Bush-fire protection of buildings using external water-spray systems
Assembled cognoscenti; it being the bush-fire season my thoughts turned to the practicability of protecting buildings , using external water-spray systems. My thoughts went something like this 1/ If one knows the air temperature , humidity, wind velocity, distance to, and composition and dryness of surrounding bush . 2/ Can't one calculate the radiant heat in KW/m2 impacting on the building ?; and 3/ the likely duration in the event of a bush-fire ? 4/ Can't one then calculate the minimum spray flow in litres / sec and the total volume of water required ? 5/ Can't one then make an informed decision about, whether such a system is physically and financially practical in a particular situation? Because such systems don't seem to receive much attention from media or insurance companies ; I assumed the answer must be that they are usually not practical. So I was somewhat surprised on reading : http://en.wikipedia.org/wiki/External_water_spray_system to find: "Issues There is a lack of scientific research regarding EWSS..........." I am contacting the CSIRO because I seem to recall they did something on this years ago; but would be interested in actual research if anyone has come across it ; regards Rohan McLeod
On 22/01/2013 3:10 PM, Rohan McLeod wrote:
Assembled cognoscenti; it being the bush-fire season my thoughts turned to the practicability of protecting buildings , using external water-spray systems. My thoughts went something like this 1/ If one knows the air temperature, humidity, wind velocity, distance to, and composition and dryness of surrounding bush.
Some of those would be quite variable but might be possible.
2/ Can't one calculate the radiant heat in KW/m2 impacting on the building ?; and 3/ the likely duration in the event of a bush-fire ? 4/ Can't one then calculate the minimum spray flow in litres / sec and the total volume of water required ? 5/ Can't one then make an informed decision about, whether such a system is physically and financially practical in a particular situation?
That all seems reasonable. There was an item in a doco a while ago (I think it included the CSIRO) and they seemed to be interested in using water absorbent crystals (sodium polyacrylate I guess). Used less water and lasted longer. Their demo looked quite impressive. I have no idea how it would be "sprayed" on to a home in practise though. Cheers, Mike
Mike Mitchell wrote:
On 22/01/2013 3:10 PM, Rohan McLeod wrote:
..................snip e then make an informed decision about, whether such a system is physically and financially practical in a particular situation?
That all seems reasonable.
There was an item in a doco a while ago (I think it included the CSIRO) and they seemed to be interested in using water absorbent crystals (sodium polyacrylate I guess). Used less water and lasted longer. Their demo looked quite impressive. I have no idea how it would be "sprayed" on to a home in practise though.
There seem to be quite a few commercial systems; but I guess I was wondering about their underlying theoretical basis ? regards Rohan McLeod
On Tue, 22 Jan 2013, Rohan McLeod <rhn@jeack.com.au> wrote:
Assembled cognoscenti; it being the bush-fire season my thoughts turned to the practicability of protecting buildings , using external water-spray systems. My thoughts went something like this 1/ If one knows the air temperature , humidity, wind velocity, distance to, and composition and dryness of surrounding bush . 2/ Can't one calculate the radiant heat in KW/m2 impacting on the building ?; and
I don't think it's the heat on the overall building that matters. It's the heat coming through the windows, to leaves in the gutters, to exposed wooden parts of the building, etc. After bushfires you see chimneys still standing, so it's obviously possible to make bricks that won't be significantly damaged by fire. Are regular brick walls sufficient? If not how much more does it cost to use fire bricks? Will a fire make a galvanised iron roof hot enough to bend or to set fire to wooden beams in the ceiling? If the former then a water spray would help, but I suspect that the latter would be the only problem in which case iron roof beams would be the solution. It seems to me that if a building was constructed to be heat resistant and had solid shutters on all the windows (EG hard wood shutters with gaps too small for embers with a sheet of galvanised iron on the outside) then you probably wouldn't need external water. But if the building has gaps that allow embers in (EG a typical tile root), has wooden window frames, has big windows with flammable curtains, or many other features of typical homes then even a water spray won't necessarily solve the problem.
