How long before flying after diving?

[cavegirl]

Someone suggested I ask in this forum.

We'll be on a 10-day cruise in Hawaii, then fly back out the day after cruise.

On the day flying out, the flight is 9pm.

The current tables show that 12 hrs is needed after diving before flying. But would that be shorter if using Nitrox?

Specifically is it ok do a morning 2-tank recreational dive (using Nitrox). The dives are probably will be 8:30am and 10am dives, finishing before 11am. That leaves 10+ hours.

Thanks a lot.

 

[Kim]

Maybe others will disagree but that sounds too short for my taste. Decompression and it's effects are not an exact science so there are no really hard and fast rules which can tell you exactly what is safe or not. Consequently people try to err on the side of caution. The general no-fly rule these days is 24 hours (and this is built into many dive computers such as my Suunto Vyper).
I would not want to get a DCS hit on a long flight over the ocean. (actually I wouldn't want it on any flight, or at all, but there's even less that could be done about it on such a flight!!)

 

[Scubagolf]

This is direct from DAN with regard to AIR dives, which calls for a minimum of 18 hours following multiple tank dives which is apparently what you are planning. I do not know of any good research on Nitrox rather than air, but a 9 or 10 hour interval seems too short:

Revised Flying After Diving Guidelines for Recreational Diving - May 2002

The following guidelines are the consensus of attendees at the 2002 Flying After Diving Workshop. They apply to air dives followed by flights at cabin altitudes of 2,000 to 8,000 feet (610 to 2,438 meters) for divers who do not have symptoms of decompression sickness (DCS). The recommended preflight surface intervals do not guarantee avoidance of DCS. Longer surface intervals will reduce DCS risk further.

For a single no-decompression dive, a minimum preflight surface interval of 12 hours is suggested.
For multiple dives per day or multiple days of diving, a minimum preflight surface interval of 18 hours is suggested.
For dives requiring decompression stops, there is little evidence on which to base a recommendation and a preflight surface interval substantially longer than 18 hours appears prudent.

 

[TheAvatar]

Use the search funciton. There have been several spirited debates on this subject recently.

 

[Dr Deco]

Hello cavegirl:

The problem here, as I have stated before, is that dive tables will only give you general gas loadings and eliminations. If there is any heavy physical activity, there can be considerable tissue bubble formation. This will prevent off gassing. Additionally, the microbubbles can grow into true DCS-causing bubbles.

If there is a considerable degree of activity in hauling dive gear or rushing because of tight plan schedules, who knows what is actually occurring in the tissues. A flight out over the ocean is a bad place to develop DCS symptoms.

Probably one should forgo at least the second of the two morning dives. Yes, nitrox will provide some advantage.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[major111]

On a commercial plane, when does the pressure drop such that is less enough to cause potential DCS? Do they actually fly at a lower pressure than "on earth" and if so, why? I thought they had complete control of in cabin pressure (except in emergency).

Does being a DSAT (for example) "A" pressure group diver mean your N2 is back to normal (pre dive)? or do you still have some? Do we start the new dive day as a Pre A or as an A? Assume no dives for past week or more. I'm trying to understand theortical status after a surface interval that makes me an A.

Why, if you can get back to PG "A" on, again for example, the DSAT tables, in 6 hours, are you not totally free of abnormal N2? On the table, under emerg Deco, it says if you mess up, do a stop for 8 minutes and no diving for 6 hours. Isn't the implication that the unknown extra accidental N2 you absorbed by overstay of the NDL is thus gone after six hours?

Doc, if you can go question by question, that would make it easier for me to understand. Grateful in advance!

MD1

Hello cavegirl:

The problem here, as I have stated before, is that dive tables will only give you general gas loadings and eliminations. If there is any heavy physical activity, there can be considerable tissue bubble formation. This will prevent off gassing. Additionally, the microbubbles can grow into true DCS-causing bubbles.

If there is a considerable degree of activity in hauling dive gear or rushing because of tight plan schedules, who knows what is actually occurring in the tissues. A flight out over the ocean is a bad place to develop DCS symptoms.

Probably one should forgo at least the second of the two morning dives. Yes, nitrox will provide some advantage.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[BigJetDriver]

Folks,

I have specifically noted cabin pressures from 6,300 to 7,400 msl cabin altitude at aircraft altitudes of 37,000 to 41,000 feet.

