The growth of a fire confined to a room is usually constrained by the ventilation-limited flow of air, smoke, and hot gases into and out of the enclosure. Confining variables may include the ceiling height, ventilation openings formed by windows and doors, room volume, and location of the fire in the room or compartment. While the fire gases are constrained, flashover may occur as a consequence of the heat release rate of the combustible materials contained within the room.

    局限在室內(nèi)的火災(zāi)，其發(fā)展通常受到有限空氣流動(dòng)、煙氣和進(jìn)出房間熱氣流的影響。限制變量包括：頂棚高度、門窗構(gòu)成的通風(fēng)開口、房間體積、房間或隔間內(nèi)的起火位置。如果火災(zāi)煙氣被限制在房間內(nèi)，就有可能因?yàn)槭覂?nèi)可燃物燃燒產(chǎn)生的熱釋放速率達(dá)到某個(gè)值而發(fā)生轟燃。

In the growth of a compartment (room) fire, flashover is defined by NFPA 921 (2017d) as the transition phase in the development of a compartment fire in which surfaces exposed to thermal radiation reach ignition temperature more or less simultaneously, and fire spreads rapidly throughout the space, resulting in full room involvement, or total involvement, of the compartment or enclosed space. This transition may occur in just a few seconds in small, heavily fueled rooms, or over a period of minutes in large rooms, or may not take place at all due to an insufficient heat release rate of the fire. A useful reference on this subject is NFPA 555: Guide on Methods for Evaluating Potential for Room Flashover (NFPA 2017d).

    在室內(nèi)火災(zāi)發(fā)展過程中，NFPA 921（2017版）將轟燃定義為在室內(nèi)火災(zāi)發(fā)展中，房間內(nèi)物體表面受到熱輻射作用，所有可燃物幾乎同時(shí)達(dá)到著火溫度，火勢(shì)快速蔓延至整個(gè)房間，造成整個(gè)房間發(fā)生燃燒或全面燃燒的過渡階段。這種過渡階段在體積小、可燃物多的房間里可能只需幾秒，對(duì)于較大房間，則需經(jīng)過幾分鐘，或者因?yàn)榛馂?zāi)的熱釋放速率過低，根本就不會(huì)發(fā)生。關(guān)于這個(gè)問題，《NFPA 555：室內(nèi)轟燃評(píng)估方法指南》（NFPA 2017版）中提供了參考。

Fire researchers have documented other observations during this transition phase. Defining observations often include one or more of the following criteria that address the effects of flashover: ignition of floor targets, high heat flux (>20 kW/m2) to the floor, and flame extension out of the compartment’s vents (Babrauskas, Peacock, and Reneke 2003; Milke and Mowrer 2001; Peacock et al. 1999).

    火災(zāi)調(diào)查員還記錄了在該過渡階段觀察到的其他現(xiàn)象。典型的現(xiàn)象包含下列一個(gè)或多個(gè)表征轟燃影響效果的標(biāo)準(zhǔn)：地面可燃物被引燃、地面接受到高的熱通量（＞20kW/m2），火焰從通風(fēng)開口處竄出。

The investigator may observe the following during flashover:

調(diào)查人員在轟燃過程中可能會(huì)觀察到以下現(xiàn)象：

Flames are emitted from openings in the compartment.

火焰從房間通風(fēng)口處竄出。

Upper-layer gas temperature rises to ≥ 600℃.

上層氣體溫度達(dá)到600℃及以上。

Heat flux at floor level reaches ≥ 20 kW/m2

地面受到的熱通量達(dá)到20kW/m2以上。

Oxygen level in upper portions of the room decreases to approximately 0 to 5 percent.

房間上部的氧氣含量下降到0~5%左右。

There is a small, short-term pressure rise of approximately 25 Pa (0.0036 psi).

存在短暫小幅度的壓力升高，約25Pa（0.0036psi）。

There are two fundamental definitions for the occurrence of flashover. The first looks at flashover as a thermal balance in which critical conditions are produced when the compartment exceeds its ability to lose heat. The second definition views the compartment as being in a mechanical fluid-filling process. In this approach, the point at which the compartment’s cool air layer is replaced with hot fire gases is flashover.

