Externally Venting Flames (EVF) dynamics and development in non-orthogonal geometries

Abstract

The building industry is increasingly favouring green building initiatives resulting in increased use of different façade materials and systems, including materials with combustible characteristics, to meet stringent energy standards. This trend has highlighted the need to address the evolving fire safety challenges associated with modern and sustainable buildings. Particularly in high-rise buildings exterior fire spread and heat transfer caused by Externally Venting Flames (EVF) pose significant challenges as evidenced by the increased number of façade fire incidents worldwide. This present work aims to progress the current state of the art by investigating EVF characteristics and development in non-orthogonal curvilinear geometries. A database of recent façade fire incidents based on type of geometries was developed, indicating that curvilinear and/or non-orthogonal structures were involved in 43% of the reported fires. An experimental investigation was conducted to examine the effects of forced draught conditions on fully developed medium-scale rectilinear and curvilinear compartment with an emphasis on EVF behaviour. Aiming at better understanding the effect of wind on fire and EVF dynamics under different ventilation conditions a parametric study has been performed investigating the influence of wind with different fire compartment opening dimensions. Experimental results indicate that in forced draught conditions there is less thermal impact on a façade wall as the wind forces EVF outward increasing its projection and decreasing its height. A complementary numerical investigation using computational fluid dynamics (CFD) was performed in curvilinear and orthogonal geometries to identify key factors influencing EVF development and their impact on the façade. A parametric study was undertaken by altering the geometry (curvilinear, rectilinear, and number of openings), ventilation conditions, and heat release rate. Sixteen different fire scenarios have been considered to investigate the accuracy of currently available empirical correlations in predicting EVF characteristics. Additionally, velocity, temperature and oxygen concentration spatial distributions were analysed in the interior and exterior of the fire compartment. Numerical results enabled assessing EVF development indicating that geometry, ventilation conditions and fire load may significantly affect fire characteristics and impact on the facade. This work provides a deeper insight into how EVF is influenced by façade design and environmental conditions advancing current understanding of EVF in the context of curvilinear non-orthogonal façade geometries. The research findings contribute to improved fire risk assessment and could potentially inform future fire safety design practices and guidelines.