Performance-Based Approaches for External Fire Spread and Thermal

Radiation CalculationsPiotr Tofilo, Ph.D., The Main School of Fire Service

Polish SFPE Chapter

Heat Radiation for Hazard Analysis• External fire spread between buildings (or its parts)• Fire spread between fire load islands• Structural fire protection• Buildings under construction• Facade fires in high rise• Warehouse / external storage fires• Oil & gas sector, pool fires, jet fires, fireballs, etc.• Wildland - urban interface fires• Modeling – flame/fire spread, pyrolysis, ignition

Main Literature for Engineers on Thermal Radiation• SFPE Handbook• Textbooks - Karlsson, Quintiere, Drysdale• SFPE Engineering Guide – Assesing Flame Radiation…• Radiative Heat transfer (Modest)

Practical Approaches and Methods

• Analytical• CFD• Other numerical

Analytical Methods• Point source (Modak)• Simple radiating rectangle (View Factor)• External radiating flame (Eurocode, NRCC)• Cylindrical flame model (Dayan/Tien, Shokri/Beyler, Modan/Croce)

Main Difficulties in Asessing External Radiation from Compartment Fires

• Fire scenarios• Resolving the field of temperature / absorption / scattering / emissivity• Complex geometries• Glazing behaviour• Probabilistic aspects• Use of sprinklers

Experimental Studies

• St. Lawrence Burns (1958)• Law (1963, 1968)• Czechoslovakia (1990)• Cheng & Hadjisophocleous, Carlton / NRCC (2012)• Mason, Fleischmann, Spearpoint et al. (2008)• Pool fires (Numerous)

Mason, Fleischmann, Spearpoint et al. (2008)View Capturedfrom 2 Cameras 3D probability shape 3D flux field

NRCC & Czechoslovakian Datasets

FDS predictions – Own Work (NRCC tests)

CFD Methods for Solving RTE

• Direct Transfer Radiation Method (DTRM) • Finite Volume Method (FVM)• Discrete Ordinate Method (DOM)• Monte Carlo • P1 (Spherical harmonics)• Rosseland• ViewFactor / Surface2Surface

Finite Volume Method

Step

Diamond

Angular discretization Intensity calculations Discretization schemes

RTE

FireRad (S2P Model)

FVM Verification Using FireRad(Single Radiating Cell)

FVM – Heat Flux Isosurfaces –Increasing Angular Resolution100 angles (FDS default) 200 angles 400 angles

FVM – Heat Flux Isosurfaces – Increasing Angular Resolution

800 angles 1600 angles Exact – view factor based

Finite Volume Method – Error Studies

Finite Volume Method – Error Studies

CFD for External Heat Flux

• Quite reasonable for compartment fires• Often less accurate for external fires• User should know the characteristics of the selected numerical method• Computationally expensive if good accuracy expected• FVM needs good spatial and angular distribution• CFD often not practical for radiation between buildings

Thermal Field - Fully Developed Fire• Standard temperaturę curve• External fire curve (Eurocode)• Parametric fire curve (Eurocode)• Flame temperatures (Eurocode)• Zone model• CFD

Radiation from Pool Fires

• Point source• Shokri & Beyler correlation• Cyllinder fire model

• Shokri & Beyler• Modan & Croce• Dayan & Tien

Emissive Power to Equivalent Blackbody Temperature

• Shokri / Beyler• Mudan / Croce

𝑇𝑇𝐵𝐵𝐵𝐵 =𝐸𝐸𝜎𝜎

0.25

FireRad vs. Cylinder Flame Model

• With equivalent blackbody temperature heat flux distribution from FireRad is equivalent to cylinder fire model

• Solid bodies with conservative temperatures can represent flames

Practical Problem

Combustible flat roof

Exposed building

Flux Distribution for Three Wind OptionsFlame = solid surface, Temperature 900 C, Emissivity = 1, Flame height = 1 floor (NFPA 80A)

Detailed Flux Distribution Assessment

Thank YouQuestions ?

piotr.tofilo@gmail.com