Pure oxygen itself does not burn. Oxygen is a colorless, odorless, and tasteless gas, a chemical element (O, atomic number 8). The misconception arises from its strong association with fire. Understanding combustion clarifies why oxygen is a supporter, not a fuel.
Understanding How Things Burn
Burning, or combustion, is a high-temperature chemical reaction that releases energy in the form of heat and light. For combustion to occur, three components must be present: a fuel, an oxidizer, and an ignition source (heat).
The fuel is the substance that burns, while the oxidizer facilitates the burning process. An ignition source provides the initial energy needed to start the reaction.
During combustion, the fuel rapidly combines with the oxidizer in a chemical reaction. This exothermic process releases a significant amount of energy. Once initiated, the heat generated by the reaction can sustain the burning process, allowing it to continue. Without any one of these three elements—fuel, oxidizer, or heat—fire cannot start or be sustained.
Oxygen’s Role as a Fire Supporter
Oxygen is not a fuel; it cannot burn. Instead, oxygen acts as the primary oxidizer in most common fires. In a combustion reaction, oxygen accepts electrons from the fuel. This electron transfer is fundamental to the chemical process that rapidly releases energy, manifesting as flames and heat.
Without fuel, oxygen has nothing to react with and cannot undergo combustion. The presence of oxygen allows other substances (fuels) to oxidize and break down, thereby releasing their stored energy. This is why removing oxygen is an effective way to extinguish a fire, as it deprives the reaction of its essential oxidizer.
The Hazards of Oxygen-Rich Environments
Though not flammable, oxygen is dangerous in concentrated or oxygen-enriched environments. An atmosphere is considered oxygen-enriched when oxygen levels exceed the normal 20.95% found in air, with some regulations defining it as over 23.5%. In such environments, the risk of fire and explosion significantly increases.
Increased oxygen concentration dramatically lowers the ignition temperature of many materials, making them much easier to ignite. Materials that burn slowly or not at all in normal air ignite vigorously and burn intensely in oxygen-rich atmospheres. This heightened reactivity means that even small sparks or normally harmless ignition sources can trigger severe fires. For instance, textiles, oils, greases, and even some metals can burn fiercely or explosively.
Oxygen-rich environments pose serious risks in various settings. Medical facilities using oxygen tanks, industrial operations like welding, and even space exploration have experienced catastrophic fires due to elevated oxygen levels. For example, the Apollo 1 incident in 1967 involved a cabin fire that spread rapidly in a pure oxygen atmosphere. The human senses cannot detect oxygen enrichment, making awareness and strict safety protocols imperative in any environment where oxygen concentration might increase.