Chapter 7 Compartment Fire Lesson 1 Development of

Chapter 7 Compartment Fire Lesson 1 Development of Compartment Fire

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

Key Words & Phrases Ventilate (ventilation) 通风 Ventilation Factor 通风因子 Opening Factor 开口因子

1. Definition of compartment fire A compartment fire is a fire that takes (室内火灾) means place that takes place in a compartment. a a fire in a compartment, such as a room, bus or a train compartement. 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.

WTC 911

The big Garley building fire Airport terminal fire, , 1996, Hongkong 1996, Duesseldorf, Germany

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)

Bus fires: Burnt to the top within 10 min Burnt completely within 10 min

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.

Outdoors, fire grows steadily. Indoors, trapped heat and smoke cause temperature to suddenly go up.

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.

3. Ignition (点燃)of a Compartment Fire Development of a Compartment Fire After ignition three kinds of fires may follow: Smouldering Fires Glowing Fires Flaming Fires 3. 1 Smouldering Fires A fire in solid fuel which is heat-limited (energy-limited) or ventilation limited will smoulder.

A Heat-limited Smouldering Fire

A Ventilation-limited Smouldering Fire

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.

After Ignition Three Kinds of Fires May Follow: 3. 2 Glowing Fires Glowing 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.

A Glowing Fire

Fate of a Glowing Fire: Glowing fire is normally of short duration and is apt to self-extinguish.

After Ignition Three Kinds of Fires May Follow: 3. 3 Flaming Fires A 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.

A Flaming Fire

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.

4. Development of a compartment fire Temperature Flashover Decay 轰燃 衰减阶 段 Fully developed stage Growth stage (post-flashover) (pre-flashover) 初期增长阶段 充分发展阶段 Time

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.

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.

4. 2 Fully developed stage (post-flashover)

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.

4. 4 Flashover Growth stage Transition 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.

• 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.

5. The Necessary Condition for Safe Evacuation tp + ta+ trs ≤ tu Where 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.

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.

Burning rate (kg/min) Influences of Ventilation factor AH 1/2(m 5/2)

Ventilation Factor k or g / m s i 1/2 is called ventilation factor. Here AH n

Theoretical Deduction of the Ventilation Factor

Ventilation Factor k or g / m s i

Control Forms of a Compartment Fire Fuel-controlled （燃料控制） fire Ventilation-controlled （通风控制） fire Air (oxygen) Supply Fuel

/Af Kg/m 2 s m/Af kg/m 2 s

Influence of Ventilation on the Control forms of fire Ventilationcontrolled fire Fuel-controlled fire

Opening Factor

Opening Factor Opening factor: a measure of the rate of temperature rise of a fire, defined as the ratio of the ventilation facto and the total bounding area of an enclosure. Fuel-controlled fire Ventilationcontrolled fire

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. Flashover Growth Fully-developed Decay • 4. Factors Affecting Fire Growth (ventilation)

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?

Chapter 8 Compartment Fire Lesson 2 Flashover

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

Development of a compartment fire Temperature Flashover Decay period 轰燃 衰减阶段 Fully developed period Growth period (post-flashover) 充分发展阶段 (pre-flashover) 初期增长阶段 Time

1. Definition of Flashover • The term 'flashover' was first introduced by UK scientist P. H. Thomas in the 1960 s and was used to describe theory of a fire's growth up to the point where it became fully developed.

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.

Other Popular. Flashover Definition of Definitions n. The 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".

2. Formation of flashover Initial development of a Fire Plume (火羽) in a Compartment.

A hot layer of smoke forms under the ceiling of the room. And it will produce radiation feedback heat （辐射热反馈）.

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.

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.

Flashover Fire Cases

Video 1: Flashover experiment

Fire in Bradford City Soccer Stadium, England, 1985. P 1: first visible flames P 2: 90 seconds P 3: 150 seconds

3. Consequences of Flashover Large number of deaths and injuries Trapped building occupants (被困居民) Firefighters Properties Great damage Building structure

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.

Death caused by flashover in some fire cases Year Place Death 1981 Dublin 48 1982 Los Angeles 24 1991 Petersburg 8 1996 Dusseldorf 17 1997 UK 3 2002 Paris 5 In 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'.

Firefighters confronted a flashover. Firefighter caught inside a flashover.

3. 2 Great damage caused by flashover Properties Great damage Building structure • Wooden beams(木梁) will char(烧焦); Structural Failure • Steel (钢筋) will be permanently weakened. Then it will expand damage surrounding structural components (构件); • Concrete (水泥) and masonry (砖瓦) will spall (破碎) and may crack into pieces.