3/ the likely duration in the event of a bush-fire ?
The radiant heat will be of very small duration. Wind-blown embers will last for a much longer time.
Because such systems don't seem to receive much attention from media or insurance companies ; I assumed the answer must be that they are usually not practical. So I was somewhat surprised on reading : http://en.wikipedia.org/wiki/External_water_spray_system
If I was living in an area that's at risk of bush fire then I'd get have an entirely concrete house built with solid shutters on the windows. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/
Russell Coker wrote:
..............snip So I was somewhat surprised on reading : http://en.wikipedia.org/wiki/External_water_spray_system If I was living in an area that's at risk of bush fire then I'd get have an entirely concrete house built with solid shutters on the windows. Well here in Pasco Vale in a solid brick block of flats, the bush-fire risk is fairly minimal; really just idle curiosity to see why such spray systems aren't more common; thanks for your interest though;
regards Rohan McLeod
On 22/01/13 4:03 PM, Russell Coker wrote:
I don't think it's the heat on the overall building that matters. It's the heat coming through the windows, to leaves in the gutters, to exposed wooden parts of the building, etc. After bushfires you see chimneys still standing, so it's obviously possible to make bricks that won't be significantly damaged by fire. Are regular There are two main issues with buildings - radiant heat directly affecting flammable materials, and ember attack (direct flame contact can be prevented with a good garden design).
Radiant heat needs to be blocked by physical barriers (e.g. brick walls, window shutters, water sprays). Ember attacks are probably best prevented by a building design that doesn't give embers an opportunity to lodge near flammable material (open eaves and under floor spaces are bad news), because ember attacks can last a considerable time before the main fire arrives (some embers can be blown over 30km ahead of the main fire on a bad day). Of course, maintenance such as cleaning gutters (or having a decent gutter guard) and keeping litter and debris away from the house will help! -- 73 de Tony VK3JED http://vkradio.com
On 22/01/13 3:10 PM, Rohan McLeod wrote:
Assembled cognoscenti; it being the bush-fire season my thoughts turned to the practicability of protecting buildings , using external water-spray systems. My thoughts went something like this 1/ If one knows the air temperature , humidity, wind velocity, distance to, and composition and dryness of surrounding bush . 2/ Can't one calculate the radiant heat in KW/m2 impacting on the building ?; and 3/ the likely duration in the event of a bush-fire ? 4/ Can't one then calculate the minimum spray flow in litres / sec and the total volume of water required ? 5/ Can't one then make an informed decision about, whether such a system is physically and financially practical in a particular situation? I can only comment on the system I know, which is the protection system used on a typical tanker (a lot smaller area to protect than a house!). For that space, the water usage is 150 litres/minute, and additional passive shielding is added, such as the vehicle body and reflective curtains for the windows, as well as individual protective clothing.
I suspect that a house would require considerably more water. Having some means to cover windows (e.g. shutters) would help reduce the total radiant heat load. Also, as a house is not mobile and covers greater length, the time of exposure would be potentially greater. However, you can use additional protection such as appropriate garden plantings (e.g. succulent plants are highly fire resistant, due to the high water content in their leaves/stems). The CFA have information on planting for fire prone areas that might help with the garden planning side of things. The bottom line is "defence in depth", a bit like network security - having multiple defences which work together to achieve the desired level of protection. 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. And no, I don't have any papers to quote on this... yet! Of course, YMMV, and consult someone with more knowledge before going down this road. -- 73 de Tony VK3JED http://vkradio.com
On Tue, 22 Jan 2013, Tony Langdon <vk3jed@gmail.com> wrote:
I can only comment on the system I know, which is the protection system used on a typical tanker (a lot smaller area to protect than a house!). For that space, the water usage is 150 litres/minute, and additional passive shielding is added, such as the vehicle body and reflective curtains for the windows, as well as individual protective clothing.
By "tanker" do you mean fire truck? If so then presumably the truck is designed to go into unsafe situations while a sensible person would cut down trees that are too close to their house and take other measures to reduce the risk.
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. 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. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/
On Tue, 22 Jan 2013, Russell Coker wrote:
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.
