Presentation on theme: "Chapter 7 Compartment Fire"— Presentation transcript:
1 Chapter 7 Compartment Fire Lesson 1Development of Compartment FireGood afternoon everyone!In the previous chapters of this book, we have learned some fundamental theories of fire, including the combustion of gases, combustion of liquids and combustion of solids. Those fundamentals are basic and important. However, they only concern about combustion of one thing.But you know in the real fire, usually different kinds of combustible materials will be involved.Look around us in our classroom, here we have wooden desks and chairs, fabric curtain and screen屏幕, as well as plastic computer. All of them are combustible. So if a real room like this were on fire, the situation would be much different from those we have learned in the previous chapters.Then what would happen?That’s we are going to learn in Chapter 7, compartment fire.And today we are going to learn the first part of it: development of compartment fire.
2 Key Words & Phrases Compartment fire 室内火灾 Flashover 轰燃 Pre-flashover 轰燃前post-flashover 轰燃后Flammable (Flame) 可燃的Combustible (combustion) 可燃的Smoulder 阴燃、无焰燃烧Smouldering fire 无焰燃烧Flaming fire 有焰燃烧First, let’s see some vocabulary.The first one is compartment fire, it means fires that take place in compartments. 汉语，中将其称之为 室内火灾The second one, flashover, flashover is a special phenomenon that usually take place in compartment fire. 汉语，将此现象称之为 轰然And we will explain what is flashover in detail later in ourThe third one is pre-flashover. The prefix pre- means ‘before’, so the pre-flashover means things that happen before flashover.Then it would be easy for you to get the meaning of the post-flashover. It means things that happen after flashover.Then next one flammable. Flammable is the adjective of flame. Flame 是火焰，那flammable 是可以发出火焰的，也就是可燃的The next one combustible. Combustible is the adjective of combustion. Combustion 是燃烧的意思，那combustible 也就是可燃的意思，它与flammable 是同义词Heat 热 flux 流量通量的意思 所以 heat flux 热通量是我们在第二章学过的，它表示的是在单位时间内通过单位面积的热量。This is the vocabulary.In today’s lesson we are going to learn about compartment fire.
3 Key Words & Phrases Ventilate (ventilation) 通风 Ventilation Factor 通风因子 Opening Factor 开口因子These two factors are very important in the study of compartment fire.
4 1.Definition of compartment fire A compartment fire (室内火灾) means a fire that takes place in a compartment.A compartment is an enclosure with walls, roof and openings (such as windows and doors).In today’s lesson we are going to learn about compartment fire.So first of all, we have to know what’s is a compartment fire.To make it easier to understand, a compartment fire means a fire that takes place in a compartment.Then what is a compartment?So a classroom like this one, it has walls, ceiling, windows and doors. And you know my office and your dormitory are compartments too.Then Besides these rooms in buildings, can you find anything else which are compartments?Think about it? Something has walls, ceiling and openings.Yes, you are right.A bus, a car, a ship or train compartment.Let’s see some examples.船舱火车厢Fires happen in a room, a bus, a car, a ship or train compartment, etc. are all compartment fires.
5 I think all of you must be very familiar with these pictures I think all of you must be very familiar with these pictures. It was the 911 terrorist attack on the twin towers in NY.It’s big tragedy. Maybe some of you know that in this tragedy, due to the collapse of the two buildings, nearly 3000 people lost their lives, and among them there were 343 firefighters.So the collapse was very disastrous.Then is there anyone of you knows what was the cause of the collapse of the two buildings.Was the collapse of the two buildings caused by the crash of the planes or explosion of the planes?No, none of them. Then what was the cause of the collapse?It’s the fire after explosion, a very typical compartment fire that led to the eventual collapse of the highest buildings in the world.It’s terrible. Then let’s see two other building fire examples.After the 767 jet liner crashed into the world trade center building creating the worst terror attack in history, a fire burned for 56 minutes inside the World Trade Center building number two. The top 20 floors of the building collapsed on the 90 floors below. The entire one hundred and ten-story building collapsed in 8 seconds... After a fire burned inside WTC tower number one for 102 minutes, the top 30 floors collapsed on the lower 80 floors. And the entire one hundred and ten stories of this building collapsed in 10 seconds. You can say the reason they collapsed was they were struck with a 185 ton jet airliner and the 24,000 gallons of jet fuel caused a fire of 1500 to 2000 degrees F which weakened the steel and cause the collapse. Of or relating to a temperature scale that registers the freezing point of water as 32=F and the boiling point as 212=F at one atmosphere of pressure.The buildings survived the impact of a plane and the consequent explosion, but failed under fire.The high temperature fires from burning aviation fuel and plane debris softened the steel core of the structure. Eventually, the loss of strength and stiffness of the materials resulting from the fire combined with the initial impact have caused the collapse of the towers.WTC 911
6 The big Garley building fire ,1996, Hongkong Airport terminal fire, During welding work in an elevator shaft in the 16-storey Garley Building in Hong Kong district on 21st November 1996, a fire broke out which killed 39 people and seriously injured around 80 others. More than 90 people were rescued, some of them in daring scenes in which a helicopter pilot risked his own life.Maintenance and repair work was in progress in the office and business tower when highly flammable material caught fire during welding work in the basement. The fire made its way up through the elevator shafts and spread like lightning through the top three floors of the building. The immense heat and smoke made these floors a death trap for the people working there: the windows could not be opened to let the heat and smoke out, and escape routes were filled with smoke or impassable on account of the fire. As a result, 22 charred bodies were subsequently found in a single office on the 15th floor.Duesseldorf, Germany, air terminal on Thursday, April 11, 1996, which burned for approximately 6-1/2 hours and killed 17 people - 16 died that day, and one died later of fire-related injuries. Another 62 people were injured severely enough to be hospitalized.The big Garley building fire,1996, HongkongAirport terminal fire,1996, Duesseldorf, Germany
7 MTR train compartment arson fire（纵火）, January 2004 (up) Ship fire: The fire broke out an hour after the ship left the port of Miami (Right)
8 Burnt to the top within 10 min Bus fires:Burnt to the top within 10 minBurnt completelywithin 10 minAnd you have seen All these pictures. And from them, you can see compartment fire is very different from what we have learned in previous chapters.And now I think you have already got a rough idea about what is a compartment fire like and how serious a compartment fire could be.In fact, Compartments fires are very dangerous. They are are much more dangerous than outdoor fires. Then why???
9 2. Why compartment fires present added danger? Compartment fires are quite different from those fires burning in the open air because of the walls and ceiling.When a fire occurs in free space, heat and smoke generated would be lost to the ambient (环境) rapidly. But for a compartment fire, most of the heat and smoke generated would be confined in the upper part of the compartment.Compartments fire are very dangerous. In fact, compartment fires are much more dangerous than outdoor fires. Then why???To make this more clear, let’s see two pictures.
10 Outdoors, fire grows steadily. Indoors, trapped heat and smoke cause temperature to suddenly go up.The first picture shows a typical outdoor fire, the fire will generate heat and smoke. However, because it’s burning outside, the heat and smoke generated would be lost to environment quickly. So the fire grows steadily. Then let’s look at the right part of this picture, form it we can see the temperature also goes up steadily at a relatively low speed.But for a compartment fire, because compartment has walls and ceiling, most of the heat and smoke generated by the fire would be trapped within the compartment. So both the development of the fire as well as the growth of temperature will be much different from the outdoor one. In fact, The fire grows much faster. And the temperature may go up suddenly at a very high speed as shown on this picture.Then Why the temperature would suddenly go up?To answer the question, we have to know the development of a compartment fire. But first of all we have to know the ignition of a compartment fire.
