不得不学的几个火灾学概念：轰燃( Flashover )、爆燃( Backdraft )、滚燃( Rollover

火灾的形成，追根究底不外乎是起火源与火灾环境的結合。也就是说任何的火灾，总有其脉络可循，往往可以从火灾学的原理，推敲其中的原因，应用科学的方法，作为火灾模型的重建。本文章将把火灾学中最容易混淆、最难分清楚的轰燃( Flashover )、爆燃( Backdraft )、滚燃( Rollover )以及其他NFPA的相关名词一一解释清楚，我们能在在学习这些火势发展现象时能更好理解。轰然(Flashover)所谓轰燃 (F.O)是指室内起火后，火势逐渐扩大过程中，因燃烧所产生的可燃性气体，蓄积于天花板附近，此种气体与空气混合，正好进入燃烧范围且达到燃点之际，一举引火形成巨大之火苗，使室内顿时成为火海的状态。NFPA：参考官网内容 Reporter's Guide: All about fire 定义如下：Flashover is the sudden, simultaneous ignition of everything in a room. This is how it happens:
轰燃指的是室内所有物品被瞬间、同时引燃。以下说明它是如何发生的：Hot gases rise to the ceiling and spread out across to the walls.高温可燃性气体上升至屋顶并横向扩散至墙壁。Heat radiates downward and intensifies until all combustible items reach their ignition temperatures and burst into flames.热辐射不断向下移动并加剧，直到所有可燃物到达引火点，最后导致全部可燃物瞬间燃烧起来。Temperatures soar to as much as 1,000 degrees Fahrenheit in a few seconds. Even a firefighter in full protective gear is unlikely survive a flashover.温度将在几秒内瞬间提升至华氏约1000度(约摄氏537度)，即使消防人员穿着完整防护装备都可能无法在轰燃中幸存。Firefighters are trained to recognize the signs that flashover is about to occur: dense black smoke with tightly packed curls (“black fire”); dense, black smoke that pushes out of a doorway or window opening; smoke that has accumulated as low as a doorknob, with the fire seen below.消防人员会接受训练，辨识轰燃即将发生的征兆：包含翻滚卷曲的浓黑烟(黑火)、窜出门窗开口的浓黑烟、烟层蓄积到门把高度且有火焰伴随在烟层下方。

滚燃(Rollover)Rollover，我们一般称为“滚燃”。新闻上常看到所谓的轰燃前兆“天使之舞”，指的就是滚燃现象。NFPA：参考官网内容( Reporter’s Guide: All about fire )定义如下Rollover occurs when ignited fire gases, or incompletely burned fuels, rise to the ceiling, and spread out horizontally. Then smoke appears to suddenly start burning. If nothing is done to ventilate the room or cool the air, this condition leads to flashover.当可燃性烟气或不完全燃烧的可燃物上升到天花板并水平扩散时，烟层会突然燃烧起来，导致滚燃的发生。如果没有适当地通风或降温可能会导致轰燃。另外参考NFPA数据Technical Committee on Fundamentals of Fire Control within a Structure Utilizing Fire Dynamics 2018 针对Rollover有更进一步的定义：Rollover: The condition in which unburned fuel (pyrolysate) from the originating fire has accumulated in the ceiling layer to a sufficient concentration (i.e., at or above the lower flammable limit) that it ignites and burns. Rollover can occur without ignition of or prior to the ignition of other fuels separate from the origin.滚燃：来自于起火点、尚未燃烧的可燃物(热裂解物质)，蓄积于天花板且达到足够的浓度(达爆炸下限或超过)时，这些可燃物起火燃烧的现象称为滚燃。没有引火物仍可能发生滚燃现象。

