Presentation on theme: "Chapter 7 Compartment Fire"— Presentation transcript:
1 Chapter 7 Compartment Fire Lesson 1Development 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 阴燃Glowing fire 无焰燃烧Flaming fire 有焰燃烧
4 1.Definition of compartment fire A compartment fire is a fire that takes place in a compartment, such as a room, a bus or a train compartement.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).Fires happen in a room, a bus, a car, a ship or train compartment, etc. are all compartment fires.
6 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 min
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.
10 Outdoors, fire grows steadily. Indoors, trapped heat and smoke cause temperature to suddenly go up.
11 3. Ignition (点燃) of a Compartment Fire For ignition of a fire to occur, a fuel must be heated above its ignition temperature (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 ignition temperature.
12 3. Development of a Compartment Fire 3. Ignition (点燃) of a Compartment Fire3. Development of a Compartment FireAfter ignition three kinds of fires may follow:Smouldering FiresGlowing FiresFlaming Fires3.1 Smouldering FiresA fire in solid fuel which is heat-limited (energy-limited) or ventilation limited will smoulder.
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.
16 After Ignition Three Kinds of Fires May Follow: 3.2 Glowing FiresGlowing combustion is associated with the surface oxidation of carbonaceous (碳的、含碳的) materials or char.Glowing combustion differs from smouldering only in that thermal degradation of the parent fuel does not occur.
18 Fate of a Glowing Fire:Glowing fire is normally of short duration and is apt to self-extinguish.
19 After Ignition Three Kinds of Fires May Follow: 3.3 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.
21 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.
22 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
23 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.
24 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.
26 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.
27 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 the combustible surfaces within the room.
28 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 a buiding.
29 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.
30 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.
31 Influences of Ventilation Ventilation factor AH1/2(m5/2)Burning rate (kg/min)
32 Ventilation Factor kg/min kg/s or Here AH1/2 is called ventilation factor.
33 Theoretical Deduction of the Ventilation Factor
39 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
41 Ventilation-controlled fire Opening FactorOpening factor: a measure of the rate of temperature rise of a fire, defined as the ratio of the ventilation factor and the total bounding area of an enclosure.Fuel-controlled fireAT is the area of the walls and ceiling of the compartment, excluding the ventilation area.1*1.2 Simplified Design for Building Fire SafetyEnclosure Fire Dynamics：The opening factor is given as the ventilation factor divided by the total enclosure surface area A1. The opening factor is therefore AH1/2/AtAnd 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.Ventilation-controlled fire
42 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)
44 Questions Definition: Compartment fire; ventilation factor Why indoor fires are more dangerous than outdoor fires?How many stages are there in the development of a compartment fire? What are they and what are the characteristics of each stage?What are the two control forms of the compartment fire? What is the difference between them?
47 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
48 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.
49 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.
50 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".
51 Initial development of a Fire Plume (火羽) in a Compartment. 2. Formation of flashoverInitial development of a Fire Plume (火羽) in a Compartment.
52 A hot layer of smoke forms under the ceiling of the room A hot layer of smoke forms under the ceiling of the room. And it will produce radiation feedback heat （辐射热反馈）.
53 When the temperature reaches a certain value, other combustible objects will pyrolyze(高温裂解) and release pyrolysis gases.When all the combustible surfaces reach a certain high T, they will pyrolyze and release flammable gases.
54 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.The T will suddenly go up and it can exceed 1000 ℃.The flames will fill the whole compartment and get out of the openings.
57 Fire in Bradford City Soccer Stadium, England, 1985. P1: first visible flamesP2: 90 secondsP3: 150 seconds
58 3. Consequences of Flashover Large number of deaths and injuriesTrapped building occupants (被困居民)FirefightersBuilding structurePropertiesGreat damage
59 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.
60 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'.
61 Firefighters confronted a flashover. Firefighter caught inside aflashover.
62 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 Failure
63 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.Firefighters must be aware that the building could collapse at any point after a compartment reaches flashover.
