2.2.4.: Additional Classification Considerations Flammability shall be determined by tests or, for mixtures where there are sufficient data available, by calculation in accordance with the methods adopted by ISO (see ISO 10156 as amended, Gases and gas mixtures — Determination of fire potential and oxidising ability for the selection of cylinder valve outlet). Where insufficient data are available to use these methods, test method EN 1839 as amended (Determination of explosion limits of gases and vapours) may be used. Chemical instability shall be determined in accordance with the method described in Part III of the UN RTDG, Manual of Tests and Criteria. If the calculations in accordance with ISO 10156 as amended show that a gas mixture is not flammable it is not necessary to carry out the tests for determining chemical instability for classification purposes.