When commercial divers operate at great depths, they often spend prolonged hours in
diving bells under
pressure breathing a
breathing gas mix like
trimix or similar, that contain the gases
helium or
hydrogen. Since helium
atoms are the
smallest natural gas particles found in nature, these gas atoms are able to work their way inside the watch, around any
o-rings or other seals the
watch may feature. This is not a problem as long as the divers stay under pressure, but when the
decompression stops during resurfacing aren't long enough, a pressure difference builds up between the trapped gas(es) inside the watch case and its environment. Depending on the construction of the
watch case and crystal, this effect can cause damage to the watch, such as the crystal popping off.
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