Research Center for Fire Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
Sci Rep. 2018 Nov 8;8(1):16528. doi: 10.1038/s41598-018-34620-3.
Dripping of molten fuels is a widely observed fire phenomenon, and, by igniting other fuels, it can promote fire spread and increase fire hazards. In this work, dripping phenomena from fires of horizontally oriented wires, coated with polyethylene (PE), are investigated in the laboratory. It is found that as long as a flame is attached to the drip, thin tissue paper can be ignited by a single drip. Below a minimum diameter (D = 0.63 mm), the drip floats up. Above a critical diameter (D = 2.3 mm), a flame can remain attached to the drip and ignite tissue paper as it falls through a distance of at least 2.6 m, thereby posing a significant fire hazard. A falling burning drip appears to the eye to be a blue chain of flame as a result of persistence of vision. Photographic evidence identifies a flame-shedding process, most likely associated with continual sequential ignition of fuel vapor within a von Karman vortex street generated behind the falling burning drip. The frequency of flame shedding agrees with both the frequency of modeled vortex shedding and the frequency of the unexpected sound that is heard during the process. This is the first time that combustion characteristics of dripping fire phenomena have been studied in detail, and this helps to better evaluate the risk and hazards of wire and façade fires.
燃料滴落是一种广泛观察到的火灾现象，通过点燃其他燃料，它可以促进火灾蔓延并增加火灾风险。在这项工作中，研究了水平方向的涂有聚乙烯（PE）的电线火灾中的滴落现象。结果发现，只要火焰附着在滴落物上，单层薄纸巾就可以被单个滴落物点燃。在最小直径（D=0.63mm）以下，滴落物会浮起。在临界直径（D=2.3mm）以上，火焰可以附着在滴落物上，并在至少 2.6m 的距离内点燃纸巾，从而构成重大火灾隐患。下落燃烧的滴落物在视觉上看起来像是蓝色的火焰链，这是因为视觉暂留。摄影证据确定了一个火焰脱落过程，这很可能与在下落燃烧的滴落物后面产生的卡门涡街内连续顺序点燃燃料蒸气有关。火焰脱落的频率与模拟的涡旋脱落频率以及在该过程中听到的意外声音的频率一致。这是第一次详细研究滴落火灾现象的燃烧特性，这有助于更好地评估电线和外墙火灾的风险和危害。
