During intense wildland fires a transient vortex pair sometimes occurs that may form with a near vertical axis but then bends over and becomes horizontal. Collapsing limbs of these vortex pairs threaten fire fighters. Therefore, this study simulated vortex collapse in a wind tunnel. Collapse was produced by cross air flow upstream of the heat source. Using an upstream, wing-shaped obstacle to create cross air flow, the wind tunnel experiments showed that small changes in wing angle, and thus cross air flow, could cause major changes in the structure of the vortex pair.

[This publication is referenced in the "Synthesis of knowledge of extreme fire behavior: volume I for fire managers" (Werth et al 2011).]