爆燃(Backdraft)Backfraft，我们把它称为“爆燃”也有火灾学称“回燃”或“复燃”。火灾学中定义：火灾在闷烧(Smoldering)状态时期，因空气中的氧气量不足，而产生大量之可燃性气体，充满整个室内空间。不久之后，由于门窗玻璃或其他处所之破裂或自外部开启开口，而形成空气之流通口。此时，若造成大量空气涌入时，将可能使充满室内之可燃性气体一举燃烧，火焰从窗口喷出，造成危险。此种现象一般称为复燃(Back Draft)现象。NFPA：参考官网内容( Reporter's Guide: All about fire )定义如下：Backdraft is an explosion that occurs when oxygen is introduced into a room full of hot gases.爆燃是一种爆炸现象，当氧气被引入充满高温可燃性气体的房间时会发生。A fire burning in a confined area consumes all the oxygen.密闭空间中所有氧气消耗完毕时会发生的一种燃烧形式。Visible flames disappear. Solid fuels smolder, and hot flammable gases accumulate and fill the room.明显可见的火焰消失，固体可燃物闷烧、高温可燃性烟气体蓄积并充满整间房间。The temperature increases, the gases expand, and pressure builds, pulsing against doors and windows. From outside, the building may look like it is breathing or throbbing.温度上升、可燃性气体扩散、压力蓄积，使门窗震动。从外部观察，建筑物看起来会像在呼吸或搏动。If an opening is made to admit oxygen, the hot vaporized fuel bursts into flames, and the pressurized gases explode through the opening, resulting in a rolling fireball.如果制造一个开口让氧气进入，高温可燃性气体会瞬间燃烧，有压力的气体会从开口处爆发出来，导致一个滚动的火球。

NFPA其他名词补充同样参考NFPA数据 (Technical Committee on Fundamentals of Fire Control within a Structure Utilizing Fire Dynamics 2018) ，可以发现轰然燃、爆燃、滚燃等火灾现象，NFPA统称为火势快速成长(Rapid Fire Development , RFD)Rapid Fire Development: A transient phase in fire behaviour accompanied by a rapid increase in heat release rate of the fire & temperature in the environment, sometimes accompanied by the generation of over‐pressure.火势快速发展：一种短暂的火灾特性，伴随着环境中热释率、温度的增加，有时也伴随着超压(很大的压力)的产生.These RFDs are subdivided into two main categories of phenomena: flashover and smoke ignition. Smoke ignition is then further subdivided into three separate developments: smoke explosion; backdraft; and flash fire (propagating flame fronts including rollovers) 。火势快速成长可分为两种现象：轰燃和可燃性烟气引火燃烧。可燃性烟气引火燃烧又可以在分为三种：可燃性烟气爆炸、爆燃、闪火(火焰前缘传播，包含滚燃)（见下图）。
根据上图，其实爆燃、滚燃都属于可燃性烟气引火燃烧的一种，而滚燃其实也只是燃烧波传播的一种方式。以下再针对可燃性烟气引火燃烧(Smoke Ignition)、可燃性气体爆炸(Smoke Explosion)、闪火(Flash Fire)做说明：Smoke Ignition: The ignition of the products of pyrolysis and incomplete combustion interior or exterior to the fire compartment due to the accumulated smoke layer falling within its flammability range and either auto-igniting or igniting due to an ignition source.可燃性烟气引火燃烧：起火处所内、外，烟层中的热裂解物质、未完全燃烧物质达到燃烧范围(或称爆炸范围)时，透过自然发火或被引火源引燃的一种燃烧现象Flash fires, where a flame moves through a flammable mixture with considerable speed, but does not develop a significant over-pressure.闪火：火焰快速地移动、通过可燃性气体混合物，但不产生明显的超压。Smoke Explosion: A rapid fire development that occurs when a smoke-air mixture falls within its flammable range, either external or internal to the room of origin and is ignited, resulting in a significant pressure front.可燃性烟气爆炸：起火处所内、外，可燃性气体与空气的混合物达到燃烧范围(或称爆炸范围)时，引火燃烧且产生压力波的一种火势快速成长现象。

Two manifestations of flame propagation that fall into this category:火焰传播的方式分为两种形式：Flash Fire和Rollover：Flash fires, where a flame moves through a flammable mixture with considerable speed, but does not develop a significant over-pressure.闪火（Flash fires）：火焰快速地移动、通过可燃性烟气混合物，但不产生明显的超压。滚燃（Rollovers）, where a flame front or pockets of smoke-air mixture ignite and move slowly through a mixture. Rollovers are also considered as an early and important indication of impending flashover滚燃：燃烧波或可燃性烟气与空气的混合物引火燃烧且缓慢移动。滚燃可以被视为轰燃发生前的重要征兆。由上面说明可知，闪火、滚燃都是火焰传播的方式。Flash fire的Flash可以想成是烟层中的可燃性烟气瞬间燃烧，火焰闪一下就没了、移动很快速。而Rollover可以想成是燃烧波持续往前移动，火焰沿着天花板水平扩散，就像海浪往前推移一样。

最后：
说实在的，要一次搞懂这么多种火灾现象确实不容易，而且虽然是不同的现象，但实际到火灾现场观察时会发现，火焰传播、可燃性烟气体燃烧的状况没有太多差别，而这也提高了消防人员在火灾现场辨识这些危险的难度。