There is no standard thought, thats the problem...
They are not endorsed within SA and I have been led to belive that companies / businesses are going around stating that they build them to the "Standard"... Bit hard to do when no such standard exists.
7 people died in bunkers in Vic...
A bunker is generally regarded as an outbuilding and may not require approval, unless it is to be buried more than 1 metre then a Development Approval must be sought from Council.
Personally, I think if you choose to defend your well prepared home in accordance with all the usual caveats (physically / mentally fit for task, etc etc) then a bunker could be your very own 'Refuge of Last Resort' if everything else goes to crap.
But they should be the absolute LAST option and only in the example I cited above, not used as a primary or secondary strategy on your Bushfire Plan...
Just my thoughts,
Cheers
Shane