Examining the Effects of Buildings on Fire Front Rate of Spread in an Incendiary Test Tunnel

Globally 20% of humans are in direct risk of loss from wildfires, predominantly in the expanding wildland urban interface (WUI). To better understand the behavior of wildfire fronts in the WUI, experiments to study the effects of fire-induced winds near structures, and the relative importance of the momentum deficits caused by canopies and structures on fire-induced winds are needed.

A tilting incendiary test wind tunnel was constructed to study the effects of tilt and wind on fire front progression. Rectangular blocks were used to approximate buildings in the WUI, and rate of spread (ROS) was measured through two techniques. First a GoPro camera was mounted above the tunnel to visually track the fire front. The time and distance from fire front ignition to fire front arrival at the building was measured to give a spatially averaged value for ROS. The second method used a discrete array of thermocouples embedded in the incendiary tunnel floor to track fire front progression throughout the array. For zero slope conditions, the inclusion of buildings in the domain increased the spatially averaged ROS by 15%, with local ROS vectors calculated through the thermocouple array differing by up to 45%. For a 10 degree slope the inclusion of buildings increased the spatially averaged ROS by 25%.