Those who examine a fire scene after extinguishment or burnout should be aware of the importance of recognizing whether flashover did actually occur and the impact it may have had on the burning of a room’s contents.
火灾调查员在灭火或可燃物烧尽后进入现场时,应该意识到是否发生轰燃以及轰燃对房间内物品燃烧造成的影响的重要性。
Post-flashover burning in a room produces numerous effects that were once thought to be produced only by accelerated arson fires involving flammable liquids such as gasoline. A fireball of burning gasoline vapors can sometimes produce floor-to-ceiling damage. The brief duration of such fires will result in shallow penetration. No matter how the fire began, walls scorched or charred from floor to ceiling can be due to post-flashover burning as well as from a fireball of burning gasoline vapors.
房间发生轰燃后燃烧产生的许多痕迹,曾被人们认为是只有汽油等易燃液体作为助燃剂实施放火时才会出现的。汽油蒸气燃烧形成的火球有时会造成从地板到顶棚的整体性破坏。这种火灾持续时间较短,形成浅层烧灼。无论火灾是如何引发的,轰燃后的燃烧和汽油蒸气燃烧的火球一样,都会使地板到顶棚的墙体烧焦炭化。
Fire damage under tables and chairs, once thought to be the result of the burning of flammable liquids at floor level, can be produced by the flaming combustion of the carpet and pad as they ignite during flashover. High temperatures and total room involvement, at one time thought to be linked to flammable liquid accelerants, are produced during post-flashover burning without accelerants. The extremely high heat fluxes produced in post-flashover fires can char wood or burn away other material at rates up to 10 times the rate at lower heat fluxes (Babrauskas 2005; Butler 1971).
过去曾认为桌椅下方的火灾破坏是由地面易燃液体燃烧造成的,但事实上轰燃时被引燃的地毯和垫子的有焰燃烧也会造成这类破坏。高温和整个房间参与燃烧,曾被认为与使用易燃液体助燃剂有关,但事实上轰燃过程中即使没有助燃剂参与也会产生这两种现象。轰燃后所产生的极高热通量,会于低热通量条件下的木材炭化速率和其他物质燃烧速率造成10倍
Prolonged post-flashover burning can make the reconstruction of the fire very difficult as post-flashover or full room involvement fires typically ignite all exposed fuel surfaces from floor to ceiling. Localized patterns of smoke and fire damage that can help locate fuel packages, characterize their flame heights, and reveal the direction of flame spread can be destroyed. Some larger rooms sometimes exhibit progressive flashover, with floor-to-ceiling ignition at one end and undamaged floor covering at the other. Brief exposure (less than five minutes) to post-flashover fires does not necessarily compromise fire patterns on walls (see Hopkins, Gorbett, and Kennedy 2007).
轰燃后的燃烧时间越长,火灾重建工作的难度就越大,因为轰燃后或全面发展阶段的一个特征就是房间内从地板到顶棚所有暴露的可燃物表面都被引燃着火。因此烟气和火灾破坏形成的局部痕迹会被销毁,而这些痕迹的存在能够帮助调查人员认定可燃物位置、确定火焰高度以及判断火势蔓延方向。在某些较大房间里,有时会出现逐步发展的轰燃——房间一端从地板到顶棚全部发生燃烧,而另一端的地板却保持完好。短时间(15min以下)暴露于轰燃后的火灾,墙壁上的火灾痕迹并不一定会被破坏(见Hopkins,Gorbett和Kennedy 2007)。
In pre-flashover burning, the most intense thermal damage will be in areas immediately around or above burning fuel packages. the higher temperatures of the hot gas layer will produce more thermal damage in the upper half or upper third of the room. In post-flashover fires, all fuels are involved, the fires may become ventilation limited, and the most efficient (highest temperature) combustion occurs in turbulent mixing around the ventilation openings, where the oxygen supply is greatest. Oxygen-depleted burning occurs in many post-flashover rooms where the available fuel exceeds the air supply.
在轰燃前的火灾中,热破坏最严重的位置位于燃烧可燃物周围或正上方。热烟气层温度越高,对房间上部二分之一或三分之一部分造成的热破坏就越为严重。轰燃发生后,所有可燃物参与燃烧,火灾变为通风控制型,效率最高的燃烧(温度最高)发生在通风口附近的湍流混合区,此处氧气供应最为充足。许多轰燃后的室内火灾,可燃物超过空气的供应量,进而发生缺氧燃烧。
Interviews of first-in firefighters may reveal whether a room was fully involved, floor to ceiling, when entry was first made. Investigators must be aware of the conditions that can lead to flashover and how to recognize whether it has occurred. A thorough understanding of heat release rates and fire spread characteristics of modern furniture and the dynamics of flashover will be of great assistance (Babrauskas and Peacock 1992).
通过询问第一个进入现场的消防员,可以了解进入房间时,是否发生了从地板到顶棚的全室性燃烧。调查人员必须熟知轰燃发生的条件,并且能够辨认是否发生过轰燃。全面理解现代家具火灾蔓延、热释放速率以及轰燃动力学的特征,对于火灾调查工作大有帮助(Babrauskas 和Peacock 1992)。