It's the ember attacks - they're horizontal bullets which drop when mother gravity takes over - then they reboot the fire at fuel depots which are buildings that get razed while still surrounded by unburnt trees as the rebooted fire blows its new embers into the next fuel depot. My earnest suggestion of what to do in bush-fire risk zones is to please get water jets (not sprinklers) mounted onto roof gables & plumbed to independent pump/motor and tanks. Our two jets throw 400 litres per minute in two 30 metre diameter circles up over and around our home - which is in a 'Bush-fire risk zone" @ 4 tonnes every ten minutes. If say 100 homes did likewise is these zones that's 400 tonnes every ten minutes. We spent $5k doing it ourselves & have 12 tonnes on standby - so maybe it should cost about twice that for others to supply and fit the pump, motor, plumbing and tank. Surely an approaching bush-fire would have trouble with a timbered ' fire risk zone' area into which 400 tonnes of water were being dumped every ten minutes. We also plumbed 120 inward facing sprinkler heads under the gutters to wet the verandahs.