Learn more about ongoing laboratory research into backing fire spread – a subject largely overlooked compared to heading fires, yet at any instant, it represents approximately ½ the active perimeter of a wildland fire. This research explores whether flame spread on individual fuel particles can be upscaled to behaviors seen in fuel beds.

Experiments using individual fuel particles have so-far revealed: 1) backing spread is highly sensitive to local wind speed, 2) unlike heading spread, particle spread depends upon a little-recognized mm-scale heat transfer mechanism called “gas-phase conduction”, 3) flame spread rate on particles varies with wind direction as a polar elliptical function, being the same without wind as at 90°, 4) external radiant heat flux greatly enhances spread rates on particles and is readily incorporated into an empirical spread model, even though it is insufficient alone for particle ignition. Experiments show that flame spread through simple cardboard fuel beds is well approximated as a sequence of single particle behaviors, but new techniques will be required to understand what, if any, statistical method could scale particle behavior to the complexity of real fuel beds.