Presumably the original poster is talking about TWA 800.
Turned out that while on the ground, the airconditioning plants, situated directly under the main fuselage fuel tank had quielty cooked up the (virtually empty) main fuselage tank and resultant vapour was ignited by faulty insulation in a fuel gauge sender circuit.
No 747's have simply taken off and exploded.
"Air conditioning plants" don't cook up the fuel tank, or fuel for that matter.
In the B747, the center wing tank presently has minimum fuel quantities when fuel is to be placed in the tank, based on speculation from the TWA 800 investigation. These AD's only apply when fuel is to be used from the CWT, and even then they're only applicable to certain segments of flight.
TWA 800 was shot down. It did not simply "blow up."
Further, the fuel gauges in the 747 CWT and wings are capacitance gauges, passive, ant not implicated and not accused of being the culprit. The current "fix" Airworthiness Directive addressing the matter requires minimum quantities of fuel in the tank when the tank is used, and that's all...never any suggestion, inference, or hinting at a need to inert anything, address "fuel sender gauge circuits," or anything of the sort.
Nitrogen systems, such as those used in the C-17, can be troublesome. The system on the C-17 in particular was originally conceived not with the concept of daily routine operation, but the prevention of a flash or explosion following a weapons strike. It's intended to make the aircraft more survivable in combat.
This is not generally a necessity for the B747 in passenger or freight service, save for TWA-800, of course. Even then, whereas the heat source for the target was the packs, which are located beneath the center wing tank, filling the tank with nitrogen wouldn't have helped them.
In most flight operations, the CWT seldom gets used.
In 1976 an Iranian 747 crashed following wing failure, the result of an explosion caused by a lightening strike. The lightening has been determined a likely contributing factor, although other ignition points have also been cited, including a fuel pump. A key issue for the aircraft, however isn't just the lightening or fuel pump issues, but that the aircraft wasn't using straight kerosine fuels; it was using a cut fuel, JP4, which is both kerosine and gasoline combined. This is considerably more volatile than straight jet fuel. The incident is sometimes used as a reference in a call for inert gas in fuel tanks, but those using it as an example seldom remember to note that there's never been an explosion from lightening based on JetA (kerosine-only).
Now this is the bit I need help with: As a result of this a gismo was developed which has subsequently fitted to all passenger jets which filters oxygen out of the air via fine filtersso that the resultant remaining nitrogen can be fed into the fuel tank airspace, reducing explosion risk.
This is untrue, and there is no such device fitted to the B747, nor mofidication used which would accomplish such a thing.
SFAR 88 has nothing to do with inerting tanks. It was a special federal aviation regulation citing a requirement to inspect existing and future fuel tanks and systems for potential ignition sources, and to ensure that no such sources were available in the tanks.