ASTM D2863 Oxygen Index Oxygen Index: Measuring the Minimum Oxygen Concentration to Support Candle-Like Combustion of PlasticsThe purpose of ASTM D2863 is to establish the lowest oxygen concentration in an oxygen/nitrogen combination necessary to sustain a flame burn on a plastic specimen. Real end use circumstances are not correlated. The test sample is placed vertically in a glass chimney, and a flow of oxygen and nitrogen is created there by starting at the bottom of the chimney. The test sample's top edge is lighted, and when the oxygen concentration in the flow falls, the flame eventually goes out. Specimen dimensions: Depending on the kind of material being tested, there are six requirements for the test specimen.