65 Does flashover occur in all the compartment fires? Video 2: Non-Flashover experiment
66 The Development of Fire With and Without Flashover
67 4. Fuel and Ventilation Conditions Necessary for Flashover
68 Fuel and Ventilation Conditions Necessary for Flashover 1. Mass burning rate:2. Ventilation factor:
69 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℃;
70 5. 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.
71 6. 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.
72 7. 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
73 7. 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
74 8. 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:
75 At a Window:If flames 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
76 SUMMARY 1) Definition of flashover; 2) Formation of flashover; 3) Sequences of flashover;4) Conditions Necessary for Flashover;5) Criteria of flashover;6) Three ways to delay flashover;7) Warning signs of flashover;8) Point of no return;9) 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.
77 QUESTIONS 1. How does a flashover happen? 2. What are the necessary conditions for the occurrence of flashover?3. What are the warning signs of flashover?4. What are the two criteria of flashover?5. What is the point of no return?
78 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
79 REVIEW 1) Definition of flashover; 2) Formation of flashover; 3) Sequences of flashover;4) Conditions Necessary for Flashover;5) Criteria of flashover;6) Three ways to delay flashover;7) Warning signs of flashover;8) Point of no return;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.
81 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.
82 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).
85 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.
88 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 )
89 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.
90 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.
92 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.
93 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.
94 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
95 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
96 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.
98 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.
99 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.
100 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)
101 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.
102 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.
103 Firefighters in Australia get to grips with an 'entry & attack-module' trainer.
104 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.
105 Tactical Firefighting Training Staffordshire County firefighters (UK) training with a backdraft demonstrator (示范装置)
106 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.
107 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.
108 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
109 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.
110 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.
111 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.
114 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。
115 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.
116 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.
117 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?
118 Chapter 8 Compartment Fire Lesson 4The Production and Movement of Smoke
119 Key Words & Phrases Volatile 挥发性的 Particulate 微粒状的 aerosol 浮质 Obscuration 昏暗Toxic (toxicity) 有毒的Fatality 灾祸、死亡Inhalation (inhale) 吸入Soot 烟灰Buoyancy 浮力Chimney/Stack effect 烟囱效应Louver/louvre 天窗/百叶窗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.
120 1. Definition of SmokeGross et al define smoke as ‘the gaseous products of burning organic materials in which small solid and liquid particles are also dispersed’.The visible volatile (挥发性的) products from burning materials. (Shorter Oxford English Dictionary)The airborne (空中的) solid and liquid particulates and gases evolved when a material undergoes pyrolysis or combustion. Together with the quantity of air that is entrained (带入) or otherwise mixed into the mass.（NFPF,1993c）1. This is wider than most common definitions
122 2. Important Features of Smoke Two important features of smoke are that:Smoke reduces visibility.Smoke contains toxic products of combustion.It is the combination of obscuration (昏暗) and toxicity (毒性) that presents the greatest threat to the occupants of a building involved in fire.
123 2.1 Reduced VisibilityWith very few exception, particulate (微粒状的) smoke is produced in all fires.The effect of reduced visibility will delay escape and increase the duration of exposure of the occupants of a building to the products of combustion.This may arise due to short exposure to high concentration of narcotic gases such as CO, or to long duration exposure to low concentrations.What is important is the dose inhaled---in simple terms, the concentration-time product (Ct). If Ct exceed a certain value, then the person is unlikely to escape unaided. The length of exposure will increase if the visibility is poor, or if the combination products contain eye and/or respiratory irritants ( e.g. HCl hydrogen chloride)The possible effect of low oxygen concentration and high temperature must also be considered.
124 2.2 Toxicity of Smoke 2) Soot in the form of smoke aerosol (浮质). 1) Toxic gases, such as HCN (Hydrogen cyanide) and CO.2) Soot in the form of smoke aerosol (浮质).The carbon particles of the soot are persistently deposited on the alveolar (肺泡) and bronchiolar (支气管的) surface.3) Sensory irritants (刺激物) in the smoke.The irritants include notably acrolein (丙烯醛) and hydrogen chloride (HCl) that lead rapidly to functional impairment (损伤). Acrolein has a synergistic (增效的) role in the toxicity of carbon particles in addition to its directly toxic lung effects.Low oxygen concentration and high temperatures must also be considered.
