how is oxygen combustible but not flammable? If it feeds the fire isn’t it essentially the same thing?


how is oxygen combustible but not flammable? If it feeds the fire isn’t it essentially the same thing?

In: Chemistry

If you lit a match in a room with 100% hydrogen, which is very flammable, the flame would go out instantly. That’s because the wood in the match needs oxygen to react with. And the hydrogen needs oxygen to react with (combust) so it would still not combust.

If you lit a match in a room with 100% oxygen, the flame would burn super bright until all the combustible material (match) was consumed, and then it would go out.

Oxygen supports the chemical reaction combustion but is not flammable itself. Hydrogen is very flammable but needs oxygen to support that reaction.

no. Though your whole question isn’t really right to start because oxygen isn’t combustible by definition. “A combustible material is something that can combust in air. ” Oxygen can’t do that. The whole “air” requirement in that definition is the oxygen in the air.

Because oxygen is what is doing the “burning” in the oxidization reaction.

if you mix carbon and oxygen and burn it you get CO2, if you mix Hydrogen and Oxygen and burn it you get H20, but if you just mix carbon and hydrogen together and try to burn them, nothing will happen. You need the oxygen. In every case you need to oxygen (or another oxidizer, like flourine, which as actually an even better oxidizer that oxygen, but it is so reactive that it doesn’t really exist naturally).

But if you have pure oxygen and try to burn it, nothing happens.

The common definition of flammable means “will readily burn in the presence of oxygen, if you get it hot enough”.

Oxygen isn’t flammable because it doesn’t burn in the presence of… itself. It’s not flammable, it’s the stuff that *makes everything else* flammable.

Oxygen is neither of those things. Let’s start with the definition of “combustion”

> Combustion: rapid chemical combination of a substance with oxygen, involving the production of heat and light.

Oxygen is not capable of combustion, thus not combustible. (Yes, there are exotic oxygen + oxygen reactions, but they produce no heat.)


> Flammable: a substance is one that burns.

Nope, you can’t burn oxygen either.

Burning is a chemical reaction called oxidation. The fuel reacts with the oxygen and this releases energy.

Pure oxygen can’t react with itself (under normal circumstances), which means pure oxygen can’t burn. It has to be in the presence of a fuel

If oxygen is combustible or not depends on what you define as combustible.

If we use the definition on [](

>A combustible material is something that can combust (burn) in air. Flammable materials are combustible materials that ignite easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable material catches fire immediately on exposure to flame.

Then oxygen is not combustible because you can’t burn it in the air. Oxygen in the air is required for combustion but you need something that can react with it, that is the fuel.

Oxygen is also not flammable because that require it to be combustible in the first place

Lets look at [](


>Combustion, or burning,[1] is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually, atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke.

So oxygen can be and often is a part of combustion but as the oxidizer not as the fuel that gets oxidized.

Oxygen can be the fuel but you need a stronger oxidizer, if I am not mistaken Florine is the only option. But Florine is not a part of our atmosphere you oxygen is not combustible in the atmosphere.

Things burn because there is a chemical reaction in response to energy input (heat). Most fires are carbon matter reacting with oxygen and forming carbon dioxide as well as some other gaseous compounds.

Fire is a chemical reaction that happens when another element is combined with oxygen. If you just have a bunch of oxygen, there’s nothing to combine it with, and so there’s no chemical reaction, and no fire.