Skip to main content

Assessment of Fire Engineering Design Correlations Used to Describe the Geometry and Thermal Characteristics of Externally Venting Flames


Externally venting flames (EVF) may emerge through openings in fully developed under-ventilated compartment fires, significantly increasing the risk of fire spreading to higher floors or adjacent buildings. Several fire engineering correlations have been developed, aiming to describe the main characteristics of EVF that affect the fire safety design aspects of a building, such as EVF geometry, EVF centreline temperature and EVF-induced heat flux to the façade elements. This work is motivated by recent literature reports suggesting that existing correlations, proposed in fire safety design guidelines (e.g. Eurocodes), cannot describe with sufficient accuracy the characteristics of EVF under realistic fire conditions. In this context, a wide range of EVF correlations are comparatively assessed and evaluated. Quantification of their predictive capabilities is achieved by means of comparison with measurements obtained in 30 different large-scale compartment-façade fire experiments, covering a broad range of heat release rates (2.8 MW to 10.3 MW), ventilation factor values (2.6 m5/2 to 11.53 m5/2) and ventilation conditions (no forced draught, forced draught). A detailed analysis of the obtained results and the respective errors corroborates the fact that many correlations significantly under-predict critical physical parameters, thus resulting in reduced (non-conservative) fire safety levels. The effect of commonly used assumptions (e.g. EVF envelope shape or model parameters for convective and radiative heat transfer calculations) on the accuracy of the predicted values is determined, aiming to highlight the potential to improve the fire engineering design correlations currently available.

This is a preview of subscription content, access via your institution.

Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10


Symbol (Units – Value):


A 0 (m2):

Opening area

A v (m2):

Total area of vertical openings on all walls of the compartment

c (4.67):

Empirical factor (Eq. 19)

C p (1005 J/kg K):

Specific heat of air at ambient conditions

D v (m):

Effective diameter of the opening

d eq (m):

Characteristic length scale of an external structural element

E b (kW/m2):

Black body emissive power

g (9.81 m/s2):

Gravitational acceleration

H 0 (m):

Opening height

H u (13,100 kJ/kg O2):

Heat release of cellulosic fuels for each kilogram of oxygen consumed

h eq (m):

Weighted average of openings heights on all walls

k (m−1):

Extinction coefficient

k fuel (m−1):

Extinction coefficient for the combustion products of a specific fuel

L L_0.05 (m):

Flame height at the “continuous flame” (5% flame intermittency limit)

L L_0.50 (m):

Flame height at the “intermittent flame” (50% flame intermittency limit)

L L_0.95 (m):

Flame height at the “far-field flame” (95% flame intermittency limit)

L L (m):

Height of EVF

L H (m):

Projection of EVF

L f (m):

Flame length

l (–):

Characteristic length scale (Eq. 9)

l x (m):

Length along the EVF centerline, originating at the opening

\( \dot{m}_{a} \) (kg/s):

Air mass flow rate (entering the fire compartment)

\( \dot{m}_{f} \) (kg/s):

Fuel mass flow rate

\( \dot{m}_{{O_{2} }} \) (kg/s):

Oxygen mass flow rate

\( \dot{m}_{g} \) (kg):

Mass flow rate of unburnt gases venting outside the fire compartment

\( \dot{Q} \) (MW):

Heat Release Rate

\( \dot{Q}_{ex} \) (MW):

Excess Heat Release Rate

\( \dot{Q}_{in} \) (MW):

Average heat release rate at the interior of the fire compartment

\( \dot{q}^{\prime\prime} \) (W/m2):

Heat flux

\( \dot{q}^{\prime\prime}_{conv} \) (W/m2):

Convective heat flux

\( \dot{q}^{\prime\prime}_{rad} \) (W/m2):

Radiative heat flux

r (–):

Fuel-to-oxygen stoichiometric mass ratio

r’ (–):

Oxygen-to-fuel stoichiometric mass ratio

r 0 (m):

Equivalent radius of the opening

T z (K):

EVF centerline temperature in relation to height from the opening lintel

T amb (K):

Ambient temperature

T f (K):

“Effective” flame temperature

T 0 (K):

Temperature at the center of the opening

T wall (K):

Facade wall temperature

V (m/s):

