Saturday, July 15, 2006

Driving to Higher Altitude After Diving

Driving to higher altitude after diving.

Several years ago I ran across this explanation of the physiology of driving to higher altitudes after diving and found it well written. Author unknown.

"So here's my understanding of the physiology: Obviously, nobody worries about the altitude of their room in that high-rise Honolulu hotel. So it's simply incorrect to say, "Never go to higher altitude after a dive." The issue is "How much altitude?" and "How do you adjust your dive plan for anticipated changes of altitude after the dive?" Increasing altitude DOES increase the risk of decompression illness, but this risk is manageable by appropriate dive planning. The atmospheric pressure at 5000 feet (my home in Alpine Utah) is approximately 640 mm Mercury. This compares to 760 mm Hg at sea level. (The difference is the equivalent of about 5 feet of water. So when diving at altitude, you become nitrogen-saturated a little less quickly. This isn't a big factor, and the deeper you dive, the less significant it becomes.) When you emerge from the water, there's less pressure to hold nitrogen in solution in your blood. Example: When diving at, say, 65 feet depth at 5000 feet of altitude, you'd absorb nitrogen 5% slower. But once you emerge, there's 15% less pressure holding the absorbed nitrogen in solution.

The pressure holding the nitrogen in solution is the critical factor in preventing decompression illness. So divers at altitude adjust their dive plan by substituting DEEPER depths for the actual depths they've dived. They assume they'll absorb nitrogen faster (they don't really). But when those numbers are plugged into the "sea level" dive table, it balances out. In other words, at 5000 feet, you assume you have 15% more nitrogen rather than 15% less pressure holding the nitrogen in solution, and it balances out. That way, you don't need a full dive table for every altitude. So how about diving at low altitude, then driving to higher altitude later? Well, let's assume we're ALREADY diving at that altitude. It poses no significant risk to travel to altitude if you've planned your dive AS THOUGH YOU'LL BE EMERGING FROM THE WATER AT THAT ALTITUDE. Got that concept? If you compute your safe level of nitrogen saturation as if you'll be emerging from the water at 5000 feet, how can it be more dangerous emerge from the water at sea level then drive to 5000 feet? Seems to me, the time it takes to drive to that altitude is one hell of a safety stop.

So my advice for diving, then driving to altitude is:
(1) Switch from computer to dive tables. The dive tables, properly used, will be more conservative. And they allow you to adjust for altitude.
(2) Use an altitude-adjusted depth in your dive table. Specifically, you should use the highest altitude you'll reach within 24 hours of the dive AS THE ALTITUDE OF THE DIVE.
(3) Substitute this "drive-altitude-adjusted depth" for the actual depth of the dive in your dive table.
(4) PLAN YOUR DIVE, AND DIVE YOUR PLAN. For example, if I'm diving at 6000 feet elevation, but driving home by way of a mountain pass at 9,500 feet, I use 10,000 feet as the depth of the dive (instead of 6000). There is a table for altitude-adjusted depths at http://www.UtahDiving.com/divetabl.htm

More information about this from Jim Grier in an article he wrote for ScubaDiving .com "Tips".
http://dive.scubadiving.com/members/divetips.php?s=517

See also:
1. history of decompression safety and dive tables
2002 Flying After Diving DEMA Flying After Diving: History, Research & Guidelines Richard Vann ... 1st Report Cabin altitude 8-10,000 ft Pilot ... 4 hrs after diving to 30 fsw Flight
http://www.scuba-doc.com/FADDEMA2002.ppt

2. Diving Physics
Diving Physics Register || Site Map || SiteSearch ... Email || Translate || Home Diving Physics and Physiology In order ... be encountered while diving, one must thoroughly understand
http://www.scuba-doc.com/physics.pdf

3. Flying After Diving-
fly too soon after diving, gives parameters for time limits and ... flying. Flying after Diving* This website is written and ... Campbell, MD, FACS 'Diving Medicine' The question is often
http://www.scuba-doc.com/flyngaft.htm

4. Microsoft Word - 3CA4866A-1252-C19C.doc
FALL PARACHUTING AFTER DIVING PROJECT REPORT Funded by U ... when flying follows diving. Male volunteers completed simulated 60 ft/60 min dives followed by three hours at 25,000 ft to
http://www.scuba-doc.com/MFFAD.pdf

5. Diving At Altitude
to correct for diving at altitude DIVING MEDICINE ONLINE Diving At Altitude (A simplified method to obtain ... Ware, PhD [CAUTION: Diving at altitude requires special training which
http://www.scuba-doc.com/divealt.html

6. Parameters for Flying After Diving
for Flying After Diving Flying after Diving* This website is written and ... Campbell, MD, FACS 'Diving Medicine'The question is often ... to fly after diving"? The answer to the question
http://www.scuba-doc.com/fad.pdf

7. Flying After Diving
take place with diving and flying HOME > Here ... Flying and Altitude Parameters for Flying After Diving Diving After Flying? DAN has ... Flying After Diving Presentation, Dr. Richard
http://www.scuba-doc.com/flyafdv.html