Oxygen index is defined as minimum concentration of oxygen, expressed as volume percent, in a mixture of oxygen and nitrogen that will just support flaming combustion of plastic materials under equilibrium condition of candle like burning. The equilibrium is established by the relation between the heat lost to the surroundings as measured by either time of burning or length of specimen burned. This point is approached from both sides of the critical oxygen concentration in order to establish the oxygen index.
Dimensions of test column 75 mm inside diameter x 450 mm long
Rota meters 0.625 to 6.25 liter/minute for oxygen
1.05 to 10.5 liter/minute for nitrogen
Temperature indicator Up to 199°C x 1°C
Timer Timer Up to 999 seconds x 1 second
The FEC Oxygen Index Apparatus consists of a test column made of borosilicate glass supported on a brass base. The mixture of nitrogen and oxygen is released from the bottom of tube, which is filled with
glass beads for mixing and evenly distributing the gas mixture. A specimen holder is provided to hold the specimen vertically in the center of the test column with its lower end more than 100 mm above the top of glass beads.
The specimen holder is supported in a glass tube fixed at the center of the test column and can be taken out and inserted from the column. A thermocouple probe is also fitted in the test column above the surface of the beads to measure the temperature of the gases inside the column, which is indicated on a digital temperature indicator. A tube with suitable orifice for pilot flame is provided for igniting the specimen by inserting it from the top of the test column.
Two Rota meters with needle valves are provided to control and measure oxygen and nitrogen flow in the test column. The rotameters are calibrated with an accuracy of 3% of full-scale range. A timer for indicating the time of burning with a switch to
ASTM D 2863 - 1997 Measuring the Minimum Oxygen Concentration to Support the Candle- like Combustion of Plastics (Oxygen Index)
BS 5734 (Part 1) - 1979 Polyester Moulding Compounds for Electrical and other Purposes Part 1 : Methods of Test