Sliced scuba tank likely didn't explode

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Lucky to be alive, Wesley Scott Murphy was scuba diving off Palm Beach, Fla., when a boat propeller hit his scuba tank, slicing into the tank but missing the 35-year-old diver as he surfaced.

Murphy, of Houston, reported hearing his tank “explode,” but Mark Gresham, an authority on scuba tank safety and inspections, said the tank almost certainly did not explode. Probably what Murphy heard was the powerful rush of air escaping a breach in the tank. Gresham said a standard scuba tank carries 80 cubic feet of air compressed to 3,000 pounds per square inch (psi), which translates to 1.3 million pounds of stored energy — “enough to lift four 88-ton locomotives a foot off the ground.”

Murphy, who had gone diving with two friends off the beach in 7 feet of water, suffered a back injury, but was released from the hospital the next day, said Florida Fish and Wildlife officer Willie Puz.

Puz said a 31-foot SeaVee struck Murphy as he surfaced while diving inshore of The Breakers Reef, a popular dive site off The Breakers hotel and resort. Murphy had ventured farther out toward the reef, becoming separated from his two companions — who were snorkeling — and from the dive flag they brought with them, Puz said. Florida law requires divers to display a dive flag and stay within 300 feet of it. The officer said the SeaVee turned around and picked Murphy up.

He said the case remained under investigation.

Gresham, owner and general manager of PSI Inc., a firm in Woodinville, Wash., that trains scuba tank inspectors, said federal regulations require scuba tanks to be designed and built so they don’t explode and fragment like a grenade if they rupture. Tank designs are tested by shooting a bullet into them, and if properly designed they just lose air, they don’t “explode.” Gresham said if Murphy was near the end of his dive when he surfaced, the pressure in his tank would have been dramatically reduced, probably to about 500 psi.

Tank failures have been a matter of concern recently in the dive industry, chiefly because of old Luxfer and Walter Kidde tanks made from 6351 aluminum alloy, which can develop tiny cracks causing fragmentation when a tank ruptures. Gresham said just 17 “catastrophic ruptures” have been reported worldwide among an estimated 25 million cylinders made from 6351 aluminum alloy. He said manufacturers stopped making tanks from the alloy in the late 1980s.

“Was this a catastrophic failure? Probably not,” Gresham said.