Smoldering ignition and transition to flaming in wooden mulch beds exposed to firebrands under wind

IF 3.4 3区 工程技术 Q2 ENGINEERING, CIVIL
Shaorun Lin , Chengze Li , Mackenzie Conkling , Xinyan Huang , Stephen L. Quarles , Michael J. Gollner
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Abstract

Spotting ignition by firebrands is a significant fire spread pathway at the wildland-urban interface (WUI), where mulch products are commonly used as landscaping materials. Mulch is typically organic in nature, thus it may be easily ignited into a smoldering mode by firebrands and subsequently transition to flaming, leading to direct flame contact and radiant heat exposure to siding materials of adjacent structures. This work quantified the thresholds of smoldering ignition of four common types of commercially available mulch (black mulch (BM), forest floor (FF), redwood (RW), and fir bark (FB)) exposed to heating by smoldering firebrand piles, and their propensity for smoldering-to-flaming transition under external winds (up to 1.4 m/s). We found that there was a minimum mass of firebrand pile to achieve smoldering ignition of mulch (e.g., ∼0.1 g for FF). Beyond this minimum mass, the required wind speed to trigger smoldering ignition generally decreased as the mass of the firebrand pile increased, agreeing well with theoretical analysis. After smoldering ignition, smoldering-to-flaming transition could be observed when the wind speed exceeded a critical value (e.g., ∼1 m/s for FF), which was not affected by the initial spotting process. To achieve smoldering-to-flaming transition, the glowing mulch had to reach a critical temperature of around 850 °C. Mulch samples with larger particle sizes were more likely to smolder and transition to flaming, due to increased oxygen supply through larger inter-particle pores and channels and better firebrand accumulation due to a more crevice-like geometry on the fuel surface. This work advances the fundamental understanding of the ignition and burning behavior of landscaping mulches, and thus contributes to the prevention of extreme WUI fire events.

在风力作用下,木质地膜床暴露在火苗下,燃烧并过渡到燃烧
在通常使用地膜产品作为景观美化材料的荒地-城市交界处(WUI),火带的点燃是火灾蔓延的一个重要途径。地膜通常是有机物,因此很容易被火烧带点燃,进入燃烧模式,随后转变为火焰,导致火焰直接接触邻近建筑物的护墙板材料并产生辐射热。这项研究量化了四种常见市售地膜(黑色地膜 (BM)、林地地膜 (FF)、红木地膜 (RW) 和杉树皮地膜 (FB))暴露在燃烧的火绒堆加热下的燃烧阈值,以及它们在外部风力(最大 1.4 米/秒)作用下从燃烧向燃烧过渡的倾向。我们发现,要实现地膜的燃烧点火,火烧堆的质量必须达到一个最小值(例如,FF 的火烧堆质量为 0.1 克)。超过这个最小质量后,引发燃烧点火所需的风速一般会随着火绒质量的增加而降低,这与理论分析非常吻合。燃烧点火后,当风速超过临界值(例如,FF 的风速为 1 m/s)时,可以观察到从燃烧到着火的转变,而这一转变不受初始点火过程的影响。要实现从燃烧到燃烧的转变,发光地膜必须达到约 850 °C 的临界温度。颗粒尺寸较大的地膜样品更容易燃烧并过渡到燃烧,这是由于通过较大的颗粒间孔隙和通道增加了氧气供应,并且由于燃料表面的几何形状更像裂缝,因此火苗积累得更好。这项工作从根本上加深了人们对景观美化地膜的点火和燃烧行为的了解,从而有助于预防极端的 WUI 火灾事件。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Fire Safety Journal
Fire Safety Journal 工程技术-材料科学:综合
CiteScore
5.70
自引率
9.70%
发文量
153
审稿时长
60 days
期刊介绍: Fire Safety Journal is the leading publication dealing with all aspects of fire safety engineering. Its scope is purposefully wide, as it is deemed important to encourage papers from all sources within this multidisciplinary subject, thus providing a forum for its further development as a distinct engineering discipline. This is an essential step towards gaining a status equal to that enjoyed by the other engineering disciplines.
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