The purpose of the limiting oxygen index (LOI) is to determine the flammability and fire resistance of materials. It provides a measure of the minimum concentration of oxygen required to sustain combustion in a material's environment.

The LOI test involves subjecting a sample of the material to a controlled atmosphere with varying oxygen concentrations while monitoring its ability to sustain a flame. The oxygen concentration at which the material stops burning is recorded as the LOI value.

By measuring the LOI, we can assess the fire safety properties of different materials. Materials with a higher LOI value require a greater oxygen concentration to support combustion, indicating their higher resistance to burning. These materials are considered more fire-resistant and have a lower risk of igniting or supporting a fire.

The LOI is particularly useful in industries such as construction, aerospace, electrical, and automotive, where fire safety and flame retardancy are critical considerations. It helps engineers and designers make informed decisions in material selection, ensuring that the chosen materials meet the required fire safety standards for specific applications.

In summary, the purpose of the limiting oxygen index is to evaluate the flammability and fire resistance of materials by determining the minimum oxygen concentration needed to sustain combustion. It assists in identifying materials with higher fire resistance and guiding material selection for various industries to enhance fire safety.