Impact of sliding window opening sizes and crosswinds on combustion characteristics of polyethylene sandwich panels in external venting façade fires

Fires can propagate along the building façade if the flame ignites the external wall insulation. Despite extensive research on this topic, there is a lack of sufficient exploration into the flame and temperature characteristics in external venting fires involving polyethylene (PE) sandwich panels. This paper investigates the impact of sliding window opening sizes and crosswinds on the combustion characteristics of PE sandwich panels in external venting façade fires (EVF). A reduced-scale three-layer burning chamber is designed, with environmental crosswind speeds generated using a wind tunnel. The study reveals that the vertical flame spread rate is directly proportional to the opening size without crosswinds. However, in the presence of crosswinds, the horizontal flame spread length follows a power law relationship with the dimensionless crosswind speed raised to the power of 1.28. The concept of temperature growth index (TGI) is introduced to quantitatively assess the fire hazard under different conditions. The TGI is maximized when the crosswind speed is 1.5 and the opening size is 4. Additionally, a vertical temperature distribution model within the sandwich panel was developed, which exhibits good agreement with the experimental results. These results provide valuable theoretical references for understanding the fire spread behavior of PE sandwich panels in EVF.