The US FAA notice of proposed rulemaking (NPRM), if adopted as drafted, would mandate the use of “promising new technologies designed to make fuel tanks effectively inert”. One of these is partial tank inerting by introducing a percentage of nitrogen or carbon dioxide into the fuel tank ullage – the empty space in the tank – as fuel is used, but the FAA is proposing “several means of compliance”, all of which are aimed at “flammability reduction” or “ignition mitigation”. Flammability reduction methods other than tank inerting could include ullage space cooling, and ignition mitigation could include the use of polyurethane foam or other means of preventing an explosion even if ignition occurs. The rule would approve any acceptable methods that reduce the “flammability exposure level” of tanks to less than 7%, says the FAA.
Source: Flight International
