I imagine myself as a diver, the crawlway as a water-filled sump and this tank as my last. I picture the escaping air pooling into bubbles in the ceiling. In water, the sand I lie in would become a brown, enveloping fog. I would float upside down, my face pressed to the roof, and breathe for the five or ten minutes it would take the loose air to vanish into tiny channels in the rock. If I were very near dry cave, I would hyperventilate, then swim for it. If not, I would have time to compose a few last words for my dive log.
The tank expires with a hiss. I light my lamp and resume the schlepp out of Climax, resolving never, under any circumstances, to go cave diving.
Diving for depth increases underwater danger geometrically. The tremendous pressure reduces body volume by up to a third, leaving divers swimming inside suddenly huge wet suits. Descent on compressed air can cause nitrogen narcosis (also called rapture of the deep), a dangerous light-headedness that can lead to fatal errors of judgment. Simple tasks become confusing; divers may feel something similar to a drug-induced euphoria. Meanwhile, oxygen becomes increasingly toxic. Dive tanks empty quickly.
At extreme depths some of the gases that divers must breathe—usually helium and nitrogen—themselves become toxic. As divers push below 600 feet, they are exposed to perhaps the greatest danger of all: high-pressure nervous syndrome (HPNS), a neurological reaction to rapidly increasing pressure. The eyes shrink, causing divers to see flashing auras around people and objects. HPNS can cause violent body tremors, convulsions, hallucinations and death.
Cave divers face the near certainty of HPNS on deep descents. The syndrome often hits in combination with a condition called compression arthralgia, known to Navy divers as "no joint juice" because it feels as if their knees, elbows and wrists have suddenly rusted solid.
In the mid-1980s Exley becomes intrigued with research on scuba and rapid decompression. He studies the records of pioneering mixed-gas dives in submersible habitats that went as deep as 991 feet. He locates a number of very deep water-filled caves in Mexico and decides that rapid descent on mixed gases is the only way for him to see where the caves go. He begins diving with Jochen Hansenmayer, a German who took away Exley's early depth record in the '70s and later set an open-circuit (as opposed to submersible-habitat) scuba mark of 656 feet.
The deep work involves travel to France, Mexico, the Caribbean and elsewhere. In 1984, Exley quits the car dealership and begins teaching advanced algebra and calculus at rural Suwannee High School in Live Oak, Fla. On weekends and school holidays and in the summer he is free to travel to deep sites.
The years Exley spent training advanced divers have helped him develop a passion for teaching. He becomes popular at the high school. He puts his home number on the board and says, "Call me day or night if this stuff gives you trouble." Soon students are calling with troubles that have nothing to do with differential equations. Exley makes personal projects of wild 16-year-old boys who have had brushes with the law or are on the verge of dropping out. One by one, he pulls them into the karate club he establishes. He teaches them to avoid danger by physical and mental discipline, to take control of their lives by thinking. One by one, he calmly breathes life into them.
In January 1989, Exley establishes a record for the longest distance traveled in a single cave dive, 10,450 feet. By the time he comes up, he has been submerged for 14 hours, a third of that in decompression—itself a world duration record. That March, in a Mexican cave called Nacimiento Mante, he sets a new open-circuit depth record with a dive to 867 feet.
Unlike other cave divers at the highest levels of achievement—notably Bill Stone and Wes Skiles—Exley makes these record dives without fanfare. He doesn't seek support from the National Geographic Society or the BBC. After he breaks the depth record, Good Morning America calls to invite him on the show. So docs Today. Exley turns them down.