Predicting the Temperature Increase of Residential Siding and Decking Materials in the WUI Due to External Heat Flux
Milke, James A
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The wildland urban interface (WUI), which is the area where houses meet or intermingle with undeveloped wildland vegetation, has more than doubled over the last 50 years. The frequency and intensity of wildfires occurring in these areas has also increased. To advance the understanding of WUI heat transfer, a multi-phase experimental series was conducted to study the impact of radiant heating on materials common in WUI wildfire scenarios. In the first phase, thermophysical properties of decking and siding materials were measured and a thermal decomposition model derived. In the second phase, the decking and siding materials were cut into 100 mm x 100 mm samples and exposed to a radiant panel at constant heat fluxes of 5 kW/m^2 and 15 kW/m^2 to mimic the incident heat flux from a wildfire. In the third phase, the materials were constructed into larger 280 mm x 410 mm assemblies and exposed to the same heat fluxes to mimic full scale exterior walls and decks in the WUI. During both the second and third phases, the back and sides of the assemblies were insulated, and the back side temperature of the assemblies was measured throughout each experiment using a 24-gauge thermocouple. In addition to the experiments, numerical simulations were performed using Fire Dynamics Simulator (FDS) to assess the utility of the model for predicting the temperature rise of materials in WUI exposure scenarios. The experimental configuration from the second phase of testing was simulated, using the thermophysical properties of materials determined from the first phase. A simplified one-dimensional model was adopted, in which materials were assumed to be homogenous and isotropic, and heat transfer was assumed to occur only in the depth of the sample. The temperature increase for each of the studied materials were compared as to provide recommendations on the safest choice for siding and decking materials in the WUI.