追溯火灾的发展过程

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时间 2020-04-14 12:04:54

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《柯克火灾调查（Kirk’s Fire Investigation）》是美国最早的火灾调查专业书籍，第1版于1969年出版，原名为《火灾调查（Fire Investigation）》，由加利福尼大学伯克利分校Dr.Paul L.Kirk教授编写，旨在推动用科学原理解决火灾和爆炸调查中遇到的问题，同时他为全世界培养了一大批的调查专家。但1970年Kirk教授不幸去世，为了纪念他对于火灾调查做出的突出贡献，缅怀他科学严谨的火灾调查精神，将之后版本的《Fire Investigation》更名为《Kirk’s Fire Investigation》，此书已成为世界范围内最具影响力的火灾调查专业书籍。《Kirk’s Fire Investigation》也是最早引入我国的火灾调查外文专业书籍，由武警学院（现中国人民警察大学）陈爱平、徐晓楠、刘义祥、杨迎、华菲等多位专家老师进行了第五版的翻译，此书的引入让我们更深入地了解了美国火灾调查技术和发展现状。随着科学技术的发展，美国调查方法的改进，《Kirk’s Fire Investigation》的内容已经有了较大的更新替换，现已更新至第8版，于2018年出版发行。课题组在阅读最新版的《Kirk’s Fire Investigation》时，发现7.1.5 Tracing the course of the fire（追溯火灾的发展过程）一节讲述鞭辟入里、易学易用，于是专门拿出来先行翻译，与各位专家同仁共享，如有不足之处请批评指正！

“您的批评意见，是我们做好此项工作最大的动力！”

图1 最新版《Kirk’s Fire Investigation》封面

图2 最新版《Kirk’s Fire Investigation》作者简介

中国人民警察大学火灾物证鉴定中心

西安科技大学火灾物证鉴定中心

2020年2月

7.1.5 Tracing the Course of the Fire

7.1.5 追溯火灾的发展过程

Fire scenes are nearly always cold and badly burned. Thus, the investigator must reconstruct the sequence of the fire backward from what is visible afterward to its point of origin. With few exceptions, fires, however large, start with a small flame, such as a match, candle, or lighter, or a spark of some type. The investigator must determine the point and source of ignition in order to determine the cause of the fire. The primary exceptions are fires where the first fuel ignited is a flammable gas or vapor. The following are key principles of fire behavior:

火灾现场往往是沉默的，而且被严重烧毁。因此，调查人员只能从当前现场还原火灾发展过程，找到起火位置。除了个别例外情况，无论多大的火灾，都是从小火苗发展而来的，如：火柴、蜡烛、打火机或某种类型的火花。调查人员通常要确定引火源的部位和种类，从而认定起火原因。但是最初可燃物为易燃气体或蒸汽的火灾是例外情况。

以下是火灾行为分析的主要原理:

1.Hot gases (including flames) are much lighter than the surrounding air and therefore rise. In the absence of strong winds or physical barriers like ceilings that force hot gases to travel elsewhere, smoke and hot gases will always move upward.

1.热烟气（包括火焰在内）比周围空气要轻的多，因此要上升。在没有强风或天花板等障碍物改变其流动路线的情况下，烟气和高温气体总是向上流动。

2.Due to heat transfer processes in the buoyant flame plume, fire will move upward more rapidly than horizontally or downward with some downward progression as a result of radiant heat and fall-down.

2.由于通过上升的火羽流进行传热，火灾向上蔓延的速度比水平或向下蔓延的速度快。有时因为热辐射和掉落物的因素，火焰可能会向下蔓延。

3.Combustible materials in the path of the flames will be ignited, thereby increasing the extent and intensity of the fire. The more intense (higher heat release rate) the fire, the faster it will rise and spread.

