https://www.reddit.com/r/sysadmin/comments/9mk2o7/mri_disabled_every_ios_device_in_facility/

In one of the strangest system admin tales of all time, one IT guy details how a new MRI machine managed to disable every single iPhone, Apple watch and iPad in a medical facility while leaving the rest of the devices untouched.
Eric Woolridge, a system administrator at Morris Hospital in Illinois, said in a detailed post on the r/sysadmin subreddit that helium was to blame for the malfunctioning iPhones. "[T]he MRI installation involves supercooling the giant magnet in the machine by boiling off liquid helium," reports Motherboard. "This evaporated helium is usually pumped out of the facility through a vent, but this vent was leaking the helium into the rest of the facility. In all, about 120 liters of helium (or about 90,000 cubic meters in its gaseous state) was pumped out of the MRI room and an untold amount leaked into the rest of the hospital."

In a blog post, iFixit notes that helium atoms can wreak havoc on MEMS silicon chips. "MEMS are microelectromechanical systems that are used for gyroscopes and accelerometers in phones, and helium atoms are small enough to mess up the way these systems function," reports Motherboard. What's odd is that Android phones were not affected. Apparently, the reason "is because Apple recently defected from traditional quartz-based clocks in its phones in favor of clocks that are also made of MEMS silicon," reports Motherboard. "Given that clocks are the most critical device in any computer and are necessary to make the CPU function, their disruption with helium atoms is enough to crash the device."