Oxygen index is the minimum percentage of oxygen in an atmosphere required to support the continued combustion of a specified material.
Oxygen index, sometimes called the limiting oxygen index, is the minimum concentration of oxygen, expressed as a percentage of the surrounding atmosphere, that is needed to keep a material burning. A higher oxygen index means a material requires more oxygen to sustain combustion, indicating that it is more resistant to burning. Since ordinary air contains about 21 percent oxygen, materials with an oxygen index above that level tend to self-extinguish in normal air.
This measure provides a useful way to compare the flammability of cable insulation and jacket materials. Flame-retardant compounds are formulated to raise the oxygen index, making them less likely to support a flame, which contributes to the fire safety of cable in occupied and demanding environments.
In commercial and industrial buildings, the fire performance of cable materials, including measures like the oxygen index, is an important consideration. Materials with higher oxygen indices contribute to safer outcomes by resisting the spread of flame.
Because ordinary air contains about 21 percent oxygen, a material whose oxygen index exceeds that level tends to self-extinguish in normal air, which is exactly the behavior flame-retardant compounds are formulated to achieve in cable for occupied spaces.
At Windy City Wire, an awareness of fire-performance measures such as the oxygen index reflects a focus on supplying cable suited to safety requirements. Understanding how materials resist combustion helps illustrate the considerations behind cable selected for demanding commercial environments.
Also called limiting oxygen index