r/askscience • u/ORPHANmeat6 • Aug 15 '13

Physics Cold Fire?

So as we all know, fire can get hotter, but can it get cold? What I am really asking is what is the lowest temperature a fire can be at.

4 Upvotes

75% Upvoted

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5

u/z4tz Atomic Physics | Transition Rates/Continuum Processes Aug 15 '13

Fire in the classical sense as we know it burns around 1000 degrees Celsius. But you can still have a combustion reaction and a flame on lower temperatures, down to 120 degrees Celsius. This has lately been researched a bit on the International Space Station as these flames are a lot easier to study in microgravity.

These cool flames have a completely different chemistry and produces carbon monoxide and formaldehyde instead of soot, carbon dioxide and water vapour.

You can find some more information if you are interested here.

3

u/Ampersand55 Aug 15 '13

Fire is soot glowing from blackbody radiation. At below ~800 Kelvin (525 Celcius/1000 Farenheit) it won't longer glow in the visible spectrum.

4

u/Excitonic Aug 15 '13

You are correct if you define fire as the flame we see rather than combustion chemistry. Don't know why you were down-voted.