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

Abstract

Externally venting flames (EVF) may emerge through openings in fullydeveloped under-ventilated compartment fires, significantly increasing the risk of firespreading to higher floors or adjacent buildings. Several fire engineering correlationshave been developed, aiming to describe the main characteristics of EVF that affectthe fire safety design aspects of a building, such as EVF geometry, EVF centrelinetemperature and EVF-induced heat flux to the fac ̧ ade elements. This work is moti-vated by recent literature reports suggesting that existing correlations, proposed infire safety design guidelines (e.g. Eurocodes), cannot describe with sufficient accuracythe characteristics of EVF under realistic fire conditions. In this context, a wide rangeof EVF correlations are comparatively assessed and evaluated. Quantification of theirpredictive capabilities is achieved by means of comparison with measurementsobtained in 30 different large-scale compartment-fac ̧ ade fire experiments, covering abroad range of heat release rates (2.8 MW to 10.3 MW), ventilation factor values(2.6 m5/2to 11.53 m5/2) and ventilation conditions (no forced draught, forceddraught). A detailed analysis of the obtained results and the respective errors corrob-orates the fact that many correlations significantly under-predict critical physicalparameters, thus resulting in reduced (non-conservative) fire safety levels. The effectof commonly used assumptions (e.g. EVF envelope shape or model parameters forconvective and radiative heat transfer calculations) on the accuracy of the predictedvalues is determined, aiming to highlight the potential to improve the fire engineeringdesign correlations currently available