INVESTIGATION OF STRUCTURAL WOOD IGNITION BY FIREBRAND ACCUMULATION

This study aims to understand the process of ignition of wooden structures by ember accumulation during wildfires. The work analyses two different sets of experiments. A high intensity large scale prescribed fire was conducted in a pine stand where ember collection plots were used to collect embers falling on the ground to measure and weigh them. Most of the particles collected were pieces of bark and burnt branches. The data collected on ember’s characteristics compared very well to previous experiments. Ember loading ranged from 0.2 to 98 gr/m 2 and most of the particles had a surface area smaller than 100 mm 2 . Later, small scale experiments were designed to understand the ignition process of structures. Results from the field experiments were used to determine the range of embers to be used. Four different types of experiments were completed. It was shown that the temperature exposure generated from ember accumulation can be simulated by an electrical heater, but the higher thermal inertia compared to the embers resulted in a lower temperature gradient. It was also shown that in the range of size and mass of the embers collected, it was possible to ignite samples of wood in different geometrical arrangements. Future work will be focused on determining how to incorporate the intensity of the thermal exposure and the time of exposure into a critical factor for ignition.