Editing Inert gas (section)

===Inert gas systems on aircraft===
Inert gas is produced on board commercial and military aircraft in order to [[Passivation_(chemistry)|passivate]] fuel tanks. On hot days, fuel vapour in fuel tanks may otherwise form a flammable or explosive mixture which if oxidized, could have catastrophic consequences.  Conventionally, '''Air Separation Modules''' (ASMs) have been used to generate inert gas. ASMs contain selectively permeable membranes. They are fed compressed air that is extracted from a compressor stage of a gas turbine engine. The pressure drives the separation of oxygen from the air due to the increased permeability of oxygen through the ASMs in comparison to nitrogen. For fuel tank passivation, it is not necessary to remove all oxygen, but rather enough to stay below the lean flammability limit and the lean explosion limit. In contrast to the oxygen concentration of 21% in air, 10% to 12% in the [[ullage]] of a passivated fuel tank is common over the course of a flight.