Editing Inerting system (section)

==Principle of operation==
[[Fire triangle|Three elements]] are required to initiate and sustain combustion in the ullage: an ignition source (heat), fuel, and oxygen. Combustion may be prevented by reducing any one of these three elements. In many cases there is no ignition source, e.g. [[storage tanks]].  If the presence of an ignition source can not be prevented, as is the case with most tanks that feed fuel to internal combustion engines, then the tank may be made non-ignitable by progressively adding an inert gas to the ullage as the fuel is consumed. At present [[carbon dioxide]] or [[nitrogen]] are used almost exclusively, although some systems use nitrogen-enriched air, or steam. Using these inert gases reduces the oxygen concentration of the ullage to below the combustion threshold.