Experimental and numerical investigations of cavity flame spread in double skin façade

Abstract

In recent decades, double-skin façades (DSFs) have gained popularity in modern commercial buildings. However, their cavities can potentially accelerate flame spread, raising significant concerns regarding façade fire safety. Given that existing studies focus on the DSF component failures and fire stop measures without modeling validation, this study presents real-scale DSF fire experiments and modeling in accordance with JIS A 1310, conducted without combustibles to clarify fire behaviors within the cavity. The experiments employ HRRs of 600–900 kW and cavity depths of 0.4 and 0.8 m, highlighting that flame attachment to the facing wall is dependent on HRRs rather than cavity depths. Subsequently, Computational Fluid Dynamics (CFD) is utilized to investigate DSF fires, with validation against experimental temperature distribution and flame morphology. Furthermore, the validated CFD modeling is applied to scenarios with extended cavity depths and varied opening shapes, indicating that a cavity depth of ≥0.7 m mitigates flame spread for an opening ratio of n ≥ 1. The Modified-McCaffrey-Yokoi (MMY) model is proposed to characterize façade flame temperatures across varied cavity depths, and its convergence, featured by opening shapes and HRRs, is categorized to distinguish cavity flame behavior.