3.火灾能引燃其蔓延路径中的可燃物，从而增大火灾作用范围和强度。火灾强度越大（热释放速率越高），火势增长和蔓延速度越快。

4.If there is not more fuel above or beside the initial flame to be ignited by convected or radiated heat, or if the initial fire is too small to create the necessary heat flux on those fuels, the fire will be self-limiting and often will burn itself out. A flame plume that is large enough to reach the ceiling of a compartment is likely to trigger full involvement of a room, for it is charging the upper gas layer in the room with gases that have not cooled by mixing or radiative losses as much as gases in a shorter plume. As a result, the hot gas layer maintains a higher temperature and is more likely to reach its critical temperature (~600°C or 1,150°F in a typical room), which then induces flashover or full-room involvement.

4.如果初始火焰周围没有过多可燃物，无法通过对流或辐射方式引燃，或者是初始火焰太小，无法产生引燃可燃物的足够热量，那么火焰只能限于局部，往往会自行熄灭。火羽流足够大时，到达房间的天花板，可能引发房间的全面燃烧，因为这种情况下，火源处产生的烟气及其周围的小羽流将源源不断进入室内上方的烟气层，从而补充顶部热烟气层因为与空气混合或向外辐射热量产生的热量损失。顶部热烟气层温度将会越来越高，并有可能达到临界温度（标准房间约为600℃或1150℉），从而引发室内轰燃或全面燃烧。

5.The fuel load of the room or structure has a significant impact on the development of a fire. The fuel load includes not only the structure itself but also the furnishings and contents, and the wall, floor, and ceiling coverings that feed a fire and offer it paths and directions with optimum fuel conditions. In evaluating a fire’s progress through a room or structure, the investigator must establish what fuels were present and where they were located. The chemical nature of the fuels and their physical forms will affect their ignitability and their expected heat release rate. In the reconstruction of a fire, the fuel load is not just the total number of joules or Btu’s of heat that can be generated but the rate at which that heat is released.

5.房间或建筑的火灾荷载对火灾发展有重要影响。火灾荷载不仅来自建筑本体，还来自建筑内部的家具和物品，以及墙壁、地板和天花板上的覆盖物等可燃物。并且，建筑本体的可燃物还将为火灾蔓延提供途径和方向。调查人员在分析室内火灾的蔓延过程时，必须查清室内存放的可燃物以及可燃物的位置。可燃物的化学性质及其物理状态能影响其可燃性能，以及可预计的热释放速率。在火场重建过程中，火灾荷载不仅包括可燃物燃烧所释放的总的焦耳或Btu值，还包括其热释放速率。

6.Variations on the upward spread of fire or smoke will occur when air currents deflect the flame, when horizontal surfaces block the vertical travel, or when radiation from established flames ignites nearby surfaces. If fuel is present in these new areas, it will ignite and spread the flames laterally.

6.空气气流使火焰发生的偏转、遇水平面阻碍（烟气）垂直向上传播以及火焰的辐射热引燃附近物质表面，都可能造成火灾或烟气向上蔓延趋势的变化。如果火势蔓延到的新区域存在可燃物，随后将引燃可燃物并造成火势进一步蔓延。

7.Upward, vertical spread is enhanced when the fire finds chimneylike configurations. Stairways, elevators, utility shafts, air ducts, and interiors of walls and hollow support columns offer openings for carrying flames generated elsewhere, and fires may burn more intensely because of the enhanced draft.

7.当火势遇到类似烟囱的结构时，垂直向上蔓延将会增强。楼梯、电梯、公共竖井、通风管道、墙壁内部和空心支柱都能为火焰提供开口。因为通风效果得到了强化，火势发展将更加猛烈。

8.Downward spread will occur whenever there is suitable fuel in the area. Fire will burn downward across a solid fuel but at a rate that is a tiny fraction of its upward spread rate. Combustible wall coverings, particularly paneling, encourage the travel of fire downward as well as outward. Burning portions of ceiling and roof coverings, draperies, and lighting fixtures can fall onto ignitable fuels below and start new fires called fall-down or drop-down fires that quickly join the main fire overhead. Radiation from rollover fires or very hot gas layers can ignite floor coverings, furniture, and walls even at some distance, creating new areas of fire. The resulting fire patterns can be complex to interpret, and, once again, the investigator must remember to take into account what fuel packages were present from the standpoint of their potential heat release rate contributions.

