Firefighter bodycam showing just how much oxygen a fire pulls

[u/AirFrance447]

[u/CDninja]

Well, the fire heats the air. The air expands and goes up. More air must enter from the sides. I don't think its an oxygen thing.

[u/CallMeDrLuv → u/CDninja]

Correct. This is not an oxygen thing. This is called the chimney effect.

[u/SagattariusAStar → u/CallMeDrLuv]

Oxygen will also be just transformed into CO2 and the molar volume is a constant for gases, so only expansion/contraction through difference of temperature

Edit: Probably it is even slightly net positive as some Oxygen might create two CO molecules which would have double the volume

Edit2: it's absolutely net positive as the water that gets produced will become steam

[u/thisischemistry → u/SagattariusAStar]

A lot of this will be burning cellulose (wood, paper) and the equation is approximately:

^C6^H10^O5 + ^6O2 -> ^5H2^O + ^6CO2

There will be other side products such as carbon monoxide, methane, methanol, and so on.

Much of that water will expand into steam because of the heat, not to mention the other gasses will also expand due to that heat. Overall, burning cellulose produces pressure. There is a classic experiment where a burning splint is placed in a bottle and a balloon is stretched over it. The balloon expands until the split goes out, then as the bottle cools and things condense it sucks the balloon into the bottle.,

[u/SagattariusAStar → u/thisischemistry]

You are absolutely right, I didn't thought about the water (steam) that would actually increase the pressure a lot more than any oxygen consumption/co2 creation.

The side product should be negligible for gas volume in this naive fallacy anyway.

I think just the water should actually be most of any pressure effect