Journal Article Reports on Heat Transfer Through Different Window Constructions for Wildland-Urban Interface Fire Protection
The peer-reviewed journal article “Experimental Study of Heat Transfer Through Windows Exposed to a Radiant Panel Heater” has been published in the Fire Technology Journal. This research explores how varying window construction may impact the heat transferred through the window during exposure to a radiant heat source, simulating exposure to an exterior fire, such as a wildfire. Rebekah Schrader, Shuna Ni, Nicholas Dow, Joseph Willi, Matthew DiDomizio, and Gavin Horn authored this paper as part of the Heat Transfer from Structure Fires research project.
The Risk of WUI Fires Spreading Through Windows Via Heat Transfer
The risk of wildfires continues to grow, particularly in wildland urban interface (WUI) areas, where wildfires can quickly spread to cities and towns. Windows are a significant vulnerability in this spread.
Fires can spread through windows in multiple ways. One way is through window pane cracking and failure, which can give flames and embers a direct path into the structure. However, fire can also ignite inside a structure, as heat from an exterior fire is still transferred through the window even if the window itself remains intact. This occurs when the window transmits enough heat to auto-ignite combustible materials inside the room, such as curtains and furniture. This article provides valuable insight into how the construction of windows can reduce those risks.
Testing Window Construction Performance Against Radiant Heat
FSRI researchers compared several window assembly characteristics: glass type (plain or tempered), number of panes (one or two), type of gas between the panes (air or argon), and the presence of a low-emissivity coating. Researchers exposed windows to various heat fluxes ranging from 10—50 kW/m2 from a radiant panel, similar to the exposure from an exterior wildland fire.
Researchers measured heat transfer through the window and the time until either pane cracking or failure.
The results showed:
- Double-pane windows reduce heat transfer through a window more than the single-pane design.
- The addition of the low-emissivity coating provided further heat transfer.
- Plain glass structurally failed earlier than tempered glass.
- The heat transfer through air-filled versus argon-filled double-pane windows was not significantly different.
- In some cases, the heat flux measured behind the windows was greater than the critical heat flux required to ignite common household furnishings. It is important for people in WUI fire areas to move curtains, furniture, and other household materials away from windows before evacuating.
“This information can be used to provide guidance to homeowners living in WUI communities on how window type impacts heat transfer into a structure and which windows may be best to promote structure hardening against exterior fires.”
—Bekah Schrader, research engineer, FSRI
Conclusion
The results from this study show significant differences in the durability of several commercially available window types when exposed to radiant heat, similar to a WUI fire. This work monitoring window breakage and measuring heat flux through intact windows enables future construction choices to be made to prioritize fire safety.
Fire Technology is a scientific journal that publishes original contributions, both theoretical and empirical, that contribute to the solution of problems in fire safety science and engineering. It is the leading journal in the field, publishing applied research dealing with the full range of actual and potential fire hazards facing humans and the environment. It covers the entire domain of fire safety science and engineering problems relevant in industrial, operational, cultural, and environmental applications, including modeling, testing, detection, suppression, human behavior, wildfires, structures, and risk analysis.
