The Influence of Cavity Widths and Lateral Ventilation Conditions on the Fire Behaviour within a Non-Combustible Ventilated Façade System

Present uncertainties in key ventilation parameters, characterising the fire performance of facades, has necessitated clarification in the foundational understanding of the Fire Science Body of Knowledge. A test program conducted in collaboration between Lunds Universitet and the Kingspan Group, studied the influence of cavity widths and lateral ventilation conditions on the fire behaviour within Intermediate-scale ventilated façades following the ISO 13785-1 standards. Experimental works were performed in parallel to a Computational Fluid Dynamics analysis performed in the Fire Dynamics Simulator software. The thesis reports on the influence of domain discretization and complex geometric substitutions on the representativeness of simulated data. The experimental and simulated data were shown to hold reasonable correlation of information referring to the influence of lateral ventilation conditions on fire behaviour. Indicating the variable influence of obstructions and openings dependent on the point of interest and proximity within the sample. Data presented more critical conditions in near-field locations when closed ventilation conditions were applied, while far-field analysis indicated open conditions to be more critical. In the absence of a full experimental schedule, extension of studies was performed in the FDS software for later validation. Demonstrating the importance in selection of performance metrics in evaluating critical cavity widths. The data indicated more critical conditions present within the 50mm cavity sample, however greater flame heights were produced in the 25mm cavity.Recent building façade fire incidents witnessed globally, have highlighted uncertainties in the understanding of fire propagation, within the cavities concealed in a ventilated façade. Experimental research, forming the foundational understanding of fire dynamics within concealed cavity spaces, have been performed under varying conditions between researchers, resulting in knowledge gaps, regarding the influence of these conditions applied. This thesis focuses on the influence of ventilation to a façade testing sample in its impact on fire behaviour within the cavity. By understanding the influence of ventilation on a fire within a cavity, engineers can adapt façade design to limit fire growth in the event of a building fire. The foundational understanding of which this research is based, is the necessity of oxygen to fuel a fire and the re-radiation of heat within a cavity. Without a sustainable supply of oxygen, a fire will extinguish, however heat and fuel from previously burnt material will remain in flammable concentrations for some time, until the supply of oxygen is restored. In the case of reduced façade cavity widths, fire is drawn up through the air gap in search of oxygen, thinning the flame. While the concealed conditions of the cavity act to retain the heat of the fire within the façade, re-radiating off the surrounding surfaces. Alternately, large cavities will see limited draw of flame up the façade due to greater oxygen supplies, while heat will be spread more readily due to the more open conditions. Hence, research is conducted to determine the optimal cavity width to minimise the growth of flame within a cavity, given that global construction norms disagree on the appropriate cavity width to employ. This thesis aims to develop understanding on the influence of lateral ventilation conditions on a non-combustible façade testing sample to comprehensively investigate the fire performance of varying cavity widths. However, due to the impacts of COVID-19, the focus of the thesis was shifted, to experimental analysis of the influence of lateral ventilation on a 50mm cavity sample, in collaboration with simulated studies in the Fire Dynamics Simulator software. The results of the thesis indicate; the usability of FDS software for preliminary development of understanding in fire performance with the understanding of errors relating to model inputs, the variable impact of lateral ventilation conditions dependent on proximity to the obstruction, the importance of exact implementation of design to as-built conditions in avoiding unexpected conditions, and the significance in selection of critical performance metrics in determining conditions of optimal fire performance