Oxygen and Nitrogen make up a significant part of the atmosphere. Fire always stretches upwards, assuming no wind, leading me to believe it’s less dense than air. Oxygen is highly flammable. That should be everything fire needs to sustain itself while flying away into the sky.
In: Chemistry
You’re thinking about fire as a physical object. Let’s look at what fire really is. When something burns, it’s chemical structure breaks down. It gives off gases when it gets hot enough. Think of it like boiling a lot of water and seeing steam. Now when it gets really hot, those gases glow. That glow is what you call fire. It’s not much different than the electric burner on your stove glowing. On a cool burning fire, like a candle, you can pass a finger through the flame without injury. On a hot burning fire, you can pass through the gases/smoke and get burns even if you’re not in the actual fire.
In the case of an electric element in a stove, you can have it hot enough that it glows without actually burning. On the flip side, you can have something burn without being on fire. Certain chemicals have “invisible” flames which is just hot gas that’s burning but not glowing.
Those gases do go into the atmosphere. You can see smoke rise very high. The bigger and hotter the reaction, the larger the flames. But why don’t we see flames rising thousands of feet with the smoke? Because it cools down. Look at that pot of boiling water again. Stand on a chair, and put your hand above it. Then get off the chair, and stick your hand in the pot of boiling water (well actually don’t do that.) You can feel the difference in temperature. It’s much cooler the farther away you get. Remember, since the fire is simply really hot gas, when it cools down, it stops being fire. If you keep those gases/smoke close to the fire, and hot enough, like in a house, the smoke can, and does burn. But let it into the atmosphere, and it’s simply not hot enough to glow.
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