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A STUDY OF THE PRECURSORS TO BACKDRAFT (SMOKE
EXPLOSION) IN A MECHANICALLY-VENTILATED
COMPARTMENT AND THE ROLE OF SOOT IN THIS
PHENOMENON
PhD student : Alvin Si-Xian LOO
Supervisors: Prof. Alexis COPPALLE (CORIA), Philippe AÎNE (AREVA)
10ème Journée des Doctorants du CORIA 2013
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
WHAT IS A B ACKDRAFT?
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
Well-ventilated case
WHAT IS A B ACKDRAFT?
F i r e p o w e r ( W )
Time (t)
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
Well-ventilated case
WHAT IS A B ACKDRAFT?
F i r e p o w e r ( W )
Time (t)
1 Ignition
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
Well-ventilated case
WHAT IS A B ACKDRAFT?
F i r e p o w e r ( W )
Time (t)
1 Ignition
2 Fire growth
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
Well-ventilated case
WHAT IS A B ACKDRAFT?
F i r e p o w e r ( W )
Time (t)
1 Ignition
2 Fire growth
3 Burning if all combustible materiels
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
Well-ventilated case
WHAT IS A B ACKDRAFT?
F i r e p o w e r ( W )
Time (t)
1 Ignition
2 Fire growth
3 Burning if all combustible materiels
4 Fire decay due to lack of fuel
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
Well-ventilated case
WHAT IS A B ACKDRAFT?
F i r e p o w e r ( W )
Time (t)
1 Ignition
2 Fire growth
3 Burning if all combustible materiels
4 Fire decay due to lack of fuel
5 Extinction of fire
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
Well-ventilated case
WHAT IS A B ACKDRAFT?
F i r e p o w e r ( W )
Time (t)
F i r e p o w e r ( W )
Time (t)
Underventilated case + Backdraft
1 Ignition
2 Fire growth
3 Burning if all combustible materiels
4 Fire decay due to lack of fuel
5 Extinction of fire
1 2 3 4
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
Well-ventilated case
WHAT IS A B ACKDRAFT?
F i r e p o w e r ( W )
Time (t)
F i r e p o w e r ( W )
Time (t)
Underventilated case + Backdraft
1 Ignition
2 Fire growth
3 Burning if all combustible materiels
4 Fire decay due to lack of fuel
5 Extinction of fire
1 2 3 4
1 Ignition
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
Well-ventilated case
WHAT IS A B ACKDRAFT?
F i r e p o w e r ( W )
Time (t)
F i r e p o w e r ( W )
Time (t)
Underventilated case + Backdraft
1 Ignition
2 Fire growth
3 Burning if all combustible materiels
4 Fire decay due to lack of fuel
5 Extinction of fire
1 2 3 4
1 Ignition
2 Fire growth
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Lets start by examining the different stages of the fire power development in a
compartment during an accidental fire:
Well-ventilated case
WHAT IS A B ACKDRAFT?
F i r e p o w e r ( W )
Time (t)
F i r e p o w e r ( W )
Time (t)
Underventilated case + Backdraft
1 Ignition
2 Fire growth
3 Burning if all combustible materiels
4 Fire decay due to lack of fuel
5 Extinction of fire
1 2 3 4
1 Ignition
2 Fire growth
3 Fire decay due to lack of air
+ accumulation of combustible
vapor and soot
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WHAT IS A B ACKDRAFT?
Limited ventilation during an enclosure fire can lead to the production of large
amounts of unburnt pyrolysis products. When an opening is suddenly
introduced, the inflowing air forms a gravity current and begins to mix with
the unburned pyrolysis products,creating a combustible mixture of gases in
some part of the enclosure. Any ignition sources, such as a glowing ember, can
ignite this combustible mixture. Resulting in an extremely rapid burning of
gases/pyrolysis products forced out through the opening and causes a fireball
outside the enclosure. 15-- Fleischmann/Pagni/Quintiere
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WHAT IS A B ACKDRAFT?
Limited ventilation during an enclosure fire can lead to the production of large
amounts of unburnt pyrolysis products. When an opening is suddenly
introduced, the inflowing air forms a gravity current and begins to mix with
the unburned pyrolysis products,creating a combustible mixture of gases in
some part of the enclosure. Any ignition sources, such as a glowing ember, can
ignite this combustible mixture. Resulting in an extremely rapid burning of
gases/pyrolysis products forced out through the opening and causes a fireball
outside the enclosure. 16-- (Fleischmann/Pagni/Quintiere)
Backdraft is sometimes called ‘smoke explosion’
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CONTENTS OF THIS PRESENTATION
What is a Backdraft?
