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1、Chapter2Chapter2 What is Fire Risk What is Fire Risk AssessmentAssessmentChapter2Chapter2 火灾风险评估的基本概念火灾风险评估的基本概念本章引入火灾风险评估的基本概念火灾风险评估fire risk assessment指对火灾人们所不希望发生的这类事故的后果，带给人员和财产的风险的评估。2.1 2.1 综述综述Basic concepts of fire risk assessment will be introduced in this chapter.The term fire risk assessm
2、ent refers to assessing risks to both people and property as a consequence of unwanted fires.2.1 overview2.1 overviewIn a simple risk assessment the probability of a certain unwanted fire scenario is considered and the consequence of that scenario are explored.In a comprehensive risk assessment all
3、probable unwanted fire scenarios and their consequences are considered.在简单的火灾风险评估过程中，仅对某些或某类火灾场景发生的可能性和结果进行分析和评估；在全面或综合的火灾风险评估过程中，对所有的可能火灾场景发生的可能性或结果进行分析和评估。一个火灾场景(fire scenario)由一系列的火灾中的事件组成，这些火灾事件是推测可能在火灾过程中发生的事件，将某些防、灭火技术或管理措施的成功或失效/失败的过程连缀起来，就能够形成一个火灾场景。因此一个火灾场景发生的可能性(probability)决定于这一系列事件中每一个防、
4、灭火技术或管理措施的成功或失效/失败的可能性。A fire scenario involves the projection of a set of fire events,all of which are linked together by whether the fire protection measures succeed or fail.The probability of a fire scenario is dependent on the individual probabilities of success or failure of fire protection mea
5、sures.对人员的风险(risk)既决定于能够对人员产生损害(harm)的火灾场景发生的可能性，又决定于火灾场景或者说火灾场景产生的后果(consequence)对人员造成损害的程度或水平(level of harm)。通常应用火势增长、烟气传播、人员疏散、建筑结构响应和消防人员灭火效能等模型来对火灾场景的结果进行计算和模拟。这部分内容不是本课程的授课内容，将在建筑防火性能化设计课程中讲述；而在了解火灾各个过程和阶段基本特征的基础上，建立相应火灾场景，分析火灾场景发生的可能性，是本课程的主要内容。The risk to the occupants depends not only on th
6、e probability of the fire scenario that can lead to harm to the occupants,but also the level of harm to the occupants as a result of the consequence of that scenario.The consequence of a fire scenario can be assessed by using time-dependent modeling of fire and smoke spread,occupant evacuation and f
7、ire department response.2.2 What is Fire Risk Assessment?2.2 What is Fire Risk Assessment?前面讲过，火灾风险评估是指对火灾人们所不希望发生的这类事故的后果，带给人员和财产的风险(risk)的评估。它所应用到的基本原理与其他领域风险评估的原理是一致的。2.2 2.2 火灾风险评估火灾风险评估(Fire Risk Assessment)(Fire Risk Assessment)的基本概的基本概念念Fire risk assessment is the assessment of the risks to t
8、he people and property as a result of unwanted fires.It employs the same basic principles of risk assessment that are used in many other fields.A simple risk assessment considers the probability of the occurrence of a certain unwanted fire scenario and the consequence of that scenario.A comprehensiv
9、e risk assessment considers all probable unwanted fire scenarios and their consequences.The definition of fire scenario will be discussed in the next section.It involves the linking of anticipated fire events by the success or failure of certain fire protection measures.例如，评估建筑中的某一个火灾场景的后果对人生命造成的风险，
10、这个预计的生命风险可由(2.1)式来表达：式中P是这个特定的火灾场景发生的可能性(频次或概率，rate或probability);C 是这个特定火灾场景造成后果预计导致的死亡人数。(2.1)Consider,as an example,the assessment of the expected risk to life to the occupants in a building as a result of one single fire scenario.The expected risk to life can be expressed by the following equatio
11、n:where P is the probability of a certain fire scenario and C is the expected number of deaths as a consequence of that fire scenario.(2.1)If the probability of a certain fire scenario occurring in a building is once every 20 years,then P=0.05 fires per year.If the consequence of that fire scenario
12、is two deaths,then C=2 deaths per fire.From Equation 2.1,the expected risk to life as a result of that fire scenario is equal to 0.1 deaths per year,or 1 death every 10 years.比如建筑中某一火灾场景发生的可能是年一次，则：P=0.05 fires per year如果这个火灾场景的后果是死亡人，则C=2 deaths per fire从式(2.1)可知，这个火灾场景的预计生命风险为the expected risk to
13、life 0.1 deaths per year或都 1 death every 10 years.每年0.1人死亡或每10年死亡人。当然在建筑中发生火灾的方式不止一种，那么对人员的风险通常要基于所有可能的火灾场景来进行评估。那么一个全面的（comprehensive fire risk assessment）风险可由(2.2)式来表达：式中的代表了对所有可能的火灾场景进行求和。Pi 是某一个火灾场景 i 发生的可能性;Ci火灾场景 i 的后果造成的预计死亡人数。(2.2)Because fires can occur in a building in more ways than one,t
