And it seems some here are think of a bushfire in terms of other fires they have experienced, although I notice self described fire fighters aren't among them. When you get burnt by a normal fire - a candle or camp fire, it is normally because you have touched something hot. Either the coals, or the heated air. Not so for a bad bushfire. By the time the central flames of a bushfire touch you, you are already dead.

It is the radiated heat that kills you - not the hot air or even contact with the flames themselves. If you are unlucky the smoke might get to you, but that is unlikely. If your doubt this, consider the pictures on TV of people running around just after the bushfire has passed.

The amount of radiated heat is unbelievable, to me anyway. For the Canberra bushfires that put it at 1.5MW per meter. To try and picture it, imagine a football field, covered with 2400 electric bar heaters so no grass is visible. Now stand the football field of heaters on its long side, so it projects 50m into the air. Now construct a corridor by putting a second football field of heaters alongside, facing it.

Those heaters will radiate the same amount of heat (1.5MW per meter) as the Canberra bushfires. Now then walk down that corridor, for 15 minutes. Anything burnable exposed to the radiated heat will spontaneously ignite. Anything - green grass, clothes, paint, your hair, your skin. It is so hot throwing water at the heaters has no effect, just as water bombing had no effect on the Canberra fires. The water evaporates before it can get to the seat of the fire.

To have a good chance of escaping from the fire get out of the way of the radiated heat. The one thing on your side it is only lasts 15 minutes. A concrete drain pipe is ideal. It heats up slowly, and is low to the ground so smoke it less of a problem because smoke is hot and rises.

rstuart,

That sounds like a more scientific explanation.

"Air filled with smoke and other rubbish is a different story - as anybody who has been in the path of a camp fire burning the wrong way knows."

It could be the folks on TV were finding it hard to breathe because of the smoke and other particles in the air, rather than a lack of oxygen. Sounds like a fair call.

"Nobody hiding in a concrete building is going to be seriously hurt by a wooden door burning."

Except for the fact that there is no longer any shielding from the radiant heat from the fire (assuming the firefront hasn't passed by then).

"So I would make sure there was no metal exposed to the fire visible inside the bunker - not even a door."

That's sound advice. In light of that, how about putting a wall of fire bricks out the front shielding the metal door (like the L-shaped wall out the front of a public toilet)? Alternatively, have a metal door on the bunker, but build its internal walls (made of firebricks)so that the heat has to go around a corner or two before it gets to the people inside.

A corrugated tin roof would be a bad idea, as you suggest. To alleviate this, if the shelter was built sturdily enough, how about hiring a bobcat and loading soil all around it and on the roof to effectively bury it? Maybe even get an old shipping container, bury that and put a row or two or firebricks out the front to protect the metal front door from direct radiant heat.

*So Yabby, I'd say your pricing is out by a factor of 10 or so.*

Ah, but this is not about you knocking something up, without shire
permission. This is about making the whole thing mandatory, as
suggested by Dickie.

For that to happen, it would have to comply to a standard, it would
have to comply with building codes etc. Every Govt employee whose
arse is on the line, would add their 5c worth, for they are not
paying for it all, house owners are paying. You'd be amazed
how quickly 100 Grand would be spent.

Now imagine if they allowed your bunkers and some people died in
them, as they were not up to scratch. No public servant would
risk his career on that, so the standards would be so high,
that people would be battling to afford them.

That American product that I linked to sounds promising, does
anyone know more about it? I've only read the promotion, not
heard the other side yet, if there is one. I'd like to hear
if anyone knows if it has been tested in Australia and if their
claims can be substantiated.

Foxy "I thought that burning-off was an essential part of land
management practice, in the appropriate seasons.

I believe that the Royal Commission will address these matters
and pass appropriate laws enforceable under penalty, including
rural Councils."

I had heard of the no-burn bye-laws and it was confirmed on 3AW from a caller this morning, who was at one stage trapped by burning trees but managed to escape... cannot remember which Shire he was in but he was, rightly very very angry and complaining about the laws which made illegal ALL and ANY clearing of dead trees from any land, public or private.

The accumulation of available fuel stocks, from leaf, twig and branch fall and dead trees, for a bushfire is a critical element in determining the severity and sustainability and resistence of a fire to the remedial / containment strategies of mere humans.

I would expect this to be toward the top of the list of things which must be fixed from the Royal Commission findings.

What sort of council do you have, Yabby? Mine, in the middle of a city, requires no council approval for a garden shed of less than 10 sq meters. 3m x 3m would be more than sufficient to house people for the 15 or 30 minutes required. Besser brick with their internal air gaps would be ideal for the walls. Probably a floor would be an overkill - dirt would be fine, but a slab gives you a solid foundation for the walls as well as a floor so you probably would not save much. The roof would be a problem - it has to not heat up during the fire and not be blown away by the wind, but I am sure a builder could come up with some simple solution.

I have no doubt the current disaster will create a wave of good intentions, just as ash Wednesday did, and just as the Canberra fires did. I am also fairly sure that government and people will remain the same, and so in 20 years time we still will have houses surrounded by fuel loads that will destroy them, just as happened this time.

I do doubt people will still be painting with the paint suggested in your link in 20 years time. A Besser brick bunker might cost 2-3 times more than a coat of your paint, but it would still be relatively cheap and it would be there forever. The only danger is it will be full of crap when the fire comes. You can't save people from themselves, I guess.

rstuart, you miss the point. If bunkers should become mandatory,
as Dickie suggests, then clearly there will have to be state building
codes and council approval of those mandatory bunkers. Those
mandatory bunkers would then not be your garden shed, but would
need approval by govt employees covering their arses against any
possible failure.

Now if a Govt employee has to choose between risking their career and
costing somebody else money, in my experience they nearly always
choose to protect themselves. Self interest prevails.

My argument was with Dickies suggestion of making bunkers mandatory,
thus having them comply with Govt building codes, not
with you fooling around with a garden shed or whatever.