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March 2006 Vol. 21, No. 3   RSS Feed for Undercurrent Issues
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DAN or Your Computer? When to Fly after Diving

from the March, 2006 issue of Undercurrent   Subscribe Now

When you decide to fly after you dive, if you follow the advice of your computer, you may be erring on the side of bends.

Divers Alert Network (DAN) recommends that after making a single no-decompression dive on air or Nitrox, a diver should wait at least 12 hours before flying. After making multiple dives in a day or diving for several days, DAN recommends waiting 18 hours. Since there is little data about flying after dives that require a decompression stop, DAN says that waiting “substantially longer than 18 hours appears prudent.” These restrictions don’t apply to puddle-jumper flights below 2,000 feet.

Their recommendations stem from a study presented at a 2002 workshop. More than 500 subjects participated in experiments at the Duke University Medical Center hyperbaric chamber, simulating depths of 40, 60 and 100 fsw, with dive times near the recommended recreational limits.

Following the dives, participants spent four hours in the chamber at a simulated altitude of 8,000 feet, the maximum cabin altitude allowed by the FAA for pressurized commercial aircraft. Although participants showed no symptoms of DCS (decompression sickness) before flying, DAN recorded 40 subsequent DCS incidents, of which 21 were moderate, 18 mild, and one serious.

Bruce Wienke, Los Alamos National Laboratory scientist and the father of the Reduced Gradient Bubble Model (RGBM), told Undercurrent that different computers calculate time to fly differently. They peg their calculations to specific tissue compartments that represent the hypothetical modeling of nitrogen absorption. The fastest tissues saturate in 25 minutes, the slowest take two and a half days. Wienke said that some computers may allow shorter surface intervals before flying, depending on which tissue compartment they use in their calculations. These include some or all models of Suunto, Mares, Dacor, Uwatec, Zeagle, HydroSpace and Explorer computers, plus decompression software from Abyss and GAP. Other computer models, such as Cochran, just tack on a set number of hours.

If your computer permits you to fly sooner than DAN recommends, abide by DAN. Even then, warns DAN, “The recommended preflight surface intervals do not guarantee avoidance of DCS. Longer surface intervals will reduce DCS risk further.”

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