Thermal characterization of firebrand piles

Hakes, Raquel S.P.; Salehizadeh, Hamed; Weston-Dawkes, Matthew J.; Gollner, Michael J.

doi:10.1016/j.firesaf.2018.10.002

Cited by 46 publications

(54 citation statements)

References 40 publications

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“…The external supply of heat flux minimises heat loss and assists the fuel heating required for self-sustained smouldering progress and pyrolyzate production. Assistive fuel heating can be in the form of external heat flux such as embers in the case of WUI fires or from pertinent features of the fuel configuration such as when heat loss is minimised by the possible presence of radiation exchange between smouldering surfaces, i.e., smouldering at the fuel crevice or smouldering in U-shaped fuels (Alexopoulos and Drysdale, 1988;Ohlemiller, 1991;Ogle and Schumacher, 1998;Manzello et al, 2008Manzello et al, , 2009Manzello et al, , 2012Stoliarov et al, 2017;Hakes et al, 2018).…”

Section: Discussionmentioning

confidence: 99%

“…Particles as small as 19.1 mm with a temperature of 650 • C can initiate flaming combustion. Embers with sizes ranging from 25 to 50 mm have been found in studies investigating StF transitions (Manzello et al, 2006a(Manzello et al, ,b, 2008Hakes et al, 2018). In pine needle beds, the time to StF transition was ∼2.5-5 min at particle temperatures within the range of smouldering temperatures, ∼630-700 • C (Wang et al, 2017).…”

Section: Embers and Stf Transition In Wildfiresmentioning

confidence: 95%

“…Once accumulated, embers can cause WUI structures such as roofing material, decks, and vents to smolder and, in some cases, transition to flaming. The generation of embers, its transport and the vulnerability of ignition of WUI fuels due to flaming and smouldering embers have been widely investigated (Manzello et al, 2008(Manzello et al, , 2009(Manzello et al, , 2012Manzello, 2014;Manzello andSuzuki, 2014, 2017;Suzuki et al, 2015;Zhou et al, 2015;Hakes et al, 2018). Embers also provide an alternative mode of fire spread during wildfires through spotting, whereby embers land and locally ignite dry fuels, often transitioning from StF and thus 1 Haze fires cost Indonesia S$ 22 b, twice the tsunami bill: World Bank, The Straits Times, Singapore, 16 December 2015. advancing the flame (Figure 2).…”

Section: Characteristics Smouldering Flamingmentioning

confidence: 99%

“…At the surface, the smouldering front also undergoes high convective heat losses. To be self-sustained, smouldering needed to be assisted with decreasing heat loss or external heat flux, i.e., a U-shaped fuel geometry to maximise radiation heat exchange between the smouldering surfaces or deposited embers on fuel bed surface (Ohlemiller, 1991;Manzello et al, 2006bManzello et al, , 2008Manzello et al, , 2009Manzello et al, , 2012Manzello andSuzuki, 2014, 2017;Hakes et al, 2018). Under this condition, the transition tends to occur at the surface of the material.…”

Section: Permeability and Consolidationmentioning

confidence: 99%

“…Thus, pyrolysis is supported by heat from smouldering embers, and flaming ignition of the fuel occurs in the vicinity of embers where heat is most available. In this case, the StF transition of the embers could also precede flaming ignition of the fuel, where flaming embers act as a heat source for the fuel pyrolysis reaction and pilot ignition of the pyrolyzates from the fuel (Hakes et al, 2018). The comparison of these two cases shows that the embers enhance flaming ignition of the fuel more in the latter case than in the former case, assuming that self-sustained smouldering can take a long time to establish and has equal probability to extinguish as to transition from StF.…”

Section: Embers and Stf Transition In Wildfiresmentioning

confidence: 99%

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Review of the Transition From Smouldering to Flaming Combustion in Wildfires

et al. 2019

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Wildfires are uncontrolled combustion events occurring in the natural environment (forest, grassland, or peatland). The frequency and size of these fires are expected to increase globally due to changes in climate, land use, and population movements, posing a significant threat to people, property, resources, and the environment. Wildfires can be broadly divided into two types: smouldering (heterogeneous combustion) and flaming (homogeneous combustion). Both are important in wildfires, and despite being fundamentally different, one can lead to the other. The smouldering-to-flaming (StF) transition is a quick initiation of homogeneous gas-phase ignition preceded by smouldering combustion, and is considered a threat because the following sudden increase in spread rate, power, and hazard. StF transition needs sufficient oxygen supply, heat generation, and pyrolysis gases. The unpredictable nature of the StF transition, both temporally and spatially, poses a challenge in wildfire prevention and mitigation. For example, a flaming fire may rekindle through the StF transition of an undetected smouldering fire or glowing embers. The current understanding of the mechanisms leading to the transition is poor and mostly limited to experiments with samples smaller than 1.2 m. Broadly, the literature has identified the two variables that govern this transition, i.e., oxygen supply and heat flux. Wind has competing effects by increasing the oxygen supply, but simultaneously increasing cooling. The permeability of a fuel and its ability to remain consolidated during burning has also been found to influence the transition. Permeability controls oxygen penetration into the fuel, and consolidation allows the formation of internal pores where StF can take place. Considering the high complexity of the StF transition problem, more studies are needed on different types of fuel, especially on wildland fuels because most studied materials are synthetic polymers. This paper synthesises the research, presents the various StF transition characteristics already in the literature, and identifies specific topics in need of further research.

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