125 2.2 Toxicity of SmokeWhat is important is the dose inhaled---in simple terms, the concentration-time product (Ct). If Ct exceeds a certain value (the effective dose which causes incapacitation 无力 or death), then the person is unlikely to escape unaided.Short exposure to high concentration of narcotic (麻醉的、有毒的) gases such as CO, or too long duration exposure to low concentrations are of the same hazard.short exposure to high concentration of narcotic gases such as CO, or too long duration exposure to low concentrations are of the same hazard.
126 The two factors are generally related The two factors are generally related. Dense smoke is usually highly toxic and reduces visibility substantially. The length of exposure will increase if the visibility is poor, or if the combination products contain eye and/or respiratory irritants ( e.g. HCl hydrogen chloride)Indeed, statistics collected in the UK and the US suggested that more than 50% of all fatalities (死亡) can be attributed to the inhalation (吸入) of ‘particulate (微粒状的) smoke and toxic gas’ (Home Office 1995; NFPA 1997)
127 Smoke Influences Safe Evacuation The Necessary Condition for Safe Evacuation:tp + ta+ trs ≤ tuSmoke conditions have great influence on trs The effect of reduced visibility will delay escape and increase the duration of exposure of the occupants of a building to the toxic products of combustion.The possible effect of low oxygen concentration and high temperature must also be considered.The Necessary Condition for Safe Evacuation
128 Huge plumes of thick smoke and flames engulf the upper half of the 56-floor East Tower in Caracas, Venezuela, October (Reuters Photo) . 25 people were injured due to the inhalation of smoke.
129 3. Production of Smoke Smouldering fire Flaming fire Smoke can be produced by1) Smoke from smouldering fire:The high molecular weight fractions condense as they mix with cool air to give an aerosol consisting of minute droplets of tar (焦油) and high-boiling liquids. If they deposit on surfaces, they will give an oily look.Particulate smoke is generated in both smouldering and flaming combustion, although the nature of the particles and their modes of formation are very different.Under conditions of complete combustion, fuel will be converted into stable gaseous products, but this rarely happens.Pyrolysis occurs at a fuel surface as a result of an elevated temperature.
130 2) Smoke from flaming combustion: Smoke from flaming combustion is different in nature and consists almost entirely solid particles. Most of them are formed in the gas phase as a result of incomplete combustion and high temperature pyrolysis reactions at low oxygen concentrations. Particulate matter can be generated even if the original fuel is a gas or a liquid.
131 Common Combustion Product Concentrations in Residential Fires part per millionAcrolein [化]丙烯醛 nitrogen dioxide; hydrogen chloride;Hydrogen cyanidesulfur dioxidesulfur trioxide*Particulates are given as mg/m3.IDLH stands for a concentration defined as ‘immediately dangerous for life and health’.
132 4. Smoke MovementThe substantial majority of fire fatalities can be attributed to the inhalation of smoke and toxic gases. While a large number of them are found at points remote from the fire due to quick movement of smoke.To know how to control smoke movement, first of all we have to know how smoke moves and what are influencing factors deciding the movement of smoke.
133 4.1 Forces Responsible For Smoke Movement For the movement of smoke within a building , the driving forces are as follows:Buoyancy generated directly by the fire;Buoyancy arising from differences between internal and external ambient temperature;Effect of external wind and air movement;The air handling system within the building.In building, the behavior of smoke may be determined by some factors which are unconnected with the fire itself. These factors are responsible for the movement of fire inside a building.Buoyancy createdPressure differences due to between internal and external ambient temperature;
134 4.2.1 Pressure Generated Directly by the Fire Burning in a compartment generates high temperatures which produce buoyancy forces responsible for hot fire gases being expelled through the upper portion of any ventilation opening. Smoke also moves due to the expansion of the hot gases.木材烧火，烟气的移动方向 上？烟，冬天哈气儿
135 Pressure Generated Directly by the Fire In addition to the natural buoyancy forces generated by the fire itself, the stack effect must be taken into account in tall buildings.If the temperature inside a fire compartment is known, then from this equation the value of ⊿P at any height above the neutral plane can be calculated.
