Nathaniel Rich’s 2013 NYRB story on saturation diving begins:

The first dive to a depth of a thousand feet was made in 1962 by Hannes Keller, an ebullient twenty-eight-year-old Swiss mathematician who wore half-rimmed glasses and drank a bottle of Coca-Cola each morning for breakfast. With that dive Keller broke a record he had set himself one year earlier, when he briefly descended to 728 feet. How he performed these dives without killing himself was a closely guarded secret. At the time, it was widely believed that no human being could safely dive to depths beyond three hundred feet. That was because, beginning at a depth of one hundred feet, a diver breathing fresh air starts to lose his mind. …