Helium Escape Valve?
prior to surfacing from great depths in a pressurized enclosure, such as a diving bell, toxic gases that have been formed in the enclosure are removed and helium is mixed into the air. The helium molecules are lighter than air and can therefore penetrate the watch. When the pressurized enclosure surfaces and is depressurized the helium rushes out of the watch so quickly that the glass on the watch pops out as well. The watch was built to withstand external pressure, not internal pressure.The glass popping out can be avoided by opening the Helium Escape Valve on the watch during resurfacing, which allows the helium to escape but prevents water from entering the watch.