External wind speed

\( \dot{V} \) (m3/s):

Air volumetric flow rate

W 0 (m):

Opening width

w f (m):

EVF width

w t (m):

Sum of opening widths on all walls of the fire compartment

w d (m):

Distance to any other opening

\( Y_{{{\text{O}}_{2} ,air}} \) (0.232):

Oxygen mass fraction in ambient air

z (m):

Height above the opening lintel

Z n (m):

Height of the neutral plane

a c (W/m2K):

Convective heat transfer coefficient

ΔT m (K):

Plume centerline temperature rise above ambient

ε (–):


ε z (–):

Local emissivity of the flame

λ (m):

Flame thickness

ρ amb (1.204 kg/m3):

Air density at ambient conditions

ρ 500°C (0.45 kg/m3):

Air density at 500°C

σ (5.67 × 10−8 kg/s3K4):

Stefan Boltzmann constant

φ f (–):

Configuration factor (radiation from fire through the opening)

φ z (–):

Configuration factor (radiation from EVF)


Externally venting flames


Forced draught


Global equivalence ratio


Heat release rate


No forced draught


Ventilation factor


  1. 1.

    Sun J, Hu L, Zhang Y (2013) A review on research of fire dynamics in high rise buildings. Theor Appl Lett 3:1–13. doi:10.1063/2.1304201.

    Article  Google Scholar 

  2. 2.

    White N, Delichatsios M (2015) Fire hazards of exterior wall assemblies containing combustible components, Springer, New York.

    Book  Google Scholar 

  3. 3.

    Peng L, Bu Z, Huang X (2013) Review on the fire safety of exterior wall claddings in high-rise buildings in China. Procedia Eng 62:663-670. doi10.1016/j.proeng.2013.08.112:

    Article  Google Scholar 

  4. 4.

    Delichatsios M (2014) Enclosure and Façade fires: Physics and applications. In: Proceedings 11th International Symposium of Fire Safety Science. University of Canterbury, New Zealand.

  5. 5.

    Yokoi S (1960) Study on the prevention of fire spread caused by hot upward current. Building Research Institute, Report No. 34, Tokyo, Japan.

  6. 6.

    Thomas PH (1977) Some problem aspect in fully developed room fires. Fire Standards and Safety, ASTM STP 614, A.F. Robertson, Eds., American Society for Testing and Materials, 112–130.

  7. 7.

    Thomas PH, Heselden AJM (1972) Fully developed fires in single compartments: a cooperative research programme of the Conseil Internationale du Batiment. Conseil Internationale du Batiment Report No 20, Fire Research Note No 923.

  8. 8.

    Thomas PH, Law M (1972) The projection of flames from burning buildings, FRN 921, Fire Research Station, Borehamwood, U.K.

    Google Scholar 

  9. 9.

    Oleszkiewicz I (1989) Heat transfer from a window fire plume to a building façade. ASME Collected papers in Heat Transfer, Book No. H00526, 123:163-170.

  10. 10.

    EN 1991-1-2. Eurocode 1 (2002) Actions on structures, Part 1–2—General Actions—Actions on Structures Exposed to Fire. European Committee for Standardization, Brussels, Belgium.

  11. 11.

    EN 1993-1-2. Eurocode 3 (2002) Design of steel structures, Part 1-2 – Structural fire design. European Committee for Standardization, Brussels, Belgium.

  12. 12.

    EN 1995-1-2. Eurocode 5 (2004) Design of timber structures—Part 1–2: General—Structural fire design. European Committee for Standardization, Brussels, Belgium.

  13. 13.

    Klopovic S, Turan OF (2001) A comprehensive study of externally venting flames, Part I: Experimental plume characteristics for through-draft and no through-draft ventilation conditions and repeatability. Fire Saf J 36:99-133. doi:10.1016/S0379-7112(00)00040-0

    Article  Google Scholar 

  14. 14.

    Klopovic S, Turan OF (2001) A comprehensive study of externally venting flames, Part II: Plume envelope and center-line temperature comparisons, secondary fires, wind effects and smoke management system. Fire Saf J 36:135-172. doi:10.1016/S0379-7112(00)00041-2

    Article  Google Scholar 

  15. 15.

