Thanks for those pics, Bob. You're right, it doesn't take much water!
"Saturated" makes more sense, though once you pressurize it with nitrogen
or helium (assuming little diffusion into the LOX) or a piston, the LOX
becomes a compressed (not saturated) liquid and it won't immediately start
boiling if you add some heat or drop the pressure a bit (just like water
under atmospheric pressure is a compressed liquid and behaves the same
way). So I think the vent valve, though it did cause the LOX to be at high
pressure rather than atmospheric, didn't cause the failure.
