WTF?! You should avoid exposing your iPhone or Apple Watch to helium. The small gaseous molecules can bleed into the devices' microelectromechanical systems and stop them from functioning.

Erik Wooldridge, a systems specialist at Morris Hospital in Chicago, shared a strange occurrence with iFixit. One day, while installing a new MRI machine, he started getting calls that cell phones had stopped working throughout the building. A few minutes later, people were reporting their Apple Watches had also quit functioning.

His first response was that the MRI had somehow set off an electromagnetic pulse (EMP), and if that were the case, it would cause big problems for the hospital.

“My immediate thought was that the MRI must have emitted some sort of EMP, in which case we could be in a lot of trouble,” Wooldridge told iFixit.

However, he soon discovered that medical equipment and Android phones were unaffected. An EMP would have taken them out too, but it seemed that only Apple products were going on the fritz. It wasn’t just a few either. More than 40 devices were seemingly bricked. A quick survey found that iPhone 6 and above were malfunctioning and all versions of Apple Watches were as well. The one iPhone 5 in the building was working normally.

“The behavior of the devices was pretty odd. Most of them were completely dead,” Wooldridge said. “I plugged them into the wall and had no indication that the device was charging. The other devices that were powering on seemed to have issues with the cellular radio. The wifi connection was consistent and fast, but cellular was very hit or miss.”

It was quite the mystery and one that Wooldridge wanted to solve. So he took to Reddit to see if anybody had any ideas. Some Redditors suggested perhaps the liquid helium used to cool the MRI magnet was to blame. Wooldridge checked out the theory and sure enough, found that there was a helium leak that had vented into the building’s HVAC system.

About 120 liters of liquid helium had vented which quickly evaporated into about 90,000 liters of gaseous helium. However, he was still unsure why only Apple devices were affected and why helium would have anything to do with it in the first place.

As it turns out, it’s all about the clocks. All electronic devices contain a clock. Most are quartz oscillators generating a frequency of 32kHz.

“Now, these frequency generators are at the heart of every electronic device,” says iFixit. “Without a clock, the system stands still. The CPU flat out doesn’t work. The clock is literally the heartbeat of a modern device.”

Quartz mechanisms are somewhat large as electronic components go, measuring about 1x3mm. In the race for smaller and thinner devices, Apple recently switched to MEMS (microelectromechanical system) oscillators — the SiT512 to be exact, which is billed as “the world’s smallest 32kHz oscillator.

The mechanical components within the SiT512 are so small they are measured by the micrometer. They are so tiny that they can be fouled up by foreign molecules. Helium gas infiltration into a MEMS oscillator would be similar to pouring sugar in your gas tank.

Small-molecule gases are a known problem for these types of devices. Even Apple is aware of the issue.

“Exposing iPhone to environments having high concentrations of industrial chemicals, including near evaporating liquefied gasses such as helium, may damage or impair iPhone functionality,” says the infrequently read iPhone user’s guide.

The thing is, occurrences of gaseous contaminations are extremely rare, so most people have never even heard of this happening. As such, there is not a lot of pressure for Apple to publicize the issue. They are surely not getting a lot of small-molecule gas-related repairs at the Genius Bar.

If you are unfortunate enough to have this problem, it is fixable usually without having to take the device in for repair. Apple’s iPhone user’s guide has a home remedy that should work to fix a contaminated iPhone (or watch).

“If your device has been affected and shows signs of not powering on, the device can typically be recovered. Leave the unit unconnected from a charging cable and let it air out for approximately one week. The helium must fully dissipate from the device, and the device battery should fully discharge in the process. After a week, plug your device directly into a power adapter and let it charge for up to one hour. Then the device can be turned on again.”

It is incredible to think that something a simple and as tiny as a helium atom can completely stop an electronic device from working. Such is the cost of miniaturization.

Microscopic Images via iFixit