    Empis CA (2010) Analysis of the compartment fire parameters influencing the heat flux incident on the structural façade. Ph.D. Thesis, University of Edinburgh, Edinburgh.

  16. 16.

    Himoto K, Tsuchihashi T, Tanaka Y, Tanaka T (2009) Modeling thermal behaviors of window flame ejected from a fire compartment. Fire Saf J 44:230-240. doi:10.1016/j.firesaf.2008.06.005.

    Article  Google Scholar 

  17. 17.

    Asimakopoulou E, Kolaitis D, Founti M (2013) Comparative assessment of CFD tools and the eurocode methodology in describing externally venting flames. 1st international seminar for fire safety of facades, Paris. doi:10.1051/matecconf/20130903003

  18. 18.

    Tang F, Hu LH, Delichatsios MA, Lu KH, Zhu W (2012) Experimental study on flame height and temperature profile of buoyant window spill plume from an under-ventilated compartment fire. Int J Heat Mass Trans 55:93-101. doi:10.1016/j.ijheatmasstransfer.2011.08.045

    Article  Google Scholar 

  19. 19.

    Delichatsios MA (1984) Flame heights in turbulent wall fires with significant flame radiation. Combust Sci Technol 39:195-214. doi:10.1080/00102208408923789

    Article  Google Scholar 

  20. 20.

    Asimakopoulou E, Kolaitis D, Founti M (2016) Characteristics of externally venting flames and their effect on the façade: a detailed experimental study. Fire Technol (2015). doi:10.1007/s10694-016-0575-5.

    Google Scholar 

  21. 21.

    Law M (1978) Fire Safety of External Building Elements—The Design Approach. AISC Eng J, Second Quarter.

    Google Scholar 

  22. 22.

    Law M, O’Brien T (1981) Fire safety of bare external structural steel. Constrado, Croydon, U.K.

    Google Scholar 

  23. 23.

    Hurley MJ (2016) SFPE Handbook of fire protection engineering, 5rd Edition. SFPE, Quincy

    Book  Google Scholar 

  24. 24.

    Drysdale D (2011) An introduction in fire dynamics. Wiley, New York

    Book  Google Scholar 

  25. 25.

    Harmathy TZ (1979) Design to cope with fully developed fires. In: E.E. Smith and T.Z. Harmathy (eds.) Design of buildings for fire safety—ASTM STP 685. American Society for Testing and Materials, West Conshohocken.

    Google Scholar 

  26. 26.

    Quintiere JG (2006) Fundamentals of fire phenomena. Wiley, West Sussex

    Book  Google Scholar 

  27. 27.

    Yoshioka H, Ohmiya Y, Noak M, Yoshida M (2012) Large-scale façade tests conducted based on ISO 13785-2 with noncombustible façade specimens. Fire Sci Technol 31:1-22. doi:10.3210/fst.31.1

    Article  Google Scholar 

  28. 28.

    Lin CY (2000) Study of exposure fire spread between buildings by radiation. J Chin Inst Eng 23:493-504. doi:10.1080/02533839.2000.9670570

    Article  Google Scholar 

  29. 29.

    Feasey R, Buchanan A (2002) Post-flashover fires for structural design. Fire Saf J 37:83-105. doi:10.1016/S0379-7112(01)00026-1

    Article  Google Scholar 

  30. 30.

    Seigel LG (1969) The projection of flames from burning buildings. Fire Technol 5:43-51. doi:10.1007/BF02591612

    Article  Google Scholar 

  31. 31.

    Sugawa O, Momita D, Takahashi W (1997) Flow behavior of ejected fire plume from an opening effected by external side wind. Fire Saf Sci 5: 249-260. doi:10.3801/IAFSS.FSS.5-249

    Article  Google Scholar 

  32. 32.

    Tang F, Hu LH, Delichatsios MA, Lu KH, Zhu W (2012) Experimental study on flame height and temperature profile of buoyant window spill plume from an under-ventilated compartment fire. Int J Heat Mass Transf 55:93-101. doi:10.1016/j.ijheatmasstransfer.2011.08.045

    Article  Google Scholar 

  33. 33.

    Beyler CL (1986) Fire plumes and ceiling jets, Fire Saf J 11:53-75. doi:10.1016/0379-7112(86)90052-4

    Article  Google Scholar 

  34. 34.