Context and Objectives of this study
Experimental apparatus for underventilated fires
Some Results of underventilated fires
Experimental apparatus for smoke deflagration
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CONTEXT OF THIS STUDY
To prevent radioactive substance leak, compartments are
sealed to ensure air-tightness. Mechanical ventilation
systems maintain an underpressure and renew the air of
the compartment
Study fire scenarios in nuclear installations.
Air
Smoke
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CONTEXT OF THIS STUDY
To prevent radioactive substance leak, compartments are
sealed to ensure air-tightness. Mechanical ventilation
systems maintain an underpressure and renew the air of
the compartment
Study fire scenarios in nuclear installations.
Problem: Maintain confinement within thecompartments during fires Air
Smoke
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CONTEXT OF THIS STUDY
To prevent radioactive substance leak, compartments are
sealed to ensure air-tightness. Mechanical ventilation
systems maintain an underpressure and renew the air of
the compartment
Study fire scenarios in nuclear installations.
Problem: Maintain confinement within thecompartments during fires
- Radioactive substance leak to the outside
- Damage of safety equipments in the compartment or in the ventilationnetwork (filters, doors, dampers…etc)
What could happen:
Air
Smoke
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CONTEXT OF THIS STUDY
To prevent radioactive substance leak, compartments are
sealed to ensure air-tightness. Mechanical ventilation
systems maintain an underpressure and renew the air of
the compartment
Study fire scenarios in nuclear installations.
Problem: Maintain confinement within thecompartments during fires
- Radioactive substance leak to the outside
- Damage of safety equipments in the compartment or in the ventilationnetwork (filters, doors, dampers…etc)
Feared events: - Overpressure caused by the fire
- Temperatures inside the compartment becomes too high
- Backdraft
What could happen:
Air
Smoke
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CONTEXT OF THIS STUDY
Overpressure and high temperatures can be caused by the fire itself:
(Internal energy of the compartment)
Backdraft can happen:
- Smoke dilution in the ventilation network
- Opening of doors by rescue personnels
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CONTEXT OF THIS STUDY
Overpressure and high temperatures can be caused by the fire itself:
(Internal energy of the compartment)
Backdraft can happen:
- Smoke dilution in the ventilation network
- Opening of doors by rescue personnels
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CONTEXT OF THIS STUDY
Overpressure and high temperatures can be caused by the fire itself:
(Internal energy of the compartment)
Backdraft can happen:
- Smoke dilution in the ventilation network
- Opening of doors by rescue personnels
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CONTEXT OF THIS STUDY
Overpressure and high temperatures can be caused by the fire itself:
(Internal energy of the compartment)
So it is important to be able to predict correcly the power generated by the fire.
Backdraft can happen:
- Smoke dilution in the ventilation network
- Opening of doors by rescue personnels
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CONTEXT OF THIS STUDY
- Interaction between the fire and its confined environment
which is under-oxygenated and polluted.
- Aeraulic pertubation caused by the mechanical ventilation
Overpressure and high temperatures can be caused by the fire itself:
(Internal energy of the compartment)
So it is important to be able to predict correcly the power generated by the fire.
Difficulty:
Backdraft can happen:
- Smoke dilution in the ventilation network
- Opening of doors by rescue personnels
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CONTEXT OF THIS STUDY
- Interaction between the fire and its confined environment
which is under-oxygenated and polluted.
- Aeraulic pertubation caused by the mechanical ventilation
Overpressure and high temperatures can be caused by the fire itself:
(Internal energy of the compartment)
So it is important to be able to predict correcly the power generated by the fire.
Difficulty:
Backdraft can happen:
- Smoke dilution in the ventilation network
- Opening of doors by rescue personnels
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CONTEXT OF THIS STUDY
- Interaction between the fire and its confined environment
which is under-oxygenated and polluted.
- Aeraulic pertubation caused by the mechanical ventilation
Overpressure and high temperatures can be caused by the fire itself:
(Internal energy of the compartment)
So it is important to be able to predict correcly the power generated by the fire.
Difficulty:
Backdraft can happen:
- Smoke dilution in the ventilation network
- Opening of doors by rescue personnels
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1. Behavior of underventilated fires in a
mechanically-ventilated compartment.• Underventilated fires in confined
compartments must occur before the
conditions favourable to Backdraft can
be created.
• Experimental study using a reduced-
scale 1m3 compartment (fire chamber)
OBJECTIVES OF THIS STUDY
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CONTENTS OF THIS PRESENTATION
What is a Backdraft?
