Lots of comments about O2 on this thread. I wanted to clairify what most already know, O2 will NOT burn on its own. O2 needs a 'fuel' to oxidize. Without something to oxidize, no fire/explosion is possible.
Atmospheric O2 is about 21%. Even in a 100% O2 atmosphere most materials react no different to the naked eye. If anyone has seen Li, it is stored in a liquid (oil????) becuase if it contacts air, the 21% O2 is enough for it to 'burn', while the O2 in liquid is not enough and thus it is more stable.
The same is true in air. There are SOME materials that will self ignite in a 100% O2 atmosphere that do not in a 21% atmosphere. Chemically this comes down to more O2 molecules being able to 'touch' the surface of the material in a given time and thus raise the heat enough to 'sustain' the reaction. (over simple I know but gets the point across)
As a SLF with a first degree in BioChem, I know little of the chemical make ups of materials in the area of the 747 O2 tanks, but would be very surprised to learn any material used on an airframe itself would self ignite even in a 100% O2 atmosphere. I may be wrong, but that is a guess in part based on the very few materials that actualy can self ignite in a 100% O2 enviroment but are 'safe' in a 21% enviroment.
Thus the idea that a leak itself CAUSED an explosion is very unlikly. I can not see pure O2 contacting any material in an aircraft and thus causing a fire. The idea obove of an O2 leak causing a fire by 'touching' a fuel source (Hat on O2 tank in cockpit, O2 leak on rust inhibitor) seems very unlikly, but I would of course not deny it without testing/research. However, if a leak were present and thus an atmosphere with high O2 concentration existed, an ignition source would have a much higher chance of causing an explosion. From posts above, THIS DOES NOT SEEM to be the case.
I would suggest that whatever caused this sitaution is independent of the actual gas compressed in the tank. (unless caused by some interaction of the gas and tank/fittings itself).
TME
Edited to correct O2 concentration to 21% from 16% (16% is after breathing and a mix up from my CPR training
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