Is fire affected by external temperature? Can a fire burn at extreme cold temperatures?
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M$3 Answers
As previous answers mentioned, fire needs fuel, oxygen, and heat. The kindling temperature is the initial application of heat to get a fire started. In cold temperatures, this might be harder to overcome. But usually, once the fire has started, it is self sustaining.
Moisture, on the other hand, can affect an ongoing fire more readily.
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M$1. Fuel
2. Oxygen
3. Energy
Fuel and oxygen are required because they are the 2 reactants in the combustion reaction, but you seem to understand that so let me explain why energy is needed.
Combustion, like every chemical reaction, requires some energy in order to start the reaction. This is called the activation energy. When we think about starting a fire in a fireplace, the match used to start the fire provides the activation energy, and the activation energy to light the match comes from the friction of the match head and the matchbox.
However, the colder the system the less energy it has, so if something is really cold you have to put a lot more energy into it in order to start the reaction. Also the reaction has to produce a lot more energy in order to keep the reaction going.
Now every substance that burns has a different minimum temperature at which it can burn. For example wood cannot burn at room temperature, it has to be heated up to a certain temperature. So wood can't burn at -100C. However if you got enough wood and a huge blowtorch, then you could heat up the wood hot enough even if the surrounding environment was very cold. But you would have to get a lot of wood burning at the same time in order to produce enough heat to keep the wood hot and the reaction occurring.
However the lowest temperature that the substance which is burning can be at depends on the substance. Triethylborane can burn at -20 C and the coldest burning substance I could find.
Hope this makes sense, feel free to ask follow up or clarification questions.
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M$
"Doesn't gasoline freeze at about -70 C? Wouldn't that mean it can still burn until then?"
-Gasoline only burns as a gas, so it has to be warm enough for enough of the gasoline to evaporate for it to catch fire. For gasoline that temperature is around -40 F.
"Let me try to rephrase it. If you already have a wood fire going, and you started lowering the ambient temperature, what's the lowest temperature that will sustain the chemical reaction?"
-This depends on how much heat the fire is producing. You have 2 things going on here:
1. The wood burning is producing heat.
2. Heat is being absorbed by the surroundings.
For the fire to continue to burn, the amount of heat being produced by the fire has to be more than the heat being sucked away from the fire by the surroundings. The lower the temperature of the surroundings, the faster heat is going to be sucked away from the fire. Conversely, the more fuel you have, the more energy is going to be generated by the fire.
So there is going to be a big difference between the temperature a huge bonfire goes out at and the temperature a burning matchstick goes out at. Again it depends on the size of the fire (how much heat is being produced) and the ambient temperature (how much heat is being sucked out). For a wood fire this temperature could be very very low, I would imagine it is less than -100C, but I couldn't really be sure without doing the calculations.
Let me try to rephrase it. If you already have a wood fire going, and you started lowering the ambient temperature, what's the lowest temperature that will sustain the chemical reaction?
Doesn't gasoline freeze at about -70 C? Wouldn't that mean it can still burn until then?
I was curious if an actual flame itself could not be sustained because the heat energy would instantly get sucked out into the cold. It makes sense that nothing can *catch* fire at those temps, but what if you somehow shoot an external flame into a room that was -100 C?
Considering that fire is a byproduct of very strong chemical reaction like oxidation, which is happening let's say when you expose wood on high temperature.
So if the fuel is not frozen, then you will have fire on any temperature.
But you should know that you will not get a violent chemical reaction on extremly low temperatures to cause the effect of fire.
Regards.
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M$
