You sure got my attention with your story. That was horrible. Was it possible that not being diligent about closing the tap, would the tap freeze open?
You had previously said “ It was an odd feeling of attenuated sound because oxygen was not reaching my eardrums.”
I’m not a medical doctor but that sounded (no pun intended) like low oxygen in the bloodstream - aka hypoxia. But never mind.
The setup with the LN2 tap was very basic, had been around for many decades. Large tank right outside that room of the building, insulated line through the wall, lever ball valve, downtube ending about 2 feet above the floor so you could stick the end in the dewar (large thermos looking like a milk can). Oh, there was ventilation as well, but just a fan in the wall blowing to the outside. There were always a few inches of dense LN2 fog on the floor when filling the cans. Poor guy had to have his head very low to pass out from nitrogen asphyxiation. How that happened...???
The tap never froze up even when filling a dozen dewars - somethink like 20 to 30 mins constant flow. Freak accident or intentional. Did not hear that anyone got indicted over it.