11 3. Ignition (点燃) of a Compartment Fire For ignition of a fire to occur, a fuel must be heated above its auto-ignition temperature (自燃点) in the presence of sufficient oxidizer（氧化剂） for a fire to occur.An ignition source is anything which can heat even a small portion of a fuel to its auto-ignition temperature.Such as Electrical source. A match, cigarette lighter, cigaretteA short circuit or insulation break-down,Static dischargePre-existing flame.Spontaneous Combustion.
12 3. Development of a Compartment Fire 3. Ignition (点燃) of a Compartment Fire3. Development of a Compartment FireAfter ignition two kinds of fires may follow:Smouldering FiresFlaming Fires3.1 Smouldering Fires4.2 Smouldering Fires.Fate of a smouldering re.The smouldering re may eventually gain enough heat(reected radiation or enhanced ventilation) to burst intoames.Alternatively, the re may self-extinguish due to radiantheat loss or lack of fuel.so it is the latter one, flaming fires we will concentrate on.A fire in solid fuel which is heat-limited (energy-limited) or ventilation limited will smoulder.
14 A Ventilation-limited Smouldering Fire There is plenty of fuel inside the box, but insufficient air supply.
15 Fate of a Smouldering Fire The smouldering fire may eventually gain enough heat (through reflected radiation or enhanced ventilation) to burst into flames;Alternatively, the fire may self-extinguish due to radiant heat loss or lack of fuel or oxygen.The fire spread is very slow. A smouldering fire withoutexternal airflow advances through a solid at approximately 5-6 cm/hour.Such a fire may burn for hours without triggering alarms- heat detectors and sprinklers will not be set off. Smokealarms may or may not be triggered.The rate of combustion and spread of the smouldering fire is very slow. Without external airflow it usually advances through a solid at approximately 5-6 cm/hour.
16 After Ignition Two Kinds of Fires May Follow: 3.2 Flaming FiresA flaming fire may develop immediately after ignition, particularly in cases of arson (纵火), or may develop from a smouldering fire after a delay which may be hours.4.2 Smouldering Fires.Fate of a smouldering re.The smouldering re may eventually gain enough heat(reected radiation or enhanced ventilation) to burst intoames.Alternatively, the re may self-extinguish due to radiantheat loss or lack of fuel.so it is the latter one, flaming fires we will concentrate on.
18 Fate of a Flaming Fire:The fire burn itself out without involving other items of combustible material;If there is enough fuel but inadequate ventilation, the fire may self-extinguish or continue to burn at a very slow rate dictated by the availability of oxygen;If there is sufficient fuel and ventilation, the fire may progress to full room involvement in which all exposed combustible surfaces are burning.1.Particularly when the item first ignited is in an isolated position;2. Which may lead to backdraftThis kind of fire is the most common and dangerous one for the fire disasters.. So the following discussion will concentrate on the third oneThen let’s look at how compartment fire develops in this way.
19 4. Development of a compartment fire TemperatureTimeFlashover 轰燃Decay衰减阶段Fully developed stage(post-flashover)充分发展阶段Growth stage(pre-flashover)初期增长阶段This picture shows how compartment temperature changes with time.the dashed line, shows the development of the fire which has burned out or self-extinguished.And the real line shows the fire that has progressed to full room involvement.we’ll have a detailed look at it. And according to its temperature change, the development of this kind of compartment fire can be divided into three stages,
20 4.1 Growth stage (Pre-flashover) (1) Average temperature is low.(2) Fire localization is small.In the growth or pre-flashover stage, the average compartment temperature is relatively low and the fire is localized in the vicinity of its origin.
21 4.2 Fully developed stage (post-flashover) (1) Average temperature is high.(2) The whole compartment is in fire.In the fully developed or post-flashover fire, all combustible items are on fire. Flames appear to fill the whole compartment and emerge from the windows and other ventilation (通风) openings. This may continue until the available fuel is consumed.
22 4.2 Fully developed stage (post-flashover) The next photo shows a big building fire at fully developed stage, flames have come out of the building and are quickly spreading to the other buildings and surrounding areas. So it’s very dangerous.
23 4.3 Decay Stage Average T ≤ 80%Tmax The decay period is often identified as the stage of fire after the average temperature has fallen to 80% of its peak value.At this stage, fire becomes smaller and temperature drops lower due to the consumption of fuel.
24 4.4 Flashover Transition Growth stage Fully developed stage Flashover The transition(转变) is very short. So flashover is considered as an event not a stage.Temperature will increase quickly. Temperature can reach as high as 1000℃.During flashover, flames will spread rapidly from the area of localized burning to all combustible surfaces within the room.The transition is very short, usually several seconds. So flashover is considered as an event not a stage.2. During flashoverIn fact, at the end of flashover, the roomSometimes even higherAt such high temperature, imagine if we were there would happen, yeah, if we were there we would be burnt into ashes.3. Besides the quick temperature increase, during flashover there is also a big change of burning area. At this point,That means within the short time of flashover, suddenly, everything combustible inside the room would be on fire and flames will be everywhere. From the 2nd point and the 3rd point, we can see that flashover is very terrible and dangerous.That’s why the phenomenon of flashover is very important in the study of compartment fire. And That’s why it is the key point in today’s lesson.And That’s why we are going to spend two hours on it in the wensday morning.And now we just skip it.So in the next part we will focus on the study of flashover.
25 Once flashover has occurred in one compartment, it’s hardly for the occupants of the rest of the building to evacuate (疏散).The duration from onset of burning to flashover is directly relevant to life safety within the buiding.
26 5. The Necessary Condition for Safe Evacuation tp + ta+ trs ≤ tuWhere tp is the time elapsed from ignition to the perception (感觉) that a fire exists; ta is the time between perception to the start of the escape action; trs is the time taken to move to a place of relative safety; tu is the time (from ignition) for the fire to produce untenable (难以忍受的) conditions at the location.ta is the time between detection to the beginning of the escape activity;While automatic detection can reduce tp in some degree, successful escape will ultimately depend on how rapid the fire grows, ie on tuThe greater its duration, the more opportunity there will be for detection and suppression (manual or automatic) and for safe evacuation of personnel.So its duration is very important.In fact how rapid the fire grows are influenced by many factors,Then let’s see what they are.
27 6. Factors Affecting Fire Growth The nature, amount and distribution of the combustible contents;The size and shape the compartment;The width and height of the ventilation openings.All of them are very important, however the first two factors can vary in a great degree, and it’s hard to study their influences and find any rule.So most researches have been concentrated on the third factor, ventilation.Then let’s look at how it influences the fire growth.
28 Influences of Ventilation Ventilation factor AH1/2(m5/2)Burning rate (kg/min)Kawagoe and his co-workers measured the burning rate of wood cribs inside compartments with different size of ventilation openings.Mass burning rate of wood cribs in enclosures as a function of ventilation factor,The mass burning rate was found to depend stongly on the size and shape the ventilation opening. Square represent small scale models, circle intermediate models; black dot full scale compartmentFrom this picture we can see very good correlation.
29 Ventilation Factor kg/min or kg/s The total supply of air will be controlled by the openings to the compartment if these are small then not all of the hot gases will be able to leave the compartment and will be recirculated through the fire. This will dilute any available fresh air and reduce the concentration of oxygen in the gases entrained into the fire. This has been studied for many years and there are well known relationships for such circumstances relating rate of heat release, or burning rate of the fuel to the size and shape of the opening e.g.The width and height of openings not only influence the burning rate of the combustible contents but also influence the control forms of compartment fire.Here AH1/2 is called ventilation factor.