You will be at these altitudes for quite some time while crossing large parts of open water.

One would be WELL ADVISED to make note of what Doc Deco has to say above, and to FOLLOW his advice! Leave as much time as you can between the last dive and your flight. It is, after all a game of statistics, and, although you might be at the low end of the statistical column, you would not want to be the one to get the "unexpected hit"!

Cheers!

(Note: Trust me on this one, folks. I've been diving and flying since Hector was a pup!)

 

[rab]

I don't know what you decided (or if you've already started your trip), but the no-fly time is based on breathing "air" while not diving. If you breathe from your Nitrox during the surface interval, then you will be lowering your N2, but you'll look funny and there's certainly no particular study that I'm quoting. After my recent set of 5 dives in a 20 hour period, my "no fly" time started at 22:10 (but I was driving back from Florida anyway, not flying). You'd be wise to skip both dives on that last day. Perhaps you can go snorkelling?

-Rob

 

[Dr Deco]

Hello major111:

"On a commercial plane, when does the pressure drop to cause potential DCS? Do they actually fly at a lower pressure than "on earth" and, if so, why?"

The pressure starts to fall in the cabin as you ascend. Your ears will begin to “pop.” The cabin is pressurized in comparison to the external pressure (at 30,000 feet), but it is less than on the ground. I suspect that this is an engineering consideration (greater internal pressure = more weight of a pressure hull). The cabin pressure is equivalent to 8,000 feet (in general).

"Does being an "A" pressure group diver mean your N2 is back to normal (pre dive)? or do you still have some? Do we start the new dive day as a Pre A or as an A? "

Nitrogen is not normal until you leave the A pressure group. It is only then that the residual tissue nitrogen is zero. [It is not actually all eliminated, but for purposes of the specific decompression algorithm, nitrogen is eliminated.] You start the day [generally] as a “pre A,” as you would call it. This assumes NDL diving, no decompression performed.

"If you can get back to PG "A" on, again for example, the DSAT tables, in 6 hours, are you not totally free of abnormal N2? On the table, under “emerg Deco,” it says if you mess up, do a stop for 8 minutes and no diving for 6 hours. Isn't the implication that the unknown extra accidental N2 you absorbed by overstay of the NDL is thus gone after six hours? "

In the PADI algorithm, the dissolved nitrogen is gone after six halftimes. The longest PADI half time is six hours (6 times 60 minutes). PADI assumes only recreational, NDL diving for this procedure. Special rules will apply if a considerable number of dives are performed.


Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[major111]

Doc, thank you for the easy to follow response!

MD1

Hello major111:

"On a commercial plane, when does the pressure drop to cause potential DCS? Do they actually fly at a lower pressure than "on earth" and, if so, why?"

The pressure starts to fall in the cabin as you ascend. Your ears will begin to “pop.” The cabin is pressurized in comparison to the external pressure (at 30,000 feet), but it is less than on the ground. I suspect that this is an engineering consideration (greater internal pressure = more weight of a pressure hull). The cabin pressure is equivalent to 8,000 feet (in general).

"Does being an "A" pressure group diver mean your N2 is back to normal (pre dive)? or do you still have some? Do we start the new dive day as a Pre A or as an A? "

Nitrogen is not normal until you leave the A pressure group. It is only then that the residual tissue nitrogen is zero. [It is not actually all eliminated, but for purposes of the specific decompression algorithm, nitrogen is eliminated.] You start the day [generally] as a “pre A,” as you would call it. This assumes NDL diving, no decompression performed.

"If you can get back to PG "A" on, again for example, the DSAT tables, in 6 hours, are you not totally free of abnormal N2? On the table, under “emerg Deco,” it says if you mess up, do a stop for 8 minutes and no diving for 6 hours. Isn't the implication that the unknown extra accidental N2 you absorbed by overstay of the NDL is thus gone after six hours? "

In the PADI algorithm, the dissolved nitrogen is gone after six halftimes. The longest PADI half time is six hours (6 times 60 minutes). PADI assumes only recreational, NDL diving for this procedure. Special rules will apply if a considerable number of dives are performed.


Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm