Combustion fundamentals of fire Don`t do the crime if you can`t do

advertisement
Combustion fundamentals of fire
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)
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
Snippet from the film of LADDER 49
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
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
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
4. Consequences of Backdraft
Pressure
Death and injure
especially
firefighters
Properties
Great damage
Building structure
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
4. Consequences of Backdraft
Pressure
Death and injure
especially
firefighters
Properties
Great damage
Building structure
Combustion fundamentals of fire
5. Warning Signs of Backdraft
Outside the room
Inside the room
Combustion fundamentals of fire
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).
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
Smoke Drawn Back through the Door
Combustion fundamentals of fire
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
bunker pants
(防护裤)
boots(长靴)
Combustion fundamentals of fire
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:
Protective
fire gear may
be hot,
cumbersome
(笨重的) and
slow you down,
but if you were
caught in an
explosion, it
may protect
you survive
from the blast
and not be hurt
hardly.
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
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)
Combustion fundamentals of fire
6. Preventing Death and Injury
6.1 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.
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
Firefighters in Australia get to grips with an
'entry & attack-module' trainer.
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
Tactical Firefighting Training
Training in
other aspects
Staffordshire County firefighters (UK) training with
a backdraft demonstrator (示范装置)
Combustion fundamentals of fire
7. Differences between
Backdraft and flashover
There are FOUR main differences:
7.1 Backdraft is an explosion,
flashover is a transition.
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.
Combustion fundamentals of fire
7. Differences between
Backdraft and flashover
There are FOUR main differences:
7.2 backdraft does not happen as often
as flashover does.
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.
Combustion fundamentals of fire
7. Differences between
Backdraft and flashover
There are FOUR main differences:
7.3 The triggering or cause of
them are different.
Basic scientific definitions of flashover and
backdraft suggest that flashover is primarily
"heat induced" whilst backdraft is "ventilation
induced".
Combustion fundamentals of fire
7. Differences between
Backdraft and flashover
There are FOUR main differences:
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.
Combustion fundamentals of fire
7. Differences between
Backdraft and flashover
There are FOUR main differences:
7.3 The triggering or cause of
them are different.
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.
Combustion fundamentals of fire
7. Differences between
Backdraft and flashover
There are FOUR main differences:
7.3 The triggering or cause of
them are different.
Page301 The last paragraph
Combustion fundamentals of fire
7. Differences between
Backdraft and flashover
There are FOUR main differences:
7.4 Flashover and backdraft occours at
different stage.
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).
Combustion fundamentals of fire
7. Differences between
Backdraft and flashover
There are FOUR main differences:
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.
Combustion fundamentals of fire
Flashover or Backdraft?
Extension Reading
Extreme Fire Behavior
Modelling
Modelling of
FLASHOVER and
BACKDRAFT Using
Fire Field Models
Combustion fundamentals of fire
Combustion fundamentals of fire
Combustion fundamentals of fire
Combustion fundamentals of fire
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
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
Combustion fundamentals of fire
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.
Combustion fundamentals of fire
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?
Combustion fundamentals of fire
Download
Related flashcards
Create Flashcards