Oxygen index tests are a method of measuring the flammability of materials by determining the minimum concentration of oxygen in a mixture of oxygen and nitrogen that will support combustion. The oxygen index (OI) is expressed as a percentage of oxygen in the gas mixture. The higher the OI, the less flammable the material is.
Oxygen index tests are useful for evaluating the fire performance of materials such as plastics, textiles, foams, and rubber. They can also be used to assess the effectiveness of flame retardants or other additives that improve the fire resistance of materials. Oxygen index tests can provide information on how materials behave in different fire scenarios, such as smoldering, flaming, or flashover.
There are different standards and methods for conducting oxygen index tests, depending on the type and shape of the material, the test apparatus, and the test conditions. Some of the most common standards are ASTM D2863, ISO 4589, and BS EN ISO 4589. These standards specify the test equipment, sample preparation, test procedure, and calculation of OI.
The basic principle of oxygen index tests is to expose a small sample of material to a vertical flow of oxygen-nitrogen gas mixture in a glass column. The sample is ignited at the top and the gas flow is adjusted until the flame just extinguishes. The OI is then calculated from the oxygen concentration in the gas mixture at this point.
The oxygen index tests can be performed at different temperatures and pressures to simulate different fire environments. For example, elevated temperature tests can mimic the effects of heat radiation or convection on materials, while elevated pressure tests can simulate high-altitude or aerospace applications.
Oxygen index tests are a simple and reliable way of assessing the flammability of materials and comparing their fire performance. They can help manufacturers and designers select materials that meet fire safety requirements and standards. They can also help researchers and engineers develop new materials or additives that enhance fire resistance.