FSRI Continues Research on Window Shutters and Frames During Exterior Fire Exposure
The Fire Safety Research Institute, part of UL Research Institutes, completed additional studies this summer, as part of its ongoing Heat Transfer from Structure Fires research project. These experiments evaluated the effectiveness of various window shutter systems and window frames in protecting against fire from a neighboring structure. Held over two weeks at the Delaware County Emergency Services Training Center facility in Sharon Hill, PA, the experiments support ULRI’s broader goal of enhancing resiliency and safety in communities exposed to wildland-urban interface (WUI) fires by preventing the spread of fire between structures.
Studying Window Shutters
The experiments utilized a setup similar to previous heat transfer studies on exterior wall assemblies, window panes, and window frames, consisting of a source compartment and a target facade wall. For each experiment, a fire was ignited in the source compartment and allowed to transition through flashover. Fire effluent flowed from the opening in the source compartment, exposing the target wall to heat from a spill plume generated by the post-flashover compartment fire. Eight double-hung, double-pane windows were installed in the target facade wall, and protective shutters covered the exterior (fire) side of the windows. Heat flux and temperature data were measured by heat flux gauges paired with thermocouples on the fire side of the target wall and behind the window assemblies. High-definition cameras were mounted behind the windows to obtain time-resolved indication of window failure events. The experiments were conducted with the source compartment and target facade arranged at both 10 ft and 14 ft apart, representing common residential separation distances in high structure density areas.
Two types of window shutters were evaluated: a stainless steel roller shutter and a 1100°C-rated fabric shutter. Last year, experiments were performed with the shutters installed over double-pane (both panes annealed glass) windows with vinyl frames — representing a “worst-case” scenario based on previous research — to study their performance protecting the window and opening. This year, the shutters were installed over double-pane (both panes tempered glass) windows with aluminum frames as a “best-case” scenario.
Exploring Covered Wood Window Frames
Researchers also studied two types of covered wood window frames: an aluminum clad wood frame and a fiberglass exterior, wood interior frame. This expanded upon a previous experimental series that compared vinyl, fiberglass, wood, and aluminum frames to reflect additional frame types commonly used in residential buildings.
Early Investigations of Window Coatings
Earlier in the summer, researchers also completed bench-scale experiments on the impact of low-emissivity coatings on window failure. They tested window pane samples with different types of Low-E coatings over a range of various heat flux exposures to understand if coating composition or placement on the window impacts glass survivability.
“Windows are a potential vulnerability of structures during exterior fire exposures, such as those from a wildland-urban interface (WUI) fire. Codes, standards, and homeowner guidance regarding window construction and protection methods in WUI areas can be improved with a better understanding of window failure mechanisms.”
– Joseph Willi, research engineer, Fire Safety Research Institute, part of UL Research Institutes
The results from these experiments, combined with peer-reviewed publications on exterior wall assemblies, window panes, window construction, window frames, and window protections, will help shape building construction decisions and the development of codes that optimize fire safety in both urban and WUI environments.
