This isn't an entirely new concept - explosives have been used for over 100 years to put out oil well fires[1] for example, due to the difficulty of cutting off the fuel source.
Using dynamite to 'blow out' the fire by forcing the burning fuel and oxygen away from the fuel source.
It sounds to me like they were using the explosives to essentially force a change in fuel air mixture. Essentially the same idea as when the wind blows out your lighter or match. Just way more fun, because explosives. :D
You misunderstand the concept of shockwave, and no, there is no contradiction in my statement. I'm pretty sure you understood the sentence, but decided to move the conversation towards my personal behavior.
I've been thinking about this exact concept since the Mythbusters tested it. I'm glad someone has gone out and prove it has legs/pushed it forward.
While I could see the benefit for the scenarios they listed (aircraft, space shuttles, etc) I actually think the real killer use could be for forest fires.
With forest fires you're constantly running out of water, and the only way to ship it the location it is needed is often multi-hour drives (which consume a lot of fuel).
If this concept worked then instead of moving water from A to B you only now have to worry about an energy source (e.g. diesel). So you could drive up a truck with generator on it and diesel in a fireproof tank, and then spend hours extinguishing fires.
Now, yes, fires can reignite. However that is also true with water, water evaporates extremely quickly from an area that was on fire both because that area is extremely dry, because of the ambient heat, and also because it likely started out hot to begin with.
PS - Fire retardants help keeping fires out, but they're bad for the environment and are also hard to keep supplied in remote areas, and when you're refilling directly from a river.
Fire has to have three things to burn, Fuel, Oxygen, and Heat. This is called the fire tetrahedron, and is the primary theory behind fire fighting. If you eliminate one, then the fire is unable to maintain a chemical reaction, and goes out.
With forest fires you're constantly running out of water, and the only way to ship it the location it is needed is often multi-hour drives (which consume a lot of fuel).
Most forest fires are not fought with water, they use fuel reduction to control the fire and eventually starve it of fuel. This is why forest fires are multi-week, or even seasonal events, because you essentially have to dig a fuel free line around the entirety of a fire to starve it of fuel, so that it eventually burns it's self out. On the largest of fires, it usually is a game of trying to drive the fire in the direction you want it to burn, and waiting for a weather event, such as a rain storm, to either put the fire out, or bed the fire down enough that you can put a line around it and contain it.
Now, yes, fires can reignite. However that is also true with water, water evaporates extremely quickly from an area that was on fire both because that area is extremely dry, because of the ambient heat, and also because it likely started out hot to begin with.
With water in direct firefighting you are removing one side of the fire tetrahedron, heat. In a small fire, say a house, you are able to use enough water, to overcome the number of BTUs that the fire is creating, via steam conversion. Water expands to steam at a ratio of 1:1700. In structure firefighting, you can put out a small room fire with a quick burst of water, say 20 - 30 gallons, and through steam conversion(because steam is still much cooler then fire) put the fire out. You will then have to follow up and cool of the remainder of the room.
In large urban fires, the use of water is less about putting the fire out, as much as controlling the expansion of the fire, and limiting it to the original building/location, and waiting for the fire to burn it's self out. Even with 20 or 30 fire trucks pumping 1000s of gallons of water, large fires produce more heat then we are capable of dissipating, so we again wait for fuel to be starved, and the chemical reaction to reduce.
Fire retardants help keeping fires out, but they're bad for the environment and are also hard to keep supplied in remote areas, and when you're refilling directly from a river.
Most fire retardants that are used in active firefighting are 100% biodegradable. Almost all toxic(and even the ones that are still legal, have a diminishing lifespan as they have been banned from being further produced, see Halon fire extinguishers for an example.) have been removed, both for environmental, and firefighter safety.
The problem that I see with device, is that is does not have the capability to scale. To be able to remove 100% of the oxygen from an environment, even the small size that they are testing on, is not realistic. When you begin to get to large fires, you are talking about having to move millions of cubic feet of oxygen, and what are you replacing that air with? They are using this on a very small fire with very volatile fuel(rubbing alcohol). My guess would be that they are not only using sound waves, but that they are getting a certain amount of air movement that is also helping with extinguish, as they are also changing the fuel to air ratio that the fire needs to burn, thus putting the fire out.
There is billions of dollars spent each year to perfect fire extinguish, and I would believe that if it was as easy as pointing a sub woofer at a fire and putting it out, we would all have sub woofers in our ceilings, not water pipes and sprinklers.
Experience: I spent 10 years in the structural and wildland fire service as a volunteer where we had an average of 100 house fires a year, and 30 wildland fires a summer.
In addition, very few people have experience with big fires.
It is hard to appreciate the difference between a small localized fire (energy drops off quadratically with distance from fire) and a small line brush fire (energy drops off only linearly with distance from fire) without personal experience.
I can't even conceive of the difference between a small line brush fire and one of the 40-50 ft seasonal conflagrations in Australia or Southern California.