136 Density of Air as a Function of Temperature Temperature (K)Density (kg/m3)2801.262901.223001.185000.707000.5011000.32
137 4.2.2 Pressure Differences due to Natural Buoyancy Forces Where F is buoyancy force per unit volume,So as long as the smoke is at a higher temperature than the surrounding air, it will rise under the driving force F.
138 Chimney/Stack EffectThe stack effect in tall buildings: (a) external temperature (T0)< internal temperature (Ti); (b) T0 > Ti , showing accompanying flows.If the temperature inside the building is uniform and greater than the external temperature, then there will be a natural tendency fore air to be drawn in at the lowest levels and expelled at the highest levels.
139 Chimney EffectThe tendency of heated air or gas to rise in a duct or other vertical passage, such as in a chimney, stairwell, or building, due to its lower density compared to the surrounding air or gas.If the temperature inside the building is uniform and greater than the external temperature, then there will be a natural tendency fore air to be drawn in at the lowest levels and expelled at the highest levels.
140 Stack Effect The origin of the stack effect (no flow) P0 is the external pressure at ground level.
142 Stack EffectThe significance of the stack effect is that it can move relatively cool smoke around a high-rise building very efficiently, moving it rapidly to some areas, while protecting others.Below neutral plane there is a tendency for air to be drawn into the stack; aboveThe effect of stack on the movement of smoke in a high-rise building (Ti> T0)
143 Smoke movement caused by stack action in heated building (a) low-level fire (b) upper-level fire Smoke movement caused by fire in shaft.
144 The Height of the Neutral Plane H1 is the distance from the neutral plane to the lower openingsH2 is the distance from the neutral plane to the upper openings
145 4.2.3 Pressure Differences Generated by Wind Wind blowing against a building will produce higher pressure at the windward side and will tend to create air movement within the building towards the leeward side where pressure is lower.The magnitude of the pressure difference is proportional to the square of the wind velocity. The pressure at surface of a building is given by:Generally speaking,Where Cw is a dimentionless pressure coefficient (ranging from +0.8 to -0.8, for windward and leeward wall respectively), po is the outside air density kg/m3, and u is wind velocity. m/s.High windspeeds can generate pressure differentials which are sufficient to overcome other forces.
146 4.2.4 Pressure Differences Caused by Air Handling System Many modern buildings contain air handling systems for the purpose of heating, ventilation and air-conditioning (HVSC).While the fans are idle, the ductwork can act as a network of channels through which smoke will move under the influence of the forces discussed above, including particularly the stack effect in multi-story buildings.CBD-133. Smoke Movement in High-Rise BuildingsG.T. Tamura, J.H. McGuireSmoke generated by fire has long been recognized as a potential threat to life. A fatality as a result of fire is often due to the effect of smoke rather than the effect of heat.Fire safety in buildings is currently provided by the use of fire resistive construction and compartmentation, and by limitations on the use of combustible materials and materials that have high flame spread ratings (CBD 11, CBD 31, CBD 33, CBD 45, CBD 53 and CBD 71). These and other measures are reflected in building and fire codes. They are directed primarily towards limiting the size of a fire, with the final objective of minimizing hazard to life and property.By confining a fire to a specific area fire resistive construction not only limits its size but also limits the amount of smoke. Fire resistive compartments, however, do not prevent the spread of smoke from the fire compartment to adjacent areas, because the enclosure constituting a compartment is not air or smoke tight. A fire may be confined to a specific area, but smoke can migrate to various parts of a building and is therefore a potential threat to occupants far removed from its source as well as to occupants in the immediate vicinity. Cases have occurred where occupants on floors far removed from the fire floor have lost their lives.In the event of fire it is customary to evacuate buildings in order to minimize life loss, and occupants of low buildings can be evacuated in a relatively short time. The time for total evacuation by stair shafts, as currently provided, however, increases with building height and can exceed one half hour for a typical building over 20 storeys