Comment by afturner
7 years ago
To be clear, not arguing, I just want to learn. Doesn't this contradict what you said before though, about it not displacing the oxygen sensors in the room because it was so little? "We do not know how much of the 120 liters ended up going outdoors and how much ended up inside. Helium expands about 750 times when it expands from a liquid to a gas, so that’s a lot of helium (90,000 m3 of gaseous He)." I wonder what this would mean in practice at any given time.
I'm very certain that there are usually oxygen sensors installed for MRI machines and NMR spectrometers. I'm not sure how sensitive they are. Either they were not triggered, e.g. because the helium concentration was low, or at least low at the position of the sensors. Or if it was high, they were disabled or ignored.
120 liters of liquid helium is a lot, but it wasn't released at once but over a longer time as far as I understand the story.
Some have sensors and some don’t. GE ones do in my limited experience (one scanner), other vendors don’t (experiece limited to half a dozen scanners).
I don't mean sensors directly attached to the machine. My experience is with NMR spectrometers, which work based on the same principle as MRI machines and have the same superconducting magnets that require liquid helium and nitrogen. And those essentially always have an oxygen sensor in the room somewhere, but not connected to the spectrometer itself.
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