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Underwater fire?


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#1 TheBFG81

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Posted 24 November 2012 - 06:25 PM

So I know that if you provide an oxygen source fire can burn underwater, either by providing enough heat tthat the water breaks down and provides the oxygen or via some other chemical or mechanical means. However my question is more specifically, could one saturate water with enough oxygen that more traditional methods of starting a fire work, such as matches, burning paper or something along those lines?


It seems like this would be possible, however the saturation may not be high enough to allow this sort of reaction.
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#2 weiming1998

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Posted 25 November 2012 - 12:34 AM

Probably not. Remember that the reason why water puts out fires is also that it has a high heat capacity. This causes it to cool down fires much more efficiently. The head of a match (which contains both fuel and oxidizer) can technically burn underwater, but that is much more difficult to achieve, since the resulting flame is not hot enough, and would be chilled by water to the point that the chain reaction of combustion stops. Sparklers can burn underwater, but the metal flame is much hotter than flame from a match, and even then, it has to be wrapped in tape to limit the amount of water that's in contact with it. So even if you saturated the water with enough oxygen to sustain combustion, I highly doubt that you can ignite anything in the water.

Also, the pressure required to dissolve enough oxygen in water to even get anywhere near sustaining combustion is extremely high. You can't achieve it at home, ever. Probably not even in a normal laboratory. And when you try and reduce the pressure, the oxygen would bubble out violently.
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#3 TheBFG81

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Posted 25 November 2012 - 01:27 AM

Probably not. Remember that the reason why water puts out fires is also that it has a high heat capacity. This causes it to cool down fires much more efficiently. The head of a match (which contains both fuel and oxidizer) can technically burn underwater, but that is much more difficult to achieve, since the resulting flame is not hot enough, and would be chilled by water to the point that the chain reaction of combustion stops. Sparklers can burn underwater, but the metal flame is much hotter than flame from a match, and even then, it has to be wrapped in tape to limit the amount of water that's in contact with it. So even if you saturated the water with enough oxygen to sustain combustion, I highly doubt that you can ignite anything in the water.

Also, the pressure required to dissolve enough oxygen in water to even get anywhere near sustaining combustion is extremely high. You can't achieve it at home, ever. Probably not even in a normal laboratory. And when you try and reduce the pressure, the oxygen would bubble out violently.




Thanks! I appreciate the answer and explanation.
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#4 EPhantom

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Posted 10 January 2013 - 07:19 PM

I am not a chemistry major or buff or anything like that, I'm just a simple student that's working to become an engineer, saftey is part of my game.

For most chemical reactions, I would have to say the main problem is the heat capacity... most. I've heard that thermite can't be put out with water, chemicals, or even the vacuum of space. I have not heard of anyone dropping a thin can of thermite into pools or lakes though, but would HIGHLY suggest against it.

With thermite, the oxygen content is out of the question, it doesn't matter at all. In fact, as weiming said, I doubt you could get enough oxygen in there to burn traditional combustables without it bubbling out.

Thermite is metal oxide with pure aluminum, both in powder form and mixed. The oxygen pops off the metal and onto the aluminum generating heat, and LOTS of it. This gives the heat to continue the reaction, the oxygen to fuel it, and the chemicals to manipulate it.

The reason why it would be a VERY bad thing to dump a bunch of this in water, is it has the potential to instantly vaporize a LOT of water, could cause some sized explosion that I wouldn't be able to measure or imagine, and send water vapor that's hot enough to catch paper on fire... and catch skin on fire/melt it... all that bad stuff. It would not be advisable to use in any way shape or form that I can think of. I'm sure even the military wouldn't want to go near this kind of experiment. My middle school science instructor tried to illustrate that water can catch things on fire, but just couldn't get the vapor hot enough before it exited it's heating pipe.

So burning things like paper or a log under water, not going to happen, but some chemicals that give lots of heat... may work, or may just blow the water up.


Edited by EPhantom, 10 January 2013 - 07:22 PM.

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