Naked Science Forum
Non Life Sciences => Technology => Topic started by: myuncle on 04/01/2020 16:56:43
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Instead of using water they use the smoke, right on the place. A U pipe system, one metal pipe suck the smoke, the other pipe blow it back to the flames.
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Two things
(1) Why bother?
(2) Do a rough calculation on the air flows near a forest fire and see if you could get a big enough fan to have any meaningful effect.
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Blowing on flames generally makes them worse...
An area of the southeast Australian coastline has been evacuated - a region something like 300km x 100km.
- The navy has been called in to evacuate some towns that are cut off by bushfires
- The problem is lack of rainfall (lots of dry grass and timber), high summer temperatures and strong winds
- Near my home, burnt leaves have been falling from the sky perhaps 100km from the fires
- Closer to the fires, the leaves are still burning when they land, starting more fires.
The high specific heat of water helps cool the fuel temperature, and makes it harder for the fire to spread.
- While spending minimal time in the high-risk fire zone
- If you can find open water to scoop up, that is!
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A few thoughts from me:
1) The fires are so big that they are creating their own wind / draught, which is fanning the flames and driving the spread.
This is because the heat causes air close to the ground to expand and reduce in density. This is displaced upwards by cooler, denser air that moves in from the surroundings, creating a wind effect that accelerates the fire.
This happened when Hamburg was firebombed in WW2; the ensuing conflagration created its own "weather" that drove the fire more rapidly and provoked spread.
2) Re-injecting the smoke into the fire would not disable the fire and may even intensify the spread.
The smoke particles are combustible and likely did not burned the first time around owing to a lack of available oxygen (excess fuel to air ratio); if you come along and blow this pre-warmed potential fuel, with its high surface area, back into the fire along with a healthy helping of fresh, oxygen-rich air from your fan blades, it's likely to burn enthusiastically and make the fire hotter.
3) The best way to stop a forest fire is to rob it of fuel; this is the role of firebreaks, which interrupt the passage of a fire, and regular controlled burning, which depletes the under-storey of combustibles and makes fire much harder to sustain.
This is all very well in smaller woods and forests, or alongside roads, but the problem in Australia is the vast scale; and not only that, the fires are moving so fast that it's impossible to intervene meaningfully sufficiently fast downstream.
Also, as alluded to above, the fires are seeding fresh fires as move along, meaning that the firefighters are combating multiple conflagrations on multiple fronts.
My thoughts are with the country and I hope that the fires will burn themselves out soon.
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Someone mentioned to me on the show yesterday when we were recording the latest Naked Scientists episode that the smoke is also causing lightning, which is spawning fresh fires. They were unclear of the mechanism. Does anyone know about this?
It sounded like the rising smoke column seeds cloud formation, which encourages thunder activity. But might there also be a process similar to volcanic lightning too?
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the smoke is also causing lightning, which is spawning fresh fires.
There is a weather front crossing the country, producing strong winds and thunderstorms.
I am under the impression that the lightning was from the thunderstorms, not from the fire smoke.
There are sometimes short-lived fire tornadoes, which look ferocious.
- One of these took out a suburb of Canberra in 2003
Start at 3 minutes 55 seconds:
This video from a California fire tornado has better graphics to explain the phenomenon:
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My thoughts are with the country and I hope that the fires will burn themselves out soon.
yes, it's getting really bad, hope they will find solutions soon enough.
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the smoke is also causing lightning
PS: Thinking about it, the fire produces hot, rising air filled with moisture from burning wood.
A weather front would find this ideal fuel for thunderstorms, which produce lightning... and so the cycle perpetuates.
On a slightly different topic...Yesterday, some tourists from Singapore were thinking of driving roughly 1,000km through NSW, and they asked about the road conditions.
I was able to point them to an App, produced by the NSW Rural Fire Service, called "Fires Near Me".
It shows that there are a lot of fires near their proposed route....
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the smoke is also causing lightning, which is spawning fresh fires.
There is a weather front crossing the country, producing strong winds and thunderstorms.
I am under the impression that the lightning was from the thunderstorms, not from the fire smoke.
There are sometimes short-lived fire tornadoes, which look ferocious.
- One of these took out a suburb of Canberra in 2003
Start at 3 minutes 55 seconds:
This video from a California fire tornado has better graphics to explain the phenomenon:
I never knew that fire tornado can occur naturally. What's the chance of it happening?
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It was fairly common for large stubble fires (which we no longer have in the UK) to seed active cumulus clouds which can produce lightning, but "volcanic" lightning is unusual in the UK - you need more heat and less moisture than we can generate.
Entirely reasonable in Australia, however. Static charge separation by rapidly moving dry particles has caused several grain elevators and a few ships to explode.
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Now the West Coast of USA is doing it tough with bushfires.
The weather hints suggest that Australia is heading for a La Niña year, with higher than average rainfall (rather than the contrasting El Niño, which brings hotter temperatures and coral bleaching to Australia).