Posted by e-shark on August 06, 2001 at 14:14:36:
In Reply to: Question about Diving and flying posted by moonpieboy on August 06, 2001 at 10:36:43:
To simplify, recreational dive tables and dive computers calculate what is a "safe" dive by reference to the amount of nitrogen in your system at equilibrium at the ambient pressure at the surface where you are diving. Altitude dive tables/computers reflect that if you aren't diving at sea level, the ambient pressure at the surface is different so what is a "safe" dive needs to be adjusted.
The concern with diving and then flying is the effect of the change in altitude during the flight (or upon arrival) on what had been safe depth and time profiles. A dive that was "safe" where the reference ambient pressure was sea level may no longer be safe when the ambient pressure is 5,000 to 8,000 feet, as it might be during the plane flight.
The 12-hour, 24-hour, and 48-hour guidelines for flying after diving are a way to make sure that what were "safe" dives do not become unsafe dives because of the lower ambient pressure.
Sometimes, these same principles affect flying then diving. If your destination is higher than your home, then upon arrival you have more nitrogen in your system than tables/computers would use a reference point. You would need to wait (offgas, reach equilibrium) before diving.
If your destination is lower than your home, then upon arrival you have less nitrogen in your system than the tables/computers would use as a reference point. Waiting before diving would not be required, at least theoretically.
There are some practical problems involved with flying and then diving for many people.
- The cabin air is very dry, leading to dehydration. Not good for divers.
- Drinks on the plane and/or the welcoming rum punch at the resort. Dehydration and impaired judgment.
- The leaving-on-vacation syndrome -- working late to finish everything up before you leave, running around like a madman making last minutes purchases and packing, getting up early to get to the airport, possible jet lag -- often means you are not well-rested upon arrival. Not the best for divers.
The bottom line is to be cautious about diving shortly after flying.