You offgas faster at 5m depth than on the surface

[boulderjohn]

IIRC the theory behind it is that smaller bubbles pass from blood into the lungs faster. I've only seen it mentioned in various write-ups on bubble models, I don't remember seeing any references to actual studies.

Agree. I have only seen this as what I would call an hypothesis, since it has not been tested and does not rise to the level of the scientific concept of a theory.

 

[dmaziuk]

Agree. I have only seen this as what I would call an hypothesis, since it has not been tested and does not rise to the level the scientific concept of a theory.

Well there is VVAL18 that says gas kinetics becomes linear at some point but I don't remember what the cited reason was, and Rubicon site is still down.

Even if you do off-gas "better" at 5 msw, I'm not sure it makes it "safer" to drive 800 m up.

 

[Alaskan Scuba Dude]

I was diving with someone the other day who had to drive to an altitude of about 800m afterwards. In order to reduce his risk he decided to extend his safety stop on the final dive from 3 minutes to 7. This was at 5m.

He reckoned that you offgas faster under slight pressure. Something to do with increased circulation and having a greater number of small bubbles instead of a small number of large bubbles.

Does anyone agree with this? Any articles or science papers that have tested this?

Boyle's law - Wikipedia

en.wikipedia.org

 

[PBcatfish]

Altitude diving is a specialty. It's covered in the US Navy Dive Manual. The no decompression limits are adjusted for the post dive altitude by doing a SLED calculation. I think that SLED stood for sea level equivalent dive, but that is just off the top of my head. I haven't done any altitude diving in more than 10 years & It's been at least as long since I've looked at that book.

 

[tursiops]

Altitude diving is a specialty. It's covered in the US Navy Dive Manual. The no decompression limits are adjusted for the post dive altitude by doing a SLED calculation. I think that SLED stood for sea level equivalent dive,

Correct.

 

[tarponchik]

I was diving with someone the other day who had to drive to an altitude of about 800m afterwards. In order to reduce his risk he decided to extend his safety stop on the final dive from 3 minutes to 7. This was at 5m.

He reckoned that you offgas faster under slight pressure. Something to do with increased circulation and having a greater number of small bubbles instead of a small number of large bubbles.

Does anyone agree with this? Any articles or science papers that have tested this?

I'd say that extending safety stop makes sense after a deco dive or for people with special conditions, like hole in the heart. But for the later driving to 800 m this should not matter.