    Cox G, Chitty R (1985) Some source-dependent effects of unbounded fires. Combust Flame 60:219-232. doi:10.1016/0010-2180(85)90027-6

    Article  Google Scholar 

  35. 35.

    Hasemi Y, Tokunaga T (1984) Flame geometry effects in the buoyant plumes from turbulent diffusion flames. Fire Saf Sci Technol 4:15-26. doi:10.3210/fst.4.15

    Article  Google Scholar 

  36. 36.

    Heskestad G (1983) Virtual origins of fire plume. Fire Saf J 5:109-114. doi:10.1016/0379-7112(83)90003-6

    Article  Google Scholar 

  37. 37.

    McCaffrey BJ (1983) Momentum implications for buoyant diffusion flames. Combustion and Flame 52:149-156. doi:10.1016/0010-2180(83)90129-3

    Article  Google Scholar 

  38. 38.

    Beuther PD, George WK (1982) Measurement of the turbulent energy and temperature balances in an axisymmetric buoyant plume in a stably stratified environment. In: Proceedings 7th International Heat Transfer Conference, Munich

  39. 39.

    Korhonen T, Hietaniemi J (2005) Fire safety of wooden facades in residential suburb multi-storey buildings. VTT Working Papers 32

  40. 40.

    Audoin L, Kolb G, Torero JL, Most JM (1995) Average centreline temperatures of a buoyant pool fire obtained by image processing of video recordings. Fire Saf J 24:167-187. doi:10.1016/0379-7112(95)00021-K

    Article  Google Scholar 

  41. 41.

    Lee Y, Delichatsios MA, Silcock GWH (2008) Heat flux distribution and flame shapes on the inert façade. Fire Safety Science 9:193-204. doi:10.3801/IAFSS.FSS.9-193

    Article  Google Scholar 

  42. 42.

    Bechtold R (1978) The role that facades play in fire spread, Fire International 59:32-40.

    Google Scholar 

  43. 43.

    Mudan SK (1984) Thermal radiation hazards from hydrocarbon pool fires, Prog Energ Combust 10: 59-80. doi:10.1205/095758297528841

    Article  Google Scholar 

  44. 44.

    Yuen WW, Tien CL (1977) A simple calculation scheme for the luminous flame emissivity. Proc Combust Inst 16:1481-1487. doi:10.1016/S0082-0784(77)80430-X

    Article  Google Scholar 

  45. 45.

    Markstein GH (1974) Radiative energy transfer from gaseous diffusion flames, Proc Combust Inst 15: 1285-1294. doi:10.1016/0010-2180(76)90005-5

    Article  Google Scholar 

  46. 46.

    Buckius RB, Tien CL (1977) Infrared flame radiation. Int J Heat Mass Transf 20:93-106. doi:10.1016/0017-9310(77)90001-1

    Article  Google Scholar 

  47. 47.

    De Ris J (1979) Fire radiation—a review. Proc Combust Inst 17:1003–1016. doi:10.1016/S0082-0784(79)80097-1.

    Article  Google Scholar 

  48. 48.

    Veloo PS, Quintiere JG (2013) Convective heat transfer coefficient in compartment fires, J Fire Sci 31: 410-423. doi:10.1177/0734904113479001

    Article  Google Scholar 

Download references


This work has been financially supported by the “Fire-Facts” project in the frame of the ARISTEIA action (operational programme “Education and Lifelong Learning”) that is co-financed by Greece and the E.U and by the E.C. in the frame of the FP7 Project “ELISSA: Energy Efficient Lightweight-Sustainable-Safe-Steel Construction” (EeB.NMP.2013, Grant No. 603086).

Author information



Corresponding author

Correspondence to Dionysios I. Kolaitis.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Asimakopoulou, E.K., Kolaitis, D.I. & Founti, M.A. Assessment of Fire Engineering Design Correlations Used to Describe the Geometry and Thermal Characteristics of Externally Venting Flames. Fire Technol 53, 709–739 (2017).

Download citation


  • Externally venting flames
  • Fire plume
  • Façade fire
  • Large-scale fire tests
  • Centreline temperature
  • Heat flux
  • Fire engineering design
  • Flame height
  • Flame width
  • Flame projection