Helium may be a gas, but it's no fun for Apple iPhone and Apple Watch users
In the Apple iPhone User Guide is a section that states "Exposing iPhone to environments having high concentrations of industrial chemicals, including near evaporating liquified gasses such as helium, may damage or impair iPhone functionality. … 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."
As mentioned in the iFixit.org blog, this was borne out by several incidents at Morris Hospital near Chicago during the installation of a new GE MRI machine that had a helium leak. The leak and the building's ventilation system allowed the gas to travel throughout the hospital. Several iPhones and Apple Watches stopped working. While 40 different devices had issues, Android handsets were not affected. The helium, which is used to cool the MRI machine, also didn't have an affect on older iPhone models.
It seems that Apple had recently had started using microelectromechanical systems (MEMS) timing oscillators to replace bulkier quartz components previously employed. The hospital's systems specialist Eric Wooldridge figured out that the helium molecules were small enough to infiltrate the MEMS chips and gum up the works. Placing an Apple iPhone 8 Plus in a sealed bag filled with helium, Wooldridge exposed the phone to a higher concentration of gas than the devices in the hospital, but it did make the handset freeze up after slightly more than eight minutes. The test was repeated in a lab, and that time the phone lasted just four minutes.
While helium will make balloons fly, it apparently makes the iPhone and the Apple Watch fall like a lead weight. Make sure that you don't expose either device to the gas.