Page 35 - AlertDiver_Summer2011

ecompression sickness (DCS) may develop after a dive when very small bubbles grow as nitrogen diffuses into them from surrounding supersaturated tissue (see Page 35). If the bubbles remain small enough, the diver never knows they are there, and another successful dive goes into the logbook. DCS occurs if the bubbles become too large, are too numerous or are located at sensitive sites. The chances of developing DCS are normally low, but they increase with extensive bubble growth. DAN ® has observed DCS incidence rates ranging from two DCS cases in 50,000 dives (one case per 25,000 dives) for Caribbean liveaboard diving to 28 DCS cases in 16,887 dives (one case per 600 dives) for cold-water wreck dives.

What would happen if the liveaboard or wreck divers flew home at an 8,000-foot cabin altitude immediately after diving? Per Boyle’s Law, any bubbles would immediately expand by one-third, and additional bubble growth would occur as the dissolved nitrogen diffused into the bubbles from the surrounding tissue. The risk of developing DCS in this situation is why divers are advised to wait at sea level after diving before they fly. For recreational divers, the recommended minimum preflight surface intervals are 12 hours following a single no-decompression dive and 18 hours after multiple dives or multiple days of diving. More flexible guidelines are available in the U.S. Navy Diving Manual. Many dive computers predict and display when flying is deemed safe, although the methods used vary among computers. NASA has flying-after-diving procedures that use oxygen breathing during the preflight surface interval so astronauts can fly soon after underwater extravehicular activity (EVA) training in the Neutral Buoyancy Lab at the Johnson Space Center (Pollock and Fitzpatrick 2004).

Page 35 - AlertDiver_Summer2011_web

Page 35 - AlertDiver_Summer2011_web