Comment by dirkt

There are more details in the original thread https://www.reddit.com/r/sysadmin/comments/9mk2o7/mri_disabl... on reddit:

I discovered that the helium leakage occurred while the new magnet was being ramped. Approximately 120 liters of liquid He were vented over the course of 5 hours. There was a vent in place that was functioning, but there must have been a leak. The MRI room is not on an isolated HVAC loop, so it shares air with most or all of the facility. We do not know how much of the 120 liters ended up going outdoors and how much ended up inside.