HP-bottle regulators can be touchy critters.
And brittle in places.
True enough that Oxygen bottles, and even the liquefied kind, both industrial and medical, have very robust stop valves. But if one or more happens to be connected to a delivery system all bets are off. Breathing regulators are very easy to adjust the flow, some by just a bump of, say, a knee, gear bag, etc. I have regulators that can adjust from barely breathing to running a cutting torch. Some adjust with a tee handle. Some with a slider knob. Some just use a black knob with a tiny pointer and you have to actually look at the flow meter to know what it’s doing.
And who’s to say a regulator wasn’t connected and leaking oxy into the cabin for , maybe, days, ahead of the flight? That Mexican crew simply might not have been watching for such a thing since it’s not likely that this patient needed Oxy? There would not be an instrument panel readout on bottle status and there’s no smell, no noise, just a real rich atmosphere.
Unless the medevac plane was totally fly-by-night the oxy bottles would have been clamped into wall bracket arrangement. That eliminates handling individual bottles during flight, etc. That, in turn, requires a manifold arrangement to connect all the bottles. Any one valve can keep the system at the ready which would be desirable for hauling seriously injured folks.
They haven’t told us yet whether the plane was coming apart in the air. But the debris field seems to be large and might indicate that. And that’s more support for my notion that there was an event in the cabin that knocked the thing out of control? Something either jammed a yoke forward or broke the tail off. That’s my notion and I’m stickin’ to it.
The ones I’ve seen/used are on bottles up to 6000 psi (Cascade systems, my HP bottle for the air rifles is 4500). You could probably knock the yoke off/loose if you swung a 3’ iron pipe wrench at it like a baseball bat... (not itchin’ to try though LOL)