    對(duì)轟燃的發(fā)生有兩個(gè)基本定義。第一個(gè)是將轟燃視為熱平衡，當(dāng)房間內(nèi)部產(chǎn)生的熱量超過其散熱能力時(shí)，會(huì)達(dá)到轟燃發(fā)生的臨界條件。第二個(gè)定義是認(rèn)為房間處于流體充填的機(jī)械過程中，在這一定義中，室內(nèi)冷空氣被火災(zāi)熱煙氣取代的點(diǎn)就是轟燃的發(fā)生。

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.

    火災(zāi)調(diào)查員在滅火或可燃物燒盡后進(jìn)入現(xiàn)場時(shí)，應(yīng)該意識(shí)到是否發(fā)生轟燃以及轟燃對(duì)房間內(nèi)物品燃燒造成的影響的重要性。

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.

    房間發(fā)生轟燃后燃燒產(chǎn)生的許多痕跡，曾被人們認(rèn)為是只有汽油等易燃液體作為助燃劑實(shí)施放火時(shí)才會(huì)出現(xiàn)的。汽油蒸氣燃燒形成的火球有時(shí)會(huì)造成從地板到頂棚的整體性破壞。這種火災(zāi)持續(xù)時(shí)間較短，形成淺層燒灼。無論火災(zāi)是如何引發(fā)的，轟燃后的燃燒和汽油蒸氣燃燒的火球一樣，都會(huì)使地板到頂棚的墻體燒焦炭化。

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).

    過去曾認(rèn)為桌椅下方的火災(zāi)破壞是由地面易燃液體燃燒造成的，但事實(shí)上轟燃時(shí)被引燃的地毯和墊子的有焰燃燒也會(huì)造成這類破壞。高溫和整個(gè)房間參與燃燒，曾被認(rèn)為與使用易燃液體助燃劑有關(guān)，但事實(shí)上轟燃過程中即使沒有助燃劑參與也會(huì)產(chǎn)生這兩種現(xiàn)象。轟燃后所產(chǎn)生的極高熱通量，會(huì)于低熱通量條件下的木材炭化速率和其他物質(zhì)燃燒速率造成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).

    轟燃后的燃燒時(shí)間越長，火災(zāi)重建工作的難度就越大，因?yàn)檗Z燃后或全面發(fā)展階段的一個(gè)特征就是房間內(nèi)從地板到頂棚所有暴露的可燃物表面都被引燃著火。因此煙氣和火災(zāi)破壞形成的局部痕跡會(huì)被銷毀，而這些痕跡的存在能夠幫助調(diào)查人員認(rèn)定可燃物位置、確定火焰高度以及判斷火勢(shì)蔓延方向。在某些較大房間里，有時(shí)會(huì)出現(xiàn)逐步發(fā)展的轟燃——房間一端從地板到頂棚全部發(fā)生燃燒，而另一端的地板卻保持完好。短時(shí)間（15min以下）暴露于轟燃后的火災(zāi)，墻壁上的火災(zāi)痕跡并不一定會(huì)被破壞（見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.

    在轟燃前的火災(zāi)中，熱破壞最嚴(yán)重的位置位于燃燒可燃物周圍或正上方。熱煙氣層溫度越高，對(duì)房間上部二分之一或三分之一部分造成的熱破壞就越為嚴(yán)重。轟燃發(fā)生后，所有可燃物參與燃燒，火災(zāi)變?yōu)橥L(fēng)控制型，效率最高的燃燒（溫度最高）發(fā)生在通風(fēng)口附近的湍流混合區(qū)，此處氧氣供應(yīng)最為充足。許多轟燃后的室內(nèi)火災(zāi)，可燃物超過空氣的供應(yīng)量，進(jìn)而發(fā)生缺氧燃燒。

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).

    通過詢問第一個(gè)進(jìn)入現(xiàn)場的消防員，可以了解進(jìn)入房間時(shí)，是否發(fā)生了從地板到頂棚的全室性燃燒。調(diào)查人員必須熟知轟燃發(fā)生的條件，并且能夠辨認(rèn)是否發(fā)生過轟燃。全面理解現(xiàn)代家具火災(zāi)蔓延、熱釋放速率以及轟燃動(dòng)力學(xué)的特征，對(duì)于火災(zāi)調(diào)查工作大有幫助（Babrauskas 和Peacock 1992）。