Earth houses can be useful too: http://en.wikipedia.org/wiki/Earth_house Fire protection Compared to other building materials, such as wood, earth houses feature efficient fire protection owing both to the use of concrete and the insulation provided by the roof. Regards Peter
On 22/01/13 5:04 PM, Peter Ross wrote:
On Tue, 22 Jan 2013, Russell Coker wrote:
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. Earth houses can be useful too:
http://en.wikipedia.org/wiki/Earth_house
Fire protection
Compared to other building materials, such as wood, earth houses feature efficient fire protection owing both to the use of concrete and the insulation provided by the roof. That looks like an interesting architectural style that has a lot of practical benefits. Wombats knew what they were doing all along. ;)
-- 73 de Tony VK3JED http://vkradio.com
On Tue, 22 Jan 2013, Tony Langdon wrote:
On 22/01/13 5:04 PM, Peter Ross wrote:
On Tue, 22 Jan 2013, Russell Coker wrote:
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. Earth houses can be useful too:
http://en.wikipedia.org/wiki/Earth_house
Fire protection
Compared to other building materials, such as wood, earth houses feature efficient fire protection owing both to the use of concrete and the insulation provided by the roof. That looks like an interesting architectural style that has a lot of practical benefits. Wombats knew what they were doing all along. ;)
I wonder why most Australian houses do not seem to have basements. Any particular reasons? Regards Peter
On Wed, 23 Jan 2013, Peter Ross <Peter.Ross@bogen.in-berlin.de> wrote:
That looks like an interesting architectural style that has a lot of practical benefits. Wombats knew what they were doing all along. ;)
I wonder why most Australian houses do not seem to have basements.
Any particular reasons?
Expense is the reason I've seen cited, that combined with the fact that it's not fashionable. In an Australian summer a basement is a really good thing, you install your favourite entertainment things and spend the hottest part of the day avoiding the heat. Expense is also the reason that houses aren't designed to be fire-proof. In addition to the things we have already discussed there's no reason why a home couldn't have sprinklers in every room in the way that hotels are required to. Hotels have a higher risk of fire due to idiots and due to people getting confused when not in their own home. But the risk of a house fire is still there and sprinklers would work well. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/
On 23/01/13 12:23, Russell Coker wrote:
On Wed, 23 Jan 2013, Peter Ross <Peter.Ross@bogen.in-berlin.de> wrote:
That looks like an interesting architectural style that has a lot of practical benefits. Wombats knew what they were doing all along. ;)
I wonder why most Australian houses do not seem to have basements.
Any particular reasons?
Expense is the reason I've seen cited, that combined with the fact that it's not fashionable. In an Australian summer a basement is a really good thing, you install your favourite entertainment things and spend the hottest part of the day avoiding the heat.
Expense is also the reason that houses aren't designed to be fire-proof. In addition to the things we have already discussed there's no reason why a home couldn't have sprinklers in every room in the way that hotels are required to. Hotels have a higher risk of fire due to idiots and due to people getting confused when not in their own home. But the risk of a house fire is still there and sprinklers would work well.
Functioning smoke detectors are much more cost effective. I dread the thought of sprinklers in every house - the commercial ones get broken enough as it is, and the false alarms from them are a pain as well.
Allan Duncan wrote:
On 23/01/13 12:23, Russell Coker wrote:
On Wed, 23 Jan 2013, Peter Ross <Peter.Ross@bogen.in-berlin.de> wrote: I dread the thought of sprinklers in every house - the commercial ones get broken enough as it is, and the false alarms from them are a pain as well. ___ Not to mention apparently horrendously expensive to reset. I have a one tonne van , 2.1m at the roof-rack which I need to drive in underground car parks, often with a height limit of 2.1m. I was truly terrified when I discovered that, hitting and setting off the sprinkler system system could cost me thousands of dollars ! Not even clear whether it is an insurable risk;
regards Rohan McLeod
On Wed, 23 Jan 2013, Russell Coker wrote:
On Wed, 23 Jan 2013, Peter Ross <Peter.Ross@bogen.in-berlin.de> wrote:
That looks like an interesting architectural style that has a lot of practical benefits. Wombats knew what they were doing all along. ;)
I wonder why most Australian houses do not seem to have basements.
