Abstract: A gas separation module 25 is disclosed for separating air into nitrogen 27 and oxygen 26 enriched fractions. The nitrogen enriched fraction 27 may be used to inert an atmosphere inside a fuel tank 32. The air is separated into nitrogen 27 and oxygen 26 enriched fractions by providing a plurality of strands of gas separation membrane wound around a core and maintaining a pressure difference across the walls of the strands of membrane. A low pressure difference of?30 psi maintained across the membrane is able to effect gas separation and provide highly nitrogen enriched air. The membrane has preferably been subjected to a modification technique to increase its gas permeability.

Abstract: A method of producing composite, hollow fibre gas separation membranes, wherein external surfaces of the porous hollow fibre tubes used in the construction of the membranes are subjected to a modification technique before the external surfaces are coated with a thin layer of selective polymer so as to increase the number of pores in the fibre surface.