30 Theoretical Deduction of the Ventilation Factor Kawagoe deduced the ventilation factor by a theoretical analysis of the flow of gases in and out of the burning compartemnt.P0 atmospheric pressureP densityG gravitational acceleration constantY is negative below neutral planeHorizontal velocity
31 The subscript F for the compartment gases The subscript 0 for the ambient air
32 Where cd is a discharge coefficient(流量系数), B is the width of the window (m), m is the mass flow kg/s and hf+ho=HThese lead to
33 Ventilation Factor kg/min or kg/s Surprisingly, the calculation result for wood is all the same with the experimental results.In fact, besides mass burning rate, ventilation also influences the control forms of compartment fire.
34 Control Forms of a Compartment Fire Fuel-controlled （燃料控制） fireVentilation-controlled （通风控制） fireAir (oxygen) SupplyThere are two Control Forms of a Compartment Fire.One isThe other isAnd I will give you a detailed explanation.You know, at the beginning of a compartment fire, the fire is small and there are plenty of air in the room, so the oxygen supply is sufficient. So at that time, how large the fire would be is depending on how much fuel is burning. That’s called fuel controlled fire. But as fire grows bigger and bigger, the oxygen supply becomes insufficient. So the growth of fire is now depending on the air supply through ventilation. That’s a ventilation (通风) controlled fire.So the Control Forms of a Compartment Fire will be decided by the combination influence of fuel and ventilation. Then a new influencing factor emerges: Opening factor.Then let’s see how the width and height of a compartment influence control forms of compartment fire。There is another factor called opening factor。Opening factor is a combination of ventilation factor AH1/2 and fuel bed area ArFuel
36 Influence of Ventilation on the Control forms of fire Ventilation-controlled fireFuel-controlled fireThere are two Control Forms of a Compartment Fire.One isThe other isAnd I will give you a detailed explanation.You know, at the beginning of a compartment fire, the fire is small and there are plenty of air in the room, so the oxygen supply is sufficient. So at that time, how large the fire would be is depending on how much fuel is burning. That’s called fuel controlled fire. But as fire grows bigger and bigger, the oxygen supply becomes insufficient. So the growth of fire is now depending on the air supply through ventilation. That’s a ventilation (通风) controlled fire.Then let’s see how the width and height of a compartment influence control forms of compartment fire。There is another factor called opening factor。Opening factor is a combination of ventilation factor AH1/2 and fuel bed area Ar
38 Ventilation-controlled fire Opening FactorFuel-controlled fireVentilation-controlled fireAT is the area of the walls and ceiling of the compartment, excluding the ventilation area.1*1.2And now we have known the influence of ventilation on the burning rate of fuel and the control forms of the fire. This is very important to the development of a compartment fire.
39 Summary 1. Introduction of compartment fire. 2. Explanation of why compartment fires are more dangerous than outdoor fires.3. Ignition & development of a compartment fire.FlashoverGrowthFully-developedDecay4. Factors Affecting Fire Growth (ventilation)
41 QuestionsWhat are the two control forms of the compartment fire? What is the difference between them?Why indoor fires are more dangerous than outdoor fires?Calculate the ventilation factor and opening factor of this classroom.
42 Please feel free to raise any question! Thanks!Please feel free to raise any question!
44 Key Words & Phrases Flashover 轰燃 Fire plume 火羽 Heat flux 热通量 Pyrolyze (pyrolysis) 高温裂解Radiation feedback heat 辐射热反馈Structural failure 结构破坏Collapse 坍塌、倒塌Hose-line 消防水带First, let’s see some vocabulary.The first one is compartment fire, it means fires that take place in compartments. 汉语，中将其称之为 室内火灾The second one, flashover, flashover is a special phenomenon that usually take place in compartment fire. 汉语，将此现象称之为 轰然And we will explain what is flashover in detail later in ourThe third one is pre-flashover. The prefix pre- means ‘before’, so the pre-flashover means things that happen before flashover.Then it would be easy for you to get the meaning of the post-flashover. It means things that happen after flashover.Then next one flammable. Flammable is the adjective of flame. Flame 是火焰，那flammable 是可以发出火焰的，也就是可燃的The next one combustible. Combustible is the adjective of combustion. Combustion 是燃烧的意思，那combustible 也就是可燃的意思，它与flammable 是同义词Heat 热 flux 流量通量的意思 所以 heat flux 热通量是我们在第二章学过的，它表示的是在单位时间内通过单位面积的热量。This is the vocabulary.In today’s lesson we are going to learn about compartment fire.
45 Development of a compartment fire TemperatureTimeFlashover 轰燃Decayperiod 衰减阶段Fully developed period(post-flashover)充分发展阶段Growth period(pre-flashover)初期增长阶段This picture shows how compartment temperature changes with time.And according to the temperature change, the development of a compartment fire can be divided into three stages,
46 1. Definition of Flashover The term 'flashover' was first introduced by UK scientist P.H. Thomas in the 1960s and was used to describe the theory of a fire's growth up to the point where it became fully developed.First, the definition of flashover.however this definition is not very precise in fact, so after that, many new definitions were proposed by other scientists.
47 Most commonly used Definitions of flashover are as follows: The transition from a localized fire to the general conflagration (大火灾) within the compartment when all fuel surfaces are burning;The transition from a fuel (燃料) controlled fire to a ventilation (通风) controlled fire;The sudden propagation (传播) of flame through unburnt gases and vapors collected under the ceiling.Among them, the most popular ones are as follows:The first one defines flashover asLet’s look at the 2nd definition again. What is a transition; What is a change from a fuel controlled fire to a ventilation controlled fire.? You know, at the beginning of a compartment fire, the fire is small and there are plenty of air in the room, so the oxygen supply is sufficient. So at that time, how large the fire would be is depending on how much fuel is burning. That’s called fuel controlled fire. But as fire grows bigger and bigger, the oxygen supply becomes insufficient. So the growth of fire is now depending on the air supply through ventilation. That’s a ventilation (通风) controlled fire.From this we can see that the 2nd definition is the just a result of the 1st one and it’s not a fundamental definition.Then let’s look at the third definition again. How can we see that there is a sudden propagation of flame? Actually, this is mainly based on our observation when we see that flames have come out of window, doors or other ventilation openings, And because this is mainly based by our observation. It is not very precise either.That’s why in our book, we use the 1st definition.Now we have already known the definition of the flashover.However, I think most of you are still amazed and confused at how flashover happens.Then I will explain that to you！
48 Definition of Flashover Other Popular DefinitionsThe definition of flashover is given in a British Standard as a:"Sudden transition to a state of total surface involvement in a fire of combustible materials within a compartment". (BS 4422, 1987)The International Standards Organisation (ISO) use a similar wording:"The rapid transition to a state of total surface involvement in a fire of combustible materials within an enclosure".
49 Initial development of a Fire Plume (火羽) in a Compartment. 2. Formation of flashoverLook at the picture, It’s a room. It has walls, ceiling and a door. So it’s a compartment. And we use a match to ignite a part of a sofa.And then a fire will be formed. As we have mentioned before, the fire will generate heat and smoke, and because of walls and ceiling, most of the smoke and heat will be trapped inside room.This is theInitial development of a Fire Plume (火羽) in a Compartment.
50 Then as time goes by, the fire will become bigger. More and more heat and smoke will be generated and trapped inside the roomSo a hot layer of smoke forms under the ceiling of the room. Because of its high temperature, it will produce heat radiation. And all the other things inside the room will receive the radiation heat.Look at the second picture, the red arrows represent the heat radiation direction.A hot layer of smoke forms under the ceiling of the room. And it will produce radiation feedback heat （辐射热反馈）.
