A common trope in video games is ice-cold fire. I know this is impossible, but I am wondering what real substances burn at low temperatures. Not asking about ignition point, but flame temperature. Could it be some form of alcohol? I have watched my friends pour hand sanitizer in their hands and light it. They did not get burned.
Whole wiki entry on just this
Cool flame can occur in hydrocarbons, alcohols, aldehydes, oils, acids, waxes[9] and even methane. The lowest temperature of a cool flame is poorly defined and is conventionally set as temperature at which the flame can be detected by eye in a dark room (cool flames are hardly visible in daylight). This temperature slightly depends on the fuel to oxygen ratio and strongly depends on gas pressure – there is a threshold below which cool flame is not formed. A specific example is 50% n-butane–50% oxygen (in volume percent) which has a cool flame temperature (CFT) of about 300 °C at 165 mmHg (22.0 kPa). One of the lowest CFTs (156 °C) was reported for a C2H5OC2H5 + O2 + N2 mixture at 300 mmHg (40 kPa).[10] The CFT is significantly lower than the auto-ignition temperature (AIT) of conventional flame (see table[8]).[2]
(Beaten to the Cool Flame link.)
Anyway …
BTW, the alcohol mix thing you saw has little to do with temperature. It’s the water, etc. in the mix that protects the skin from the flame. It also helps to not have a lot of skin hair.
Standard science lab demo: put a dollar bill in a water/alcohol mix. Set it on fire. The alcohol burns off, leaving the bill untouched (but wet).
Apparently, there are “ultracold plasmas”, that can be created as far down in the 0.1 Kelvin range:
But given the lack of photos of anything but computer charts, in relation to this topic, I’m gathering that it’s not a phenomenon that’s interesting to the naked eye.
And it’s a stretch to call it “flame”.
Okay, I will bite. Why is sub-zero fire impossible? Oxygen is a gas well below zero centigrade and I have seen things burned in liquid oxygen.
Is sub-zero fire possible? If I were to light a fire on top of a piece of ice, are there conditions that wouldn’t melt it?
That is just a party trick like walking on coals. Burning alcohol isn’t like burning oil but it is still quite hot and can severely burn you given just a little bit of time. It won’t burn you immediately because of the moisture barrier protecting your skin but it will burn you quite badly if you leave it on fire for more than a few seconds.
My best friend and I used to do it as a bet when we were teenagers. We filled a bathtub full of cold water, poured rubbing alcohol all over our hands and arms and then lit them on fire. The loser was the one that put it out first although ‘loser’ is relative. It is really just a pain game of Chicken and the ‘winner’ was the one that could endure the most burns and hair loss. It is exactly as dumb as it sounds so just take my word for it and don’t try it on your own.
Acetone ignites at a very low temperature. When I was in college, I had a classmate who did that trick (burning it in his cupped hands) and the fumes ignited and scorched off his arm, underarm, and chest hair on that side. :eek: However, he was not burned except maybe for a very small spot.
Is there a lowest theoretical temperature at which you could have a flame?
Does the ignition temperature (flash point) have any relationship to the flame temperature?
Most people know the trick where you fill up your closed hand with butane from a cigarette lighter, light it and let it flash as you open your hand quickly. I took that trick well beyond that. If you add enough butane and close your hand just right with a small hole opened between your thumb and index finger, you can turn your hand itself into a cigarette lighter. I used to be able to light up to three people’s cigarettes at a time or other things like pieces of paper that way. It is obviously very hot because I was lighting stuff with only my hand and you will get burned if you let it go for too long. My secret was that I was doing lots of manual labor at the time and I had thick callouses on the parts of my hand that were in direct contact with the flame. Still, I got fairly badly burned a few times and I wouldn’t even think about trying that today.
White phosphorus burns (i.e. reacts with air oxygen while producing visible light) at room temperature and possibly well below.
(Disclaimer: Don’t try the following yourself! White phosphorus is quite poisonous!)
My mother has told me that when she was a kid, she and her friends used to collect the striking surfaces from matchboxes, set fire to a pile of them and then quench the fire by putting a glass upside down over it. When they smeared the white residue from the inside of the glass on their hands and faces, they glowed in the dark…! :eek:
(Cf. Conan Doyle, The Hound of the Baskervilles)
I would think its toxicity is the least of its dangers.
My son once did something similar but stupider. He cut off a bunch of match heads, put them in a bowl, and started to grind them up with a pestle. After a few minutes, at which point his hand was covered with match head dust, the pile ignited. It took several weeks for the burns on his hand to heal.
–Mark
No.
White Phosphorous causes burns, but the real damage is caused by the poisoning of small particles which have been burned into the skin.
It depends on what you mean by “flame.” If you just mean “combustion process that produces gaseous products” then, sure, you can have such a thing well below room temperature, and indeed at exceedingly cold temperatures. You’re limited only by the boiling point of O2 (very low) and your products.
But if you mean “visible fire” then the problem is that the particles in your flame have to be hot enough to glow in the visible part of the spectrum. That requires temperatures well above room temperature.
There are chemical reactions other than combustion that can produce visible light at or below room temperature, such as those in a glow stick. They just don’t do it by heating the products to the point where they glow. Whether you could call that a “flame” or not is a matter of taste, I suppose.
Huh.
I always thought of it simply as an incendiary weapon.