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Diving at Altitude
>Living at a subsea level and diving above sea levelI am the medical officer for Peace Corps Jordan. While I am not a diver, many Peace Corps volunteers and staff dive in Aqaba, in the Red Sea, at the southernmost point of the country. Because of the difference in elevation between Aqaba and Amman, divers are advised to spend the night in Aqaba in order to avoid the bends. One of our volunteers is living in a village at the southernmost end of the Dead Sea, at approximately 365 meters / 1,197 feet below sea level. This young man is 29 years old, a diver, and in good health. My questions are:
>1. What are the long-term side effects of living for a prolonged period (two years) at approximately 1,200 feet below sea level?
>2. Would this person need to take any precautions before diving in the Red Sea in Aqaba?
>3. If he would need to be transported via medevac for any reason from Jordan, would he not be able to fly within a specific period?
- There is no evidence that living at depth, at least at such a small water-equivalent depth, has any deleterious effects. The barometric pressure at the surface of the Dead Sea is about 800mmHg (normal atmospheric pressure is 760mmHg). Prolonged subsea living, such as experienced by those divers exposed to saturation dives in underwater habitats (e.g., Tektite II at 50 feet/15 meters, or 1,150 mmHg), may have numerous side effects, ranging from decompression illness to dysbaric osteonecrosis (the death of portions of the long bones in the body in a proportion of those exposed to increased pressure). The dangers of Dead Sea living come more from exposure to the sun and the extreme salinity of the water.
- The young man should consider himself to be diving at altitude in the Red Sea in Aqaba (when coming from his subsea home); this is a theoretical answer to the question as there is no data to support the following proposition. Standard tables were designed for sea-level dives only. The Theoretical Ocean Depth (TOD) concept was suggested by NOAA (National Oceanographic and Atmospheric Administration) to cope with diving at altitude. NOAA looked at the difference in barometric pressures at various altitudes and recalculated the dive tables based upon the new equivalent water depth, both for fresh water and sea water. This calculation converted for the Dead Sea would add about three feet (one meter) to any given dive. This in turn means he should count each dive as being one stop deeper. The U.S. Navy tables recommend, in fact, that no alteration be made for dives at altitudes lower than 2,300 feet / 701 meters. A few dive computers use the Buhlmann correction for altitude, using the same principle as the TOD. Unfortunately, as they assume a sea-level starting point they would make an incorrect assumption for this diver.
- DAN's preliminary research findings indicate that waiting to fly or go to elevation after diving requires at least a 12-hour wait after a single no-stop dive and a wait for an extended surface interval beyond 12 hours after multiple dives in a single day before flying. If the diver developed symptoms of decompression illness and required a medical evacuation, there should be no problem if the plane could pressurize the cabin to 800mmHg. In a dire situation in which the diver requires transportation over a mountain pass or other elevation to reach a medevac aircraft, then he should breathe 100 percent oxygen during the trip to prevent or lessen any effect that altitude may have on symptoms of decompression illness.