Another thought: Is the fuel vender used by multiple airlines? Did they continue fueling aircraft after this happened?
We used to do "fuel sampling" on taxi out overseas; we would configure the fuel panel to first sample the center tank and then sample each main tank before take off. This took several minutes and was hard to do on a short taxi.
Yes I agree, that O2 mystery is solved. I too thought that maybe the crashaxe (which security doesn't believe we have when you tell em about it after they take away your nail clippers) was an antiquated holdover from the prop days but I guess I was wrong. A Long time ago a (Southern Airlines?) DC-9 F/O slid off the runway forgetting to power the rudder and brakes IIRC, forgot to depressurize the cabin (open the outflow valves) for the evac, nobody could get out.... so he took the crashaxe and tried to evac by taking a herculean swing at one of the windscreens.
It bounced and nailed him right in the forehead.
That's were I lost faith in some of the on board survival equipment...