Experiments and modeling of fire spread in big sagebrush and chamise shrubs in a wind tunnel

Fire spread in live shrubs (chamise and big sagebrush) was measured in a wind tunnel and used to validate a semi-empirical shrub combustion model. The fuel bed was designed to contain two shrubs in their natural arrangements (nominally 2 m long x 1 m wide x 1 m high). Shrub geometry dimensions were measured manually or determined from images. LiDAR scanning was also performed in some experiments to establish a 3-D voxel data matrix for potential fuel placement. Wind speed was held constant at 1.4 m/s while fuel density and moisture content varied across natural levels. Mass, fuel surface temperature, gas temperature, radiative heat flux and total heat flux data were collected throughout each experiment. Combustion characteristics and time-dependent fire behavior were measured continuously using three digital camcorders at different locations around the fuel bed. After each experiment, the terminal end diameter of burned branches was measured as an indicator of fire intensity. Results indicate that fire behavior under these conditions is highly dependent on species and fuel moisture content, overall fuel bed density, and local fuel density fluctuation. Comparison of bush model simulations with the shrub combustion experiments show promise.