Ignition propensity of structural materials exposed to firebrand in wildland-urban interface (WUI) fires

Case Western Reserve University, Cleveland OH

Investigators

Abstract

This project will characterize the ignition process of materials caused by firebrand attacks, a key mechanism of wildfire spread into Wildland-Urban Interface (WUI) communities. Firebrands are small burning pieces lofted by flame plumes and transported by ambient winds. Although they are small, firebrands can travel in large groups for long distances from the fire front. These firebrands can shower unto structures in WUI communities far from the wildfire itself and therefore pose serious threats to human lives and properties. In this project, lab-scale experiments and computational modeling will be used to systematically study such phenomena. By providing a better understanding of firebrand attacks, this project will promote the development of new testing standards for building codes and materials. This work will contribute to the effort in increasing the safety of structures at the wildland-urban interface, such as optimal geometry of structure for mitigating fire risks. For a combustible solid subjected to external heating, ignition depends not only on the total energy input but also on the spatial distribution of the heating. For ignition due to firebrand attack, the distribution of firebrands and their individual shapes, sizes, and contact areas with the target structure will determine the distribution of heat flux on the structure surface. Environmental conditions (e.g., background radiant heating and air flow speed) also have a significant effect on the kinetics of the burning firebrands and the interactions between firebrands and the target structure. The goal of this study is to obtain a fundamental understanding of how these parameters affect the ignition propensity of a structure material. A combination of lab-scale experiments and computational modeling will be used. The experiment will involve firebrands burning under the influence of air flow and external radiant heating. Temperatures, burning durations, and heat release rates of the burning brands, as well as the temperature of the substrate, will be analyzed. The ignition propensity of the fuel bed will be characterized according to firebrand attributes and environmental factors. A combustion model will also be developed for simulating the thermo-kinetic process of each aspect of the firebrand attack. The simulation results will provide detailed information about gases and solids during the combustion process, thus facilitating the interpretation of the experimental observation. The numerical simulation will also allow the investigation of the underlying physics of these processes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.