Window Pane Failure During Exterior Fire Exposure

Windows are a potential vulnerability of structures during exterior fire exposures, such as those from wildland-urban interface (WUI) fires or a neighboring structure fire in a residential community. Window failure creates a pathway for embers, flames, and hot gases to enter a building and ignite interior combustibles. There is a need to investigate the failure of different types of multi-pane windows during exposures similar to those incident on buildings immediately adjacent to a burning structure. Eight experiments were performed with 16 window pane assemblies mounted in a target facade placed in front of a compartment fire that transitioned through flashover. Double pane window assemblies with both panes plain (annealed) glass, both panes tempered glass, and one plain glass, one tempered glass pane were examined. Window pane assemblies with a fire side plain glass pane and back side tempered glass pane performed notably better than assemblies with the opposite orientation. The heat load (heat flux integrated over time) at the time of complete failure (both panes cracked) was typically between 2.5 MJ/m² and 10.0 MJ/m² for window pane assemblies with a plain glass back side pane and between 9.0 MJ/m² and 17.5 MJ/m² for those with a tempered glass back side pane. Total heat flux measured behind the pane assemblies exceeded critical values for non-piloted ignition of common household materials, even before complete failure. Results from this study can be used to inform building codes and homeowner guidance related to the installation of tempered pane windows in areas prone to WUI fire hazards.