Critical Drip Size and Blue Flame Shedding of Dripping Ignition in Fire

Abstract

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 (Dmin = 0.63 mm), the drip floats up. Above a critical diameter (Dcrt = 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.

Opposed-Flow Flame Spread and Extinction in Electric Wires: The Effects of Gravity, External Radiant Heat Flux, and Wire Characteristics on Wire Flammability

“…Since the residence time of the combustion gases in the reaction zone could basically be longer under microgravity than under normal gravity due to the absence of the buoyancy-induced flow, a microgravity Although the effects of the LDPE melting, dripping, and deformation on the flame spread and its limits are hard to quantify, there were clear differences in the behaviors observed under normal gravity and microgravity since dripping and deformation are results of gravity. Their impact on the flame spread over thermoplastic materials has been examined by several previous works and the effect of fuel type, size, and orientation and the surrounding ambient conditions have also been discussed [12,13,20,[44][45][46][47]. The change of the dripping behavior associated with that of the gravity condition would have a non-negligible effect on the difference in the flame spread limits between normal gravity and microgravity because it not only carries away the enthalpy from the downstream burning region but also transports energy to the upstream unburned area.…”

Fluctuation and extinction of laminar diffusion flame induced by external acoustic wave and source

“…Our recent works used a loudspeaker and low-frequency acoustic waves (without tube between speaker and flame) to extinguish the stationary candle flame 14 , the moving flames in plastic drips 14 , 24 , and the flaming firebrand 15 . By converting the sound pressure into a velocity component, a characteristic Damköhler (Da) number was introduced as an indicator for the acoustic extinction limit.…”

Reduced‐scale test to assess the effect of fire barriers on the flaming combustion of cored composites: An upholstery‐material case study

“…and an increase in heat release rate due to (a) an increase in total burning area and (b) due to feedback (ie, increased heat transfer) between the pool-fire and the original burning item. 14,24,25 In this scenario, the FB can delay or prevent pool-fire formation and dramatically decrease the heat release rate of the item by suppressing the mass transfer of LPs. Materials that generate LPs include not only thermoplastic polymers (eg, polyolefins) but also thermosetting polymers (eg, flexible polyurethane), which degrade to yield, in part, liquid pyrolyzates (eg, regenerated polyols for FPUFs) 26 when pyrolyzing.…”

“…At this stage, LPs are released under the burning item and can be ignited (LPs are now outside the FB envelope and potentially exposed to flames and radiation produced by the burning item) to produce a flaming liquid. Prolonged dripping and consequent accumulation of flaming liquid under the item can lead to the generation of a pool‐fire and an increase in heat release rate due to (a) an increase in total burning area and (b) due to feedback (ie, increased heat transfer) between the pool‐fire and the original burning item 14,24,25 . In this scenario, the FB can delay or prevent pool‐fire formation and dramatically decrease the heat release rate of the item by suppressing the mass transfer of LPs.…”