and robust instrumentation for experimental crown fires is necessary for further data collection of firebrand production and transport processes in addition to the established and valuable methods above.…”

Determination of Firebrand Characteristics Using Thermal Videos

“…Recently, several studies have been conducted in an attempt to solve this problem [16][17][18][19][20][21][22][23]. In order to conduct this research, a series of prescribed fire experiments within pine forests were performed to study the generation of firebrands and their properties as a function of fire behavior [16][17][18].…”

“…The formation of firebrands from thermally degraded vegetative elements was also investigated in the study [19]. [23] used 3D Particle Tracking Velocimetry and 3D Particle Shape Reconstruction to reconstruct 3D models of individual particles and their trajectories. Additionally, particle tracking velocimetry and flame front detection techniques were also tested to explore [21] commercial aircraft debris striking.…”