high(1). In very tall buildings, many occupants would be physically incapable of negotiating the stair shafts from the upper floors to the ground level, particularly under emergency conditions. Although smoke spread is a factor that must be considered for low buildings, it takes on much more serious significance for high-rise buildings because escape routes may become untenable before the occupants can be evacuated. This Digest discusses the causes and the characteristics of smoke movement in buildings.Characteristics of SmokeTwo important features of smoke are that it contains toxic products of combustion and reduces visibility. The two factors are generally related. Dense smoke is usually highly toxic and reduces visibility substantially.The physical properties of a smoky atmosphere are similar to those of a normal atmosphere; the main constituent for both is nitrogen. Oxygen and carbon dioxide may vary about 10 per cent from normal amounts without substantially affecting the physical properties of the atmosphere. The concentration of particulate smoke, even under conditions of very low visibility, is not sufficient to alter the characteristics of an atmosphere enough to affect its movement. It can be assumed, therefore, that smoke will probably follow the over-all air movement within a building.Mechanism of Smoke MovementAlthough a fire may be confined within a fire resistive compartment, smoke can readily spread to adjacent areas through such air leakage openings in the enclosure of the compartment as cracks, openings around pipes, ducts and doors. These leakage openings will permit a substantial smoke flow even with quite small pressure differentials. The principal factors that cause smoke to spread to areas outside a fire compartment are:temperature effect of fire,weather conditions, particularly wind and temperature,mechanical air handling system.Molecular diffusion is significant as a mechanism for dispersing gases (odours, etc.) within buildings, but in comparison with the various other mechanisms that create smoke movement it may be ignored.Temperature Effect of FireHeat generated by fire results in increased gas temperature. This causes smoke to move outside the fire compartment by two mechanisms: thermal expansion and stack action. With any increase in the temperature of a fire compartment, there is a corresponding increase in the volume of gas. Assuming that a fire compartment leaks sufficiently to preclude an appreciable buildup of pressure, it follows that the gas volume increases approximately in proportion to its absolute temperature. With a temperature rise from ambient to 1000°F in the fire compartment, the volume of gas is increased to approximately three times its original volume and approximately two thirds of the original gas in the fire compartment is forced outside it. This flow of gas out of the compartment due to thermal expansion will continue as long as the temperature in the compartment is rising.When the fire temperature reaches a steady value, however, the gas is no longer expanding and the principal mechanism by which smoke moves out of the compartment is stack action (the same mechanism that prevails in heated buildings in winter (CBD 104, CBD 107)).With fire in a single floor area, stack action acts over one floor height. Air flows through leakage openings in the walls of the fire compartment at low levels and smoke flows out of the compartment at upper levels to adjacent areas. With fire in a vertical shaft such as an elevator and service shaft, stack action involves the whole height of the shaft and its effect is therefore much greater. Air flows into the shaft from the floor areas in the lower portion of the building and smoke flows from the shaft to the floor areas at high levels. This flow pattern induces a downward flow of air in any remaining shafts and through leakage openings in the floor construction (Figure 1). Fire in a shaft, therefore, can cause recirculation of smoke throughout a building.Figure 1. Smoke movement caused by fire in shaft.A similar flow pattern involving recirculation can result from fire in a floor area when there is a substantial flow of hot gases from the floor area into a vertical shaft. This might happen where a door between a vertical shaft and a fire floor is left open.Effect of WeatherExternal conditions can also cause smoke to move from a fire area to various parts of a building. Under certain conditions, wind action can cause smoke to move vertically upward within a building, but its principal effect is to cause air or smoke to move in a horizontal direction towards the leeward and side walls.Stack action associated with building heating