The greatest escape

Watchmakers overcame the destructive force of deep-sea helium penetration with clever valves

- Mark McArthur-Christie

WE'VE NEGLECTED our saturation diving readership for too long. Apart from a brief foray into the depths with our now-famous Casioil (an oil-filled £10 Casio F-91W that damn’ nearly survived a proper sat-diving job in 2020), we've barely touched on the issues that spending a couple of weeks at 300m down brings for your wristwatch.

A Sub or a Fifty Fathoms will give you some decent pub boasting rights, but to have serious bar-diver credibility you need something with a helium escape valve (HEV). Yet you don’t only have to have the watch; for full kudos you have to understand the whys and the hows of helium and diving.

The air you're breathing now (unless you do happen to be reading this in a sat-diving chamber) is, near as spit, 78% nitrogen. That's fine at normal atmospheric pressure, but nip down 30 or 40 metres underwater and it'll start doing some nasty things to your nervous system. The impairment looks and feels rather similar to being drunk. Drop much further below that and you'll be incapacitated by full-on nitrogen narcosis.