51 When the temperature reaches a certain value, other combustible objects will pyrolyze(高温裂解) and release pyrolysis gases.As the fire develops, the hot smoke layer will become thicker and its temperature will be higher.From the Radiation heat flux formula we have learned the chapter 2, the radiation energy will increase quickly with the increase of temperature. So Everything inside the room will receive more and more radiation flux from the hot gases layer.Then what will happen to the other combustible materials in the room?Let’s see another picture.After reception of the heat, their temperature will go up quickly. And at high temperature, those combustible things will pyrolyze and release flammable gases.a times b times t to the power of fourI=oT4 where T is the absolute temperature, o the Stefan Boltzman constant 5.669x10-8 W/m2K4 and I the radiation intensity). This intensity is sufficient to support ignition of most materials.When all the combustible surfaces reach a certain high T, they will pyrolyze and release flammable gases.
52 There is a certain auto-ignition temperature (AIT) (自燃点) for a certain mixture of flammable gases.When T reaches the auto-ignition temperature of the flammable gases inside the room, suddenly, all the flammable gases and all the combustible surfaces will be on fire.As the temperature of the room continues to go up, it will eventually reaches the auto-ignition temperature of the flammable gases. And at this point, all the combustible surfaces will be on fire.At that time, because everything is burning now, the room temperature will suddenly go up and it can exceed 1000 ℃ and sometimes it can reach as high as 1200 ℃.And flames will get out of openings, such as doors and windows. As shown on the picture, it got out of the door.This phenomenon is called flashover.And now, I think you have understood how flashover happens.However, just from these two pictures, you still can not see how serious a flashover could be. Then let’s see two real photos.auto ignition temperature (AIT)中间那段话的位置可能需要调整。The T will suddenly go up and it can exceed 1000 ℃.The flames will fill the whole compartment and get out of the openings.
53 Flashover Fire CasesThe first one is a household fire. You can see this is a window. And in fact, here used to be a door. Because flashover happened so suddenly that nobody was prepared for it. Just before it happened, as shown on the picture, our firefighters were still using hose line to fight the fire. And fortunately, they were still at the door and not inside the house. If they were inside the house, they could hardly survive.The next photo shows a big building fire after flashover happened, flames have come out of the building and are quickly spreading to the other buildings and surrounding areas. So it’s very dangerous.From previous pictures and these two photos, I think you have already got a rough idea about what a flashover is and how it happens.Then Let’s see a short video where you can see the whole process of how a compartment fire develops into a flashover.
54 Video 1: Flashover experiment This is a compartment fire experiment conducted by fire safety department of Rockwool group.A polyurethane insulation was used here. We can see the fire develops very fast.At about 15 seconds after the ignition, the whole room is in fire and flames begin to come out of the door. That means flashover happens. After that the fire enters fully developed stage.More and more flames come out of the door.The big fire was finally extinguished by hose line.According to the time bar on the video, we can see from the ignition to the fully of the fire, the whole process only takes about a 15 s time. So we can draw a conclusion that the occurrence of flashover will speed up the development of a compartment fire.However, what we have seen in the video is only an experiment.Then in a real big fire, how fast will the fire develop?Let’s see a real fire case.
55 Fire in Bradford City Soccer Stadium, England, 1985. P1: first visible flamesP2: 90 secondsThis is the big fire happened in Bradford City Soccer Stadium, England, 1985.The first photo shows the first visible flames.The second photo shows the scene 90 seconds after the first sight of the flames. At this point, the fire is pretty big and smoke layer is pretty thick. And flames began to come out of the door. And flashover began to happen.Now let’s look at the third the photo, that’s 150 seconds after the first sight of the flames. The whole stadium is in fire. Everything inside it was burning. The fire has entered fully developed stage. Then we can see from the first sight of fire to the fully developed stage, it only took about 2 and a half minutes. So from this we can see that fire develops very fast after flashover happens.Then look at the third picture again.Do you think anyone inside the fire could escape?No, that’s impossible.So, during this big fire altogether 56 people lost their lives, and over 200 others were badly injured.From previous study we know that after flashover happens the compartment temperature will be very high, and fire will be everywhere.That’s very terrible. Then what will happen after the disastrous flashover. What are the consequences of flashover?P3: 150 seconds
56 3. Consequences of Flashover Large number of deaths and injuriesTrapped building occupants (被困居民)FirefightersBuilding structurePropertiesFirst, just as we seen from the previous fire case that flashover will lead to aAnd it will cause a great damage to inside the buildingAnd it also doesAnd let’s have a detailed look at it.Great damage
57 3.1 Death and injury caused by flashover Flashover happens very suddenly.During flashover, fire grows so rapidly that people do not see the need for evacuation(疏散) until evacuation is impossible.Flashover usually leads to tripled(三倍的) death in fire.Firefighters : If wearing full protective clothes, any firefighters caught in a compartment which reaches flashover still have seconds to evacuate.Most firefighting tragedies happen because most of time firefighters are too focusing on searching and rescuing others without noting that flashover is going to happen.Why flashover will cause great amount of deaths and injuries?That’s because first, Flashover happens very suddenly, so it usually catches people unprepared. That means nobody is prepared for that.Just as what we have seen in the Soccer Stadium fire, from the first sight of the flames to the fully developed fire, it only took about 2 and a half minutes.That’s very short. When you see the fire, you know you have to run, but you don’t have enough time to run out of it.That’s why Flashover usually leads to tripled(三倍的) death in fire. This number is based on the fire statistic of the whole world. Triple means three time. So it’s a great number.Of course, this is not only the case for occupants, but also for our firefighters.Although if wearing. There still lots of died of flashover. Then why?
58 Death caused by flashover in some fire cases YearPlaceDeath1981Dublin481982Los Angeles241991Petersburg81996Dusseldorf171997UK32002Paris5In the USA, NFPA (美国消防协会) statistics recorded between 1985 and 1994 demonstrated a total of 47 US firefighters lost their lives to 'flashover'.This table shows the deaths caused by flashover in some fire casesFlashover has often resulted in multiple life losses at fires. In a 'flashover' in the Stardust Disco in Dublin, Ireland caused the deaths of 48 young people.In there were 24 deaths in the Dorothy Mae apartments flashover in Los Angeles.In 1991 eight Russian firefighters died in corridor flashovers that occurred during a major hotel fire in St. Petersburg. In 1996 there were seventeen deaths as a flashover occurred in a Dusseldorf airport terminal fire.In 1997 three UK firefighters were killed in flashover related incidents.In the new millennium several firefighters have lost their lives to 'flashover' during live training burnsin 'real' structures, notably in Denmark and the USA, and in 2002 five Paris firefighters diedtrapped by two 'flashover' related incidents.
59 Firefighters confronted a flashover. Firefighter caught inside a This picture just showed one case of them. Died in flashover is terrible, because the temperature is very high.These firefighters confronted a flashover, and one of them was inside the room when flashover happened and he didn’t have time to get out.When we look at it, I think the grief and sadness is here with everyone of us.In fact, besides this kind of tragedy, during flashover, something worse might happen after flashover.
60 3.2 Great damage caused by flashover PropertiesGreat damageBuilding structureWooden beams(木梁) will char(烧焦);Steel (钢筋) will be permanently weakened. Then it will expand and damage surrounding structural components (构件);Concrete (水泥) and masonry (砖瓦) will spall (破碎) and may crack into pieces.Structural FailureYou know When flashover happens, everything combustible inside the compartment will be on fire, and temperature will be very high. So any property inside the room would be destroyed.at the same time, due to the high temperature, great damage will occur to the building itself and result in structural failures as follows:will be permanently weakened when exposed to temperatures above 500 ℃, it
61 Structural FailureAfter those structural failures, the roof of a building will generally collapse(倒塌) first, due to the concentration of high temperature gases and flames at the top of the structure.The walls may follow.Will all compartment fire develop into flashover?Firefighters must be aware that the building could collapse at any point after a compartment reaches flashover.