during cold weather (CBD 104, CBD 107) is another mechanism by which smoke can spread upwards from a fire on a lower floor. Stack action causes air to flow into the building at low levels and out at upper levels. Air flows upwards within the building through openings in the floor construction and through vertical shafts, with most of the upward flow occurring in the vertical shafts. Smoke generated by a fire on a lower floor thus migrates to vertical shafts and hence to upper floors (Figure 2a). With fire in an upper floor there is little tendency for smoke to migrate to other floors as a result of this mechanism, except for the floor immediately above the fire floor (Figure 2b).Figure 2. Smoke movement caused by stack action in heated building (a) low-level fire (b) upper-level fireUnder summer conditions, with an outside temperature higher than that inside, the flow pattern is the reverse of that under winter conditions. The air flows are, however, considerably lower because the inside-to-outside temperature difference is much smaller. Smoke movement to various floors under summer conditions is, therefore, due principally to the heat generated by the fire.Effect of Air-Handling SystemAn air-handling system can also contribute to smoke migration in the event of fire. It can recirculate smoke throughout a building by the return and supply air systems. For this reason some standards call for a shut-down of all major air-handling systems as soon as excessive smoke or heat is detected in the return air system. With the system off, however, vertical air ducts may still act as additional paths for smoke migration to upper floors.
147 4.2.4 Pressure Differences Caused by Air Handling System This will promote the fire spread throughout the building , an effect which can be even greater if the system is running when fire breaks out.Should fire occur anywhere in that part of the building served by HVAC system, this situation can be avoided by automatic shutdown, activated by smoke detector.Alternatively, on a different level of sophistication, the HVAC system can be designed to ‘handle’ the smoke, moving it from the building while protecting other spaces by remote operation of isolation valves.Of course, this requires the facility to reverse flows of air within the system and would demand expert supervision and management.
148 5. Smoke Control System Smoke containment Smoke extraction There are two basic approaches that may be adopted at the design stage to prevent lethal (致命的) concentration of smoke accumulating in certain areas of a building to protect its occupants:Physical barriers such as walls, windows and doors, as well as smoke curtain.Smoke containmentBy use ofNatural ventingSmoke extractionManual ventingSmoke reservoirsPressurization
149 5.1 Smoke Control in Large Spaces For undivided single-story building1) To vent the smoke by creating an opening in the roof .Improvement of visibilityPrevention of flashover and backdraft(such as assembly line): It may be fully sprinkled, but smoke can still spread throughout the building.On arrival of at the fire ground, the first action of the fire brigade may be to vent the smoke by creating an opening in the roof .This canThe number , size and location of vents necessary for efficient venting can be calculated considering: The size of the fire; the height of the building; the type of roof; and the pressure distribution over the roof.
150 2) Use of smoke curtain or screen (烟幕) under the ceiling. Smoke curtain will not only limit the spread but also allow the smoke to build up a buoyancy head below the ceiling which will enhance the flow through the vent.
152 If there is a positive pressure on the roof, created by the wind, then the effectiveness of the venting will be largely reduced: if this pressure is too great, the vent may operate in reverse.
153 5.2 Smoke Control in Shopping Centers Should a fire develop in a shopping center, the mall would become smoke-logged very quickly. Then there are two methods of controlling this situation:1) Vent the smoke directly from the shop to the outside;2) Provide smoke ‘reservoirs’ fitted with automatic ventilators in the ceiling of the shopping mall.
154 A FULLY INTEGRATED SMOKE CONTROL SYSTEM Natural Smoke Control ProductsCasement ventilatorsLouvred ventilatorsSingle Panel ventilatorsDouble Panel ventilatorsMoveable louvresAttenuated ventilatorsPowered Smoke Control ProductsPowered extract fansIn-line powered extract fansSmoke Curtain SystemsFixed and retractable
155 Operation of a vent in the absence of a substantial buoyant head (thin smoke layer). The same effect will occur with a deep layer if the area of vent is too large.
