Thermal characteristics of externally venting flames and their effect on the exposed façade surface

Abstract

In a compartmentfire, Externally Venting Flames (EVF) may significantly increase the risk offire spreading toadjacentfloors or buildings, especially when combustible insulation materials are installed on the buildingfaçade. An increasing number of recent reports suggest that existingfire engineering design methodologiescannot describe with sufficient accuracy the characteristics of EVF under realisticfire load conditions. In thiscontext, a series offire safety engineering design correlations used to describe the main EVF thermalcharacteristics, namely EVF centreline temperature and EVF-induced heatflux on the exposed façade surface,are comparatively assessed. Towards this end, measurements obtained in a medium- and a large-scalecompartment-façadefire test are employed; aiming to broaden the scope of the validation study, predictionsof the investigated correlations are further compared to measurements obtained in 6 large-scalefire tests foundin the literature. It is found that the correlation proposed in EN1991-1–2 (Eurocode 1) for the estimation of theEVF centreline temperature is under-predicting the measured values in large-scalefire tests. In addition, it isconcluded that estimation of the localflame emissivity should take into account the specific fuel type used ineach case.