62 Catastrophic Collapse of a Building This picture shows a catastrophic collapse of a large building after the flashover happened.When a building collapsed, escape from the building would be even harder and the rescue work of firefighters would be much more difficult.And these are all the serious consequences of flashover. They are very terrible.However, I want to ask another question: will all compartment fires develop into flashover?
63 Does flashover occur in all the compartment fires? Video 2: Non-Flashover experimentTo answer this question, let’s first see anther video downloaded from rock wool website.This time, they used different insulation material: it’s their own product called rock wool insulation.Look at the time bar, from it we can see the fire self-extinguished 20 minutes after the ignition.The hazard brought by a fire like this will be much smaller than those with flashover.In the video, no flashover occurs. Right?Then why flashover occurs in some compartment fires, while not in others?Because flashover has its own necessary conditions to occur.What are those conditions?Let’s turn to the next slide: Criteria of flashover
64 The Development of Fire With and Without Flashover
65 4. Fuel and Ventilation Conditions Necessary for Flashover
66 Fuel and Ventilation Conditions Necessary for Flashover 1. Mass burning rate:2. Ventilation factor:
67 4. Criteria of flashover (轰燃判据) Based on the observations and measurements of compartment fires, different criteria of flashover were proposed:Radiation heat flux at floor level (地面热辐射通量) reaches 20kW/m2;Gas Temperature at ceiling level (顶棚气体温度) reaches 600℃;The first one was proposed by Waterman he found that when ~, flashover will occur. (But he used paper as the combustible material. Paper can be ignited when heat flux reaches 20 kW/m2, but for other combustible things, this value will change. )Some other scientists propose that when ~, flashover will occur.In fact, these two criteria are not very precise, but they do provide us a method to judge whether a flashover could happen.However, no matter the value of heat flux at floor level or the gas temperature at the ceiling level are both decided by many factors.flashover is often identified with a hot gas layer temperature of approximately 550°C when a blackbody emitter of infinite area would cause a radiant intensity of 30 Kw/m2 (Reference 9) at floor level (these values are related by I=oT4 where T is the absolute temperature, o the Stefan Boltzman constant 5.669x10-8 W/m2K4 and I the radiation intensity). This intensity is sufficient to support ignition of most materials..
68 Influencing Factors of Flashover The building materials of the walls and ceiling.The height and width of the opening.The kinds of combustible materials.Such as:The first two factors are concerning combustible materials inside the compartmentAnd the latter two concern about the structure of the compartmentthen, whether a compartment fire will develop into a flashover or how long a flashover will occur both depends on the above factors!Then how each of these factors influences?I want to explain that, but it’s too complex to explain here in today’s class.Instead I will introduce the equipment used to study these influencing factors in the compartment Fire Research Lab in our department.The amount of combustible materials.
69 6. Three ways to delay flashover: Venting: By venting windows of a burning room you release the build up of heat in the room. This slows down flashover in addition to improving visibility in a smoke-filled room.Not venting: by not venting and instead closing the door to the burning room, you can also delay flashover. By not venting, you starve the fire of oxygen, which slows down the combustion rate and the build up of heat in the room. This may be done when there is a delay in stretching a hose-line and all persons are out of the burning room.Portable extinguisher: The use of a portable extinguisher can cool the heat down in a burning room temporarily and delay flashover.To avoid getting trapped by flashover, firefighters must know the warning signs of flashover.
70 7. Warning signs of flashover Flames are running overhead on the ceiling;Perception of rollover:Rollover is defined, as sporadic (零星的) flashes of flame mixed with smoke at ceiling level.The sudden lowering of the existing smoke layer (smoke interface).Sudden increases of heat forcing you to crouch low;Just before flashover happens, there will be following signs.First you can see,Rollover is caused by heated combustible gases in smoke, which ignites into flashes of flame when mixed with oxygen in the air. Rollover precedes flashover. Rollover is another warning sign of flashover, which may be seen in the smoke coming out of the tops of doorways or window openings of burning rooms before flashover occurs.And you can also note there is a , this means the smoke layer suddenly becomes thicker.At same time you can feel the sudden increase of T and heat that force you to crouch down or to crouch low; When heat mixes with smoke, it forces a firefighter to crouch down on hands and knees to enter a room to perform search and rescue. This must be considered a warning sign that flashover may occur. Heat is the triggering event 触发事件 for flashover. If the heat in the smoke filled room causes us to crouch down near the floor, we must consider the danger of flashover.When you first note these signs, you still have several seconds to get out there. So ,Don’t hesitate, just run away as fast as possible!Do remember these warning signs, they might save your or other people’s life someday in the future. Unless the firefighters are able to "read" the signals that the fire is sending, they could become a victim instead of a rescuer.In many parts of the world there has been a tendency to blame this on the fact that the combination of improved protective clothing and SCBA use allows firefighters to go further into a structure. At the same time the insulative properties of the protective clothing reduce the ability to sense the greater heat.
71 8. Point of no returnThe point of no return is a distance inside a burning room beyond which a searching firefighter will not escape and will not reach the door or window entered.How far inside a burning room can a firefighter be and still escape back out the door alive and not suffer serious bums after a flashover occurs? How far into the burning room that appears about to flashover should a firefighter go?Five feet is the point of no return after the room explodes into a flashover.After a flashover occurs, firefighters may have past the point of no return.1foot= 0.305m
72 8. Point of no return Five feet is the point of no return 1. Fire temperatures of 280‘-320’ F cause intense pain and damage to exposed skin. ( ℃)2. The average temperature in a room that flashes over is 1000' to 1500' F. ( ℃)3. The average person moves 2.5-feet per second when walking4. How long can a firefighter take 1000'-1500' F on the neck, ears, wrists and any other exposed portion of the body? Just two seconds.不可返回点；无还点一架飞机飞行中，飞机没有足够的油料返回出发点的那一点We can figure this distance out by putting together several facts. For example, tests conducted in 1960 in California discovered that Fire temperatures of 280'-320' F Fahrenheit cause intense pain and damage to exposed skinOf or relating to a temperature scale that registers the freezing point of water as 32=F and the boiling point as 212=F at one atmosphere of pressure.. time and motion tests in the Handbook of Fire Protection reveal that the average person moves 2-1/2-feet per second when walking.If there is 1000' F flame in a burning room that has just flashed over and a firefighter is five feet inside the room, and crawls back to the doorway at 2-1/2-feet per second, he will feel 1000'-1500' F on exposed portions of skin not covered by fire gear for two seconds. If you say you can enter 10 feet into a room about to flashover and it does, and you try to escape you will experience 1000' -1500' F on the exposed portions of your body for four seconds. Think about itFive feet is the point of no return
73 9. Defensive Search Procedures: At a Doorway:A firefighter should check behind the door for the victim, then enter the hallway or room not more than five feet, sweep the floor, look for unconscious persons, call out and listen for a response. If no response is forthcoming, close the door and wait for the hose-line. As the attack hose-line advances, conduct a search and rescue behind the line, searching room and space outward from the hose-line.They should know the warning signs of this danger heat in smoke and rollover. Also firefighters must know how to delay flashover - a room bursting into flames. And most important for firefighters' safety and survival, they must know defensive firefighting procedures - how to search and stay alive.There are two defensive search procedures that can reduce the risk of death and injury from flashover:
74 At a Window:If smoke and signs of rollover are seen in the smoke, the firefighter should not enter the burning window. Instead the firefighter should crouch down below the heat and sweep the area below the windowsill (窗台) with a tool.In some instances a person may collapse at the window and fall right below the sill. If a victim is found, a firefighter on the ladder might be able to crouch below the heated smoke and flashes of flames mixed with smoke coming out the window and pull the victim to safety on the ladder.When climbing a ladder placed at a window and the window breaks from either the heat of the fire or because it is opened by the firefighters at the top of the ladder
75 SUMMARY 1) Definition of flashover; 2) Formation of flashover; 3) Sequences of flashover;4) Conditions Necessary for Flashover;5) Criteria of flashover;6) Equipment to study those influencing factors;7) Three ways to delay flashover;8) Warning signs of flashover;9) Point of no return;10) Defensive Search Procedures.That’s the main content for today.And now let’s have a review of today’s lessonIn today’s lesson, we have learned and ThenAnd there is a transition event happens between growth period and fully developed period.It’s flashover.
