Simulation of Heat Transfer Through Soil for the Investigation of Wildfire Impacts on Buried Pipelines

Wildland urban interface (WUI) communities in the Western United States have recently dealt with historic and devastating wildfires year after year. The fires have cost tens of billions in damage, burned tens of thousands of structures, displaced thousands of residents, and killed hundreds of people. In particular, the 2017 Tubbs fire, 2018 Camp fire, and 2020 Labor Day fires in Oregon caused catastrophic infrastructure losses, and extensive fire damage to the water distribution systems in the towns of Santa Rosa and Paradise CA, and Detroit, OR, respectively. Fire damage caused the water distribution system to become contaminated with volatile organic compounds including benzene, a well-known carcinogen. This study investigates a modeling method to evaluate the heat transfer of wildfires through the soil to quantify if the upper limit temperature for pressure service of common service pipelines is exceeded during a wildfire. This model utilizes one-dimensional transient heat conduction, looking at the effects of surface heat flux, surface temperature, heating duration, thermal diffusivity, and burial depth, on below ground soil temperatures. After considering these effects, the below ground conditions are applied to a representative buried service lateral to assess the influence of increased soil temperatures on buried pipes and the water contained within. For the purposes of this study, the model is run based on service laterals in a typical intermountain West WUI community. Under the wildfire conditions expected in these communities, the model determined that the upper limit temperature for pressure service of the pipelines was exceeded at depths up to 0.45 m. The model’s fragility analysis of burial depths reveals that this upper limit temperature will be exceeded at least 50% of the time at depths up to 0.19 m. This model will provide useful information for municipalities in WUI communities to plan for future resiliency against wildfires.