Sheck Exley was an Americancave diver. He is widely regarded as one of the pioneers of cave diving, and he wrote two major books on the subject: and Caverns Measureless to Man. On February 6, 1974, Exley became the first chairman of the Cave Diving Section of the National Speleological Society. During his career, he established many of the basic safety procedures used in cave and overhead diving today. Exley was also a pioneer of extreme deep scuba diving. For purposes of rescue during cave diving, Exley helped standardize the usage of the "octopus", a redundant secondstage diving regulator that can be used as a backup in the event the diver's primary second stage fails, or alternatively, to allow the diver and his buddy to have simultaneous access to the diver's gas if the buddy has an out-of-gas emergency. The octopus is now considered an essential piece of equipment among virtually all scuba divers, whether caving or in open water. He died at age 45 while trying to set a depth record by diving the world's deepest sinkhole, Mexico's deep, Zacatón, a fresh water cenote. In the book, Diving into Darkness, the author comments: "Exley's status in the sport is almost impossible to overstate".
Exley was the first in the world to log over 1000 cave dives ; in 29 years of cave diving he made over 4000 dives. Exley had an unusual resistance to nitrogen narcosis, and was one of the few divers to survive a open-water dive on simple compressed air. In acting as a safety diver for two divers trying to set an air-only depth record in 1970, Exley reached in salt water, but could go no deeper due to narcosis and the start of blackout. During his diving career, he set numerous depth and cave penetration records. Exley is one of only eleven men in the history of technical SCUBA diving to dive below, as well as the first. His carefully planned multistage decompressions from these dives, in open water, sometimes required times of as much as 13.5 hours. However, he never suffered a classic case of decompression sickness in his career. Exley and German cave diver Jochen Hasenmayer became friends and rivals in the 1980s, each repeatedly attempting to break the depth records of the other.
Death
Exley died, aged 45, on April 6, 1994 while attempting to descend to a depth of over in a freshwater cenote, or sinkhole, called Zacatón in the state of Tamaulipas, Mexico. He made the dive as part of a dual dive with Jim Bowden, but Bowden aborted his descent early when his gas supply ran low. Exley's body was recovered when his support crew hauled up his unused decompression tanks. It was found that he had looped into the descent line, perhaps to sort out gas issues. His wrist-mounted dive computer read a maximum depth of. The cause of Exley's death could not be determined. Team members concluded the causes "...could include stress of HPNS exacerbated by the narcotic effects of nitrogen at that depth". The line was also wrapped around Exley's tank valves. Bowden and other experts have theorized that Exley might have done this in anticipation of his own death to prevent any dangerous body recovery operations. The remipedeL. exleyi, discovered by Australian cave divers Andrew Poole and Dave Warren in August 1993, was named in honor of Sheck Exley.
