Window Frame Failure During Exterior Fire Exposure

Structure-to-structure fire spread has been identified as a key factor in the devastating losses from large fire incidents, specifically wildfire-initiated urban conflagrations. Previous research has shown that the propensity for a window to fail in a wildland-urban interface (WUI) fire incident depends on the window frame material and construction. However, the degree to which window frame materials affect their performance in a WUI fire incident is unclear. The objective of the present work is to identify failure mechanisms and rank the relative performance of common window frame materials, which will ultimately provide guidance on window selection in regions susceptible to WUI fire events. Experiments were conducted to investigate the performance of four types of window frame assemblies (vinyl, wood, fiberglass, aluminum) under fire exposures similar to those from a structure fire to an adjacent structure. Window failure events were identified, and the number of occurrences of each event, the time to the occurrence of each event, and heat load (heat flux integrated over time) at each event occurrence were compared between window frame assembly types. Failure mechanisms differed between frame types, and both the design and construction of components within the frame assemblies notably impacted failure. Wood and vinyl frame assemblies were the most vulnerable to failure, having the greatest number of sash failures. Furthermore, all wood frame assemblies ignited. Aluminum frame assemblies performed best and would likely provide the highest level of performance in regions susceptible to WUI fires.