Experimental investigation of Externally Venting Flames in under-ventilated compartment fires

In a compartment fire, Externally Venting Flames (EVF) may significantly increase the risk of fire spreading to adjacent floors or buildings, especially now-a-days that there is an ever-increasing trend of using combustible insulation materials in building façades. The main scope of this work is to investigate the fundamental physical phenomena governing EVF development. In this frame, a series of medium-scale fire compartment experiments is performed, utilizing a ¼ scale model of the ISO 9705 compartment, equipped with an extended façade. Recording of the dynamic behaviour of EVF is carried out using a selectively installed sensor network that allows measurement of important physical parameters, such as flame envelope geometry, gas and wall surface temperatures, façade heat flux, fuel mass loss and gas species concentrations. A dedicated image-processing tool is developed, aiming to record the dynamic development of the flame envelope (e.g. height, width, volume). A range of realistic fire scenarios, relevant to building fires, is implemented as part of the experimental campaign. An “expendable” fuel source (n-hexane liquid pool fire) is utilized to effectively simulate realistic building fire conditions. A parametric study is performed by varying two important physical parameters, i.e. fire load and opening dimensions. Experimental results suggest that the flame geometry and EVF duration are mainly affected by the opening dimensions, whereas the fuel load has a significant impact on the heat flux to the façade. An increasing number of recent reports suggest that existing fire engineering design methodologies cannot describe with sufficient accuracy the characteristics of EVF under realistic fire load conditions. In this context, the obtained experimental data are used to assess a range of fire engineering design correlations, commonly used to estimate the centreline temperature of the EVF plume and the heat flux to the adjacent façade surface. The obtained extensive set of experimental data can be used to validate CFD fire models or to evaluate the accuracy of available fire engineering design correlations.