Any particular reasons?
Expense is the reason I've seen cited, that combined with the fact that it's not fashionable. In an Australian summer a basement is a really good thing, you install your favourite entertainment things and spend the hottest part of the day avoiding the heat.
I wonder how save it is to hide if you are surrounded by a fire. Basically whether it becomes too hot or you are running out of oxygene inside. Or other risks I did not think of.. Regards Peter
On Thu, 24 Jan 2013, Peter Ross <Peter.Ross@bogen.in-berlin.de> wrote:
Expense is the reason I've seen cited, that combined with the fact that it's not fashionable. In an Australian summer a basement is a really good thing, you install your favourite entertainment things and spend the hottest part of the day avoiding the heat.
I wonder how save it is to hide if you are surrounded by a fire.
Basically whether it becomes too hot or you are running out of oxygene inside. Or other risks I did not think of..
Oxygen is the issue. I've heard reports of people going back to their hotel room for their luggage and dying from smoke inhalation while their luggage survives... There's no reason why you can't have a basement with an external door, that's not an uncommon design. One of my friends has such a basement, I think that he needed to have a separate exit to have it considered as a separate office (rather than part of his home) for tax benefits at the time. With such a design you could hide in your basement while the main fire passes and then if your home catches on fire you could escape. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/
On Thu, Jan 24, 2013 at 9:38 AM, Russell Coker <russell@coker.com.au> wrote:
On Thu, 24 Jan 2013, Peter Ross <Peter.Ross@bogen.in-berlin.de> wrote:
Expense is the reason I've seen cited, that combined with the fact that it's not fashionable. In an Australian summer a basement is a really good thing, you install your favourite entertainment things and spend the hottest part of the day avoiding the heat.
I wonder how save it is to hide if you are surrounded by a fire.
Basically whether it becomes too hot or you are running out of oxygene inside. Or other risks I did not think of..
Oxygen is the issue.
I've heard reports of people going back to their hotel room for their luggage and dying from smoke inhalation while their luggage survives...
There's no reason why you can't have a basement with an external door, that's not an uncommon design. One of my friends has such a basement, I think that he needed to have a separate exit to have it considered as a separate office (rather than part of his home) for tax benefits at the time. With such a design you could hide in your basement while the main fire passes and then if your home catches on fire you could escape.
I have just read a book *Disasters That Changed Australia* by historian Richard Evans. In his book he talks of the Black Sunday fire of 1932 and how 6 mill workers were killed in the high country. I quote.... *"After six mill workers were killed in the 1932 fires, the Victorian Forests Commission began to urge mill owners to establish a safe refuge fo their workers, in the form of a dugout. This was to built in a cleared area and topped with a thick layer of earth..." page 107* * * *"The men, woman and children of the little mill settlements sheltered in dugouts -- where dugouts had been built. There, people were reasonably safe..." page 108* He goes on to say that the dugouts had risks but like a lot of wildlife that sheltered in dugouts or burrows it was the safest option from a fire, he talks of men being boiled alive in water tanks and others burying themselves in sawdust piles at the mills to try and get away from the heat. Richard Evans has a PhD in history from Monash and is a research fellow at Swinbourne, he is very passionate about Australia's history with fire so has researched it a great deal. The book *"Disasters That Changed Australia" *is published by Victory Books, Melbourne University Publishing. ISBN 978-0-522-85649-1 It is a good book and covers many natural and man made disasters that shaped Australia, I really enjoyed reading it even f it was in dead tree format and I had to get used to turning pages as it didnt have turn buttons on the side :) -- Mark "Pockets" Clohesy Mob Phone: (+61) 406 417 877 Email: hiddensoul@twistedsouls.com G-Talk: mark.clohesy@gmail.com GNU/Linux..Linux Counter #457297 - "I would love to change the world, but they won't give me the source code" "Linux is user friendly...its just selective about who its friends are"
On 22/01/13 4:57 PM, Russell Coker wrote:
By "tanker" do you mean fire truck? If so then presumably the truck is designed to go into unsafe situations while a sensible person would cut down trees that are too close to their house and take other measures to reduce the risk. Yep, and I did say garden design would be part of making a house fire resistant, which would cover cutting down trees, etc. 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. The water would limit damage to the concrete or other structural materials, but the use of such materials would minimise any extra protection needed.
