Author: Sangkyu Lee
Date/Time: June 16th, 2025 at 1:15 pm EST
Location: JMP 3106B, J.M. Patterson
Committee members:
- Dr. Stanislav I. Stoliarov, Chair
- Dr. Peter B. Sunderland
- Dr. Fernando Raffan-Montoya
- Dr. Shuna Ni
- Dr. Kyuyong Choi, Dean’s Representative
Title of dissertation: Analysis of fire behavior of pressure treated wood and wood-plastic composite subjected to deposition of glowing firebrands
Abstract: The frequency and severity of Wildland-Urban Interface (WUI) fires continue to rise globally. Firebrands are smoldering embers generated from vegetative or structural materials during a WUI fire, lofting up to several kilometers and travelling ahead of the main fire front. Firebrands serve as pilot ignition sources and contribute to the spread of wildland fires into communities. However, complex ignition processes and response of structural materials to firebrand exposure have yet to be fully understood. In this work, representative building materials, pressure treated wood (PTW) and wood-plastic composite (Trex), were exposed to glowing firebrand piles in a bench-scale wind tunnel. The air flow velocity was 0.9 – 2.7 m s-1, the firebrand coverage densities were 0.06 and 0.16 g cm-2, and the pile footprint was 5 × 10 cm2 with either the 10-cm or 5-cm sides perpendicular to the incident air flow. Several types of flaming ignition events were observed including flames attached to the substrate surface in front of the pile (preleading zone ignition), and flames attached to the pile that sometimes spread onto the substrate downstream of the pile (downstream ignition). The most frequent and long-lasting flaming combustion occurred in experiments performed at 2.4 – 2.7 m s-1 using 0.16 g cm-2 firebrand coverage density piles with 10-cm sides perpendicular to the air flow. Trex was less prone to preleading zone ignition but was more prone to downstream ignition. Unlike Trex, PTW exhibited a propensity for sustained smoldering for a wide range of air flows. To further analyze the ignition processes, pyrolysis property sets were obtained for PTW and Trex following a well-established hierarchical approach where thermogravimetric analysis, differential scanning calorimetry, and microscale combustion calorimetry were used to parametrize kinetics and thermodynamics of the thermal decomposition and combustion, while controlled atmosphere pyrolysis and cone calorimetry tests performed on coupon-sized samples were used to parameterize thermal transport properties and validate performance of the fully parametrized pyrolysis models. The developed pyrolysis models were used to simulate the preleading zone ignitions of PTW and Trex observed in the wind tunnel experiments. An empirical model of firebrand heat flux developed in an earlier work was employed to model boundary conditions for the combustible substrates in the preleading zone and dependence of these conditions on the air flow velocity and firebrand coverage density. It was determined that the critical value of the peak average heat release rate, HRRPeak = 120 kW m-2, computed in these simulations successfully delineated between the low ignition probability, < 0.5, and high ignition probability, > 0.5, firebrand deposition scenarios.