Testing for Limiting Oxygen Index (LOI) is a method used to determine the minimum concentration of oxygen in a mixture of oxygen and nitrogen that will just support the combustion of a material. It's often used to assess the flammability of polymers and other materials. Here's how you can perform the LOI test:
1. Preparation of Test Samples:
- Cut or prepare samples of the material to be tested. These samples should have specific dimensions and be uniform in thickness.
- Generally, the dimensions of the samples are 150 mm long and 10 mm wide, with a thickness between 3 mm to 6 mm.
2. Test Apparatus:
- The primary apparatus used for LOI testing is a vertical combustion chamber with controlled oxygen and nitrogen flow.
- This chamber is equipped with a holder for the sample and provisions for controlling the gas mixture and ignition source.
3. Test Procedure:
- Mount the sample vertically in the combustion chamber.
- The chamber is initially filled with a mixture of oxygen and nitrogen. The oxygen content is gradually reduced while maintaining a total gas flow rate.
- The sample is ignited at its upper end, usually with the help of a pilot flame.
4. Observations:
- As the oxygen concentration is reduced, the sample will either continue to burn or eventually extinguish due to insufficient oxygen.
- The LOI is the minimum oxygen concentration at which the material just continues to support combustion. It's expressed as a percentage.
5. Interpretation:
- A higher LOI indicates that the material is less flammable since it requires a higher concentration of oxygen to sustain combustion.
- A lower LOI suggests that the material is more susceptible to ignition and rapid combustion.
It's important to note that this test provides a relative measure of a material's flammability and should be interpreted along with other fire safety tests and considerations. Additionally, safety precautions should be taken while conducting LOI testing, as it involves handling flammable materials and ignition sources. Always refer to relevant standards and guidelines for specific instructions on performing LOI testing.