It doesn't seem like adding water will be guaranteed to save a house that wasn't already fairly safe without the water.
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.
They certainly get hot enough to _melt_ aluminium. A school friend had a "souvenir" from being burnt out during Ash Wednesday. It looked like a bit of modern sculpture, like something poured out and painted silver. What it was, in fact, was the remains of the engine block from their lawnmower. The heat from the fire had turned the engine block into a pool of molten metal. -- 73 de Tony VK3JED http://vkradio.com
On 01/22/2013 04:57 PM, Russell Coker wrote:
On Tue, 22 Jan 2013, Tony Langdon <vk3jed@gmail.com> wrote:
I can only comment on the system I know, which is the protection system used on a typical tanker (a lot smaller area to protect than a house!). For that space, the water usage is 150 litres/minute, and additional passive shielding is added, such as the vehicle body and reflective curtains for the windows, as well as individual protective clothing.
an Australian Standard fire hydrant is to supply for 300 litres/minute at 700kPa and should be supplied from a system 4 hours supply with positive feed.
Do bushfires get hot enough to ignite aluminium?
Melting is a bigger problem as Al melts below 650C depending on the other elements in the alloy, as pure Al is almost never used, so 550C and cooler is found. Steve previously worked in the fire protection industry
Steve Roylance wrote:
On 01/22/2013 04:57 PM, Russell Coker wrote:
On Tue, 22 Jan 2013, Tony Langdon <vk3jed@gmail.com> wrote:
I can only comment on the system I know, which is the protection system used on a typical tanker (a lot smaller area to protect than a house!). For that space, the water usage is 150 litres/minute, and additional passive shielding is added, such as the vehicle body and reflective curtains for the windows, as well as individual protective clothing. an Australian Standard fire hydrant is to supply for 300 litres/minute at 700kPa and should be supplied from a system 4 hours supply with positive feed. Please correct me if I am reading this incorrectly; street fire hydrants are intended to supply 300 litres/ minute at a pressure of 700kPa ? presumably with a much higher pressure with no flow ? Further the supply to such a hydrant must be sufficient in volume, for 4 hours flow at this rate ; that is 720,000 litres or 720 m^3 ?; where an Olympic swimming pool say contains 50 x 25 x 1 m^3 = 1250 m^3 ?
thanks Rohan McLeod
On 01/22/2013 06:59 PM, Rohan McLeod wrote:
Steve Roylance wrote:
On 01/22/2013 04:57 PM, Russell Coker wrote:
On Tue, 22 Jan 2013, Tony Langdon <vk3jed@gmail.com> wrote:
I can only comment on the system I know, which is the protection system used on a typical tanker (a lot smaller area to protect than a house!). For that space, the water usage is 150 litres/minute, and additional passive shielding is added, such as the vehicle body and reflective curtains for the windows, as well as individual protective clothing. an Australian Standard fire hydrant is to supply for 300 litres/minute at 700kPa and should be supplied from a system 4 hours supply with positive feed. Please correct me if I am reading this incorrectly; street fire hydrants are intended to supply 300 litres/ minute at a pressure of 700kPa ? presumably with a much higher pressure with no flow ? Further the supply to such a hydrant must be sufficient in volume, for 4 hours flow at this rate ; that is 720,000 litres or 720 m^3 ?; where an Olympic swimming pool say contains 50 x 25 x 1 m^3 = 1250 m^3 ?
