Numerical Assessment of Safe Separation Distance in the Wildland–Urban Interfaces
Abstract
:1. Introduction
2. Materials and Methods
2.1. Characteristics of the Case Study
2.1.1. Site Description
2.1.2. Characterization of the Vegetation and Meteorology
2.1.3. Description of the Targets
- Human body target: A person with an average height of 1.70 m is considered as the target for the calculation of the different heat fluxes (radiative and convective). As shown in Figure 3, the person is assumed to be standing perpendicular to the ground at a distance d from the flame front.
- Building target: A three-level building with a 10 m wide façade is considered. R0 is the level at 0 m, R1 is the level at 3 m, R2 at 6 m and the roof R3 at 9 m (Figure 4). Radiative and convective heat fluxes are assessed at these levels, and the SSD values are then determined based on the maximum tolerable heat flux related to the type of construction material at each level of the building.
2.2. Numerical Method
2.2.1. Numerical Configuration
2.2.2. Calculation Methods
- Rate of spread
- Fireline intensity
- Heat fluxes
3. Results and Discussion
3.1. Fire Behavior
3.2. Fire Impact
3.2.1. Human Body Target
3.2.2. Building
3.2.3. Numerical Correlations for the SSD Evaluation
4. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Nomenclature
B | Stephan–Boltzmann constant (W/m2·K4) |
Ct | Turbulent natural convection constant (W/m2·K4/3) |
Cp | Fuel specific heat (J/kg/K) |
e | Fuel bed depth (m) |
FMC | Fuel moisture content (mass of water/mass of dry fuel) |
g | Gravity (m/s2) |
Convective heat transfer coefficient for a human body (W/m2·K) | |
Convective heat transfer coefficient for the exterior surface building (W/m2·K) | |
Hf | Flame height (m) |
Byram fireline intensity evaluated numerically (W/m) | |
I | Radiation intensity (W/m2) |
J | Total irradiance (W/m2) |
Qconv | Convective heat flux received by a target (W/m2) |
Qrad | Radiative heat flux received by a target (W/m2) |
Qtot | Total heat flux received by a target (W/m2) |
RH | Relative humidity (%) |
ROS | Rate of spread (m/s) |
s | Surface area to volume ratio (m−1) |
sg | Absorption coefficient of gas/soot mixture |
T0 | Gas mixture temperature (K) |
Ta | Ambient temperature (K) |
Ts | Fuel particle temperature (K) |
Ux | Wind speed at x meters above the ground (m/s) |
V0 | Gas flow speed (m/s) |
ΔHc | Fuel yield heat (J/kg) |
Vegetation mass loss rate (kg/m·s) | |
Rate of dry material pyrolysis (kg/m·s) | |
Rate of charcoal combustion (kg/m·s) | |
Greek | |
α | Slope angle |
ρs | Fuel particle density (kg/m3) |
βs | Volume fraction of the solid phase |
σ | Dry fuel load (kg/m2) |
βg | Volume fraction of the gaseous phase |
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Region | Type | Fuel Bed Depth, e (m) | Dry Fuel Load, σ (kg/m2) | Surface Area to Volume Ratio, s (m−1) | Fuel Moisture Content, FMC (%) |
---|---|---|---|---|---|
Corsica | Shrubland | 4 | 0.89 (1.79) | 5544 (4766) | 8 (100) |
(kg/m3) | Fuel Specific Heat, Cp (J/kg/K) | Heat of Combustion, ΔHc (J/kg) | |||
720 | 1912 | 19,640 |
Fuel Characteristics | |
---|---|
Fuel moisture content, FMC (%) | 69.45 |
Fuel bed depth, e (m) | 4 |
Dry fuel load, (kg/m2) | 2.68 |
Volume fraction, | |
Surface area to volume ratio, s (m−1) | 5024 |
Meteorological and Topography Conditions | |
Average wind speed in the slope direction, U10 (m/s) | 16.6 |
Ambient temperature, Ta (°C) | 35 |
Relative humidity, RH (%) | 20 |
Terrain slope value, (°) | 12 |
Wind Direction | (W/m2·K)4/3 | a (W/m2·K (m/s)b) | b | rms (W/m2·K) |
---|---|---|---|---|
Windward | 0.840.015 | 2.380.036 | 0.890.009 | 0.91 |
Heat Flux Threshold (kW/m2) | Criterion |
---|---|
5 | Maximum tolerable value for non-protected people |
7 | Maximum tolerable value for completely protected firefighter |
12 | Unpiloted wood ignition |
10 | Ignition of certain polymers |
25 | Thin steel can lose mechanical integrity |
37.5 | Instantaneous death, damage to process equipment and collapse of mechanical structures |
A | B | R2 | |
---|---|---|---|
Human body (1.7 m height) | −2 | 0.9474 | |
Building level R0 (0.21 m) | −1.756 | 0.9829 | |
Building level R1 (3 m) | −2.285 | 0.9999 | |
Building level R2 (6 m) | −2.71 | 0.9906 | |
Building level R3 (9 m) | −1.417 | 0.9316 |
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Fayad, J.; Accary, G.; Morandini, F.; Chatelon, F.-J.; Rossi, L.; Marcelli, T.; Cancellieri, D.; Cancellieri, V.; Rahib, Y.; Morvan, D.; et al. Numerical Assessment of Safe Separation Distance in the Wildland–Urban Interfaces. Fire 2023, 6, 209. https://doi.org/10.3390/fire6050209
Fayad J, Accary G, Morandini F, Chatelon F-J, Rossi L, Marcelli T, Cancellieri D, Cancellieri V, Rahib Y, Morvan D, et al. Numerical Assessment of Safe Separation Distance in the Wildland–Urban Interfaces. Fire. 2023; 6(5):209. https://doi.org/10.3390/fire6050209
Chicago/Turabian StyleFayad, Jacky, Gilbert Accary, Frédéric Morandini, François-Joseph Chatelon, Lucile Rossi, Thierry Marcelli, Dominique Cancellieri, Valérie Cancellieri, Yassine Rahib, Dominique Morvan, and et al. 2023. "Numerical Assessment of Safe Separation Distance in the Wildland–Urban Interfaces" Fire 6, no. 5: 209. https://doi.org/10.3390/fire6050209