Flying and Diving, bring me up to speed

[ColdH2Odvr]

I’ve been doing the math on diving and flying and I’d like a little input.

Conventional wisdom is, stay within recreational limits, do your 15ft safety stop and poof, you’re done. But, jump in a plane and fly to Wichita and you’re likely to get bent.

I believe most commercial flights are pressurized to 4000 feet; if this is true then any bubbles in your system will increase about 16% during the flight (Boyls law). So we wait... 24hrs. Ascending from 15 fsw after your safety stop any residual bubbles will increase in size by 45%, for this we wait 5 minutes. So, if a gradual ascent from 15 fsw is ok, why so much fuss about flying afterward? All of the non-divers on the flight are saturated at sea level and don’t get bent (or is jet-lag low grade dcs?). It seems that if you get bent on the flight home, you were probably bent when you got out of the water.

What am I missing?

Dave

 

[Rick Murchison]

Without getting into the details, the main concern isn't growth of existing bubbles, but bubble formation in the first place.
Airliners are pressurized to 8000 MSL, not 4000.
General guidance is to wait 12 hours or more after a single dive, 24 hours or more after multiple dives.
There is a table in the NOAA diving manual that gives specific FAD recommendations based on the maximum repetitive group you have reached (Navy tables) in the 24 hours preceding the flight.
Rick

 

[Alban]

Hello ColdH2Odvr

Even after you exit the water your body still contains an excess of N2 this needs time to escape , non divers obliviously do not have this problem .

I think as Rick said cabin airliners are pressurised but the tables may also allow for a problem with the airplane if this occurs pressure can be dropped to ambient levels , some computers use the mid range compartments to determine the " No fly " times as they believe this is where any problems will occur. Other computers will use slower tissue compartments or increase the specified cabin pressure which will increase the " No fly times " . It is worth remembering that it could take several days to completely desaturate from a series of dives . So the recommendations for 24 hours would seem prudent.

If on a liver board I used to try and get the most out of my last day by doing long shallow dives ,this loads up the slower compartments which tolerate the least overpressureization .

I hope this helps a little Alban

 

[notabob]

is another problem to worry about and likely one of the reasons why it is recommended that you wait after diving. General dangers of sudden and complete depressurization at high altitudes aside (i.e. at 35k feet you literally have seconds to put that mask on before you pass out), with the excess amounts of N2 in your system shortly after a dive, your blood will likely boil if the airplane happens to depressurize for whatever reason, even if depressurization is not sudden. Non-divers will likely be fine or maybe get a slight case of non-clinical DCS since the amount of N2 in their bloodstream was fairly low to begin with.

-Roman.

 

[ColdH2Odvr]

Thank you for your time and replies. Actually, I’m looking for the details. After posting my question, I started slogging through Dr. Wienke’s Basic Decompression Theory. I’ve made a few runs at his book before but never made it through (when I bought the book I took the word basic to have a different meaning than the one he intended).

So far it seems bubble growth is the issue. My initial impression is that bubble formation is a function of depth and repeated exposure. The rest of the decompression profile is dedicated to keeping bubble size small enough for the body to handle.

The only thing I’ve found specifically addressing flying after diving is under his discussion on altitude diving. He treats flying after diving as a dive at 9000ft. This would restrict the diver back to group D (Navy air tables) prior to either exiting the water at 9000ft or ascending to 9000ft (cabin pressure). The tables I’ve been able to find show 4 to 5 hours from worst case to group D. The letter designations in the Navy tables are based on the slowest compartment. You most certainly do have residual N2 built up after diving, more so after repetitive diving. The question is weather or not you’re fit to fly. The tables I’ve looked at show a relatively short time to reach group D.

As for loss of cabin pressure, sudden decompression to 35K will probably result in everyone aboard bubbling. This extreme pressure gradient will only last for a few seconds (assuming the pilots are still conscious) as they will descend rapidly to 10000 ft (or 4000ft above local terrain) to re-pressurize the cabin. [The FAA lists the likelihood of experiencing a cabin depressurization as about once in every 6.3 years flying time].

So, where am I going with this? I’ve been told flatly that you must not fly within 24hrs of diving. I’ve also been told flatly that the no fly limit is a bogus band-aid for poor diving habits. Though my bias leans toward the latter, I’m suspicious of both extremes and would like to better understand the physiological mechanisms to decide for myself.