AS-2419 which I am quoting is about in building hydrants, and AS-2118 for sprinklers. this is about right, if the mains cannot supply the pressure then a booster pump is needed and if it cannot do the volume then a tank is needed. Cannot get exact clause quotes as all is behind a paywall, even as they are required by govt. regulations. Steve
On 22 January 2013 16:57, Russell Coker <russell@coker.com.au> wrote:
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.
Don't forgot that most houses burn down after the fire front has passed. If the house survives or not depends on if there is somebody around (risking their necks) to put out the small spot fires before they result in the house burning down. Of course exceptions exist. Have heard that one house had its roof blown away, after which there was no saving it. The other problematic area in the Marysville's fire was the gas cylinder venting valves pointing at other houses, and resulting damage, including broken windows which embers could enter. I see a number of problems with the sprinkler system: * Relying on mains water pressure or mains electricity is a big no no, there probably won't be any. That fire truck up the road will be using all the water pressure, and a tree will be down across the power lines. * If it is a petrol/diesel pump, somebody has to be able to start it. Plus it may not start when required. * The system would be very exposed as the main fire front passes. * If you start it before the fire front, you use up all your water before it is needed (after the front passes). * If you start it as the fire front is passing through you get burnt. Plus the water will evaporate and has no affect whatsoever. * Ideal is to start it after fire front has passed, but you have to be around (and exposing yourself to danger) to do so. * After fire passes there is no guarantee that you will get water where it is needed (to put out the spot fires). So a sprinkler system that gets its supply from tanks and has diesel/petrol powered pump, that somehow can be activated after the main fire front has passed might be a good thing. Although not as good as being there to put out spot fires with a wet mop (yes, I have heard stories of people saving their houses with nothing more then mops and a bath previously filled with water). The problem is with activating the sprinklers at the appropriate time. And obviously you can't rely on mains power, telephone, ADSL, 3G, etc, which you normally would use for remote control applications. -- Brian May <brian@microcomaustralia.com.au>
On 22/01/2013 7:33 PM, Brian May wrote:
I see a number of problems with the sprinkler system:
* Relying on mains water pressure or mains electricity is a big no no, there probably won't be any. That fire truck up the road will be using all the water pressure, and a tree will be down across the power lines.
An appropriate header tank would take care of that but may not be of use with your other concerns. Cheers, Mike
Brian May wrote:
On 22 January 2013 16:57, Russell Coker <russell@coker.com.au <mailto:russell@coker.com.au>> wrote:
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.
Don't forgot that most houses burn down after the fire front has passed. If the house survives or not depends on if there is somebody around (risking their necks) to put out the small spot fires before they result in the house burning down.
Of course exceptions exist. Have heard that one house had its roof blown away, after which there was no saving it.
The other problematic area in the Marysville's fire was the gas cylinder venting valves pointing at other houses, and resulting damage, including broken windows which embers could enter.
I see a number of problems with the sprinkler system:
* Relying on mains water pressure or mains electricity is a big no no, there probably won't be any. That fire truck up the road will be using all the water pressure, and a tree will be down across the power lines. * If it is a petrol/diesel pump, somebody has to be able to start it. Plus it may not start when required. * The system would be very exposed as the main fire front passes. * If you start it before the fire front, you use up all your water before it is needed (after the front passes). ..............snip It may be that it is only practical ( physically achievable and cost effective) in certain situations. Which was why I was interested in the fundamental research. Consider an all weather-board house I visited in Belgrave ( in the middle of winter); which had state-forest with 30m gums and heavy undergrowth within 10m of the back of the house; I suspect the radiant flux from a crown-fire there would heat the air inside so rapidly it would almost explode !;
regards Rohan McLeod
On 22 January 2013 20:16, Rohan McLeod <rhn@jeack.com.au> wrote:
It may be that it is only practical ( physically achievable and cost effective) in certain situations. Which was why I was interested in the fundamental research. Consider an all weather-board house I visited in Belgrave ( in the middle of winter); which had state-forest with 30m gums and heavy undergrowth within 10m of the back of the house; I suspect the radiant flux from a crown-fire there would heat the air inside so rapidly it would almost explode !;
Yes, very important to consider your own set of circumstances before deciding to risk your own neck and stay and protect your property. If there is a large build up of leaves, etc, next to the weatherboard you could be in trouble. In fact, have heard weatherboard is a problem anyway. There is a free evaluation system offered by the government to have somebody inspect your property and rate it for fire danger. Not sure if this applies to properties you are considering buying. I haven't seen the details. Also you probably shouldn't even consider staying if you are looking after kids (for example). -- Brian May <brian@microcomaustralia.com.au>
On 22/01/13 19:33, Brian May wrote:
On 22 January 2013 16:57, Russell Coker <russell@coker.com.au <mailto:russell@coker.com.au>> wrote:
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.