8.只要有适合的可燃物，火势就会向下蔓延。火焰将沿着固体可燃物向下蔓延，但是速度要比向上蔓延慢得多。可燃的墙面覆盖物，尤其板面装饰，将会使火势向下或向外蔓延。天花板和顶棚覆盖物、窗帘和灯具的燃烧部分可能滴落至下方可燃物，造成新的火灾燃烧区域，称为坠落或滴落（drop-down）火灾。新的起火区域将快速地连接到上方主体燃烧区域。滚燃或高温烟气层产生的热辐射也可以引燃一定距离内的地面覆盖物、家具和墙壁，并产生新的火灾燃烧区域。由此产生的火灾痕迹可能很难解释，一旦遇到，调查人员必须记住，要从其潜在热释放速率的出发，分析存在什么可燃物。

9.Suppression efforts can enhance fire spread. Positive-pressure ventilation (PPV) or an active hose stream attack on one face of a fire may force it back into other areas that may or may not have already been involved, and push fire down, even under obstructions such as doors or cabinets. The investigator must remember those unusual conditions and check with the firefighters present.

9.灭火行动可能加速火灾蔓延。正压送风排烟（PPV）或对火头展开的主动射流进攻，可能使火头退回并发展至其他区域（可能是未过火区域），并且造成火势向下的蔓延，甚至蔓延至门、柜等障碍物的下部。调查人员必须记录下这些反常的情况，并向当时灭火的消防员进行核实。

10.Fire tends to flow through a room or structure much like a liquid—upward in relatively straight paths and outward and around barriers.

10.火灾非常类似于流体，倾向于穿过房间或建筑进行流动，可以沿着笔直的通道向上流动，也可以绕过障碍物向外流动。

11.Ventilation from open doors, windows, or vents, or forced by heating, ventilating, and air conditioning (HVAC) systems or PPV fans can affect fire growth and movement as much as fuel arrangement. All ventilation must be documented.

11.就像可燃物的分布会对火灾发展蔓延造成影响一样，敞开的门、窗或通风开口的自然通风，以及热量、通风、空调系统（HVAC）或正压送风排烟（PPV）的强制通风，都可能对火灾的发展和蔓延造成影响。应该对所有的通风情况进行记录。

12.The hot gas layer in a room can reach its critical intensity (producing a heat flux of >20 kW/m2) if the fire is large enough to overcome the leaks of hot gases due to openings or due to radiant and conductive losses. As seen in the 1985 Bradford (UK) football stadium fire, even a compartment that is open on three sides can develop flashover conditions when the fire gets big enough.

12.如果室内火势足够大，热烟气产生量高于开口溢出量，热量高于热辐射和热对流损失量，热烟气层可以达到其临界强度（产生的辐射热流量＞20kW/m2）。正如1985年Bradford足球场火灾（英国）所见，当火灾变得足够大时，甚至一个三面开口的房间都会发生轰燃。

13.Fire intensity in a post-flashover room is often greatest around ventilation sources. Thus, damage occurs more quickly around door sills, windows, or other openings where fresh air can be drawn into the room and can even reach walls opposite the opening.

13.在发生轰燃的房间，通风口附近火灾强度往往最大。因此，在门框、窗户或其他开口处，新鲜空气可以进入房间、甚至能够到达开口对面墙壁，这些区域呈现的火灾破坏往往是快速并且严重的破坏。

14.The total firedamage to an object is the result of both the intensity of heat applied to thatobject and the duration of the exposure (with the realization that intensity ofheat varies considerably during a fire and that all the exposure may not have occurredat the same time).

14.火灾对物体的整体破坏，既是热量强度作用于物体的结果，也是作用持续时间的结果(应认识到，在火灾中热作用强度将会发生较大变化，所有的热作用时间可能也不会同时发生)。