Structural Failure • After 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.

Catastrophic Collapse of a Building

Does flashover occur in all the compartment fires? Video 2: Non-Flashover experiment

The Development of Fire With and Without Flashover

4. Fuel and Ventilation Conditions Necessary for Flashover

Fuel and Ventilation Conditions Necessary for Flashover 1. Mass burning rate: 2. Ventilation factor:

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 20 k. W/m 2; • Gas Temperature at ceiling level (顶棚气体温度) reaches 600℃;

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.

6. Warning signs of flashover n Flames are running overhead on the ceiling; n 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;

7. Point of no return • The 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.

7. Point of no return 1. Fire temperatures of 280‘-320’ F cause intense pain and damage to exposed skin. (138 -160 ℃) 2. The average temperature in a room that flashes over is 1000' to 1500' F. (537 -816 ℃) 3. The average person moves 2. 5 -feet per second when walking 4. 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. Five feet is the point of no return

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.

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.

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.

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?

QUESTIONS 4. According to fire protection engineers flashover is caused by which one of the following? A. Radiation heat B. Radiation feedback heat C. Conduction heat D. None of the above 5. Which one of the following is not a method used by firefighters to delay flashover? A. Venting to release heat B. Not venting to starve the fire of oxygen and thus slow down heat generation C. Use a portable extinguisher on the fire to cool it down D. Remove combustible from the fire area

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;

Chapter 8 Compartment Fire Lesson 3 Backdraft

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

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. " n 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. "

Smoke Is Combustible

Air Introduction

A Basic Scenario Limited ventilation can lead to a fire in a compartment producing fire gases containing significant proportions of partial combustion products and unburnt 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.

BACKDRAFT

BACKDRAFT

2. Formation of Backdraft • • • 1) A fire burning in a room with poor ventilation 2) Accumulation of flammable gases 3) Air introduction at the breaking of openings 4) Formation of mixture within flammability limits 5) Ignition of the mixture 6) Explosion or deflagration and pressure rise

3. Conditions Necessary for Backdraft • 1) The accumulation of smoke consisting of unburnt 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 (autoignition), without a source of ignition being introduced.

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.

Backdraft Is a Kind of 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 cause serious burns and an explosion can collapse walls, partitions and iron shutters (卷帘铁门), crushing firefighters beneath them.

4. Consequences of Backdraft Deaths and injuries (Firefighters) Properties Great damage Building structure

Destructive Effects Caused by Backdraft Explosion Pressures Effect of Explosion Glass shattering (破碎) Firefighter knock down Wood partition collapse Cinder block (煤渣空心砖) wall collapse Brick wall collapse Firefighter lung(肺) damage Threshold for fatalities 50% fatalities Destructive Peak Pressure (psi) 0 -5 1 1 -2 2 -3 7 -8 15 35 50

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);

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 sounds It 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.

Smoke Drawn Back through Opening

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.

The Peru (秘鲁) firefighters force entry just prior to the backdraft Amazing Peru Backdraft The Aftermath (后期)!!! An exterior defensive operation is mounted following the backdraft.

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) Flanking (侧翼攻击)

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.

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.

Firefighters in Australia get to grips with an 'entry & attack-module' trainer.

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.

Tactical Firefighting Training Staffordshire County firefighters (UK) training with a backdraft demonstrator (示范装置)

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 unburnt 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.

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.

Differences • 2. 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.

Differences • 3. The triggering or cause of them. Backdraft: a ventilation induced ignition of the gases 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; Flashover: a heat induced development of the fire 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 autoignition temperature and triggers a flashover.

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.

Flashover or Backdraft?

A Backdraft Case The backdraft that blew apart an Illinois church on February 9 th, 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 (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.

SUMMARY • • 1. Definition of backdraft 2. Formation of backdraft 3. Conditions Necessary for Backdraft 4. Consequences of Backdraft 5. Warning Signs of Backdraft 6. Preventing Death and Injury 7. The differences between Backdraft and flashover.

QUESTIONS • 1. What are the warning signs of a backdraft? • 2. What are three firefighting tactics that can reduce destructive effects of a backdraft explosion? • 3. What are the differences between a backdraft and flashover?

Chapter 8 Compartment Fire Lesson 4 The Production and Movement of Smoke

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

1. Definition of Smoke • Gross 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, 1993 c）

Smoke

2. Important Features of Smoke Two important features of smoke are that: Smoke reduces visibility. Smoke contains toxic products of combustion.

