Saturation divers live under pressure for weeks, commuting to the seafloor in a sealed bell and spending more than a week decompressing when the job ends. The method rests on a 1942 insight by U.S. Navy medical officer Albert R. Behnke: after roughly 72 hours the body’s tissues hold all the inert gas they can, so decompression time stops growing. The first intentional saturation exposure came in 1938, when Edgar End and Max Nohl spent 27 hours at a simulated 101 feet in a Milwaukee hospital chamber. George F. Bond’s Genesis project and Jacques Cousteau’s Conshelf habitats followed, and the North Sea oil boom made the technique commercial.

Going deeper meant fighting the body. Below about 500 feet helium causes high pressure nervous syndrome, with tremors, jerks, and microsleeps, so researchers added narcotic hydrogen. Peter B. Bennett’s Atlantis III at Duke simulated 2,250 feet in 1981, and in 1992 COMEX diver Theo Mavrostomos reached a simulated 701 meters on hydreliox. Dense gas makes breathing hard work, and cold helium drains heat from the lungs, so divers wear hot water suits while chambers run at 85 to 93 degrees Fahrenheit. Decompression proceeds at three to six feet per hour, and in a disaster divers cannot leave the chamber.

• Compression arthralgia brings aching joint pain on the way down.
• Humid, oxygen rich chambers breed ear infections and fungal skin problems.
• Divers need 44 to 52 kilocalories per kilogram of body mass each day.
• Excursion limits restrict how far above or below storage depth a diver may swim without risking the bends.
• In 2015 there were only 336 registered saturation divers in the United States.