Posted: 7/10/2008 7:04:08 PM EDT
| For forest & brush fires, not houses. Has this ever been tested? Seems like it would both cool and smother. I'd propose dropping tanks of it, just to see if the idea is worth developing. Of course, you wouldn't want to smother your engines. |
| I imagine there is a cost factor involved with using liquid nitrogen to fight fires. Hell, while we're at it, perhaps we can get a superhuman type being to blow a cold breeze across a lake, freeze it and then lift it- fly it to the fire - and dump it on top of it? |
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liquid nitrogen boils away when you expose it to air. You couldn't even drop the stuff from fire-fighting airplanes since it a lot of it would be gone before it even touched the ground. Even if you were somehow able to get it on the ground, its not a fire retardant since it boils away so quickly. |
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~$25/gal IIRC... probably a deep discount if bought in industrial quantities. I'm pretty sure we don't pay that at the refinery, but I don't know how much it is. Oh, and it would be gas before it ever hit the ground. Not to mention the asphyxiation problem for bystanders. |
Don't be unrealistic. The eco-nuts would sue for a restraining order. |
I was thinking more of an insulated tank/bomb that would not release it until it hit the ground. Or maybe a cluster-bomb type approach. |
No, that's why stuff doesn't burn better than it does. If the atmosphere were pure oxygen, you could start a campfire with a cigarette in about 1 minute. Nitrogen is unreactive. |
Better to just go with plain old water. Still WAY cold enough to bring anything below its combustion temp, and has a MUCH higher latent heat of vaporization... i.e. pound for pound packs more punch than any other coolant. |
You know I do rather like the idea of dropping napalm-like canisters of liquid nitrogen on stuff.  But it's practically impossible to pull off... You could probably manage it, but only at extreme cost... And it doesn't really do anything other methods won't do better, either as an anti-fire weapon or anti-people weapon. But thanks, I now have the image of a Chinese human-wave assault frozen in mid charge, fingers snapping off as pissed off Marines throw rocks at them... I'll have that in my head all night. |
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I'm kinda in the biz, but take it for what it's worth. Water is the absolute best thing in the world with which to put out fires. It is abundant. No clean up necessary. It works. --------------------- now to what you were asking about: Nitrogen makes up about 2/3 of our air that we breathe. the other part is oxygen and other stuff. Liquid nitrogen is what we breathe, minus the oxygen and other stuff... just really cold. when a really big fire gets working... it breathes. It makes it's own wind, drawing in "fresh air". It burns the oxygen, and draws in fresh oxygen from the atmosphere. On a small scale, your Idea would work... but not on a large scale. |
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Why would it work better than WATER? It has LESS cooling effect (fire is hot, hotter than the boiling point of water) and even less residual effect than water. And it is VERY EXPENSIVE compared to water. And requires special handling. Yes, it will put fires out. But so will water. It would have less bouyancy than water vapor but that would mean nothing in forest fires where the wind blows away any smothering gas. |
| we use liquid nitrogen at work to shrink stuff (mostly bussings and sleeves) . when poured out it does hit the ground. if poured into a bucket of water it freezes it on contact but its not just the surface , it freezes down into the water also . I have poured it onto small fires . it works instantly ,by both the extreem coldand the complete lack of oxygen. wood/paper , oil , gasoline , alcohol , it really doesn't matter. the cost would make it virtually unpossible as would the handeling of it. |
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wow.... i tried hard, but i couldn't think of a dumber idea. do you realize the volume of liquid it takes to fight a large scale forest fire? We're talking millions of gallons of water here. they literally drain lakes sometimes with how much water they pull out to dump on a fire. the logistics of transporting liquid nitrogen would be ridiculous. unlike water, LN needs a special insulated container, which is much bulkier and heaver than a container to hold water. that means that an aircraft that could carry X amount of water would carry a LOT less LN, simply becuase of the bulk of the container. Then as mentioned before comes the problem of delivery. Even if you were to make tanks the size of canoes, holding maybe 100 gallons of the stuff, and every drop of it made it to the ground, it would cover a very insignificant area. It would put out the fire that it immediately contacts, but then would quickly evaporate. Whatever it was in contact with would then be freeze dried, and thus be able to burn EVEN BETTER, and would subsequently re-ignite. LN is not a fire retardant, it simply cools something to the point where it is unable to burn. once the LN is gone, the object is able to warm back up and can burn just as well as it did before. |
You sure about that part? I thought there needed to be a pressure differential for that process. Where do you get that?
If the area is cooled below the flash point, where are you getting the heat from? I agree there are some issues to work out, one being the relative time to refill compared to water in addition to the efficacy, but I'm not convinced that it's unworthy of exploration; it might have limited application in some circumstance where no crew has arrived. Or maybe dry ice. |
n/m The air we breathe is about 20% oxygen. If the atmosphere were pure oxygen, it might actually be toxic. |
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is there anybody who can recall a show that had an foam fire retardant made from corn starch, soap, and whipped up and sprayed onto a object, this stuff was shown to protect a sheet of plywood that was half covered and hit with a flame thrower and the unprotected side was burnt away, the protected side was just above room temp. if you remember the mix ratios please post, I wish to make a spray machine for the farm. thanks. |
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Last I checked, I could get liquid nitrogen for $0.05/liter. Who is paying $25/gallon? I agree that the thermodynamics and logistics would make it nearly impossible to use for fighting forest fires. And they DO get the water for free, sucking it out of lakes and whatnot. |
| Liquid nitrogen is dangerous stuff. Years ago I used to tour the deep cold labs at the Jet Propulsion Labs in Pasadena Calif. Things take on interesting properties when they are super chilled, way out of proportional to their normal every day properties at room temps. Anyway, the public is now banned from the lab because Ni displaces oxygen, you could actually suffocate and die before you can react, say for instance a Ni pipe leaked etc. |
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Again, water absorbs 11 times more heat than liquid nitrogen. People confuse heat with temperature. The extreme cold temperature of liquid nitrogen does little good to offset the much lower heat absorption. All you need to do is reduce the temperature to under 500 F. Water boils at 212 F. |
N2 is inert. |
So is CO2... |
I agree but there is one other factor, oxygen displacement. When the oxygen is pushed out by nitrogen the fire would die. Or at least slow down. BTW it is totally unfeasable to use liquid nitrogen as fire supression, just making a point. |
Water vapor has the same effect. It has been used in the past on cargo ships as the primary fire fighting measure. The Texas City Disaster in 1946 was partly due to this, ammonium nitrate started burning in a cargo ship. Captain flooded the hold with steam, increasing the temperature and since ammonium nitrate has its own oxygen, it did nothing. But on all non-oxidizer fires in closed holds, it is quite effective. A shift in 4 percentage points of oxygen rapidly slows a fire. A 10 point reduction snuffs it out. |
| The water vapor thing does make sense, never thought about it. I would suspect that an oxygen displacing gas would be more effective, like the halon gas used in computer room fire suppression systems. I have seen in older buildings around town, little glass balls filled with r-11 refrigerant hanging from lead couplings. When a fire melts the lead coupling the glass ball falls and shatters on the floor thus releasing the R-11 which displaces oxygen. I suspect they didn't work very well but the idea is there. |
Halon works by combining with the hydrogen, chemically inhibiting the fire. Some Halon has low toxicity and will inhibit fire without severe health effects. |