Context and Objectives of this study
Experimental apparatus for underventilated fires
Some Results of underventilated fires
Experimental apparatus for smoke deflagration
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Diagram of the experimental apparatus for studying underventilated fires in a
reduced-scale mechanically-ventilated compartment (fire chamber)
EXPERIMENTAL APPARATUS FOR FIRES
• Compartment made of steel - 1m2 steel plates are fixed onto a frame
• Braids are crushed between the steel plates and the frame to ensure air-tightness
• Refractory ceramic fibres on the inner wall to ensure thermal insulation.
•Water seal between the scale and the fuel to ensure air-tightness
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CONTENTS OF THIS PRESENTATION
What is a Backdraft?
Context and Objectives of this study
Experimental apparatus for underventilated fires
Some Results of underventilated fires
Experimental apparatus for smoke deflagration
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Fuel Mass Loss Rate (MLR) estimation of pool fires (Hamins 1996) :
Smoke
Fuel
flameQ
reflect Q
smokeQ
SOME RESULTS FOR UNDERVENTILATED FIRES
One example of study: Determination of the fuel’s Mass Loss Rate J o urn
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Fuel’s mass loss rate is caused by
the heat flux from various sources:
flame, smoke, compartment walls
The fuel reflects and reradiatessome part of the heat away.
wall Q
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SOME RESULTS FOR UNDERVENTILATED FIRES
ARR = 5
ARR = 0,3
ARR =11
MLR at Free-burning (fire in non-enclosed area)
- Flames are extinguished due to lack of air
- MLR in these cases do not reach free burning rates
Development of the fuel’s Mass Loss Rate (MLR) at different ventilation rates:
Fuel : Heptane
Size of fuel pan: 2 x 10.8cm
*ARR = Air Renewal Rate
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0.2s 0.2s 0.2s
Expanding flames
SOME RESULTS FOR UNDERVENTILATED FIRES Visual results:
Flames extend outside
the perimeter of the fuel
pan periodically
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0.2s 0.2s 0.2s
Expanding flames
Wandering flames:
Ghosting flames:
0.2s 0.2s 0.2s
0.2s 0.2s 0.2s
SOME RESULTS FOR UNDERVENTILATED FIRES Visual results:
Flames extend outside
the perimeter of the fuel
pan periodically
Flames move around the
compartment towards
the opposite side of the
air inlet
Flames are lifted above
the fuel pan and float
around
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CONTENTS OF THIS PRESENTATION
What is a Backdraft?
Context and Objectives of this study
Experimental apparatus for underventilated fires
Some Results of underventilated fires
Experimental apparatus for smoke deflagration
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Fresh air
Smoke from the fire chamber
EXPERIMENTAL APPARATUS FOR B ACKDRAFT
Diagram of the experimental apparatus (under construction):
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Methane gas
Fresh air
Smoke from the fire chamber
EXPERIMENTAL APPARATUS FOR B ACKDRAFT
Diagram of the experimental apparatus (under construction):
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E B
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EXPERIMENTAL APPARATUS FOR B ACKDRAFT
What do we wish to study?
(thesis of Courty 2012)
1) Conditions of Backdraft :- Concentration of the different species
- Temperature
- Soot properties (size distribution, mass concentration)Gas analyser Testo 350
Thermocouples
2) Flame propagation
- Dynamic pressure (pressure increase during the
deflagration)
- Flame speed-Ombroscopy technique (thesis of Courty 2012)
-PIV technique (thesis of Varea 2013)
(thesis of Varea 2013)
Dynamic pressure sensor
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E B
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EXPERIMENTAL APPARATUS FOR B ACKDRAFT
Role of soot -- What do we wish to determine?
We suspect that during the deflagration, the thermal radiation of soot cancontribute to the heating the fresh gases, thus increasing the flame speed.
+
?
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E B
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EXPERIMENTAL APPARATUS FOR B ACKDRAFT
Role of soot -- What do we wish to determine?
We suspect that during the deflagration, the thermal radiation of soot cancontribute to the heating the fresh gases, thus increasing the flame speed.
Heating of the fresh gas can be caused by radiation
Combustion productsFresh gas
SL
Pre-heating zone Reaction zone
Flame propagation mecanism:
+
?
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E B
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EXPERIMENTAL APPARATUS FOR B ACKDRAFT
Role of soot -- What do we wish to determine?
We suspect that during the deflagration, the thermal radiation of soot cancontribute to the heating the fresh gases, thus increasing the flame speed.
Heating of the fresh gas can be caused by radiation
The radiation emission and
absorption of soot increase the
radiated heat received by the freshcombustible mixture
More powerful deflagration ?
Combustion productsFresh gas
SL
Pre-heating zone Reaction zone
Flame propagation mecanism:
+
?
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