14、he risk to the occupants is usually assessed based on all probable fire scenarios.A comprehensive fire risk assessment can be expressed by the following equation:(2.2)要注意的是，火灾风险评估不仅包括对人员生命风险的评估，还可能包括对财产损失、对经营或生产的影响等造成损失的评估。此时方程(2.1)和方程(2.2)中的后果也相应地更换为财产损失的后果。It should be noted that fire risk assessm
15、ents involve more than the assessment of the risk to life.It involves also the assessment of the loss of property,loss of business and so on,as a result of fires.Equations similar to Equation 2.1 and 2.2 can also be expressed for the other losses.2.2.1 Fire Scenarios2.2.1 Fire ScenariosA fire scenar
16、io is a sequential set of fire events that are linked together by the success or failure of certain fire protection measures.A fire event is an occurrence that is related to fire initiation,or fire growth,or smoke spread,or occupant evacuation,or fire department response.2.2.1 2.2.1 火灾场景火灾场景-Fire Sc
17、enarios-Fire Scenarios一个火灾场景由一系列火灾中连续发生的事件组成，通过把某些特定的防、灭火技术或管理措施成功或失败/失效的结果连缀起来而得到。火灾中的一个事件A fire event 是火灾中发生的，与起火、火灾增长、烟气传播、建筑物结构响应、人员疏散或消防人员响应相关的事件，如果不是在火灾中发生的，或与火灾的上述过程无关的事件，则不视为火灾中的一个事件。比如，火灾中发生的声、光报警是一个火灾事件；火灾中发生的断电或停水也是火灾不同的两个事件；而没有发生火灾时的停水，就不是一个火灾事件了。For example,a fire event can be:a fire de
18、velops into a post-flashover fire,or the occupants can not evacuate quickly enough and are trapped in the building,or the fire department responds in time and rescues the trapped occupants.A fire protection measure is a measure that can be a fire protection system,such as sprinklers and alarms;or a
19、fire protection action,such as occupant evacuation training and drills.防、灭火技术或管理措施包括消防装置，比如自动喷水灭火系统、火灾探测、报警系统、防排烟系统等；还包括人员应急响应的演练，如处置火情，报警、扑灭初期火灾的训练和疏散演练等。A simple example of a fire scenario is the following set of events that are linked together by the failure of fire protection measures:Another si
20、mple example is the following set of events that are linked together by the success of fire protection measures:a fire does not develop into a post-flashover fire,the alarm system activates,and the occupants receive the warning signals and evacuate the building.火灾场景的简单例子：(1)火灾发生了轰燃报警系统没有启动人员没有接收到报警信
21、号人员被因于火场中。(2)没有发生轰燃报警系统启动成功人员及时接收到报警信号人员成功疏散。In real-world fires,fire scenarios are much more complex and the possible number of fire scenarios can be many.The number of fire scenarios depends on the number of permutations that can be constructed based on all the fire protection measures that are in
22、 place and all the fire events that are anticipated.The proper construction of fire scenarios and the proper analysis of the consequence of the fire scenarios,however,are the key to a credible fire risk assessment.就真实的火灾而言，火灾情况要复杂得多，因此可能的火灾场景数量也会有很多。火灾场景的数量决定于火场中防灭火技术和管理措施的数量和预计的火灾事件的数量。合理构建火灾场景并分析其
23、发生的可能性，对所建立的火灾场景后果的尽量符合实际的分析、计算或模拟，是决定火灾风险评估结果可信度的关键。前者是本课程所要达到的主要目的；而后者将重点在建筑防火性能化设计课程中探讨。The general principle of how fire scenarios can be constructed will be discussed in the next section.But before we discuss how they can be constructed,take the simple case where there is no fire protection mea
24、sure at all.Take,for example,the case where a fire occurs at the only exit door in a room with a number of people inside the room.在后续的部分中，我们将阐述构建火灾场景的基本方法。在此之前，我们要讨论一个极端的情况：没有任何防、灭火技术和管理措施的情况。比如，我们以一个发生在房间唯一安全出口处的火灾为例，发生火灾的房间中有一定数量的人员。With no fire protection in the room to control the fire,the fire
25、develops into a post-flashover fire and subsequently kills all the people in the room.The risk of this simple fire scenario is the probability of a fire occurring at the only exit door of a room,multiplied by the number of people killed by this fire.Obviously,fire risk assessment is not as simple as
26、 this.在房间中没有任何控制火势增长的措施的情况下-轰燃迅速发生-火灾进入全盛期-房间内所有人员死于火灾。这个比较简单而极端的火灾场景，火灾的风险等于火灾发生于此房间唯一安全出口处的可能性与死于火灾中人员数量的乘积。当然，一般火灾风险的评估，情况都要比这个例子复杂得多。通常建筑内有控制火灾增长或迅速传播的措施，为人员和财产提供了保护，延缓了火灾的传播，如灭火系统或烟气阻隔措施；通常还有火灾早期探测和报警的措施，帮助人们在火势扩大前及时疏散到安全的区域；通常消防人员也可能较早地接收到火警，能够及时赶赴火场并展开灭火和人员施救。There are normally fire protectio