2. 1 Reduced Visibility With 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.

2. 2 Toxicity of Smoke • 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.

2. 2 Toxicity of Smoke • What 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.

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)

Smoke Influences Safe Evacuation The Necessary Condition for Safe Evacuation: tp + ta+ trs ≤ tu Smoke 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.

Huge plumes of thick smoke and flames engulf the upper half of the 56 -floor East Tower in Caracas, Venezuela, October 17. 2004 (Reuters Photo). 25 people were injured due to the inhalation of smoke.

3. Production of Smoke Smouldering fire Smoke can be produced by Flaming fire 1) 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.

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.

Common Combustion Product Concentrations in Residential Fires *Particulates are given as mg/m 3. IDLH stands for a concentration defined as ‘immediately dangerous for life and health’.

4. Smoke Movement • The 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.

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 air movement; • The air handling system within the building.

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.

Pressure Generated Directly by the Fire

Density of Air as a Function of Temperature (K) Density (kg/m 3) 280 1. 26 290 1. 22 300 1. 18 500 0. 70 700 0. 50 1100 0. 32

4. 2. 2 Pressure Differences due to Natural Buoyancy Forces

Chimney/Stack Effect • The stack effect in tall buildings: (a) external temperature (T 0)< internal temperature (Ti); (b) T 0 > Ti , showing accompanying flows.

Chimney Effect • The 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.

Stack Effect

Chimney Effect

Stack Effect • The effect of stack on the movement of smoke in a high-rise building (Ti> T 0)

Smoke movement caused by stack action in heated building Smoke movement (a) low-level fire caused by fire in shaft. (b) upper-level fire

The Height of the Neutral Plane neutral plane

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:

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.

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.

5. Smoke Control System 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: n. Smoke containment Physical barriers such as walls, windows and doors, as well as smoke curtain. Natural venting • Smoke extraction Manual venting Smoke reservoirs Pressurization

5. 1 Smoke Control in Large Spaces For undivided single-story building • 1) To vent the smoke by creating an opening in the roof. Improvement of visibility Prevention of flashover and backdraft The 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.

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.

• 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.

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.

A FULLY INTEGRATED SMOKE CONTROL SYSTEM Natural Smoke Control Products • Casement ventilators • Louvred ventilators • Single Panel ventilators • Double Panel ventilators • Moveable louvres • Attenuated ventilators Powered Smoke Control Products • Powered extract fans • In-line powered extract fans Smoke Curtain Systems • Fixed and retractable

• 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.

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 fire • B. persons using the door to reach the escape route not keeping the doors open for a prolonged period.

• 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 2550 N/m 2 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.

5. 3 Smoke Control on Protected Escape Routes

Pressurized Escape Route

SUMMARY • • • 1. Definition of smoke 2. Important Features of Smoke 3. Production of Smoke 4. Forces Responsible For Smoke Movement 5. Smoke Control System

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 T 0 is 290 K and the temperature inside the building Ti is 700 K, then how much the pressure difference would be between the inside and the outside of the building?

Chapter 8 Lesson 5 Study on the compartment fire

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

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

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 Fire Modeling

Bench Scale Fire Test Compartment Fire Research Lab

Intermediate Scale Fire Test Pacific Fire Laboratory, Inc.

Intermediate Scale Fire Test

Full Scale Fire Test Department of Fire Protection Engineering, University of Maryland

Real Scale Fire Test The University of Tokyo & Building Research Institute, Japan

2. Study on flashover

2. Study on flashover 1 1. A box with opening 2. A tray (托盘) 2 3. An electronic Balance (电子天平) 4. A printer (打印机) 5. Signal detector 4 3 5 (信号检测仪) ①~⑦Thermal couples (热电偶)

Use of Each Device • Tray (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.

• 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 ceiling • 2. Both the width and height of the door can be adjusted. The height, width and localization of the opening

• 3. Different materials of different mass ( 质量) can be put on the tray and used as combustible material. The kinds of combustible materials The amount of combustible materials • 4. 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.

3. Study on backdraft

3. Study on backdraft

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.

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.

4. St udy o n s m o ke m o v e m e nt

Evaluation of CFD to predict smoke movement in complex enclosed spaces

Figure F. 6 - Temperature distribution and velocity vectors 2 metres above the ground, 120 seconds after ignition.

6. Modeling Smoke Visibility in CFD

Distribution of smoke mass fraction in the center plane of the room.