The Limited Oxygen Index (LOI) standard is a measure to quantify the flammability of materials or fabrics. It represents the minimum concentration of oxygen that will support the continuous burning of a material under a specified set of conditions once ignited. This method is widely acknowledged and included in the standards issued by professional organizations such as ASTM (American Society for Testing and Materials) and ISO (International Organization for Standardization).
The standard for the test method to determine LOI may differ among regions or countries, but two commonly cited standards are ASTM D2863 and ISO 4589-2.
- **ASTM D2863**: This is a method used to determine the minimum concentration of oxygen in the atmosphere that will just support flaming combustion under the specific test conditions. The test apparatus involves supporting the test specimen vertically in a transparent chimney placed in a mixer. The whole setup is placed under controlled conditions of temperature and humidity.
- **ISO 4589-2**: Likewise, this standard stipulates a method for determining the minimum volumetric fraction of oxygen that sustains candle-like burning of small vertical test specimens under specified controlled laboratory conditions. It compares the behavior of the material with that of a selected reference material under the same environmental conditions.
Bear in mind that these standards do not provide measures of the fire hazard or fire safety assessment under actual conditions, but they offer comparable measures of material performance in a controlled setting.
The LOI value is typically expressed as a percentage (%). Higher LOI values indicate better flame resistance since more oxygen would be required for the material to burn. Specific LOI requirements may vary depending on different application fields and local regulations, such as those for consumer products, construction materials, or medical devices. Moreover, it's important to consider that these indices alone do not encompass all factors of fire safety and therefore must be used in conjunction with other measures and regulations.
As with all standards and regulations, they can evolve and change over time to adapt to new technologies, novel materials, and improved scientific understanding. Therefore, it is always advisable to refer to the latest editions of these standards for the most accurate information.
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