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September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Albert Simeoni
UMR 6134
CNRS UMR 6134 – Univerità di CorsicaBP 52 - 20250 Corte, France
+33 495 450 638 – simeoni@univ-corse.frhttp://spe.univ-corse.fr
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Physical description ofForest Fires
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
1
Introduction
• Physical description of forest fires aim to understand the behaviour of forest fires and predict their spreading
• This research started 50 years ago in Australia, USA and USRR
• The involved mechanisms are very complex
• The operational objectives are to predict the fire spread and to estimate the impact of the fire
The predictions are done thanks to fire spread models inserted in simulators
The impacts are estimated thanks to modelling and experiment
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Fire scale (km)Plot scale in field experiments (100 m)
Vegetation species (20 cm to 20 m)Fuel particule (mm to cm)
Reaction (m)
Wind (O2)
Combustion
Difficulty to model the time
scales
Difficulty in modelling the huge variable variability (fuel gases…)
Fire Spread Modelling
Where does the difficulty in the modelling of forest fire lay? The Physical laws are knownGIS and weather models provide the Environmental data
Difficulty to model the
space scales
Wind, Topography
Heat transferts
2
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Three kinds of modelling:
• Empirical (Mc Arthur, 1966; simulator = Fire grass meter)
• Semi-empirical (Rothermel, 1972; simulator = Farsite or Behave)
• Physical
• Simplified (Albini, 1981; simulator in development by our team)
• Detailed (Grishin, 1996; simulator = Firetec or Firestar)
Fire Spread Modelling
The problems in the modelling of forest fires are due to the numerical solving of mixed complex problems at different scales
3
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Drawbacks: less accurate and less general than detailed models Advantages: possibility to implement them at the field scale
- Simple models that only take into account the main mechanisms involved in fire spreading
Drawbacks: small times and lengthsAdvantages: detailed description of the phenomena
- Detailed models that describe as finely as possible the mechanisms
Two ways to describe fire spreading with physical modelling:
Fire Spread Modelling
Knolwedge and prevention
Simulation
4
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Gas Phase
• Convection • Turbulence• Gas mixture• Combustion• Radiation• Soot
Solid Phase
• Heat transfer • Drying• Pyrolysis• Combustion• Radiation
Transfers
MassHeat
MomentumEnergy
Fire Spread Modelling
Detailed models – A multiphase model
Fuel layer
Gas phaseControl volume
Solidphase
5
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
For each phase: Mass, species, momentum and energy balances
Interface relationships
Radiative Transfer Equation
Sub-models
Example – Mass balance:
kgkggggg MV
t
.
Example – Arrhenius type laws
prksurfkkk MM
t
0.. LaLadSenLgLe gggggk p S
gggg
pk
prksurfkgk MMM
Detailed models – A multiphase model
Fire Spread Modelling
Example – Interface equation for mass:
6
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Radiation
Heat release
Losses
Advection
Radiation Radiation
Assumptions:
•One single equivalent phase
• Assumed flame geometry
Fire Spread Modelling
Medium equivalent to the fuel
Burned area Unburned areaCombustion area
Simplified models – A semi-Physical model
7
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Rt
QTKTTkTVktT k
agv
)(.
Energy balance
t
Vx
VxV k
g
zgg
g
xgxg
1,,,
Mass conservation
vS
flvfl
flflvdvfl dSdSr
TBafl
24 coscos
Radiative transfer
sla
zg gTTV cos12,
Buoyancy
aag TT Perfect gas
Fire Spread Modelling
8
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Meeting “Combustion Theory and modelling”Institute of Physics – Combustion Physics Group
London, 24 June 2009
9
Fire Spread Modelling
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
410June 24, 2009 Theoretical and Experimental Tools for Combustion in Forest Fires
Fire Spread Modelling
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
burnedunburnedempty
Modelling Heterogeneity – Non flammable areas
Fire Spread Modelling
burnedunburnedempty
11
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
12
Experiments under controlled conditions (heat flux, flow)
BRE Centre for FireSafety Engineering
Fire Impact
0
2
4
6
8
10
12
0 50 100 150Time (s)
HR
R (k
W)
0% - Ph26% - Ph63% - Ph0% - Pp26% - Pp63% - Pp
Fire intensity:
0
500
1000
1500
2000
2500
0 50 100 150 200 250 300Time(s)
CO
2 (p
pm)
-5
0
5
10
15
20
25
30
CO
(ppm
)
Exhaust CO2 Molar FractionExhaust CO Molar Fraction
Fire emissions:
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Smouldering
Fire Impact
13
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Fire Spread and Severity
0 200 400 6000
20
40
60
80
100 COCO2
Yiel
d(%
)
Moisture content (%)20 30 40 50 60 70 80
0
20
40
60
80
100 COCO2
Yiel
d(%
)
Heat flux (KW/m²)
Emissions
Fire Impact
BRE Centre for FireSafety Engineering
Smouldering
14
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Fire Impact
Thermal impact (but also influence on vegetation and wind on fire spread)
15
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300 350 400time (s)
heat
flux
(W/m
²)
1st spread - 5 m1st spread - 10 m2d spread - 5 m2d spread - 10 m
Limits of exposure
Firefighter: 7000 W/m² (90 s)
Unprotected person: 6400 W/m² (8 s)
Fire Impact
16
Thermal impact (but also influence on vegetation and wind on fire spread)
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
17
Conclusions and perspectives
• Physical modelling of forest fires is a young science
• Two kind of tools arte developed:
• Fire spread simulation
• Fire impact estimation
• Many improvements are necessary but simple answers can be provided
• A strong perspective is the coupling between fire and atmosphere:
• Integration of satellite data to evaluate the fire
• Using fire simulations to detect fires
• Characterize the fire as a source of gases
September 15, 2009 Physical description of forest fires
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Albert Simeoni
UMR 6134
CNRS UMR 6134 – Univerità di CorsicaBP 52 - 20250 Corte, France
+33 495 450 638 – simeoni@univ-corse.frhttp://spe.univ-corse.fr
ESF Exploratory WorkshopImproved Quantitative Fire Description With Multi-
Species Inversions Of Observed PlumesFarnham Castle, 14-16 September 2009
Physical description ofForest Fires
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