On Tue, 22 Jan 2013, Russell Coker wrote:
On Tue, 22 Jan 2013, Tony Langdon <vk3jed@gmail.com> wrote:
I think it is feasible to build an active protection system, but it would be most effective (in both performance and cost) as part of an overall fire resistant house and garden design.
If you had a house made of solid relatively airtight concrete including a concrete roof with solid shutters then it doesn't seem that you would need any water protection system. If you had a house of a typical suburban design then it seems that no reasonable amount of water would save it unless you also have water inside the roof cavity to stop embers that get through gaps in the tiles.
It doesn't seem like adding water will be guaranteed to save a house that wasn't already fairly safe without the water.
Most of the buildings on Siding Spring are 1960/70's era, brick, tin roof. Following the 2003 Mt Stromlo fires, they were all retrofitted with fire screens over the windows, clearing of the trees around any building and not much else (this was cost effective enough). The fires last week took out the lodge, which was still quite close to trees and right on the ridge, but little else (it's ironic that that part of the mountain is now off limits because much asbestos has been spread around. The fire proof asbestos didn't do its job properly and has now spread over half of NSW!). The ember screens did their job as expected. The external temperature according to the met station was observed at 104 degrees for less than a minute as the fire went overhead (may have of course peaked higher). That wouldn't be measuring radiant heat (the sensor is inside a stevenson screen), but most house fires are from ember attack through broken windows. My memory is that the trees are quite close to the met tower.
Do bushfires get hot enough to ignite aluminium? A quick google suggests that aluminium ignites at about 2000C which combined with being a great reflector of light and even better for infra-red means that it's probably going to resist anything a bushfire can do from a distance. So aluminium shutters should do.
I've got a spluttered piece of aluminium dome as souvenir from one of the Mt Stromlo domes, obtained 2 weeks after the fire went through. Melting point is more relevant than ignition point. That was a *freakin* hot fire. Having seen timelapse footage of the #SSO fires, I don't think it was quite so ferocious. Incidentally, this is my ex-bosses house: https://twitter.com/702sydney/status/293641215155523584/photo/1 According to my other ex-boss, a coworker in the RFS was driving the tanker back into town after the fire had already been fought, and they noticed in the nick of time that it had flared up again. -- Tim Connors