Oxy cyilnders
I know it`s some years since i worked on the Qantas 747-400 but some points need answering from memory.
1st There are several bottles in the rack 6 or 8 from memory. there is a non return valve between each bottle so the loss of one especially at the end of rhe line would not drain all the others.
2nd The way the bottles are secured it is very uinlikely that the bottle exited the aircraft in one peice, I would suspect a bottle failed & the shrapnel caused the damage.
3rd The crew have their own supply of oxygen totally seperate from the pax supply.
tristar 500