Manzello Samuel L, Suzuki Sayaka, Nii Daisaku
Fire Research Division, National Institute of Standards and Technology (NIST), Gaithersburg, MD USA.
Large Fire Laboratory, National Research Institute of Fire and Disaster (NRIFD), Chofu, Tokyo, JAPAN.
Fire Technol. 2017 Mar;53(2):535-551. doi: 10.1007/s10694-015-0537-3. Epub 2015 Oct 8.
Structure ignition by wind-driven firebrand showers is an important fire spread mechanism in large outdoor fires. Experiments were conducted with three common mulch types (shredded hardwood mulch, Japanese Cypress wood chips, and pine bark nuggets) placed adjacent to realistic-scale reentrant corners. In the first series of experiments, mulch beds were placed adjacent to a re-entrant corner constructed with wood studs and lined with oriented strand board (OSB) as the sheathing. The premise behind conducting experiments with no siding treatments applied was predicated on the notion that bare OSB mulch contact would be a worst-case scenario, and therefore, a wall assembly in the most vulnerable state to mulch ignition. In the second series of experiments, vinyl siding was applied to the re-entrant corner assemblies (wood studs/OSB/moisture barrier/vinyl siding), and the influence of vertical separation distance (102 mm or 203 mm) on wall ignition from adjacent mulch beds was determined. The vertical separation distance was maintained by applying gypsum board to the base of the re-entrant corner. The siding itself did not influence the ignition process for the mulch beds, as the mulch beds were the first to ignite from the firebrand showers. In all experiments, it was observed that firebrands produced smoldering ignition in the mulch beds, this transitioned to flaming ignition, and the re-entrant corner assembly was exposed to the flaming mulch beds. With no siding treatments applied, the flaming mulch beds ignited the re-entrant corner, and ignition was observed to propagate to the back side of re-entrant corner assembly under all wind speeds (6 m/s to 8 m/s). With respect to the re-entrant corners fitted with vinyl siding, the mulch type, vertical separation distance, and wind speed were important parameters as to whether flaming ignition was observed to propagate to the back-side of a reentrant corner assembly. Mulches clearly pose an ignition hazard to structures in large outdoor fires.
由风力驱动的火星阵雨引发结构着火是大型户外火灾中一种重要的火灾蔓延机制。使用三种常见的覆盖物类型（碎硬木覆盖物、日本柏木片和松树皮块）在实际尺寸的凹角附近进行了实验。在第一系列实验中，覆盖物床放置在由木立柱构建并用定向刨花板（OSB）作为护墙板衬砌的凹角附近。进行未施加护墙板处理实验的背后前提基于这样一种观念，即裸露的OSB与覆盖物接触将是最坏的情况，因此，墙体组件处于最易被覆盖物点燃的脆弱状态。在第二系列实验中，将乙烯基护墙板应用于凹角组件（木立柱/OSB/防潮层/乙烯基护墙板），并确定垂直分隔距离（102毫米或203毫米）对相邻覆盖物床引发墙体着火的影响。通过在凹角底部应用石膏板来维持垂直分隔距离。护墙板本身并未影响覆盖物床的着火过程，因为覆盖物床是首先被火星阵雨点燃的。在所有实验中，观察到火星在覆盖物床中产生阴燃着火，这种阴燃着火转变为明火着火，并且凹角组件暴露于明火覆盖物床。在未施加护墙板处理的情况下，明火覆盖物床点燃了凹角，并且观察到着火在所有风速（6米/秒至8米/秒）下传播到凹角组件的背面。对于安装了乙烯基护墙板的凹角，覆盖物类型、垂直分隔距离和风速是关于是否观察到明火着火传播到凹角组件背面的重要参数。覆盖物在大型户外火灾中显然对建筑物构成着火危险。
