Abstract: An oxygen generating device (11, 211) to which a gas mixture containing oxygen is fed, and which is operable to separate the gas mixture into oxygen rich and oxygen depleted gas components, the device (11, 211) including a negative temperature coefficient material (36a 36b 36c; 236) which is active at an elevated temperature above a minimum operating temperature, to separate the gas mixture into oxygen rich and oxygen depleted gas components, there being an electronic control unit coupled to the device to pass an electrical current through the device (11, 211) to produce a heating effect within the device to heat the gas mixture at least towards the minimum operating temperature wherein the device includes a plurality of active sections (A, B, C) through each of which the gas mixture passes in turn, and the electrical current supply is connected to each of the sections (A, B, C) so that the sections electrically are connected in series.

Abstract: An oxygen generating device to which a gas mixture containing oxygen is fed, and which is operable to separate the gas mixture into oxygen rich and oxygen depleted gas components, the device comprising a first material which when at an elevated temperature at or above a minimum operating temperature, is active to separate the gas mixture into oxygen rich and oxygen depleted gas components wherein a second material is provided which produces a heating effect within the device when an electrical current passes therethrough, to heat the gas mixture at least when the gas mixture is at a temperature below the minimum operating temperature.