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Marine Science and PhysiologyPost all medical questions related to decompression or diving here. Questions and discussions about the marine life we love to share the ocean with and how to protect them are also welcome.
My dive computer, an Oceanic Veo 250, gives me a 24:00 hour countdown as "Time to Fly" following any dives, at any depth. I know computers are built with fairly conservative limits.
My question is, would shallow depth diving (average 15 feet, MAX 20') on the day before flying cause any problems? I wouldn't consider doing anything deep, but I'm curious to get some medical opinions.
24 hours should keep you safe but PADI says 12 hours + after a shallow dive!
Is that in their OW or AOW course material, or something you came across on their website? Need to look into it, as a dive buddy will be faced with this scenario next weekend.
Is that in their OW or AOW course material, or something you came across on their website? Need to look into it, as a dive buddy will be faced with this scenario next weekend.
The flying after diving recomendations are right on the RDP.
12 hrs. for shallow one day dive, 18 hrs. for multiple days of diving.
My question is, would shallow depth diving (average 15 feet, MAX 20') on the day before flying cause any problems? I wouldn't consider doing anything deep, but I'm curious to get some medical opinions.
Thanks!
I'm not an MD, but would make a point that under current decompression theory that shallow isn't necessarily better. Given a fixed amount of air and a choice of making a long, shallow or short, deep dive a fixed time before flying, I'd choose the short, deep dive. The No Decompression Limit of the shallow dive is set by the slower tissue groups (in the model), which then are slow to off-gas when you reach the surface. The deeper dive NDL is set by the faster tissue groups. Under this theory, you'd have less residual gas when you flew after the deeper dive!
In reality the diving-flying time rules are not based on much data and likely overly conservative. A much bigger factor than whether you waited 18 or 24 hours is what the quality of your ascents were. If you're able to keep it smooth and well under 30fpm *especially* when ascending from the safety stop to the surface, you're going to have a much lower bubble load in your body when you go to fly.
I would not worry about flying after a 15 to 20 fsw dive. Here’s why. And no doubt someone will correct me if I got any of this wrong.
Offgasing is driven by the change in ambient pressure. So at 20 fsw you have 1.61 ATA and while flying you have 0.74 ATA, for a change of 0.87 ATA. The 0.74 ATA figure assumes a cabin pressure of 8000 feet above sea level which I understand to be typical.
So just using the pressure change flying after a 20 feet of seawater (fsw) dive is like doing a direct ascent to the surface from a 29 fsw dive. So if you try to look up what your no decompression time for a dive to 30 fsw you will likely find there is no limit. And this is the case because the pressure gradient from a 30 fsw dive is not enough to generate DCS symptoms.
So how deep a dive could you do? M values give you the maximum tolerable pressure gradient in fsw. The lowest M value in Buhlman’s ZH-L16 table is 41.8 fsw for the 635 minute tissue compartment. That is the slowest tissue compartment and all other compartments have higher M values. So in essence this is saying that you could surface directly from 42 fsw if you were fully saturated for all tissues and still not be symptomatic for DCS. So taking the 9 fsw off for the flight this is saying you could dive to 33 fsw indefinitely and then fly with low risk of DCS.
Of course these values were experimenatly determined and if your body behaves differently you could get bent, but it is unlikely.
This member has said "Thank you." to Mr Carcharodon for this useful post:
NOAA has a table for your convenience. Airplanes are pressurized to 5000 - 7000 feet. Calculate accordingly using their RDP as well. The letter groups are not interchangeable with other dive tables:
So a dive (based on these tables) to 20 feet for 100 mintues puts you in Pressure group I, and would require a 12 hour surface interval.
Also: the current DAN reccomendation is:
"Dives within the No-Decompression Limits
* A Single No-Decompression Dive: A minimum preflight surface interval of 12 hours is suggested.
* Multiple Dives per Day or Multiple Days of Diving: A minimum preflight surface interval of 18 hours is suggested. "
If you don't cheat the tables, and do safety stops 12 hours is really ok in my non-medical opinion.
It looks like a dive to 40 feet for 100 minutes puts you in pressure group I, and gives you a 13 hour surface interval before flying. But the original question was about a dive to an average depth of 15 fsw. That dive is certainly less than group I and so the required SI is less than 13 hours but the table is not useful in determining how much less.
Flying after diving... what if it's shallow?
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