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Two years before last month’s Concorde disaster, L’Air Liquide of Paris filed
patents on a system for making aircraft fuel tanks safer (WO 00/00389). As the
fuel level drops, the space above the fuel is filled with relatively inert
nitrogen-enriched air. The system controls the flow of gas into the tank by
bleeding off compressed air from the engines. The gas passes through a permeable
membrane that allows more nitrogen than oxygen to pass.