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Here at the end of the first dive, it is perhaps the right time to explain, in case you’re new to this, a little about breathing gases and decompression, to start breaking you in gently!

The open-circuit (OC) divers in our group arriving at the deco station were breathing from standard diving regulators, where, as you breathe out, your exhaled breath is vented as bubbles from your regulator that rise up to the surface.

As the dive was deeper than the safe recommended limit for diving standard compressed air, they were using a helium-rich breathing gas for the deep part of the dive, known as bottom mix. As they ascended at the end of the dive and began their decompression stops at about 20 metres or shallower, they were able to switch over to a cylinder of enriched air nitrox (EAN) slung under their arm on their webbing and designed purely for use during decompression; it is called deco mix. Perhaps it is best if I also explain a little about diving gases and accelerated decompression at this early stage.