David Frank wrote:
As long as this is a theoretical discussion, is there a difference between doing a dive then flying and doing a dive at altitude (say, a lake dive in the Rockies at 5000 feet? tables such as these http://www.sierradive.com/Altitude.htm exist for diving at altitude. In theory, a dive to 50 feet at an altitude of 5k feet should be the same as a sealevel dive followed immediately by a flight to the same altitude.
I am certainly NOT advocating this, having no training or experience in altitude diving. And the obvious difference is that at an alpine lake one really doesn't have the choice of just waiting longer. But can anyone see a difference in terms of diving theory?
-David
Mike wrote:
David,
You asked a question about Altitude diving that I don't think anyone responded to! Actually I got lost a little in this post myself.
I dive at altitude several times a year in Oregon, and the main difference is that your loading your tissues based on the altitude that your diving at. If using the tables, then you'd use a conversion table for 1,000 to 2,000, 2,000 to 3,000, 3,000 to 4,000, 4,000 to 5,000 etc.... Two things come in to play. One, you should allow yourself up to 6 hours for your body to get acclimated to the altitude and two, you are limiting you depth and bottom times based on the altitude in which your diving. IE. on the tables, you may be actually diving at 83 feet, but with the conversion table based on the altitude you may need to calculate as though you were at 92 feet. On your RDP, that would be a difference of calculating the dive at 90 feet versus 100 feet - several different rules would then apply, as well as a shortened bottom time. If using a computer, such as Suunto, then you'd put it into altitude mode for 1,000 to 5,000 or above 5,000 feet. In this mode, the computer would calculate your no-deco time limits.
You asked if doing a 50fsw dive at sea level and then going to no more than 5,000 feet would be any different than doing a dive at 5,000 feet. The short answer is Absolutely. The main difference, is that after doing the dive at 50 fsw at sea level, you may completely load your tissues depending on your bottom times. Going to altitude right after, even under 5,000 feet would have a much larger risk of creating a bubble that may cause damage to the nerves and tissues. Anything above 1,000 feet is considered altitude. We deal with that on a regular occurence in Oregon, as we have mountain passes that we sometimes may have to cross. It's not that much different than jumping in a plane that's pressurized to 5,000 to 8,000 feet. When your diving at altitude, your loading your tissues baseed on the altitude that your diving, therefore, your not reducing the atmospheric pressure around your tissues by flying or driving over the passes, which may cause bubble formation. Typically, when diving at altitude, your going to stay at or go below the altitude your diving at, thereby leaving the atmospheric pressure the same or increasing it slightly as you descend from altitude. So diving at altitude, does not increase your risk of DCS if following the tables or computer. Whereas, flying even at low elevations and reducing the atmospheric pressure around your tissues could have an impact on DCS, the same as driving to altitude. I always remind my students that you can jump off a plane and dive, but don't do it the other way around, as well as a lot of tropical destinations have some form of volcanoes, such as Maui and Haleakala (sp), of which I just returned!!hehe Don't dive in the morning and then go up the volcano - it's just like jumping in a plane!!!
Mike,
Thanks for the detailed answer.
I read a bit after posting it and realized the fallacy in my thinking.
So...new extreme sport: Skyba Diving. Spend 6 hrs flying at 5k feet, parachute in full scuba (skyba?) gear, do your dive, then fly after diving to your heart's content!
-David
|
By David Frank (Experienced BonaireTalker - Post #494) on Thursday, November 30, 2006 - 7:51 pm: 