I'm pretty sure you didn't read or take seriously his post. He pointed out specific reasons why water wasn't relevant and that the suggested method didn't scale. Please reconsider and edit your post as your tone is far more problematic.
I've flagged this comment for two reasons: Your tone is unnecessarily hostile, and you haven't provided any additional information. This is pure flamewar material (and may actually mark the first time I've seen a flamewar about offline flames!); please consider a more constructive approach to the conversation.
You could put the fire out with the sound waves and then quash it with water(?)... more wasteful than not using water at all, but perhaps more effective at keeping fires out and still a huge amount less wasteful and destructive than the current method.
I completely agree. I bet I could take a leaf blower, and with the right application of air on that size of a fire, blow it out. On a fire that small, it doesn't take much air to change the fuel-air mixture creating a fire that won't burn.
Best illustrated when you throw a match at a small container of gasoline, and it flies into the gas, and is put out by the fuel. But if you slowly move it towards the gas, eventually it will start a fire, because the match passes slowly enough through the right air mixture to allow the gas to burn.
PSA I don't recommend doing this. We did this in the fire service as a training example. We also had full body bunker gear, helmets and the guy lighting the gas was also wearing a SCBA to prevent any sort of flash fire injuries. Gas and fire are really, really dangerous.
There's a limit to db, something like 190, where the noise creates a vacuum followed by a blast wave, followed by a vacuum and so on.
Get something that makes that kind of noise next to a fire, then something on the other side of the noise (away from the fire) that either dampens or cancels the noise travelling away from the fire, and they might be onto something.
“One of the problems with sound waves is that they do not cool the fuel,” Isman said. “So even if you get the fire out, it will rekindle if you don’t either take away the fuel or cool it.”
Not to dumb it down, but I can see this being an effective tool for preventing grease flare-ups in my grill. It won't cool the coals, but it will kill the flames.
Sound is a compression wave, so you have areas of high pressure(peaks) and low pressure (valleys) as it propagates. What they're doing here sounds like making a standing wave that holds a low pressure zone around the fire, depriving it of oxygen.
I'm a bit rusty on my physics, but I suspect what happens is that it measures the sound when it reflects back and adjusts the frequency of the wave to put the reflection in phase with the original wave. The sum of the forward and backward components creates the standing wave.
Alternately, maybe the rapid switching between high/low pressure is enough to do it without any standing wave shenanigans. I'd guess not, but it's not my area of expertise.
It pushes/removes the air, so the fire goes out. As I read, this was something that's been researched but it's not useful for anything but blowing out candles, since in a real fire whatever's burning will just reignite since the burning material is not cooled or anything. Simply, the flame is suppressed momentarily.
Another interesting possibility is that rather than pointing your sound at where the fire is now, point it at where it is about to go. What may not be able to put out an active fire may be able to suppress its spread, which would also be an enormous win in many circumstances. Even if it could just significantly retard the fire while conventional techniques are deployed in combination, it could be a potent addition to the arsenal.
To be honest, I'm sort of skeptical, especially of the "glorified speaker" approach, but as it happens there are ways to produce some very loud noises at 30-60 Hz which is very well-established off-the-shelf tech: http://epb.apogee.net/res/rehpuls.asp This used to be a standard furnace technology in American homes. Much like cars, it would be tuned to be as quiet as possible (which I've heard could still be annoyingly loud), but just as I'm sure you've all heard a car without its muffler and marveled at the difference, I'm sure something based around this technology, only meant to be as loud as possible, could achieve some serious decibalage, quite efficiently. Probably a great deal more efficiently than converting something to electricity and then converting that to sound.
I was wondering: if it starves the fuel of oxygen, it stops the fuel from burning, even if it's still hot, yes? So if it could scale from frying-pan-level to house-level, at the very least, couldn't it be used to suppress the fire, the smoke production, and the further weakening of the structure, to allow a squad to search and rescue more safely? Then when you turn off the sound, maybe the material has cooled below the reignition point, but even if it hasn't, at that point you can fight the fire traditionally.
My understanding is that it doesn't starve the fuel of oxygen, but rather starves it of activation energy. I'm fuzzy on the chemistry, but I remember it being like this:
fuel + O2 + activation energy -> CO2 + H2O + energy
The propagating sound waves move two of the input components of the reaction.
fuel: stationary
O2: moves, but is replaced by more O2
activation energy: moves and is missing from future reactions unless/until new activation energy is introduced.
Again, I took chem long ago, but I think that's what's going on.
This could reduce the amount of water required ... previously the water is used to cool down the fuel (wood) and also to cool other water from evaporating...
Could be useful if a home fire alarm can detect a small fire and start the fight at same time in places when the use of water is not advisable (libraries).
Or you could equipate an electric ashtray with this.
[1]: http://en.wikipedia.org/wiki/Oil_well_fire#Extinguishing_the...