Saturation diving treads the razor’s edge of what a human body can endure. The human frailty that saturation diving eludes is the tendency of our bodies to absorb gases when we’re under high pressures and trying to breathe. At the same time, the air inside the saturation chamber phases over to a mixture of helium and oxygen, called heliox. Crowded into the bell with the divers are their bulky Kirby Morgan dive helmets—which the divers call “hats.” Typically, divers work in groups of three for six-hour shifts, four teams rotating so work goes on around the clock. In these early days of saturation diving, the toilets operated like simple airlocks.