Application of ISO 4589-4 to determine limiting oxygen concentrations for opposed-flow flame spread over thin electric wires and their comparison with microgravity data

High gas flow velocity oxygen index test, ISO 4589-4, for measuring the limiting oxygen concentration of flat specimens in opposed flow configuration is applied to electric wires and its applicability is examined. Furthermore, data obtained on the ground are compared with those obtained in microgravity to verify the validity of estimating the minimum limiting oxygen concentration from the high gas flow velocity oxygen index test. The wire samples used in this study consist of LDPE and ETFE insulation over metallic cores. The gas flow velocity is varied from 4 to 100 cm/s to obtain the flammability data in wide range of flow velocity. Limiting oxygen concentrations of wire samples are accurately determined by following ISO 4589-4. All samples tested in this study are more flammable under microgravity than normal gravity. It is also confirmed that the relationship between the limiting oxygen concentration acquired on the ground and in microgravity is well connected.