Flying After Shallow Dives

[scubadobadoo]

I really was interested as grunzster stated. It seems the more I read and learn about decompression from this board and from attending talks, the more I realize that the science of deco is somewhat new and still evolving. I think most new divers are really surprised to realize just how much is theory and guessing. I know I was surprised. Nonetheless, I want to support DAN more now and I dive more conservatively now knowing that the tables aren't set in stone. Thanks again for those well written replies.

 

[jagfish]

To further support DepartureDiver and Charlie99s position, one can even get bent while flying without diving at all, albeit its rarer and its depends how high one is in an unpressurized aircraft.

At sea level, one has a stable amount of N2 absorbed, but if one were to decompress too quickly during flight, such as in a rapid ascent, there is a possibility of taking gas out of solution and into bubble form. This is a common complication in bailing out of a plane at altitude where the decompression is rapid and explosive.

Help me understand this...If someone is bailing out of an airplane, the door is already open, so there is no pressure. Or maybe you are talking about ejecting from a pressurized cockpit?

 

[Kim]

Help me understand this...If someone is bailing out of an airplane, the door is already open, so there is no pressure. Or maybe you are talking about ejecting from a pressurized cockpit?

Either way you'd get a sudden change of pressure. If you start in a pressurized cabin, opening the door is going to reduce the pressure very quickly. If you eject it'll be faster still. Presumably though DCS caused like this must be very rare. If you bail out you'd presumably fall quickly enough to prevent much bubble formation.

 

[Saturation]

Help me understand this...If someone is bailing out of an airplane, the door is already open, so there is no pressure. Or maybe you are talking about ejecting from a pressurized cockpit?

Yes. To further Kim's position: everyday sport sky-diving and most private pilots fly unpressurized aircraft. These planes cannot ascend fast enough to bends folks on a regular basis nor is the decompression 'explosive' i.e., sudden and with large pressure differences.

The take home message of the story is that bends is a disease based on the changes in pressure and important co-factors, not just diving in water.

 

[Charlie99]

Actually, most sport and sky-diving is done at altitudes low enough that DCS is quite unlikely. I don't have the link at my fingertips, but IIRC, below 18,000' DCS is quite unlikely. And by 18,000' you ought to be on O2 anyway.

HALO skydivers (30,000' sort of stuff) do indeed prebreathe O2 to avoid DCS.

 

[DEEPLOU]

going from earth surface to outer space now I am not that well educated, but it seems to me you are going from 1 ATM to 0 ATM.

HALO skydivers (30,000' sort of stuff) do indeed prebreathe O2 to avoid DCS.

At that hight, don't they breath the O2 because at that hight the air is so thin, PPO2 so low, that it cannot support life?

 

[Charlie99]

At that hight, don't they breath the O2 because at that hight the air is so thin, PPO2 so low, that it cannot support life?

In addition to breathing while actually doing the jump, they also prebreathe O2 for a while before getting up to altitude.

Typical HALO briefing: http://halojumper.com/halobriefing.html

Jumps over 22,000 will require a 30 - 45 minute pre-breathing period to flush the nitrogen from our blood stream. Jumpers will begin breathing 100% 02 (ABO) in the plane for 30 minutes and after take off continue breathing 100% 02 (ABO) all the way to exit altitude for a total of 50-55 minutes...........NOTE: If you are pre-breathing for a higher jump and you remove your mask prior to exit altitude, you will negate your nitrogen purge and could suffer symptoms of the Bends. Just one breath of regular air will return your blood levels close to normal and you may need to abort your jump for safety reasons.

I won't vouch for the accuracy of the "one breath will return your blood levels close to normal", but did meet a pilot at Holloman AFB that got bent during an explosive decompression drill. It was a rather amusing tale in that after he got bent, he went to the clinic, was misdiagnosed and released. Then he and his girlfriend headed off to Las Cruces. Only later that evening did another doctor review the case. It took a massive manhunt to retrieve him and get him recompressed. He doesn't admit to going off the O2 during his prebreathe period, but did say that he didn't really take it that seriously until after the incident. OTOH, the profile of the explosive decompression drill is pretty nasty.