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The '''limiting oxygen index (LOI)''' is the minimum concentration of [[oxygen]], expressed as a percentage, that will support [[combustion]] of a [[polymer]]. It is measured by passing a mixture of oxygen and [[nitrogen]] over a burning specimen, and reducing the oxygen level until a critical level is reached.
LOI values for different plastics are determined by standardized tests, such as the ISO 4589 and ASTM D2863.<ref>[[ASTM]] D 2863, ''Standard Test Method for Measuring the Minimum Oxygen Concentration to Support Candle-Like Combustion of Plastics (Oxygen Index).''</ref>
▲The '''limiting oxygen index (LOI)''' is the minimum concentration of [[oxygen]], expressed as a percentage, that will support [[combustion]] of a [[polymer]]. It is measured by passing a mixture of oxygen and [[nitrogen]] over a burning specimen, and reducing the oxygen level until a critical level is reached. <ref>Definition taken from Principles of Polymer Engineering (2nd edition) by N.G. McCrum , C.P. Buckley, and C.B. Bucknall</ref>
The LOI value is also dependent on the surrounding temperature of the sample. The percent of oxygen required for combustion reduces as the surrounding temperature is increased.
Plastics and cable material is tested for its LOI value at both ambient temperature and elevated temperature to understand its oxygen requirement under actual fire conditions.
Materials with an LOI greater than the atmospheric oxygen concentration are called fire retardant materials.<ref>{{Cite web|url=https://www.ias.ac.in/article/fulltext/boms/015/01/0067-0076|website=www.ias.ac.in|access-date=2019-01-11|title=Fire-retardant materials}}</ref>
==See also==
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[[Category:Passive fire protection]]
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