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.
Thanks!
El Orans
June 19th, 2009, 04:43 AM
Well, here's a non-medical opinion.
Given that decompression is still a rather inexact science, I'm quite happy to wait 24 hours before boarding my flight.
I also use a Suunto (well known for its conservatism).
There's always another dive.
Gen San Chris
June 19th, 2009, 05:46 AM
24 hours should keep you safe but PADI says 12 hours + after a shallow dive!
Glock Diver
June 19th, 2009, 08:07 AM
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.
ScubaRich
June 19th, 2009, 10:24 AM
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.
adelman
June 19th, 2009, 10:46 AM
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.
Mr Carcharodon
June 19th, 2009, 06:31 PM
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.
HowardE
June 19th, 2009, 06:47 PM
Returning to altitude after diving.
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.
Mr Carcharodon
June 19th, 2009, 08:31 PM
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.
shark_tamer
June 19th, 2009, 08:40 PM
Personally, 24 hour " no dive " after ANY dive .....
And as El Orans did say
There's always another dive.
:coffee:
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HowardE
June 19th, 2009, 08:45 PM
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.
To use a dive table...You round down to the next deepest depth.
The US Navy (NOAA's table is the same BTW) tables start at 40 fsw. Theoretically, you can't get bent at 10,20, or 30 feet. Since you're at a depth less than 2 atmospheres. However, for safety, round any dive shallower than 40 feet - to 40 feet. That's how tables work ;)
Mr Carcharodon
June 19th, 2009, 09:08 PM
To use a dive table...You round down to the next deepest depth.
The US Navy (NOAA's table is the same BTW) tables start at 40 fsw. Theoretically, you can't get bent at 10,20, or 30 feet.
A lot of the rules associated the tables are there to make them simple to use, but that does not necessarily make them safer. In this case rounding 15 feet to 40 is not safer, and using a 12 hour surface interval is not safer than getting right on the plane. But establishing a simple rule that people can remember may be safer than a complicated one that many people get wrong.
HowardE
June 19th, 2009, 09:31 PM
I don't like tables either. I use my computer... and I wait 12 hours. But if people want something to go by other than arbitrary rules like 12 hours, or 24 hours. There's a table.
Zippsy
June 19th, 2009, 10:51 PM
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!
Spot on!
H2Andy
June 19th, 2009, 11:22 PM
DAN suggests 12 hours for a single dive, or 18 hours for multiple dives or multiple days of diving ... depth of the dive is not a consideration
(that doesn't include decompression dives)
DAN Divers Alert Network (http://www.diversalertnetwork.org/medical/faq/faq.aspx?faqid=54)
my practice is not to fly for at least 24 hours after my last dive. that means that on dive trips, the last 24 hrs prior to flight departure are for land-based fun only
Walter
June 20th, 2009, 08:24 AM
Returning to altitude after diving.
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.
Excellent info, Howard. I do believe it should be stressed that this chart can only be used with US Navy based dive tables. Do NOT use it with PADI's RDP. It is not designed for that. The RDP's letter groups are not the same (A does not equal A) as the letter groups for the US Navy dive tables.
Theoretically, you can't get bent at 10,20, or 30 feet.
I'm told you can get bent if you dive to 18 feet or deeper and then return to the surface. If you reduce pressure to less than sea level, you can get bent even if you've never dived. That's why NASA conducts research on decompression sickness.
TSandM
June 20th, 2009, 10:25 AM
The problems with decompression are related to the amount of nitrogen absorbed, and the rate at which the ambient pressure is dropped. The models of nitrogen dynamics use a variety of compartments with different absorption and off-gassing half lives, and assign a value (M-value) to the maximum nitrogen tension acceptable before excessive bubbling begins.
