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Safe flame

  1. Jan 15, 2016 #1
    Is it possible to have a flame that's not hot to the touch?

    I'm not sure how fire/flames work but if they can burn underwater I don't see how they can't somehow be safe to the touch
     
  2. jcsd
  3. Jan 15, 2016 #2
    A flame is light emitted when something is burning.
    Generally that mean a substance is combining with atmospheric Oxygen and releasing energy as both heat and visible light.
    There is a lot of free oxygen in the atmosphere but very little in water (None in pure water), so burning cannot take place.
     
  4. Jan 15, 2016 #3
    One idea: if you consider that a flame is the rapid oxidation of the fuel, a slow oxidation process is rust forming on an iron bar. This is not too hot to touch.
     
  5. Jan 15, 2016 #4

    jbriggs444

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    High temperature torches (e.g. oxy-acetylene for welding) use their own supply of oxygen and are capable of operating both in the air and underwater. The fact that they are burning underwater does not magically make them cool to the touch -- they still melt metal.

    Edit: A trip to Google suggests that wet underwater welding is normally arc welding rather than gas flame welding.
     
  6. Jan 15, 2016 #5

    russ_watters

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    Generally, by definition a flame is a flame because it gives of light, which it does because it is hot.
     
  7. Jan 15, 2016 #6

    NascentOxygen

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    Substances which combust with cooler flames are used in special effects in movies, where a person's clothing catches alight, etc. That's not gasoline burning on their coat as they run towards the lake, you know!

    I think I've seen shows where the performer has a flame burning in his cupped hand, but extra special effects may be used here, to achieve this feat with impunity.

    Nothing like this should be attempted by our readers. It is way too dangerous. (There was a news item last week about a copycat would-be firebreather rushed to A & E suffering burnt lungs when he mistakenly inhaled just before torching the airborne spray.)
     
  8. Jan 16, 2016 #7
    A flame is the thin reaction zone we see when the combustion of fuel with an oxidizer occurs . Each fuel and oxidizer combination has a unique flame temperature associated with its combustion, which is the temperature associated with the net release of bond energy. I don't know of any combustible fuel-oxidizer combination that has a flame temperature low enough to not burn your skin. The lowest flame temperatures I know of are in the 200° C range. Still hot enough to hurt!
     
  9. Jan 17, 2016 #8

    mfb

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    The usual trick in shows is to not have the flame touch the person, or limit exposure time. Reactions between gases can happen at safe temperature but then you don't get visible flames.

    I could imagine a chemical reaction that happens at low temperatures, but emits light directly from the reaction (instead of thermally induced emission in normal flames). No idea if you can get enough Chemiluminescence in a reaction of cold gases to make it visible. The two examples given there involve toxic substances.
     
  10. Jan 17, 2016 #9

    Nidum

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    I have just once seen marsh flame .

    Very elusive and unstable areas of flickering blue flame very low to the ground .

    Many explanations but commonly attributed to catalytic combustion of natural methane or bio-luminescence .

    No explanation that I have seen has been entirely convincing .

    Doesn't seem to have much heat output since flies and moths are untroubled by it when they fly over or through it .
     
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