Chapter 7 Compartment Fire Lesson 3 Backdraft Don’t do the crime if you can’t do the time. （要想人不知，除非己莫为）

Key Words & Phrases 回燃 热解产物 可燃极限 爆燃 通风、排出 熄灭、结束 侧翼攻击 Backdraft/backdraught 回燃 Pyrolyzate (pyrolyze) 热解产物 Flammability Limits 可燃极限 Deflagration 爆燃 Vent 通风、排出 Quench 熄灭、结束 Flank 侧翼攻击

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

Snippet from the film of LADDER 49

1. Definition of Backdraft Definition from NFPA: 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 supply of oxygen due to fire. insufficiency Other definition from IFE (Institution of Fire Engineers) : An explosion of greater or lesser degree, caused by the inrush 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).

A Basic Scenario想象 Limited 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 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 ，pressure rise (Partial combustion products and un-burnt pyrolysis products )

Smoke is Combustible 'When the temperature is too low to support flaming combustion, or when oxygen levels drop below 15%, the fuel package breaks down (pyrolysis) with out active flaming and most of the carbon remains on the material. This produces a lighter colored smoke. It is important to realise that as the fire develops, heat will be transferred to neighboring compartments, which can result in pyrolysis of the contents and an accumulating of white smoke, which contains a very high percentage of unburnt fuel. As a general guide; Lighter colored smoke often indicates that there is an accumulation of pyrolysis products due to increasing compartment temperatures. This is often seen in rooms or spaces adjacent to the fire compartment'......... Photos courtesy of Wayne Atkins (Australia) '3D Firefighting' (FPP/IFSTA) 2005

3.Necessary Conditions 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. (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.

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

4. Consequences of Backdraft Pressure Death and injure Great damage especially firefighters Properties Building structure

4. Consequences of Backdraft 4.1 Pressure Pressure rise because backdraft will force the burning gases in the compartment out through the openings with a high velocity, possibly igniting some of the unburned pyrolyzates that had be left in the compartment. This can create a significant fire-ball outside the compartment.

4. Consequences of Backdraft 4.2 Death and injure 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.

4. Consequences of Backdraft 4.3 Great damage Flame accompanying the explosion can cause serious burns, collapse walls, partition and iron shutters (卷帘铁门) and crush firefighters beneath them.

Destructive Effects Caused by Backdraft Explosion Pressures Effect of Explosion Destructive Peak Pressure (psi) Glass shattering (破碎) 0-5 Firefighter knock down 1 Wood partition collapse 1-2 Cinder block (煤渣空心砖) wall collapse 2-3 Brick wall collapse 7-8 Firefighter lung(肺) damage 15 Threshold for fatalities 35 50% fatalities 50 99% fatalities 65 The other fact firefighters should know is that it does not take much explosive pressure in a confined space for an explosion to cause destruction and death. 1psi=6.89 kPa

4. Consequences of Backdraft Pressure Death and injure Great damage especially firefighters Properties Building structure

5. Warning Signs of Backdraft Outside the room Inside the room 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

5. Warning Signs of Backdraft 4.1 Outside the room Before opening a door or window to the compartment, the firefighter should be aware of: (1) A fire in a compartment with few openings has been burning for a long time. (2) Oily deposits on windows. (3) (跳动的) Pulsating smoke from openings. (4) Hot doors and door handles (windows). aware 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 see feel

5. Warning Signs of Backdraft 4.2 Inside the room (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(进行), there is probably little action that can be taken by a firefighter to prevent it. 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 Inside, or looking into a compartment a potential backdraft may be indicated by:

Smoke Drawn Back through the Door

Backdraft is very dangerous, Firefighters should know that explosions happen fast, sometimes too fast for firefighters to take cover and protect themselves. Full protective gear: helmets(头盔) fire water branch hoods(防护帽) gloves(手套) coat Face mask boots(长靴) bunker pants (防护裤)

Backdraft is very dangerous, Firefighters should know that explosions happen fast, sometimes too fast for firefighters to take cover and protect themselves. Full protective gear: but if you were caught in an explosion, it may protect you survive from the blast and not be hurt hardly. Protective fire gear may be hot, cumbersome (笨重的) and slow you down, Face mask

The Peru (秘鲁) firefighters force entry just prior to the backdraft Amazing Peru Backdraft! The 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.

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

6. Preventing Death and Injury There are three tactics(战术) that can reduce the chances of getting caught in a backdraft: 6.1 Venting (通风) 6.2 Quenching (熄灭) 6.3 Flanking (侧翼攻击) 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 explosion After firefighters understand what a backdraft is, they must know how to prevent death and injury from such an explosion.

6. Preventing Death and Injury Venting a roof skylight (天窗) over a burning room is one of the most effective method to protect firefighters from the blast of the backdraft. (1) When roof conditions permit, the quick removal of the skylight can vent smoke-filled room and break up the explosive mixture. (2) Even if the smoke explosion occurs, the blast will be diverted(转移) upward and out of the room from the opening, and be away from the firefighters advancing the hose-line.

6. Preventing Death and Injury 6.2 Quenching Before entering a superheated confined room, charged hose-line (fire water branch) 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)The water can cool a potential and explosive atmosphere. (2)The powerful water stream might break up the explosive atmosphere.

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

6. Preventing Death and Injury 6.3 Flanking When venting and quenching are impossible, the officer in command can order two hose-lines into position, one on each side of a door or window of the 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 Training in other aspects Staffordshire County firefighters (UK) training with a backdraft demonstrator (示范装置)

7. Differences between Backdraft and flashover There are FOUR main differences: There will be shock waves (冲击波) during backdraft fire, which will break the confining structure and windows around the explosion; blasts of smoke and flame may blow out a doorway; part of the structure may collapse. Flashover is rapid fire development, but without the speed of explosion of the chemical reaction. 7.1 Backdraft is an explosion, flashover is a transition. 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. 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.

