Of course the most dangerous and violent Aussie bushfire occurs in eucalyptus - The US is now prone to these in some parts, having planted the trees over there... ;-)

The most dangerous circumstance is when there has been a long hot dry spell - the eukys give off a flammable vapour that is almost like the US military 'vapour bombs'. Flames will explode, throwing burning ash in front, and the infrared heat can ignite things at considerable distance. Also the most extreme is when the blaze starts 'crowning' - racing thru the tops of the trees much faster than thru the underbrush - this is at a speed that nothing, even vehicles can get away from. Very nasty is when such a crowning blaze heads uphill, the speed (and the noise) is immense.