76 QUESTIONS 1. How does a flashover happen? 2. What are the consequences of flashover?3. What are the warning signs of flashover?
77 QUESTIONS4. According to fire protection engineers flashover is caused by which one of the following?A. Radiation heat B. Radiation feedback heatC. Conduction heat D. None of the above5. Which one of the following is not a method used by firefighters to delay flashover?A. Venting to release heatB. Not venting to starve the fire of oxygen and thusslow down heat generationC. Use a portable extinguisher on the fire to cool it downD. Remove combustible from the fire area
78 Relative Code and standard for flashover NFPA Guide on Methods for Evaluating Potential for Room FlashoverCurrent Edition: 2004
79 Please feel free to raise any question! Thanks!Please feel free to raise any question!
80 5. Compartment Fire Research Lab Under the leadership of Prof. Chen, this lab was set up in 2001 with support from our academy and fire engineering department.And this equipment represents the first class level inside our country.With support from our academy and fire engineering department, this lab was set up in 1996 under the leadership of Prof. Chen.And the equipment of this lab represent the advanced level in the world and the first class level inside our country.
81 5. Compartment Fire Research Lab 213451. A box with opening2. A tray (托盘)3. An electronicBalance (电子天平)4. A printer (打印机)The equipment our department is most advanced one in our country.This picture shows the experiment.This is a box which can be disassembled. That means we can change the material of its walls and ceiling.This is a door, it’s the ventilation opening, both its width and height of can be adjusted.Inside the box, different materials of different mass are used are used as the combustible material.1 to 7 are all thermal couples connected with signal detector. They are used to measure the heat flux and temperature.So using this equipment, every influencing factors listed in the slide can be studied.我们现在的室内火灾实验室，是陈爱平教授，在学院和我们工程系的大力支持下组建起来的，它代表了国际先进水平、国内的一流水平，那么陈教授部分博士论文达的科研工作，也是在这个实验室中完成的。如果你们感兴趣的话，在校园网的精品课程建设上，可以找到有关我们实验室的照片和相关的一些介绍，当然也欢迎大家去参观我们的实验室，来加入我们的科研工作。If you are interested, you are welcome to our lab to know more about it or to participate in our research.And now we have to continue our lesson.From previous slides, we know flashover in a compartment fire is very dangerous. And because it happens so suddenly and develops so rapidly that nearly nobody can survive if caught by a flashover.Then can we know that flashover is going to happen before it really happens so that we can avoid the disaster?Yes, you can. Because there are some warning signs before flashover happens:5. Signal detector(信号检测仪)①~⑦Thermal couples(热电偶)
82 Use of Each DeviceTray (托盘): combustible materials will be put on the tray.Electronic balance (电子天平): Detect the mass change (质量变化) during the fire process.Printer：Print out the detected mass change.Signal detector (信号检测仪): Detect the temperature and radiation heat flux (辐射热通量) both inside and outside the compartment.
83 1. This box can be disassembled 1. This box can be disassembled. That means we can change the material of its walls and ceiling.The building materials of the walls and ceiling2. Both the width and height of the door can be adjusted.The height and width of the opening
84 3. Different materials of different mass (质量) can be put on the tray and used as combustible material.The kinds of combustible materialsThe amount of combustible materials4. Besides the above influencing factors, using this equipment, we can also study the mass burning rate（质量燃烧速率）during process of each compartment fire.
85 To Know More about Our Study To Participate in Our work Welcome to Our lab!To Know More about Our StudyTo Participate in Our work
87 Key Words & Phrases Backdraft/backdraught 回燃 Explode (explosion) 爆炸 Pyrolyzate (pyrolyze; pyrolysis) 热解产物Flammability Limits 爆炸极限Deflagration 爆燃Vent 通风、排出Quench 熄灭、结束Flank 侧翼攻击First, let’s see some vocabulary.
88 1. Definition of Backdraft The NFPA definition:“The explosive or rapid burning of heated gases that occurs when oxygen is introduced into a building that has not been properly ventilated and has a depleted (减少的) supply of oxygen due to fire."The IFE (Institution of Fire Engineers) definition:“An explosion, of greater or lesser degree, caused by the inrush (涌入) of fresh air from any source or cause, into a burning building, where combustion has been taking place in a shortage of air."Backdraught does not appear in any British or ISO Standards. There are however definitions given by the Institution of Fire Engineers (IFE) (Reference 10) and the National Fire Protection Association (NFPA) (using the American spelling - backdraft) (Reference 11).
91 A Basic ScenarioLimited ventilation can lead to a fire in a compartment producing fire gases containing significant proportions of partial combustion products and un-burnt pyrolysis products, which are all combustible. If these accumulate then the admission of air when an opening is made to the compartment can lead to a sudden deflagration. This deflagration moving through the compartment and out of the opening is a backdraft.
94 2. Formation of Backdraft 1) A fire burning in a room with poor ventilation2) Accumulation of flammable gases3) Air introduction at the breaking of openings4) Formation of mixture within flammability limits5) Ignition of the mixture6) Explosion or deflagration and pressure rise(Partial combustion products and un-burnt pyrolysis products )
95 3. Conditions Necessary for Backdraft 1) The accumulation of smoke consisting of un-burnt pyrolyzates and incomplete combustion products in a poorly ventilated compartment.2) Air introduction when windows or doors are opened or broken.3) The newly formed mixture of air and flammable smoke is within its flammability limits (爆炸极限).4) An ignition source of sufficient energy such as a flame, spark or glowing ember (余火). It is also possible for super-heated gases to ignite (auto-ignition), without a source of ignition being introduced.. For example, the flammability limits for carbon monoxide are 12.5% and 74%, for methane the range is between 5% and 15%, (SFPE, 1995, 3-16).It is also possible for super-heated gases to ignite (auto-ignition), without a source of ignition being introduced.
96 4. Consequences of Backdraft Pressure rise due to backdraft will force the burning gases in the compartment out through the openings with a high velocity, possibly igniting some of the unburnt pyrolyzate (热解产物) that had already left the compartment. This can create a significant fire-ball outside the compartment.
97 Backdraft Is a Kind of Explosion Explosions kill and injure firefighters in several ways. The blast (爆炸) can blow a firefighter across a street; flying glass and shrapnel (碎片) can decapitate (斩首) a firefighter; flame accompanying the explosion can cause serious burns and an explosion can collapse walls, partitions and iron shutters (卷帘铁门), crushing firefighters beneath them.
98 4. Consequences of Backdraft Deaths and injuries (Firefighters)Building structurePropertiesGreat damageFirst, just as we seen from the previous fire case that flashover will lead to aAnd it will cause a great damage to inside the buildingAnd it also doesAnd let’s have a detailed look at it.