27、n measures in place to protect the occupants and property.For example,there are normally fire protection measures in place to control the development of a fire and also to prevent the fire from spreading to other parts of a building.There are also normally fire protection measures in place to provid
28、e early warnings to the people and to help the people to get to a safe place before the fire spreads.There are also expectations that the fire department is notified and that they will come to extinguish the fire and rescue the people.Hence,fire risk assessment involves the use of fire scenarios tha
29、t are based on the success and failure of these fire protection measures in order to assess the expected risks to the occupants and the property.因此，火灾风险评估中的火灾场景必须包含和考虑到这些防灭火技术和管理措施，考虑它们成功启动、发挥其效能的程度，或失败/失效的可能性，这样才能对人员和财产所面临的预期风险进行估计或计算。A set of fire scenarios can be constructed based on the well-kno
30、wn event-tree concept,where events are linked together like the branches of a tree(Custer and Meacham,1997).应用广为所知的事件树方法 event-tree concept，能够构建一系列的火灾场景；在这种方法中，火灾中的事件被连缀起来，形成树状。(Custer and Meacham,1997).Figure 2.1 A simple event tree where an initiating Figure 2.1 A simple event tree where an initia
31、ting event can lead to different events depending on event can lead to different events depending on the success and failure of fire protection the success and failure of fire protection measures at the branch points.measures at the branch points.Figure 2.1 Figure 2.1 一个简单的事件树一个简单的事件树Figure 2.1 show
32、s a simple event tree where an initiating event can lead to different events depending on the success or failure of the fire protection measures at the branch points.For example,Event A terminates in Event C if the fire protection measure for that event succeeds,whereas Event A continues with Event
33、B to others if the fire protection measure fails.由图2.1可件，在分支点上，事件的成功或失败，即某一防、灭火技术或管理措施的成功与否，将使得初始事件产生不同的结果。比如，事件（应用灭火器灭火）成功，则接下来到事件C（燃烧熄灭，火灾终结）结束；而如果事件（应用灭火器灭火）失败，则接下来继续到事件B（应用消火栓灭火）。如此，将建立起一系列的火灾场景。A particular set of events that are linked together forms one fire scenario.For example,the set of Ev
34、ent A and Event C forms one scenario.A set of all possible combinations of the linked events forms a complete set of all possible fire scenarios.For example,the combinations of AC,ABD and ABE form a complete set of three fire scenarios.一系列的火灾事件连缀起来，则能够形成一个火灾场景。例如，事件A-C构成一个火灾场景。而事件AC,ABD 和 ABE 形成了此事件
35、树全部的火灾场景，共有三个。场景：A-C场景2：ABD场景3：ABEFigure 2.1 also shows the probability of success or failure of these two fire protection measures at the two branch points.The probabilities of failure at the two branch points are assumed,for this example,to be the same,at 10%or 0.1.在图2.1的分支上，还给出这两个防、灭火技术措施成功和失败的概率
36、，在此例中，假定这两个措施成功的概率均为90%，失败的概率为10%。基于此，场景AC 发生的可能性为0.9.场景ABE 发生的可能性为0.09,由AB(0.1)的可能性与BE(0.9)的可能性相乘得到.类似地，场景ABD发生的可能性0.01.三个场景发生的联合概率为(combined probability)为1。注：因为三个不同的火灾场景之间是互斥的。Mutually exclusive eventsMutually exclusive eventsBased on this,Scenario AC has a probability of 0.9.Scenario ABE has a pr
37、obability of 0.09,obtained by multiplying the probability of AB(0.1)and that of BE(0.9).Similarly,Scenario ABD has a probability of 0.01.The combined probability of all three fire scenarios is one.The important thing to note here is that the probabilities of success or failure of fire protection mea
38、sures affect the probabilities of all fire scenarios.The lower the probabilities of failure of fire protection measures,the lower the probabilities of all those fire scenarios that will lead to an undesirable outcome.这里有一点比较重要，需引起我们的注意。显然，某一防灭火技术或管理措施成功或失败的可能性可能影响到所有或全部火灾场景发生的可能性。某一防灭火技术或管理措施失败的可能性越
39、低，则那些导致不希望发生后果的火灾场景发生的可能性就越低。For example,if Event D is not the desired end point,then lower probabilities of failure of fire protection measures will lead to a lower probability of the undesirable fire Scenario ABD.If the probabilities of failure of the two fire protection measures are reduced to 0.
