Recent Advances in Fire Suppression Modeling
Issues & Perspectives of Fire Safety Engineering Applications
Pianet Grégoire
Studies and modelling section manager
Fire and Environmental Department, CNPP
Talk overview
• FSE in France
• Fire control and suppression phemomena
• Fire control and suppression models
• Research results on experimental setup
• Left issues and large scale tests modeling attempts
• Application perspectives to FSE
• Conclusions, related projects
FSE in France
• Today numerical modeling is of common use in France for specific Fire Safety Engineering fields
Propagation and detection of smoke and heat
Smoke exhaust systems
Thermal response of structures to fire
• This is not yet the case for fields of interest
Advanced evacuation models (regulation constraints)
Fire control and suppression by sprinkler or water mist (due to high complexity of control and suppression phemomena)
Fire control and suppression phenomena
• Heat absorption by vaporization
Hot Gases cooling
Surface cooling
Surface pre-wetting
• Inerting by oxygen dilution
• Radiative heat flux attenuation
Fire control and suppression models
• Base CFD and multiphysics models
+ Structured/unstructured meshes, accuracy of fluid flow solver
- Lack of verification and validation, not designed for fire apps. generally expensive in time and memory, “black boxes”
• Specific CFD models : Open-Foam + Fire-Foam
+ Structured/unstructured meshes, accuracy of fluid flow solver, large open toolbox of fire models, water spray models, accurate surface wetting model, 1:1 validation cases, open
- FV implicit solver : very expensive in time and memory
OF+FF is concretely not suited to building size FSE studies today, but is a powerful research tool for building intermediate models
• Specific CFD models : FDS
+ FD Explicit solver : fast calculations, large library of fire models, many verification and validation cases with fire tests, water spray, very large engineering and research community, used worldwide for engineering studies
- FD solver : accuracy and conservation issues, structured, Suppression model based on empirical constants (A, E)
Since 2011, we have funded R&D projects for testing and developing control/suppression models in FDS with a view to open engineering applications
Fire control and suppression models
• Study of the interactions between fire and water mist systems. Development of a suppression model for FDS software A. JENFT PhD Thesis
(see Fire Safety Journal 67:1–12 · July 2014 [DOI:10.1016/j.firesaf.2014.05.003])
• Context No software able to predict fire suppression by water sprays for complex fuels;
Increasing demand for engineering studies to determine impact of sprinkler or water mist systems on smoke and fire development;
Good qualitative knowledge on the way water and fire interact to achieve suppression but no consensus on a model, to take into account every effects.
Research results on experimental setup
• Implementation Through experiments, building a significant database to understand suppression
mechanisms and physics behind interaction between fuel, flame, smoke and water ;
Analyzing and integrating test results into a physical model that could be used in a predictive approach;
Include the model in Fire Dynamics Simulator (FDS) source code;
Perform numerical simulations with the modified version of FDS to verify model capability to predict suppression.
Research results on experimental setup
• An experimental campaign of 84 fire tests has been carried out to understand and quantify water spray effect on fire, thanks to video recordings and measuring: Air temperature
fuel surface temperature
O2 concentration
Heat flux
Pyrolysis rate
• Tests carried out in a 4m4m 3m high room
Research results on experimental setup
Fuel oil fire
tapp = 1 min
a) t0+10 s b) tapp-1 s
c) tapp+5 s d) tapp+20 s e) tapp+40 s
f) tapp+60 s g) tapp+90 s h) tapp+130 s
Experiments highlight a link between heat release rate (HRR) and fuel surface temperature during water application.
Research results on experimental setup
• Link between HRR and fuel surface temperature is actually well known on the fire growth phase (before water application) and usually described by Arrhenius law
• After a few modifications to this model to assess our problematic a new model is obtained
ignfuelpyro
ignfuel
fuel
ignfuelpyro
TTtm
TTtRT
ETtTBtm
if 0)(
if ))(
exp()()(
''
''
Tfuel
- [°C]
mp
yro
-[k
g/s
]
100 150 200 250 3000
0.2
0.4
0.6
0.8
1
1.2
1.4
Experiments
Model
x 10-3
.
Research results on experimental setup
• Results
The new model predicts all suppression cases by fuel cooling in every tests, just like in real tests
One test has shown no suppression, and confirmed by simulation
Suppression by inerting still needs improvement (FDS suppr. model)
Suppression time prediction still needs improvement
N° 13 14 20 21 31 32 33 34 35 36 37
tsup,exp - (s) 40 65 65 70 31 30 69 99 106 105 129
tsup,num - (s) 22 39 50 66 8 17 32 43 57 74 86
Gap - (s) 18 26 15 4 23 13 37 56 49 31 43
Gap - (%) 45 40 23 6 74 43 54 57 46 30 33
Research results on experimental setup
Left issues and large scale tests modeling attempts
• Predictive model for surface cooling by aspersion must be tested at
larger scales
• Water drops/Wall heat exchanges still need improvement
• Evaporation model is quite efficient for smoke cooling (see E. Blanchard
et al., FSJ, 2012) but heat absorption is still over predicted
• Still issues due to under-ventilated conditions
• 1.7 MW pool fire in engine room + water mist
• 0.4 MW/5 MW in aircraft hangar + water mist
Suppression in testsSuppression in simulationsTrend to underestimate suppression time due to over estimated surface/drops exchanges
No suppression in testsSlow suppression in simulationsDue to overestimated surface/drops exchanges but uncertainty concerning nozzle type and spray PSD has a strong impact on simulation sensitivity
Left issues and large scale tests modeling attempts
Left issues and large scale tests modeling attempts
• 0.8 MW Fire in hotel room + water mist
suppression in testsSuppression in simulations within comparable delays Combustion zones persist for screened surfaces (under bed) in simulationThis is due to FDS suppression model since suppression in test is partially due to inerting
Application perspectives to FSE
• 3 engineering approaches are identified
Determining approach (e.g. predict suppression time or no suppression at a given accuracy)
Security oriented approach (e.g. evaluating whether a system is able or not to control a developing fire)
Relative approach (e.g. determining which of two systems is best suited to a particular situation)
Smoke cooling Control/suppression
determining
approach
security oriented
approach
relative
approach
determining
approach
security oriented
approach
relative
approach
With care /
test support
is preferable
yes yes Not without
dedicated
Test support
With care /
test support
is preferable
With care /
test support
is preferable
Conclusions
• A new predictive model of surface cooling developed for FDS has proven effective with medium scale tests
• Model parameters for a well defined material can be determined using simulations of the free-burning phase
• Determining approaches of control or suppression modeling still need dedicated test support
• Modeling research should now focus on better drop/wall exchanges, inerting, evaporation
• Security oriented approach or relative approach could be considered with a good background in suppression tests and simulations
Related projects
• Experimental and numerical modelling of interactions between sprinklers and natural smoke vents (N. Trevisan PhD Thesis, see Interflam 2016 conf. paper)
72 fire tests in a 110 m² × 4 m facility
Aspersion
Aspersion
Smoke vent
Smoke vent
Related projects
• Experimental and numerical modelling of interactions between sprinklers and natural smoke vents (N. Trevisan PhD Thesis, see Interflam 2016 conf. paper)
Fire tests to come in a 280 m² × 12 m high testing aera
Thanks for your attention