99 Destructive Effects Caused by Backdraft Explosion Pressures Effect of ExplosionDestructive Peak Pressure (psi)Glass shattering (破碎)0-5Firefighter knock down1Wood partition collapse1-2Cinder block (煤渣空心砖) wall collapse2-3Brick wall collapse7-8Firefighter lung(肺) damage15Threshold for fatalities3550% fatalities5099% fatalities65The other fact firefighters should know is that it does not take much explosive pressure in aconfined space for an explosion to cause destruction and death.1psi=6.89 kPa
100 5. Warning Signs of Backdraft Before opening a door or window to the compartment, the firefighter should be aware of:1) A fire in a compartment with few openings that has been burning for some time.2) Oily deposits (沉淀物) in windows.3) Pulsating (跳动的) smoke from openings.4) Hot doors and door handles (windows);In addition the colour of the smoke can indicate an under-ventilated fire, however this will be difficult to determine under different lighting conditions and is dependent on the type of fuel. This may not always be a reliable warning sign for a potential backdraught scenario.Before opening a door or window to the compartment, the firefighter should be aware of:1) Fires in securely closed premises:If the building is securely closed, it may also be poorly ventilated in the event of a fire until the building is opened for access. There is the potential for an accumulation of pyrolysis products.2) Oily deposits in windows:Pyrolysis products may condense on cooler surfaces such as windows providing an indication of a ventilation-controlled fire.3) Hot doors and door handles (windows)It’s important to check whether doors or door handles are hot before a door is opened. This also applies to windows.4)Pulsating (跳动的) smoke from openings:The pulsation of smoke through small cracks and openings and rattling of windows can be due to the pulsation mechanisms of an oxygen-starved fire or possibly the turbulent mixing created by ghosting flames.Fires in concealed spaces (e.g. ceiling voids) may also present the same problem.premise[5premIs]n.前提"If your premise is established, your conclusions are easily deducible.""如果你的前提成立,那么就很容易推断出你的结论了。"(pl) 房屋及其周围的房基地
101 5. Warning Signs of Backdraft When inside, or looking into a compartment a potential backdraft may be indicated by:1) Blue flames (‘ghosting’ or ‘dancing’ flames) in the hot gas layer.2) Smoke drawn back through opening:3) Whistling and roaring soundsIt may be an indication that a backdraft is in progress at which stage there is probably little action that can be taken by a firefighter to prevent it.Blue flames:Grimwood attributes the observation of blue flames to the burning of carbon monoxide from incomplete combustion. They may also be related to the "ghosting" or "dancing" flames reported earlier. Both explanations indicate the presence of un-burnt pyrolysis products and a potential backdraught scenario.Smoke drawn back through opening:Hot smoke will be leaving at high level, possibly through a different opening, and replacement air being drawn in to the compartment will change the local direction of smoke movement. When ventilation of the fire is first instigated, smoke at low level may move toward the fire carried by the gravity current.In addition: The colour of smoke:This is often referred to, however several colours are mentioned depending on the type of fuel. For example thick black smoke is associated with un-burnt hydrocarbons, yellow smoke with nitrous and sulphurous polymers and cool white smoke with smouldering latex foam.
103 Lessons Learned 1. These warning signs are important to know. 2. Firefighters must know that explosions happen fast, sometimes too fast for firefighters to take cover and protect themselves.The only real protection from the blast of a backdraft or a flashover is full protective gear: helmets(头盔), hoods(防护帽), gloves(手套), boots(长靴), bunker pants(防护裤), coat and face mask(面具). Protective fire gear may be hot, cumbersome (笨重的) and slow you down, but if you are caught in an explosion, it will determine whether you survive the blast and how serious your burns will be.Warning signs of backdraft explosions must be taught to firefighters. They are, reversal of air pulling smoke back into a smoke filled doorway, black smoke pushing out around a closed door or window frames and glass windows, stained with smoke condensation and pulsating from the pressure of the fire.
104 The Peru (秘鲁) firefighters force entry just prior to the backdraft Amazing Peru BackdraftThe quality of their protective clothing undoubtedly saved them from serious injuries;Peruvian firefighters suffered minor burns and injuries when they were caught by this explosive backdraft;The Aftermath (后期)!!! An exterior defensive operation is mounted following the backdraft.
105 6. Preventing Death and Injury There are three tactics that can reduce the chances of getting caught in a backdraft:Venting (通风)Quenching (熄灭)Although full protective cloth with good quality can save life and reduce burns in some degree when backdraft happens.The most important thing for firefighters to know is not only what a backdraft is, but also how to prevent death and injury from such an explosionAfter firefighters understand what a backdraft is, they must know how to prevent death and injury from such an explosion.Flanking (侧翼攻击)
106 6.1 Venting (通风)Venting a roof skylight (天窗) over a burning room is one of the most effective methods of protecting firefighters from the blast of a backdraft.1) When roof conditions permit, the quick removal of a glass skylight by firefighters can vent a smoke filled room and break up an explosive mixture.2) Even if the smoke explosion occurs, the blast will be diverted upward out of the roof vent opening away from the firefighters advancing the hose-line.
107 6.2 Quenching (熄灭)Quenching: Before a superheated confined room is entered, charged hose-line should be positioned near the entrance. Firefighters in full protective equipment should immediately discharge (射水) a hose stream into a fire area when it is opened up.1）This water can cool a potentially explosive atmosphere.2）Before the air and searching firefighters enter a potentially explosive fire area, the stream of a powerful water discharge might break up the explosive atmosphere.the superheated confined fire area is another safety and survival tactic firefighters can use to prevent backdrafts.This is not as effective as roof venting, but sometimes it is the only alternative.
108 6.3 Flanking (侧翼攻击)Flanking: When there can be no venting and the quenching of a quick dash of a hose stream is not possible, the officer in command can order two hose-lines into position, one on each side of a door or window of a burning room.After the hose lines are charged with water and firefighters are in full protective equipment, the door or window is broken. Both flanking hose lines, safely out of the path of any potential explosive blast coming out of the opening, can be directed into the burning room.When there can be no venting and the quenching of a quick dash of a hose stream is not possible,firefighters can protect themselves from a backdraft explosion in some instances by flanking a doorway to a burning room operating hose-lines.
109 A Backdraft CaseThe backdraft that blew apart an Illinois church on February 9th, 2004 has been named the largest backdraft ever documented in the U.S.The firefighters determined it was too hot and smokey to enter the church basement, so they opened the ground level windows. The door to the basement felt cold but suddenly blew out when the backdraft occurred.Riddle had been in his command vehicle when the backdraft occurred. "I heard the noise and I looked up... this piece of roof was just being removed - it went up about 10 feet and then came back down," he said.There was no warning except that immediately before he blast, "The guys on the scene said they heard a sucking sound," Riddle said.The backdraft blew the roof off the Church and knocked flat the eight firefighters on scene and two firefighters were injured。
110 Riddle had been in his command vehicle when the backdraft occurred Riddle had been in his command vehicle when the backdraft occurred. "I heard the noise and I looked up... this piece of roof was just being removed - it went up about 10 feet and then came back down," he said.There was no warning except that immediately before he blast, “The guys on the scene said they heard a sucking (吸气) sound," Riddle said.The backdraft blew the roof off the Church and knocked flat the eight firefighters on scene and two firefighters were injured. A firefighter who had felt the door suffered burns to his hand because he had taken his glove off. Another firefighter was blown out of the cab of the engine, and another was blown across an alley.
111 7. Backdraft and flashover, what is the difference? Flashover and backdraft are distinctly different events which occur in different ways.A flashover can occur in a compartment when a small localized fire rapidly develops into a fire involving all the combustible surfaces.In contrast a backdraft occurs after air is admitted to a poorly ventilated compartment and mixes with un-burnt pyrolysis products from the oxygen starved fire. Any ignition source, such as a glowing ember, can ignite the resulting flammable mixture. Expansion due to heat created by combustion can then expel burning gases out through the opening.Both are sudden events that represent a serious hazard to firefighters.It is important to distinguish the difference between a backdraught and a flashover. Both are sudden events that represent a serious hazard to firefighters. Backdraught is an often explosive consequence of admitting air into a compartment containing a fire deficient in oxygen. It is an event of short duration burning off un-burnt gaseous flammables which have accumulated in a compartment. Flashover is a sudden jump in fire growth from a relatively localised fire to one having a sustained involvement of all combustible surfaces in a compartment.Both of them are rapid fire progress.
