Sheck Exley

Exley was the first person in the history of technical SCUBA diving to dive below 800 feet (240 m), a feat only 20 people have performed as of 2021. His carefully planned multistage decompressions from these dives, in open water (not in a decompression tank), sometimes required times of as much as 13.5 hours. However, he never suffered a classic case of decompression sickness in his career.

Exley died, aged 45, on April 6, 1994 while attempting to descend to a depth of over 1,000 feet (300 m) 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 906 feet (276 m).

The remipede L. exleyi, discovered by Australian cave divers Andrew Poole and Dave Warren in August 1993, was named in honor of Sheck Exley.

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.

In spring 1973, Exley served as an aquanaut during an eight-day mission aboard the Hydrolab underwater habitat in the Bahamas.

Exley had an unusual resistance to nitrogen narcosis, and was one of the few divers to survive a 400-foot (120 m) 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 465 feet (142 m) in salt water, but could go no deeper due to narcosis and the start of blackout (the two record-depth attempting unconscious divers died just out of reach beneath him, and such air-depth records are no longer sought or recorded). During his diving career, he set numerous depth and cave penetration records.

Exley began diving in 1965 at the age of 16. That same year he entered his first cave and was hooked on cave diving for the rest of his life. To finance this passion, Exley worked as a mathematics teacher at Suwannee High School in Live Oak, Florida.

Sheck Exley (April 1, 1949 – April 6, 1994) was an American cave diver. He is widely regarded as one of the pioneers of cave diving, and he wrote two major books on the subject: Basic Cave Diving: A Blueprint for Survival and Caverns Measureless to Man. On February 6, 1974, Exley became the first chairman of the Cave Diving Section of the American 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.