Effect of firebrand size and geometry on heating from a smoldering pile under wind

Tao, Zhenxiang; Bathras, Bryce; Kwon, Byoungchul; Biallas, Ben; Gollner, Michael J.; Yang, Rui

doi:10.1016/j.firesaf.2020.103031

Cited by 26 publications

(28 citation statements)

References 32 publications

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“…This was attributed to a higher magnitude of the radiation heat flux from the cylindrical ember compared to conduction heat transfer from the disc shaped ember. The findings are in agreement with those of Tao et al [32] and Matvienko et al [77] discussed above.…”

Section: Types Of Emberssupporting

confidence: 93%

“…In this context/review, thermal characteristics include ember temperature, mass loss rate, burning rate, heat flux from the burning ember, and amount of heat transferred to the substrate. The shape and size are important physical properties that govern burning [22,32] as well as transport [68] of embers while the ignition probabilities or spotting potential of embers depend upon their thermal properties.…”

Section: Physical and Thermal Characteristics Of Embersmentioning

confidence: 99%

“…However, most of these data are qualitative, and the studies largely report on ignition probabilities of the fuel studied. Very recently, the research groups at the University of Edinburgh [23], University of Maryland [29][30][31][32], University of California Berkeley [33], and others [34] performed advanced experiments to study thermal characteristics of embers (e.g., ember temperature and heat transfer as well as factors and conditions that affect each one) and identify conditions under which the wooden substrate would ignite. These experiments provide insights into measurement techniques and associated uncertainties.…”

Section: Introductionmentioning

confidence: 99%

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Ignitibility of structural wood products exposed to embers during wildland fires :

Nazaré¹,

Leventon²,

Davis³

2021

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Ignitability of structural components due to ember accumulation is a common cause of structural fires in wildland urban interface (WUI) communities. To fire harden structures in WUI communities, it is important to quantitatively predict the ember ignitability of wooden substrates. To commence this effort, past studies have been compiled and analyzed to identify knowledge gaps. Key topics including ignition of structures in WUI fires, measurement of thermal response of solid wood products used in residential structures, controlling mechanisms in ignition and sustained smoldering of wood, measurement of ember properties, real-scale and bench-scale experiments on assessing ember ignitability of structural components, and surrogate ignition sources for assessing smoldering propensity of the wooden substrate have been reviewed. Existing test methods have also been reviewed in the light of common exposures seen WUI environment.

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Section: Types Of Emberssupporting

confidence: 93%

Section: Physical and Thermal Characteristics Of Embersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ignitibility of structural wood products exposed to embers during wildland fires :

Nazaré¹,

Leventon²,

Davis³

2021

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“…This wind test presented a dramatic increase in heating and reduction in the time to flaming ignition of the tested target fuel. Another recent study led by the senior author investigated the effect of firebrand size and shape on heating under different wind speeds (Tao et al, 2020). They found that piles from real firebrand fuels, such as barks and sticks, achieved higher peak heat fluxes at higher wind speeds than firebrand piles produced from artificial birch fuels, which exhibited little change with firebrand geometry.…”

Section: Literature Reviewmentioning

confidence: 99%

“…The goal of this study is to quantify heat flux conditions at ignition of dense fuels representative of WUI fuels. This work applies the methodology developed by Hakes et al (2019) and later used by Tao et al (2020) to measure heat fluxes from piles of firebrands under various wind conditions and understand how these conditions relate to those which cause flaming and smoldering ignition of various WUI materials. Measurements are conducted over both an inert substrate and with representative WUI fuels, allowing for the influence of a target material to be separated from firebrand pile heating.…”

Section: Introductionmentioning

confidence: 99%

Critical Ignition Conditions of Wood by Cylindrical Firebrands

2021

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This study investigated the thermal conditions preceding ignition of three dense woody fuels often found on structures by firebrands, a major cause of home ignition during wildland-urban interface (WUI) fires. Piles of smoldering cylindrical firebrands, fabricated from wooden dowels, were deposited either on a flat inert surface instrumented with temperature and heat flux sensors or on a target fuel (marine-grade plywood, oriented-strand board, or cedar shingles) to investigate critical conditions at ignition. The former provided thermal data to characterize the time before and at ignition, while the latter provided smoldering and flaming ignition times. Tests were conducted in a small-scale wind tunnel. Larger firebrand piles produced higher temperatures at the center of the pile, thought to be due to re-radiation within the pile. Ignition was found to be dependent on target fuel density; flaming ignition was additionally found to be dependent on wind speed. Higher wind speeds increased the rate of oxidation and led to higher temperatures and heat fluxes measured on the test surface. The heat flux at ignition was determined by combining results of inert and ignition tests, showing that ignition occurred while transient heating from the firebrand pile was increasing. Ultimately, critical ignition conditions from firebrand pile exposure are needed to design appropriate fire safety standards and WUI fire modeling.

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