112 Differences There are four main differences: 1. First of all, backdraft does not happen often at fires as flashover does.You may experience only one or two during your entire career. Flashover - sudden full room involvement in flame - happens often. You will probably see one at your next fire.Firefighters sometimes confuse the terms backdraft and flashover. These two dangerous violent events are different and knowing these differences helps us understand each one better.
113 Differences2. A second difference is that a backdraft is an explosion; a flashover is not.There will be shock waves (冲击波) during a backdraft that will break the confining structure around the explosion. Windows may break blasts of smoke and flame may blow out a doorway or a part of the structure may collapse. Flashover is rapid fire development, but it stops short of an explosion's speed of chemical reaction.stop shortv.突然停止
114 Differences 3. The triggering or cause of them. Backdraft: a ventilation induced ignition of the gasesAir introduction sets off the backdraft explosion. As firefighters enter a confined smoke filled area and bring fresh air with them, sometimes a backdraft or smoke explosion happens;Flashover: a heat induced development of the firea) a heat induced development of the fire (flashover);b) a ventilation induced ignition of the gases (backdraft);Air introduction sets off the backdraft explosion. As firefighters enter a confined smoke filled area and bring fresh air with them, sometimes a backdraft or smoke explosion happens;The trigger or cause of a flashover is heat, not air. The theory of flashover is that heat, which is re-radiated back into a burning room from the ceiling and upper walls, raises the gases and furnishings in the room to the auto-ignition temperature and triggers a flashover.The trigger of a flashover is heat. The theory of flashover is that heat, which is re-radiated back into a burning room, raises the gases and furnishings in the room to the auto-ignition temperature and triggers a flashover.
115 Differences 4. The stage of fire growth in which they occur. Backdraft explosions occur when there is smoke in a confined space that is during the first and third stage of a fire. During the growth and decay stages, smoldering can take place and generate explosive CO gas;Flashover, on the other hand, only occurs in the growth stage of a fire and signals the end of the growth stage.There are three stages to a fire: the growth stage, the fully developed stage and the decay stage.
116 Flashover or Backdraft? Flashover? Backdraft? Fire Gas Ignition? VotesFlashover 29%91Backdraft 35%108Fire Gas Ignition 34% votes totalThe ignition is occurring at an entry point which suggests that an in-flow of air (gravity current) may have occurred. On arrival firefighters had reported a single storey frame house fully involved in the rear with fire showing through the roof. This fire was not demonstrating any signs of backdraft conditions and did not appear in an under-ventilated state. However, as Fort Worth firefighter Danny Morgan prepared to advance his 1 ¾” hose-line he felt it was going to ‘flash’. He said ‘there was heavy black smoke pouring out the top (of the doorway) and cool air was being drawn inside in front of me….if we’d had one piece of protective clothing missing we’d have gotten burned’….A close study of the entire sequence of seven pictures shows the ignition of gases occurred as the door was opened for entry. Although the fire was well vented at the rear of the structure a build-up of fuel-rich gases was accumulating in the hallway at the front. As Danny Morgan and his colleagues opened the door a classic ‘gravity current’ was set into motion. The resulting backdraft occurred within just a second or two! A more controlled approach to the door opening & entry procedure may have averted the ignition of fire gases.
117 Au centre d'instruction, les instructeurs pompiers reconstituent le phénomène meutrier du Backdraft (Retour de flammes) pour sensibiliser les jeunes recrues. En France le "Backdraft" a tué cinq sapeurs pompiers de Paris en septembre 2002 alors qu'ils intervennaient sur un feu de chambre de bonneFirefighters in Australia get to grips with an 'entry & attack-module' trainer.
118 Tactical Firefighting Training Staffordshire County firefighters (UK) training with a backdraft demonstrator (示范装置)
119 SUMMARY 1. Definition of backdraft 2. Formation of backdraft 3. Conditions Necessary for Backdraft4. Consequences of Backdraft5. Warning Signs of Backdraft6. Preventing Death and Injury7. The differences between Backdraft and flashover.
120 QUESTIONS 1. What are the warning signs of a backdraft? 2. What are the three firefighting tactics that can reduce destructive effects of a backdraft explosion?3. What are the differences between a backdraft and flashover?5.Which one is not a warning sign of a potential backdraft explosion?A. Reversal of air pulling smoke back into a doorwayB. Black smoke pushing out around a doorwayC. Glass window stained with smoke pulsatingD. A lack of smoke and active flamingSmoke Explosions 与 backdraft 的区别？截取电影片段Flashover or Backdraft?
121 Compartment Fire Research Lab Under the leadership of Prof. Chen, this lab was set up in 2001 with support from our academy and fire engineering department.And this equipment represents the first class level inside our country.With support from our academy and fire engineering department, this lab was set up in 1996 under the leadership of Prof. Chen.And the equipment of this lab represent the advanced level in the world and the first class level inside our country.
122 5. Compartment Fire Research Lab 213451. A box with opening2. A tray (托盘)3. An electronicBalance (电子天平)4. A printer (打印机)The equipment our department is most advanced one in our country.This picture shows the experiment.This is a box which can be disassembled. That means we can change the material of its walls and ceiling.This is a door, it’s the ventilation opening, both its width and height of can be adjusted.Inside the box, different materials of different mass are used are used as the combustible material.1 to 7 are all thermal couples connected with signal detector. They are used to measure the heat flux and temperature.So using this equipment, every influencing factors listed in the slide can be studied.我们现在的室内火灾实验室，是陈爱平教授，在学院和我们工程系的大力支持下组建起来的，它代表了国际先进水平、国内的一流水平，那么陈教授部分博士论文达的科研工作，也是在这个实验室中完成的。如果你们感兴趣的话，在校园网的精品课程建设上，可以找到有关我们实验室的照片和相关的一些介绍，当然也欢迎大家去参观我们的实验室，来加入我们的科研工作。If you are interested, you are welcome to our lab to know more about it or to participate in our research.And now we have to continue our lesson.From previous slides, we know flashover in a compartment fire is very dangerous. And because it happens so suddenly and develops so rapidly that nearly nobody can survive if caught by a flashover.Then can we know that flashover is going to happen before it really happens so that we can avoid the disaster?Yes, you can. Because there are some warning signs before flashover happens:5. Signal detector(信号检测仪)①~⑦Thermal couples(热电偶)
123 Use of Each DeviceTray (托盘): combustible materials will be put on the tray.Electronic balance (电子天平): Detect the mass change (质量变化) during the fire process.Printer：Print out the detected mass change.Signal detector (信号检测仪): Detect the temperature and radiation heat flux (辐射热通量) both inside and outside the compartment.
124 1. This box can be disassembled 1. This box can be disassembled. That means we can change the material of its walls and ceiling.The building materials of the walls and ceiling2. Both the width and height of the door can be adjusted.The height and width of the opening
125 3. Different materials of different mass (质量) can be put on the tray and used as combustible material.The kinds of combustible materialsThe amount of combustible materials4. Besides the above influencing factors, using this equipment, we can also study the mass burning rate（质量燃烧速率）during process of each compartment fire.
126 To Know More about Our Study To Participate in Our work Welcome to Our lab!To Know More about Our StudyTo Participate in Our work
127 Please feel free to raise any question! Thanks!Please feel free to raise any question!