156 5.3 Smoke Control on Protected Escape Routes 1) Smoke doors between the fire and protected escape route will help smoke back but this relies on:A. the door being closed at the time of fireB. persons using the door to reach the escape route not keeping the doors open for a prolonged period.However, smoke will migrate with the natural movement of air within the building, and pressure differentials may encourage movement into the escapeways.
157 2) Pressurization.One is to pressurize the escape route sufficiently so that even under most unfavorable conditions smoke will not enter as there is a net flow of air from the escape route into the adjacent spaces.Early studies show that the differentials of 25-50N/m2 would be sufficient to overcome the worst conditions that might naturally (stack effect and wind), although with a very tall building the stack effect might override even this.In British Standard Code of Practice, a pressure differential of 50 Pa is called under emergency conditions.
160 SUMMARY 1. Definition of smoke 2. Important Features of Smoke 3. Production of Smoke4. Forces Responsible For Smoke Movement5. Smoke Control System
161 QUESTIONS 1. chimney effect 2.What are driving forces responsible for the smoke movement?3. What are the basic approaches to control the movement of smoke?4. For a 30 m high building, if the ambient temperature T0 is 290K and the temperature inside the building Ti is 700K, then how much the pressure difference would be between the inside and the outside of the building?
162 Lesson 5 Study on the compartment fire Chapter 8Lesson 5Study on the compartment fire
163 Key Words & Phrases Simulator 模拟设施 Modeling 模拟 Thermocouple 热电偶 Electronic balance 电子天平Pressure regulator 压力控制器Pressure gauge 压力计Hatch 开口、舱门Data/image acquisition system 数据/图像采集系统Water mist 水雾喷淋Rotameter 旋转式流量计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.
164 Key Words & Phrases Slot 开口、狭槽 Contour 等高线，等温线 Diesel oil 柴油 Exhaust system 排气/废气系统Digital thermometer 数字温度计Voltage regulator 压力控制器Valve 阀门Transformer 变压器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.
165 1. 火灾模拟分类 (Fire Modeling Classification) 实验模型(Experimental Models)数学模型(Mathematical Models)1、实验模型1）小尺寸(Bench/Small Scale )2）中尺寸(Intermediate Scale )3）全尺寸(Full Scale )Bench scale modeling involves a smaller piece of what needs to be tested. Bench models save time, energy and money. These models are also a valuable tool because of their versatility. In a testing laboratory, an engineer has burned a small part or parts of the floor under you to determine its burning characteristics. When we test just a small piece of material, such as some carpeting, we can use that information for the same material used in other applications, such as hospitals, dorms, etc. This way we only need to do one test and apply the information to as many applications as necessary.Intermediate tests like the room/corner test are a step closer to full scale testing. This test is a NFPA standard, NFPA 286: Standard Method of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth. This standard specifies the design of the testing apparatus; a single room with one opening, how to line it with a test specimen and then how to burn it and take measurements. This test is useful for determining the characteristics of the test specimen.models are very rarely run (comparatively to all the other types of tests). Full-scale tests are very expensive (imagine the cost of building a new house just to burn it down) and very bad for the environment. Although in a full-scale test you would have little doubt about how a real fire might proceed, you cannot use that information with other types of configurations. (i.e., if you burn down a single story house, you cannot apply most of your information to a two-story house because the fire would be different.)CFAST, ASET 区域模拟软件；FDS, FLUENT 场模拟软件Cfast 适合的典型场所是多室及单室房间火灾发展，但不适用于大空间建筑，FDS 可以得到较详细的火灾发展过程和较精确的模拟结果，但对计算机速度要求较高，占机时量大，难于计算形状复杂，小区域过多的场所的火灾场景
166 Bench Scale Fire Modeling Bench scale modeling involves a smaller piece of what needs to be tested. Bench models save time, energy and money. These models are also a valuable tool because of their versatility. In a testing laboratory, an engineer has burned a small part or parts of the floor under you to determine its burning characteristics. When we test just a small piece of material, such as some carpeting, we can use that information for the same material used in other applications, such as hospitals, dorms, etc. This way we only need to do one test and apply the information to as many applications as necessary.Intermediate tests like the room/corner test are a step closer to full scale testing.CFAST, ASET 区域模拟软件；FDS, FLUENT 场模拟软件Cfast 适合的典型场所是多室及单室房间火灾发展，但不适用于大空间建筑，FDS 可以得到较详细的火灾发展过程和较精确的模拟结果，但对计算机速度要求较高，占机时量大，难于计算形状复杂，小区域过多的场所的火灾场景
167 Compartment Fire Research Lab Bench Scale Fire TestWith 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.Compartment Fire Research Lab