Don't forgot that most houses burn down after the fire front has passed. If the house survives or not depends on if there is somebody around (risking their necks) to put out the small spot fires before they result in the house burning down.
Of course exceptions exist. Have heard that one house had its roof blown away, after which there was no saving it.
The other problematic area in the Marysville's fire was the gas cylinder venting valves pointing at other houses, and resulting damage, including broken windows which embers could enter.
I see a number of problems with the sprinkler system:
* Relying on mains water pressure or mains electricity is a big no no, there probably won't be any. That fire truck up the road will be using all the water pressure, and a tree will be down across the power lines. * If it is a petrol/diesel pump, somebody has to be able to start it. Plus it may not start when required. * The system would be very exposed as the main fire front passes. * If you start it before the fire front, you use up all your water before it is needed (after the front passes). * If you start it as the fire front is passing through you get burnt. Plus the water will evaporate and has no affect whatsoever. * Ideal is to start it after fire front has passed, but you have to be around (and exposing yourself to danger) to do so. * After fire passes there is no guarantee that you will get water where it is needed (to put out the spot fires).
So a sprinkler system that gets its supply from tanks and has diesel/petrol powered pump, that somehow can be activated after the main fire front has passed might be a good thing. Although not as good as being there to put out spot fires with a wet mop (yes, I have heard stories of people saving their houses with nothing more then mops and a bath previously filled with water). The problem is with activating the sprinklers at the appropriate time. And obviously you can't rely on mains power, telephone, ADSL, 3G, etc, which you normally would use for remote control applications.
The usual way is to use thermal sensors, and of course it needs to auto-start the pump that uses local storage.
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
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.
Ignites, maybe not.. melts tho @ 660.32°C
On 01/24/2013 04:12 AM, Anthony Hogan wrote:
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.
Ignites, maybe not.. melts tho @ 660.32°C hi
that is for pure Al, which is unusual, as a alloy 577°C or lower, would be more likely as adding other elements makes it easier for the casting & machining. Steve
On 22/01/13 15:10, Rohan McLeod wrote:
Assembled cognoscenti; it being the bush-fire season my thoughts turned to the practicability of protecting buildings , using external water-spray systems. [...]
The term "bushfire protection" needs to be better defined before you can move on to numbers on a page. If there is heavy vegetation right up to the house, then radiant heat and flame impact is the operating mode, and the figures for burn-over protection of a fire truck applies (mentioned by another reply). If you have done a proper preparation and the house is more than three times the tree height away from the bush, then the operating mode is ember attack. CSIRO recommended (years ago) that the house was painted white if timber, had all sub-floor areas fully boxed in, and eaves/roofing was gap filled. Even then there is a good chance of embers getting in, and this is where a water spray can help. Its function is to damp down all surfaces and cracks to extinguish embers that contact the structure, and it must do that in winds that easily exceed 50Kph. This means that any sprays must generate large droplet sizes, and direct the flow parallel and close to the surface to be protected. Sprinklers on the roof are largely a waste of water - if you must have them, then use a supply pipe along the ridge with the sprays under it so the spray pattern is close to the roofing. Roof spray water can be collected, filtered and recirculated to extend the running time IF you can design a system and filter that won't get clogged by all the flying debris. Its main use is filling the gutters to extinguish said flying debris since the gutters were spotless before the fire started, weren't they?
