A helium escape valve is a device integrated into some watches designed for professional divers whose work involves spending long periods of time in pressure chambers or diving stations filled with helium-enriched air. During that period, tiny helium molecules can penetrate a watch through its joins. Unfortunately, these do not escape in the same way and on return to normal air conditions can expand and cause damage to the watch. This is solved by opening the helium escape valve so that the excess pressure caused by expanding helium molecules can escape. The valve must not be opened in the water. Helium is a noble gas and not harmful to health.