The question is whether, during a typical recreational dive to 15 fsw, enough nitrogen can be absorbed into the longer half-life compartments to cause symptoms with an ambient pressure drop from sea level to 8 or 10,000 feet. I'm quite sure that, with SATURATION diving to 15 fsw, it might be possible to absorb enough nitrogen into slow compartments to get symptoms in areas like joints/synovial fluid, which are poorly perfused. But I suspect it probably isn't possible to do this during the time a typical scuba tank will last, even at those shallow depths.
If you think about it, you have to get out of the water, doff and pack or return gear, get home or to your hotel to clean up, to the airport, go through the ridiculous security system and the boarding -- I can't imagine anybody who isn't talking about private aviation being able to go from the water to an airplane in less than four hours. This is going to empty compartments with half-lives less than 40 minutes, and will have largely emptied a 60 minute compartment. Any compartment with a longer half-life than that (say a 120 minute compartment) will be only partially or minimally saturated, because of the limited time of a typical recreational dive (expecting that to have been no MORE than 90 minutes, and more likely to have been 60). Although the M-values for longer half-life compartments are far lower than for the faster ones, I think you'd still be far from them, especially given that you have significant offgassing time.
Although I don't want to tell someone to go against generally accepted practice, I can tell you that I, personally, wouldn't worry at all about flying after such a dive.
smellzlikefish
June 20th, 2009, 02:25 PM
"Theoretically, you can't get bent at 10,20, or 30 feet"
Theoretically, you can get bent at 15 feet, believe it or not. You'd have to stay down there a while, I don't imagine it would kill you, and I don't think everyone would experience it, but its possible.
As far as flying, the different organizations offer different opinions, but what about just adding 33 feet (1 atm) onto whatever your dive profile? The plane won't decompress past 1 atm, so in theory, and this is only my opinion, if you dive at 60 feet with the time you would normally use at 100, you should, in theory, be okay to fly shortly after. Of course, in theory, communism works, too. Please don't try this on my advice alone.
Web Monkey
June 20th, 2009, 02:56 PM
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.
The real question is "Do you feel lucky?"
If you don't dive too deep or too long, aren't too dehydrated, or have too much nitrogen in you and the plane doesn't change altitude to rapidly and the pilot maintains cabin pressure at what you're expecting and doesn't have any sort of depressurization problem and your computer is actually mapping your personal offgassing properly, then "maybe".
Even if you do everything right, there's no guarantee that you won't get bent.
Personally, I'd use the last day to wake up late, have a nice breakfast around 11am, take a nap or two and enjoy a great sunset.
Terry
Web Monkey
June 20th, 2009, 02:59 PM
The plane won't decompress past 1 atm, so in theory, and this is only my opinion,
Planes are only pressurized to 8000', which is about .75 ATM.
Terry
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Mr Carcharodon
June 20th, 2009, 03:50 PM
"Theoretically, you can't get bent at 10,20, or 30 feet"
Theoretically, you can get bent at 15 feet, believe it or not.
Really, based on what?
I do not think any of the dissolved gas models support this. And remember those models are grounded by animal and human subject studies. They are a bit more than just theory. If there is a basis for this statement I would like to hear it.
Also at least the VPM version of the bubble models does not support this. I ran VPM for a 25 foot dive for 3200 minutes (a saturation dive) and it shows no required decompression. The pressure swing from 25 feet to surface is about the same as going from 15 feet to a plane at altitude. I do have an older version of VPM. It would be interesting to repeat this in VPM-B, RGBM and decoplanner.
Glock Diver
June 21st, 2009, 12:15 AM
Wow! Some good responses here, thanks.
I have a buddy who is flying down to Ft. Lauderdale for a long guys weekend of diving in South Florida. Mostly we'll be shore diving, but will probably do a charter dive on Saturday. Since he flies back Monday a.m., and will only have 3 full days to dive (Fri, Sat, Sun), I'm just trying to see if doing shore dives (15' fsw average) would be safe on Sunday. According to the tables, we'll be fine observing a 12-hour NO-FLY window.
