May 2005

Vol. 20, No. 5     What's this?

Should We Dive with Overfilled Tanks?

from the May, 2005 issue of Undercurrent  

Jeremy Anschel of Cozumel’s Living Underwater overfills his steel tanks knowing that the practice will shorten their life span. He’s willing to replace his tanks more frequently to provide his customers more air, and thus more bottom time. What he hasn’t factored in, however, is the danger that a consistently overfilled tank could blow up before it ever fails a 5-year hydrostatic test.

Undercurrent discussed overfilling tanks with Bill High, President of Professional Scuba Inspectors, Inc. (PSI) and the dive industry’s leading expert on tanks. He told us unequivocally that continuous over-pressurizing of either aluminum or steel scuba tanks has a “cumulative effect, so the danger of an explosive rupture increases over time.” High adds: “The practice of overfilling cylinders is illegal in the U.S.” About half of all scuba tank ruptures studied by PSI have occurred in steel cylinders.

Although 90 percent of explosive ruptures studied by High have occurred while the tanks were being filled, in the past year two filled cylinders exploded while being stored, one seven months after being filled. High says that several people have been injured or killed by explosive cylinder ruptures, although — so far — no explosions have occurred while a tank was on a diver’s back.

High also notes that hydrostatic exams don’t test the integrity of the crown or bottom of a cylinder, and he knows of at least two cases where the bottoms blew out of steel tanks.

Contrary to Anschel’s claim that the rust around the boots on some of his tanks merely affected the galvanized coating, High says that exterior rust is definitely a red flag. “The walls of a 2400-psi steel cylinder are only 190/1000s of an inch thick,” he points out, “so a pit that’s no deeper than 1/16 of an inch is cause for a tank to be condemned.” If you’re going to dive with any operation, don’t accept a rusty cylinder.

The rusted LU tanks our correspondent spotted were “inherited” from the previous owner, according to Anschel, and due to be replaced soon. One simple solution would be to replace them with higher-rated tanks. For instance, PST-Scuba (www.pstscuba.com) is offering steel tanks with service pressures as high as 3442 psi in sizes from 65 to 130 cu. ft.