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I understand this is probably too costly to be practical, but was intrigued how one might use the mechanism of fire combustion against itself. Fires produce their own retardants (water and carbon dioxide). If you could cool this with quantities of subzero air (e.g. from above) would the dense air attack the flow mechanism that feeds the fire (the oxygen intake at ground requires the upward escape of combustion products). If you had a mobile store of liquid nitrogen and a high-throughput turbine & heat exchanger, using the heat of vaporisation and heat capacity of liquid N2, could you 'hose' down a fire using subzero air?

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I think the heat produced by the combustion is far and away greater than the heat you'd absorb using the cold air. So dumping cold air on a fire would only stoke it even more.

I could back this assertion up with some thermodynamics, or we could just watch this video of what happens when you pour liquid oxygen on a fire:

https://www.youtube.com/watch?v=9Floi2gQEb4

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  • $\begingroup$ Say you used just nitrogen gas just above evaporation, its density would be a multiple of the air at combustion and would quantitatively reduce temperature if you directed it near actual combustion $\endgroup$ – JKB Feb 6 at 14:15
  • $\begingroup$ No, I suppose the combustion drives the air flow cycle and thats too powerful to 'reverse' . $\endgroup$ – JKB Feb 6 at 14:21
  • $\begingroup$ @JKB Nitrogen would put it out. So would any not-very-reactive gas. Fire needs three things: fuel, $O_2$ and ignition temp. You first have to cut off the oxygen to stop the combustion reaction and then cool the fuel below the ignition point so that it doesn't flare up again when the $O_2$ comes back. That's how $CO_2$ extinguishers work. $\endgroup$ – Oscar Bravo Feb 6 at 19:40

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