How do bushfires spread?
Bushfires can spread because of embers and burning debris, radiant heat exposure, direct flame contact, and convection (not detailed here).
Embers and other debris can be swirled around in the strong winds that accompany a bushfire. These debris often land on buildings, vegetation and other combustible objects, spreading fire and igniting new fires. In a bushfire, most house fires start because of these wind-driven embers, rather than through direct flame contact. Ember attack can occur at any time during a bushfire, including long after the fire front has passed.
Embers are usually made up of burning plant materials such as bark, leaves and twigs
Radiant heat is the heat that emanates from a fire. Radiant heat travels in a straight line and is invisible to the naked eye. Radiant heat can dry and ignite fuels, and can be fatal in a bushfire. Radiant heat can be felt up to 150m from the fire. Protection from radiant heat can be offered by shielding behind a non combustible object.
The amount of radiant heat that a fire produces is influenced by the fires size
Direct flame contact
Fire can also spread because of direct flame contact between a combustible fuel (such as unmanaged vegetation) and the fire.
Flames can flow over and wrap around structures, impacting the sides of object not directly facing the bushfire