168 Intermediate Scale Fire Test Pacific Fire Laboratory, Inc.
170 Department of Fire Protection Engineering, University of Maryland Full Scale Fire TestDepartment of Fire Protection Engineering, University of Maryland
171 The University of Tokyo & Building Research Institute, Japan Real Scale Fire TestThe University of Tokyo & Building Research Institute, Japan
172 2. Study on flashoverWith 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.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.
173 2. Study on flashover 1. A box with opening 2. A tray (托盘) 3451. 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)
174 Use of Each DeviceTray (托盘): combustible materials will be put on the tray. (PMMA, polymethyl methacrylate, 聚甲基丙烯酸甲酯)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.
175 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, width and localization of the opening
176 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.
177 3. Study on backdraftThe apparatus is made up of a reduced-scale compartment, fuel system, ignition system, water mist system, dataacquisition system.
178 3. Study on backdraftA special compartment was constructed to withstand the dangerous overpressuresexpected in backdrafts. The experimental apparatus (1.2 m x 0.6 m x 0.6 m) was roughly1/4 that of a residential room to minimize this hazard and to carry out backdraftexperiments more precisely. Because of the explosive nature of backdrafts, the internaland external surfaces of the compartment were totally covered with 2 mm thick stainlesssteel, welding together to ensure strength. The filler between the two layers of stainlesssteel was a refractory aluminosilicate blanket (200 mm thick), whose thermalconductivity was 0.36 W/mK at 1200 K, to provide the primary thermal resistance for thestructure. An observation window (quartz glass, 0.45 m high by 0.75 m wide, capable ofwithstanding 1200 K and 10 kPa) was installed in one of the long walls.In one of theshort walls and ceiling, shown in Fig. 2, bolt holes were built so that different openinggeometries, shown in Fig. 3, could be easily modified by replacing a face plate bolted tothe compartment. These end and ceiling openings were covered with acomputer-activated hatch, which was opened after the fire had been burning for apredetermined time. The angular speed of the hatch was ~ 45o/s.
180 3. Study on backdraft Study is concentrated on the following issues: 1. The opening geometries: six end opening geometries and two ceiling opening geometries.2. The experimental variables included the fuel flow rate, the time during which the fuel was burned.3. The quantities recorded before backdraft included temperature and the concentrations of oxygen, carbon dioxide, and carbon monoxide.4. The gas velocities in the opening and also the pressures in the compartment were measured.To quantify the effect of backdraft, the gas velocities in the opening and also the pressures in the compartment were measured.The effects of different opening geometries on the occurrence of backdraft are discussed.
181 3. Study on backdraft Study results: 1. The mass fraction of unburned fuel, whose critical value varies with the opening geometry, is a key parameter determining the occurrence of backdraft.2. In addition, the experimental results using water mist, generated by a downward-directed pressure nozzle that was operated at pressure of 0.2 MPa, to mitigate backdraft are presented. The experimental results show that water mist is an effective mitigating tactic able to suppress backdraft in a compartment primarily by means of diluting the gas in the compartment and reducing the mass fraction of unburned fuel, rather than by a thermal mechanism of cooling.To quantify the effect of backdraft, the gas velocities in the opening and also the pressures in the compartment were measured.The effects of different opening geometries on the occurrence of backdraft are discussed.
182 4. Study on smoke movement Alternating Current