7. Differences between Backdraft and flashover There are FOUR main differences: You may experience only one or two backdraft during your entire career. But flashover happens often (flame suddenly full the whole room). You will probably face flashover again next time. 7.2 backdraft does not happen as often as flashover does. 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. 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.

7. Differences between Backdraft and flashover There are FOUR main differences: Basic scientific definitions of flashover and backdraft suggest that flashover is primarily "heat induced" whilst backdraft is "ventilation induced". 7.3 The triggering or cause of them are different. 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. 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. The basic scientific definitions of flashover or backdraft suggest that flashover is primarily "heat induced" whilst backdraft is "ventilation induced". however, it is also scientifically documented that an inflow of air/oxygen into an under bentilated fire compartment can cause a situation leading to "thermal runaway". This is where ventilation (intentional or as a result of fire development) causes an increase in the burning rate but allows the temperature to increase in the compartment as the vent opening is not large enough to allow sufficient heat to escape.As more heat is beijing generated by the air inflow feeding the fire than can escape from the opening, a flash-over may result. therefore it can be seen that it is sometimes very hard to differentitate between a flashover or a backdraft.

7. Differences between Backdraft and flashover There are FOUR main differences: backdraft is "ventilation induced". 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. 7.3 The triggering or cause of them are different. 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. 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. The basic scientific definitions of flashover or backdraft suggest that flashover is primarily "heat induced" whilst backdraft is "ventilation induced". however, it is also scientifically documented that an inflow of air/oxygen into an under bentilated fire compartment can cause a situation leading to "thermal runaway". This is where ventilation (intentional or as a result of fire development) causes an increase in the burning rate but allows the temperature to increase in the compartment as the vent opening is not large enough to allow sufficient heat to escape.As more heat is beijing generated by the air inflow feeding the fire than can escape from the opening, a flash-over may result. therefore it can be seen that it is sometimes very hard to differentitate between a flashover or a backdraft.

7. Differences between Backdraft and flashover There are FOUR main differences: flashover is primarily “ heat induced“. The trigger of a flashover is heat. The theory of flashover is heat, which raises the temperature of the gases and furnishings in the room to the auto-ignition temperature and triggers a flashover. 7.3 The triggering or cause of them are different. 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. 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. The basic scientific definitions of flashover or backdraft suggest that flashover is primarily "heat induced" whilst backdraft is "ventilation induced". however, it is also scientifically documented that an inflow of air/oxygen into an under bentilated fire compartment can cause a situation leading to "thermal runaway". This is where ventilation (intentional or as a result of fire development) causes an increase in the burning rate but allows the temperature to increase in the compartment as the vent opening is not large enough to allow sufficient heat to escape.As more heat is beijing generated by the air inflow feeding the fire than can escape from the opening, a flash-over may result. therefore it can be seen that it is sometimes very hard to differentitate between a flashover or a backdraft.

7. Differences between Backdraft and flashover There are FOUR main differences: Page301 The last paragraph 7.3 The triggering or cause of them are different. 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. 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. The basic scientific definitions of flashover or backdraft suggest that flashover is primarily "heat induced" whilst backdraft is "ventilation induced". however, it is also scientifically documented that an inflow of air/oxygen into an under bentilated fire compartment can cause a situation leading to "thermal runaway". This is where ventilation (intentional or as a result of fire development) causes an increase in the burning rate but allows the temperature to increase in the compartment as the vent opening is not large enough to allow sufficient heat to escape.As more heat is beijing generated by the air inflow feeding the fire than can escape from the opening, a flash-over may result. therefore it can be seen that it is sometimes very hard to differentitate between a flashover or a backdraft. 37

7. Differences between Backdraft and flashover There are FOUR main differences: Backdraft explosions occur during the first and the third stages of fire, when the combustible smoke is in a confined space. During the growth and decay stages, smoldering can take place and generate explosive gas such as CO (carbon monoxide). 7.4 Flashover and backdraft occours at different stage. 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. 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.

7. Differences between Backdraft and flashover There are FOUR main differences: On the other hand, flashover is the transition of and , so it only occurs between the two stages, it signals the end of the growth stage. 7.4 Flashover and backdraft occours at different stage. 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. 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.

Flashover or Backdraft? Extension Reading Extreme Fire Behavior Modelling Modelling of FLASHOVER and BACKDRAFT Using Fire Field Models Flashover? Backdraft? Fire Gas Ignition? VotesFlashover  29%91Backdraft  35%108Fire Gas Ignition  34%105 304 votes total The 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.

14.Oktober 2004 05:57

A Backdraft Case The backdraft that blew apart an Illinois church（伊利诺斯州教堂） on February 9th, 2004 has been named the largest backdraft ever documented in the U.S. 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。

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 was in his command vehicle（消防指挥车） when the backdraft occurred Riddle was in his command vehicle（消防指挥车） when the backdraft occurred. “I heard the noise and I looked up... the piece of the roof was being removed - it went up about 10 feet and then came back down.” he said. There was no warning except that immediately before the 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 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. Study the case in detail

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

Homework 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?

Key words and 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 Entrain 卷吸 First, let’s see some vocabulary & Phrases. The first one is volatile, it means evaporating readily at normal temperature and pressures. 汉语，挥发性的 The second one, particulate, of ,relating to or formed of separate particles. 汉语为，微粒状的，名词为particle 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,因温差而使局部空气或其它气团向上移动的现象 ,we will explain it in detail in later class. Louver/louvre 天窗/百叶窗

Thank You !