On 22/01/13 22:35, Allan Duncan wrote:
On 22/01/13 15:10, Rohan McLeod wrote:
Assembled cognoscenti; it being the bush-fire season my thoughts turned to the practicability of protecting buildings , using external water-spray systems. [...]
The term "bushfire protection" needs to be better defined before you can move on to numbers on a page.
If there is heavy vegetation right up to the house, then radiant heat and flame impact is the operating mode, and the figures for burn-over protection of a fire truck applies (mentioned by another reply).
If you have done a proper preparation and the house is more than three times the tree height away from the bush, then the operating mode is ember attack. CSIRO recommended (years ago) that the house was painted white if timber, had all sub-floor areas fully boxed in, and eaves/roofing was gap filled. Even then there is a good chance of embers getting in, and this is where a water spray can help. Its function is to damp down all surfaces and cracks to extinguish embers that contact the structure, and it must do that in winds that easily exceed 50Kph. This means that any sprays must generate large droplet sizes, and direct the flow parallel and close to the surface to be protected. Sprinklers on the roof are largely a waste of water - if you must have them, then use a supply pipe along the ridge with the sprays under it so the spray pattern is close to the roofing. Roof spray water can be collected, filtered and recirculated to extend the running time IF you can design a system and filter that won't get clogged by all the flying debris. Its main use is filling the gutters to extinguish said flying debris since the gutters were spotless before the fire started, weren't they?
I forgot one use of roof sprays - tile roof. Most houses around here are steel roofed, so it slipped by me. Tiles without a fire blanket are a bad idea - on Ash Wednesday I saw a two story place with 30m of green grass and a 2m brick front fence between it and the fire front catch fire in the roof an hour after the front had passed either side. Just a small trickle of smoke from the end of the ridge, would have been an easy save except no ladder and there were other houses under threat from the flank of the fire. When we came back past there was just a heap of rubble.
Allan Duncan wrote:
On 22/01/13 15:10, Rohan McLeod wrote:
Assembled cognoscenti; it being the bush-fire season my thoughts turned to the practicability of protecting buildings , using external water-spray systems. [...]
The term "bushfire protection" needs to be better defined before you can move on to numbers on a page. Many thanks for the practical advice; my interest as mentioned is more idle curiosity though and the theoretical limits of spray systems. As far as 'bush-fire protection' goes; I am thinking specifically of avoiding fire damage during the actual bush-fire; as far as 'bush-fire' goes I would prefer some kind of continuum definition; that is a function of height, distance, intensity and duration; don't know if that helps, regards Rohan McLeod
On 22/01/13 22:56, Rohan McLeod wrote:
Allan Duncan wrote:
On 22/01/13 15:10, Rohan McLeod wrote:
Assembled cognoscenti; it being the bush-fire season my thoughts turned to the practicability of protecting buildings , using external water-spray systems. [...]
The term "bushfire protection" needs to be better defined before you can move on to numbers on a page. Many thanks for the practical advice; my interest as mentioned is more idle curiosity though and the theoretical limits of spray systems. As far as 'bush-fire protection' goes; I am thinking specifically of avoiding fire damage during the actual bush-fire; as far as 'bush-fire' goes I would prefer some kind of continuum definition; that is a function of height, distance, intensity and duration; don't know if that helps,
The biggest risk to my house is the neighbouring house to the north, which is open underneath the floor. It's called Exposure in the firefighting business: Rescue Exposure Confinement Extinguishment Overhaul
On 22/01/13 11:20 PM, Allan Duncan wrote:
The biggest risk to my house is the neighbouring house to the north, which is open underneath the floor. It's called Exposure in the firefighting business: Rescue Exposure Confinement Extinguishment Overhaul Yep, know that one well. :)
-- 73 de Tony VK3JED http://vkradio.com
participants (12)
-
Allan Duncan -
Anthony Hogan -
Brian May -
Hiddensoul (Mark Clohesy) -
Mike Mitchell -
Peter Ross -
Rohan McLeod -
Rohan McLeod -
Russell Coker -
Steve Roylance -
Tim Connors -
Tony Langdon