Limiting Oxygen Index (LOI)- Fire Resistance of Plastics Testing

The Limiting Oxygen Index (LOI) test is a common test method used to evaluate the fire resistance of plastic materials. This test is based on the minimum concentration of oxygen required for a material to support combustion in an oxygen environment.

LOI testing typically involves the following steps:

1. Sample preparation: A sample is prepared from the plastic material to be tested. The sample may be in the form of a sheet, film or wire. Ensure that the sample size and shape conforms to the relevant codes and standards.

2. Laboratory Equipment: LOI testing usually requires a vertical combustion unit or flame combustion chamber. It provides a controlled oxygen environment and measures the desired oxygen concentration.

3. Experimental Procedure: The sample is placed vertically in the combustion device and one end is ignited. The oxygen concentration is then gradually reduced by adjusting the flow of oxygen in the device until the sample no longer burns or self-extinguishes. The oxygen concentration at this point is recorded as the LOI value.

4. Evaluation of results: The fire resistance of the plastic material is evaluated based on the LOI value obtained from the test. A higher LOI value indicates that the material requires a higher concentration of oxygen to sustain combustion and therefore has better fire resistance.

It should be noted that the LOI test, as a single indicator, does not fully represent the overall fire resistance of the material. In practice, other factors such as burning rate, smoke generation, toxic gas release, etc. need to be taken into account.

LOI tests are usually conducted by specialized laboratories or certification bodies with reference to international or industry standards such as ASTM D2863 (American Standard) or ISO 4589 (International Standard). For specific materials and applications, it is recommended to consult with the relevant professionals or laboratories for more accurate and detailed testing information.