40、01,the probability of the undesirable Scenario ABD is reduced to 0.0001.2.2.2 2.2.2 将将防、灭火技术或管理措施视为“火灾阻碍措施”在建筑火灾风险评估的过程中，可基于以下五个重要事件来构建事件树：.起火fire ignition,2.火势增长fire growth,3.烟气传播smoke spread,4.人员疏散失败failure of occupants to evacuate,5-消防人员响应失败failure of fire department to respond(Yung and Benichou,
41、2003).将它们视为重要事件是因为每个事件都与火灾发展的主要阶段或危害有关。2.2.2 Fire Protection Measures as Fire Barriers2.2.2 Fire Protection Measures as Fire BarriersFor fire risk assessments in buildings,the event tree can be constructed based on the following five major fire events.They are considered major events because each is
42、 related to a major phase of fire development and hazard:fire ignition,fire growth,smoke spread,failure of occupants to evacuate,and failure of fire department to respond(Yung and Benichou,2003).1.起火是初始事件，比如烟蒂引燃卧室床上物品或引燃起居室的沙发。防、灭火技术或管理措施包括防火教育、控制火源、使用阻燃材料等，这些都将降低起火的可能性和相应的风险。1.Fire ignition is the
43、initiating event,such as cigarette ignition of a couch in a living room or a mattress in a bedroom.Fire protection measures include fire prevention education,or the use of fire-retarded material in furniture,which would help to reduce the probability of occurrence of this event and the consequential
44、 risks.2.火势增长是第二个重要事件，这个过程包括多种火势增长类型，比如阴燃火灾(smouldering fires)或轰燃后的全盛期火灾(post-flashover fires)。防、灭火技术或管理措施包括喷水系统、防火分隔和带有自闭器的门，这些措施能够控制或限制火势并降低其相应的风险。风险降低的程度决定于这些火势增长控制措施的可靠性和有效性(reliability and effectiveness)。2.Fire growth is the second event,which includes various types of fire growths,from fires d
45、eveloping into smouldering fires to fires developing into post-flashover fires.Fire protection measures include sprinklers,compartmentation and door self-closers,which would help to contain these fires and reduce their consequential risks.The reduction in risk depends on the reliability and effectiv
46、eness of these fire control systems.3.Smoke spread to critical egress routes and other locations in a building is the third event.Fire protection measures include door self-closers,smoke control,and stairwell pressurization,which would help to contain the smoke and reduce its consequential risks.The
47、 reduction in risk depends on the reliability and effectiveness of these smoke control systems.3.烟气传播到疏散必经的路径上或传播到建筑内某些位置上，是第三个重要的事件。防、灭火技术或管理措施包括带有自闭器的门、防排烟系统和疏散楼梯间/前室的加压送风系统等，这些措施有助于将火灾产生的烟气限制在一定空间内或排出到建筑外，从而降低其相应的风险。风险降低的程度决定于这些控烟措施或系统的可靠性和有效性(reliability and effectiveness)。4.人员疏散失败是第四个重要事件，它通常是火
48、或烟气传播到疏散路径上的结果。防、灭火技术或管理措施包括感烟、感温等火灾报警器、语音通讯设备、被保护的疏散通道、避难区或避难层、应急响应教育和疏散演练，这些措施能够向人员提供火灾的早期报警，安全的疏散通道，快速的应急响应和迅速的疏散，疏散到暂时安全的避难区域或疏散到着火建筑外。风险降低的程度决定于早期报警系统和疏散通道保护系统的可靠性和有效性，常规的人员应急响应教育和疏散演练的实施贯彻情况。4.Failure of occupants to evacuate as a result of the spread of fire and smoke to egress routes is the
49、fourth event.Fire protection measures include smoke alarms,voice communication,protected egress routes,refuge areas,and evacuation training and drills,which would help to provide early warnings to occupants,safe egress routes,quick occupant response and evacuation to either exit the building or to s
50、eek temporary protection in refuge areas.The reduction in risk depends on the reliability and effectiveness of these early warning and evacuation systems and the implementation of regular occupant training and evacuation drills.5.消防人员响应失败为第五个重要事件，即消防人员没能及时响应，赶至火场解救被困人员和实施灭火。防、灭火技术或管理措施包括向消防部门的火灾早期报警