Pretty fascinating story and conclusion for a nerd like me.
A medical facility was having a new MRI machine installed. Shortly after, dozens of iPhone/Watch owners reported that their devices froze. Other devices were fine, as were the humans.
It wasn’t an electrical problem, like you might expect. Instead, what happened was that a fairly small amount of helium was released during the MRI cooldown. MRI machines use liquid helium for cooling their superconductors.
Most of this will be vented outdoors, but this is an imperfect process. There’s not much need to do better since helium is completely inert and nobody will notice a percent or two of extra helium in the atmosphere.
However, newer Apple devices use what’s called a MEMS oscillator. MEMS are micromachines: very small devices with moving components. Apple uses an oscillator (a device meant to keep time by pulsing at a well-defined rate) rather like the balance wheel on a watch–a mass on a spring that swings back and forth at some rate–just much smaller.
As one might imagine, the vibration frequency depends on the ambient atmosphere. Pressure and atmospheric composition both play a role. And so MEMS oscillators are hermetically sealed in order to keep atmospheric variation in check.
However, helium is a very crafty atom. It is tiny, even as atoms go, and monatomic as well, being a noble gas. And so it is virtually impossible to build a perfect seal against helium. It will invade solid metal simply by squeezing between the metal atoms. A thin metal shell like on the MEMS device is not much of a barrier to helium.
What happened is that the very low helium concentration infiltrated the MEMS oscillators and changed their timing ever so slightly. iOS did not like this change in timing for whatever reason, and the devices hung. Airing them out and letting the battery discharge was sufficient to revive them.