Decompression risks in aviation

[NJMike]

Very interesting. I looked at the links that GH provided but they all pretty much say the same thing - all based on cabin pressures up to 18,000'.

There was one 128 page report of a study funded by DAN at Duke University. But I'm only on page 10 and I don't think it will cover the rapid decompression scenario anyway.

Rick, thanks for your feedback.

 

[Gene_Hobbs]

There was one 128 page report of a study funded by DAN at Duke University. But I'm only on page 10 and I don't think it will cover the rapid decompression scenario anyway.

It will not cover rapid decompression but you will be hard pressed to find much like what you are asking. The Air Force has rapid decompression literature and data but none that I am aware of with dives first. The main focus of most of that work was hypoxia and not DCS. There is some interesting case reports on rapid decompressions in Aviat Space Environ Med. but you have got to read a lot to find them (PubMed). WWII publications might be worth a look too. They did a bunch of research then we could not repeat in humans now (nor is there really a need to.).

And, for the record, the majority of the funding for the "Military Freefall After Diving" 25,000' trials did come from the Navy. They deserve credit for their part.

Good luck on your quest...
G

 

[Dr Deco]

Hello NJ Mike:

As is true with most cases of DCS, it will require time for the dissolved nitrogen to diffuse to the microbubbles. This will depend on the “dose” of nitrogen, i.e., the decompression [change of pressure].

In those pressure changes involving passenger airliners, this is ten to twenty minutes at 35,00 feet. During this time, the plane will have [hopefully] been able to descend to about 10,000 feet. At this level, the problem of DCS is nil.

If you were one of those individuals who like to dive and then fly with “wet hair” as they call it, these time limits might be too large, and you could be in for real trouble.:no

Dr Deco :doctor:

 

[Rick Murchison]

As far as "research" on explosive decompression, there's plenty of anecdotal data... As a normal part of a PMCF (Post Maintenance Check Flight) on military fighter and attack aircraft we'd dump cabin pressure at 40,000 feet, which created an explosive decompression event - took about 1 to 2 seconds to reach ambient. You had to make sure your ears were clearing easily and your oxygen mask was on nice & tight for the dump, but it was routine. We'd leave it off for a minute or two while we checked some stuff and then repressurize. To my knowledge no one ever took a DCS hit doing this.
Rick

 

[Charlie99]

As far as "research" on explosive decompression, there's plenty of anecdotal data... As a normal part of a PMCF (Post Maintenance Check Flight) on military fighter and attack aircraft we'd dump cabin pressure at 40,000 feet, which created an explosive decompression event - took about 1 to 2 seconds to reach ambient. ..... We'd leave it off for a minute or two while we checked some stuff and then repressurize. To my knowledge no one ever took a DCS hit doing this.
Rick

OTOH, I did meet an Air Force pilot that got bent doing his annual (?) explosive decompression drill in a chamber at Hollomon AFB. He was the neighbor and buddy of another officer I was visiting.

I can't absolutely vouch for the reliability of the story, but it did make for an amusing story while playing crud with a bunch of American and German pilots in the O-club.

Normally they pre-breathe O2 for a while before the exercise to offgass N2 before the explosive decompression. He went off it for just a couple of minutes. The drill went normally, but a few hours later he starting getting tingly feelings and sore joints. He went to the infirmary, was examined, told "take 2 aspirin and come back tomorrow" or some equivalent. He then took off to Las Cruces for a night out with his girlfriend. A while later, the doctor in charge heard about the case, freaked out, and eventually started a massive manhunt to find and treat him. He was flown in a pressurized plane to some other base for a hyperbaric chamber treatment which completely resolved the symptoms. The medical staff then got some training about the potential of DCS in pilots that had gone through the explosive decompression drill.

Charlie Allen

 

[NJMike]

All very interesting info. At dinner tonight, I had a soft drink. As I unscrewed the top, I was able to see the gas come out of solution and bubble up to the surface. I only unscrewed the top slightly, so the bubbling was controlled.

But as we all know, unscrewing the top quickly will result in a lot more bubbles forming...and a lot quicker. Also, if it has been shaken, the result will be more dramatic.

That's what caused me to wonder in the first place. Even if the change from 8000' to 36,000' is a small change in ATA's, the RAPID change is what made me wonder...like unscrewing the top on the soda bottle too quickly, know what I mean?

 

[Charlie99]

Even if the change from 8000' to 36,000' is a small change in ATA's, the RAPID change is what made me wonder...like unscrewing the top on the soda bottle too quickly, know what I mean?

A lot of decompression depends not on the absolute change in ata, but the RATIO of pressure changes. 8,000' to 36,000' is a fairly large pressure RATIO.

For example, JS Haldane's rough approximation of decompression limits was that one could change pressure by a factor of 2 ---- from 33' to the surface, without getting bent.

You also have a 2 to 1 pressure change going from sea level to 18,000'. Crews of the unpressurized bombers of WWII didn't get DCS at 18,000', but it did become a problem by the low 20,000' range --- just over a 2 to 1 ratio.

 

[ArcticDiver]

Remember half the earth's atmosphere is below 18,000ft and the rest is below approximately 100,000ft(Standard Atmosphere Conditions). So, the pressure differentials aren't that awfully great when compared to water.

There was a pretty good discussion on this some time ago:

http://scubaboard.com/showthread.php?t=114913