Flying after diving... what if it's shallow?

[HowardE]

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]

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]

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]

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]

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

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]

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:

http://www.ndc.noaa.gov/pdfs/AscentToAltitudeTable.pdf

http://www.ndc.noaa.gov/pdfs/NoDecoAirTable.pdf

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]

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]

"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]

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]

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