Is oxygen itself flammable? I understand that oxygen is crucial for combustion and that many materials readily burn in its presence. We often hear about "oxidizers" and how they support or enhance burning. However, I’m specifically interested in the flammability of pure oxygen. Can oxygen itself be ignited and sustain a flame in the absence of any other fuel source? I am looking for an explanation, not just a yes/no answer, considering the chemical properties involved. Furthermore, does the state of oxygen (gas, liquid, solid) affect its ‘flammability’ in this context, and are there any conditions (extreme pressure, temperature) where oxygen might exhibit behavior that resembles self-combustion?

Answer

Oxygen is not flammable, but it is a strong oxidizer.
Combustion is a chemical process that requires three components: a fuel, an ignition source (heat), and an oxidizer.

• Fuel: A substance that can burn.
• Ignition Source: Heat to start the combustion.
• Oxidizer: A substance that accepts electrons from the fuel during combustion. Oxygen is a very common and effective oxidizer.

A flammable substance is a fuel that readily ignites and burns in the presence of an oxidizer and an ignition source. Oxygen itself does not burn. Instead, it supports and intensifies the combustion of flammable materials. The higher the concentration of oxygen, the easier it is for flammable materials to ignite and the more vigorously they burn.

Consider these points:

• A piece of wood does not spontaneously combust in air (which is about 21% oxygen) at room temperature. You need to apply heat (an ignition source) to start it burning.
• If you were to increase the concentration of oxygen around the wood, it would ignite more easily and burn more fiercely when you applied heat.
• A material that is normally difficult to burn in air (e.g., steel wool) can burn readily in a pure oxygen environment.
• Some materials that are normally considered non-flammable can become flammable in a high-oxygen environment.