 

[Alban]

Hi again ColdH2Odvr

I am afraid I do not have the book or the Navy tables so I am unable to comment on them but as far as I understand the Navy tables they where designed for a single exposure dive not muti diving or flying after diving. All tables are designed to bring the diver to the surface 0.79 bar with an amount of excess N2 in the tissues ( M nought value in Haldainian tables ) the tissues are supersaturated with dissolved N2 . At altitude ambient pressure is further reduced to less than 0.79 bar this may provide enough of a gradient to pull gas out of solution and form bubbles. A reduction in ambient pressure coupled with tissues in a supersaturated state will fuel bubble growth . A rapid deprezzurization as you described would cause an instantaneous decompression much like taking the top of the coke bottle !

I think it is over recent years that diving holidays and liver boards have become so popular where it is not unusual for 20 or so dives to be conducted in a week then fly home .
Remember decompression is any reduction in pressure , this includes travelling by car over high Mountains . There is a small town in the Red sea called Dahab where shore diving is popular if you are unfortunate to have problems there the nearest chamber is over a Mountain range in Sharm ! There have been cases there where divers have travelled from Sharm dived at the infamous Blue hole & Canyon ( deep dives 60 mts ) & drove back over the Mountains and suffered hits .

The advise of 24 hours before flying or taking a day off diving is sensible.

Yours Alban

 

[Dr Deco]

Dear Readers:

Flying after diving

This is a problem not yet solved except in a very general way. Divers can tell this because, while dive depths and times are very closely regulated, the time-to-fly duration is more or less just a general rule of thumb.

Considerable research has gone into the development of dive tables. This same degree of testing has not gone into dive/fly rules. This is most likely because government agencies (e.g., US Navy) are the biggest providers of money and they do not dive and fly. When a question such as this arose at NASA, we had a very specific protocol in mind and tested only that protocol. Scuba diver schedules are a varied mixture. Unless a dive computer maker would wish to test this, little will probably be done - - except for the DAN study.

Bubble Growth

If you wish to determine if a preformed gas phase exists in a liquid (of tissue), the easiest way to do this is to depressurize it and look for visible gas bubbles. All decompression bubbles in water or tissue start from preformed bubbles. These are termed the nuclei (by EN Harvey in the 1940s).

When one goes from sea level to altitude in an airplane, DCS can only result if the preformed nuclei are larger than a certain size, and in sufficient number, that pain will result. An ascent to 8,000 feet (cabin altitude) would require micronuclei of several microns in size (to overcome the surface tension = Laplace pressure). These are not present in sufficient number to cause problems. This is obvious because people do not get the bends from riding in a commercial aircraft cabin.

Diving and Bubble Growth

If you are a diver, and board an airplane with residual bubbles from diving , you may indeed have a sufficient number of microbubbles larger than the Laplace limit. When going to altitude, the will grow.

When you go diving, these will shrink, and they can be controlled to some degree. You do not have the “luxury” of compression prior to flight.

Emergency Depress

This was something I looked into for the FAA. Generally, DCS will not be a problem within a realistic timeframe up to about 40,000 feet of altitude. If you are bringing back nuclei as a souvenir of your dive trip, you might get an unexpected problem. This type of a depress is not common, but sometimes there are failures of the cabin pressurization systems.

Dr Deco :doctor:

 

[xoomboy]

Anything wrong with diving soon after you get off the plane? Say I arrived at my vacation destination around noon. Would it be a bad idea to go for a night dive?


Matt

 

[notabob]

xoomboy once bubbled...
Anything wrong with diving soon after you get off the plane? Say I arrived at my vacation destination around noon. Would it be a bad idea to go for a night dive?


Matt

Nothing wrong with that, as far as I know. Dive right in. As you descend at the end of your flight the ambient pressure increases, actually reducing the size of the potential N2 bubbles in your system, assuming you had them in the 1st place, say for example descending down to sea level after diving in a 9000ft lake.

-Roman.

 

[madmole]

Jut add my 2p's worth as I fly nearly every Monday and dive nearly every weekend

For the 2 years I've been doing this I've just calculated the flight as an ascent to an equaivalance of 10,000 ft for (safety)

Normally I limit my Sunday dive to 20 mins of deco in the morning (If I'm flying) and do a shallow 15 lounge in the afternoon (All on rich deco mixes or the rebreather)

Interestingly the VR3 calculates an actuall No fly time and I now take that as gospel and have flown right after it has cleared with no probs

The Sunnto's gives a longer No fly time and I have often flown while it was still flashing with no probs

Big grey area and I wished there was some good answers. But to me the VR3 (Proplanner) seems to have it right, but Thats only for me, your milage will vary and of course having said this I expect I'll bend next monday :upset: