Shaking the Rust in Thumbs Up Cozumel

In our May review of Cozumel's Living Underwater dive operation, Undercurrent gave the outfit and its proprietor, Jeremy Anschel, generally high marks. One area of concern was the rust on some of Anschel's steel tanks. Bill High, president of Professional Scuba Inspectors, Inc. and the leading expert on tanks, confirmed that exterior rust raises 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."

Recently Anschel wrote Undercurrent to report: " We now have twenty low pressure steel tanks from Fabor (120 cu.ft. and 95 cu.ft. and thirty-four low pressure steel tanks from Worthington (120 cu.ft and 95 cu.ft.)." We applaud Anschel's willingness to address this problem once we pointed it out. But we must repeat a previous caution.

Both sets of Living Underwater's new tanks are low pressure (rated around 2400 psi). When our reviewer dove with Living Underwater, he noted that tanks were typically filled more than 10 percent over the rated pressure to allow more bottom time. This practice is unsafe, according to Bill High. Continuous over pressurizing has a "cumulative effect," he told us, "so the danger of an explosive rupture increases over time."

In fact, the Faber website (www.divefaber.com) contains the caveat: "Do not exceed the allowed filling pressure." Faber points out that for some tanks (classified DOT3AA in the US) overfilling is allowed if a plus (+) symbol is marked on the dome of the cylinder. It's always a good idea, with any dive operator, to compare the pressure rating with your actual fill levels. While extra bottom time is great, it's not worth the risk of diving with an habitually overfilled tank, or one filled to higher pressure than your regulator's first stage can handle (as explained in last month's Undercurrent).