Effects of side walls on facade flame entrainment and flame height from opening in compartment fires

Longhua Hu ,Fei Tang ,Kaihua Lu ,Michael Delichatsios ,Li He

doi:10.1051/matecconf/20130903001

Longhua Hu , Fei Tang + Show 3 more

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https://doi.org/10.1051/matecconf/20130903001

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Abstract

This paper presents an investigation of the side wall effects on facade flames ejected from the opening (such as a window) of an under-ventilated room fire. Experiments are carried out in a reduced-scale experimental setup, consisting of a cubic fire compartment having an opening with a vertical facade wall and two side walls normal to the facade wall. By changing the distance of the two side walls, the facade flame heights for different opening conditions (width, height) are recorded by a CCD camera. It is found that as the distance of the two side walls decreases the behavior the flame height can be distinguished into two regimes characterized by the dimensionless excess heat release rate, , outside the opening: (a) for the “wall fire” ( ≤ 1.3 ), the flame height is shown to change little with decrease of side wall distance as the dominant entrainment is from the front direction (normal to the facade wall) independent of the side wall distances; (b) for the “axis-symmetrical fire” ( > 1.3), the flame height increases significantly with a decrease in side wall distance as both the entrainment from the two side directions (parallel to the facade wall) and that from the front direction (normal to the facade wall) together apply. A global physically based non-dimensional factor K is then brought forward based on the side wall constraint effect on the facade flame entrainment to characterize the side wall effect on the flame height, by accounting for the dimensionless excess heat release rate, the characteristic length scales of the opening as well as the side wall separation distance. The experimental data for different opening dimensions and side wall distances collapse by using this global non-dimensional factor.

Highlights

For under-ventilated fully developed room fires in a building, there is a threat that flames can be ejected from the opening, induce fire spread to the upper floors leading to catastrophic loss of life and property
This paper presents an investigation of the side wall effects on facade flames ejected from the opening of an under-ventilated room fire
It is found that as the distance of the two side walls decreases the behavior the flame height can be distinguished into two regimes characterized by the dimensionless excess heat release rate, Q ∗ex, outside the opening: (a) for the “wall fire” (Q ∗ex ≤ 1.3), the flame height is shown to change little with decrease of side wall distance as the dominant entrainment is from the front direction independent of the side wall distances; (b) for the “axis-symmetrical fire” (Q ∗ex > 1.3), the flame height increases significantly with a decrease in side wall distance as both the entrainment from the two side directions and that from the front direction together apply

Summary

Introduction

For under-ventilated fully developed room fires in a building, there is a threat that flames can be ejected from the opening (such as a window), induce fire spread to the upper floors leading to catastrophic loss of life and property. The facade flame height is a key parameter in fire spread to the adjacent upper floors, as a result of the radiation and convection of the flames on the facade. The flames on the facade eject from the compa√rtment opening when the heat release rate in the compartment is higher than the critical value (1500A H kW) with the mean facade flame height determined by the excess fuel burning outside the opening as well as by the opening geometry of the compartment. The mean flame height normalized by a characteristic opening length scale is given as a function of dimensionless excess heat release rate Q ∗ex: Zf = f (Q ∗ex ) = f

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