I wanted to avoid thinking about that failure mode where you accidentally cleave some part of the gas regulator by damaging it, and that turns the tank into a cold-gas rocket motor. We were shown pictures of the aftermath of those lab accidents—I think there was one were a tank embedded itself into a ceiling?
edit: Now I remember the follow-up—after a professor witnessed us, they showed us the correct method. It was simply to send the tank up in the elevator unattended—one undergrad pushing the "up" button and stepping out, the other waiting for it on the destination floor. Stupidly simple.
That works great until somebody in an intermediate floor enters the elevator oblivious to the risk and suffocates.
A stairwell you can run up, or out a door. An elevator can get stuck - or just take awhile - and there is nothing you can do about it.
Also an issue with liquid nitrogen, but that usually takes a little longer to sublimate.
Dry ice is one of the few grocery store substances (in many areas) with a similar issue, but at least co2 causes a suffocation reflex we can feel. So less dangerous.
