Chapter 7 Compartment Fire

Combustion fundamentals of fire

Don’t do the crime if you can’t do the time.

（要想人不知，除非己莫为）

Lesson 3 BackdraftLesson 3 Backdraft

Chapter 7Compartment Fire


1. Definition of backdraft2. Formation of backdraft3. Necessary Conditions for Backdraft4. Consequences of Backdraft5. Warning Signs of Backdraft6. Preventing Death and Injury7. Differences between Backdraft and

flashover.

contentcontent


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.

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.

insufficieninsufficiencycy


Limited ventilationLimited ventilation can lead to a fire in a can lead to a fire in a compartment producing compartment producing fire gasesfire gases containing significant proportions of containing significant proportions of partial combustion productspartial combustion products and and un-un-burnt pyrolysis productsburnt pyrolysis products, which are all , which are all combustiblecombustible..

If these accumulate then If these accumulate then the admission the admission of airof air when an opening is made to the when an opening is made to the compartment can compartment can lead to a sudden lead to a sudden deflagrationdeflagration. .

This deflagration moving through the This deflagration moving through the compartment and out of the opening is compartment and out of the opening is BACKDRAFTBACKDRAFT..

A Basic Scenario 想象


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


3.Necessary Conditions for Backdraft(1) The accumulation of smoke consisting of un-burnt pyrolyzates ANDAND 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.



flashover.

contentcontent


4. Consequences of Backdraft

Pressure

Death and injure

Great damage

firefightersespecially

Properties

Building structure


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.


4.1 Pressure




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.



4.3 Great damage

Flame accompanying the explosion can cause cause serious burns, collapsecollapse walls, partitionpartition and ironiron shutters ( 卷帘铁门 ) and crushcrush firefighters beneath them.



Pressure

Death and injure

Great damage

firefightersespecially

Properties

Building structure


5. Warning Signs of Backdraft

Outside the roomOutside the room

Inside the roomInside 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).


4.1 Outside the room

awareaware

seesee

feelfeel



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.


Smoke Drawn Back through the Door


Full protective gear:

helmets( 头盔 )

hoods( 防护帽 )

gloves( 手套 )

boots( 长靴 )bunker pants

( 防护裤 )

coat

Backdraft is very dangerous, Firefighters should know that explosions happen fast, sometimes too fast for firefighters to take cover and protect themselves.

fire water branch


but if you were caught in an explosion, it may protect you survive from the blast and not be hurt hardly.

Full protective gear:

Backdraft is very dangerous, Firefighters should know that explosions happen fast, sometimes too fast for firefighters to take cover and protect themselves.

Protective fire gear may be hot, cumbersome ( 笨重的 ) and slow you down,


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.



flashover.

contentcontent


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 (6.1 Venting ( 通风通风 ))

6.2 Quenching (6.2 Quenching ( 熄灭熄灭 ))

6.3 Flanking (6.3 Flanking ( 侧翼攻击侧翼攻击 ))


6. Preventing Death and Injury6.1 Venting

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 Injury6.2 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 Injury6.3 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

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

Training in other aspects


7. Differences between Backdraft and flashover7. Differences between Backdraft and flashover

There are FOURFOUR 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.




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.




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.




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.





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.





Page301 The last paragraph





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.




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.


Flashover or Backdraft?Extension Reading

Extreme Fire Behavior

Modelling

Modelling of FLASHOVER and BACKDRAFT Using Fire Field Models






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.

A Backdraft Case


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. “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 Study the case in detailin detail



flashover.

SummarySummary


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?

Homework


Documents

Chapter 7 Compartment Fire