The ASTM D2863 Oxygen Index is a standardized test method used to measure the flammability or burning characteristics of polymers and other materials in the presence of oxygen. It provides a numerical index value that indicates the minimum concentration of oxygen required to support combustion.
The Oxygen Index (OI) is an important parameter used in material selection, as it can help assess the fire safety of different materials and determine their suitability for specific applications. A higher Oxygen Index value indicates a material's improved resistance to burning and greater fire retardancy.
The ASTM D2863 test method involves subjecting a vertically mounted specimen of the material to a controlled flow of oxygen-enriched atmosphere. The specimen is ignited from the top and exposed to the oxygen concentration gradient. The test measures the oxygen content at which the material self-sustains its own combustion.
Here are the key steps involved in the ASTM D2863 test:
1. Specimen Preparation: The material sample is prepared as a rectangular specimen, typically with dimensions specified by the standard.
2. Test Apparatus: A test chamber with a vertical specimen holder is used. The chamber has adjustable oxygen and nitrogen gas supplies to create an oxygen concentration gradient. Additionally, a pilot flame is used to ignite the specimen.
3. Test Procedure: The specimen is vertically mounted in the test chamber. The gas flow rates of oxygen and nitrogen are adjusted to create a specific oxygen concentration gradient in the chamber. The pilot flame is then applied to the top edge of the specimen to initiate combustion.
4. Oxygen Concentration Determination: The oxygen concentration at which the specimen just sustains its own combustion is recorded as the Oxygen Index, expressed as a percentage.
The Oxygen Index is derived from the ratio of the oxygen concentration in the gas mixture to the total oxygen concentration (including oxygen and nitrogen). The test is repeated multiple times to ensure accuracy and consistency of results.
The ASTM D2863 test is primarily applicable to solid materials, such as polymers, textiles, and films. It is not suitable for porous or highly cellular materials. The test evaluates the material's self-sustaining combustion characteristics, which can be an indicator of flammability and fire resistance.
The Oxygen Index value can be used comparatively to assess different materials. A higher Oxygen Index value implies that the material requires a higher oxygen concentration to burn, indicating better fire resistance. Conversely, a lower value suggests a higher flammability. However, it is important to note that the Oxygen Index alone does not provide a complete assessment of a material's fire behavior, and additional fire testing methods may be necessary for a comprehensive evaluation.
In conclusion, the ASTM D2863 Oxygen Index is a standardized test method used to measure the flammability and fire resistance of materials in the presence of oxygen. It provides a numerical index value indicating the minimum oxygen concentration required to sustain combustion. This information is crucial for material selection and evaluating fire safety in various applications.