Saturation diving systems

Saturation diving is, in its basic form, a centuries-old technique adapted to the scale of the human submerged civilization. A diver is taken to the working depth, allowed to saturate — that is, to come into pressure equilibrium with the surrounding water — and then lives at that pressure, in a sealed habitat, for as long as the work requires. They decompress only at the end. A two-week rotation may carry a single decompression cycle of three days at its close.

Gas

The breathing mix is heliox: helium and oxygen, with the helium fraction increasing with depth to keep nitrogen narcosis and oxygen toxicity within acceptable bounds. Helium is the engineering challenge that limits the architecture; the supply chain of high-purity helium from the surface remains the most expensive line in any saturation budget.

Habitat

The pressurised module is small, well-lit, and cold. The interior climate is held at a temperature that would, on the surface, feel uncomfortable; the high helium fraction strips heat from the body faster than air does. Crew rotations of eight to fourteen days are typical. Longer rotations are physiologically possible and operationally avoided.

Limits

The technique is canonical to three hundred metres. Below that, ADS takes over for short work, and submersibles for longer transits. Saturation has been performed deeper, in research conditions, but the cost and recovery times scale unhelpfully with depth.