I've copied this from the thread on R&N... just to pre-empt the comments and questions which may otherwise appear...
It seems pax are now saying that the oxygen system failed (at least at some seats). Just a thought here that it may not have failed but that pax are required to pull the mask down for it to work, and unlike other aircraft which use the chemical oxygen generators, activiating one mask on the 744 will NOT activate the entire row.. so maybe the 02 didnt fail, maybe the pax just didnt know how to use it properly??
B747 300 & 400 Pax Oxy
Pax oxy sys on this aircraft, as stated previously, is of the 'stored gaseous type'.
Pulling down on a mask will activate o2 flow to THAT MASK ONLY.
Therefore, if pax are too shocked/innattentive to briefing to REMEMBER this, they may NOT have pulled down on their mask- if it was flapping in front of them my guess is they'd remember the part to grab it and put it on- but possibly forgot the part of "Pull down on it firmly"" in favour of put it on quickl˙, and ensure the strap is tight"
Most pax wouldn't know what a flow indicator is or how to check for oxy flow. (In this case, bag MAY inflate)
Flow can be shut off at individual units/masks when no longer required. Duration would vary on time of descent, number of pax, demand etc...
Yes, flight crew also have backup in the form of a portable bottle similar to those seen worn by the cabin crew in that video.