You offgas faster at 5m depth than on the surface

[Akimbo]

Now that you say it, it's clear. ppO2 max.

Never confuse simple with obvious or facts with understanding. Sometimes all it takes is looking at something from a different perspective for the latter to occur. Glad I can help.

 

[Subcooled]

Never confuse simple with obvious or facts with understanding. Sometimes all it takes is looking at something from a different perspective for the latter to occur. Glad I can help.

I absolutely love your comments
- even if they would highlight my mistakes. Or, perhaps that's the very reason.

I did learn some things from some books (Mark Powell's book was the most advanced I ever read about diving),
but as those things were not frequently applied, I forgot a lot.
This does not happen to people who have done demanding dives as a profession.
Your insight is golden.

 

[broncobowsher]

I need to take a picture of my Shearwater after a long, high O2 deco showing on-gassing on the surface (fast tissues)

 

[boulderjohn]

I need to take a picture of my Shearwater after a long, high O2 deco showing on-gassing on the surface (fast tissues)

If you take the picture just before you surface, you will see that it will be on-gassing at the surface.

 

[EFX]

On a recent flight I looked at my Shearwater Perdix and it was flashing red showing a ppO2 of 0.16 at cruising altitude. You add a mask on top of alcohol and dehydration and no wonder some people are going nuts.

 

[boulderjohn]

On a recent flight I took I looked at my Shearwater Perdix and it was flashing red showing a ppO2 of 0.16 at cruising altitude. You add a mask on top of alcohol and dehydration and no wonder some people are going nuts.

If I did not change the default settings on a Shearwater before my normal dives in colorado or New Mexico, I would get a low PO2 warning breathing air on the surface.

 

[Akimbo]

- even if they would highlight my mistakes. Or, perhaps that's the very reason.

That was the opposite of my intent. I apologize if that was the perception. My intent was that everyone gains from alternate perspectives and nobody can be a master of every concept.

 

[Wibble]

I'm not so sure the effect of extending a safety stop on air or nitrox will have as little effect as you imply. I believe there have been studies (DAN?) that attempted to compare the effects of various safety stop lengths on bubble formation. If I recall, longer stops were found to reduce bubble formation but with diminishing returns, so the recommendation continues to be for a 3-minute safety stop.

For technical dives, yes. Not sure about NDL dives though — they keep telling us that it’s a safety stop, not a decompression stop. Apparently there’s a big difference (yes of course there is!)

 

[DAJ]

The only real difference, one is recommended while the other is required.

 

[dmaziuk]

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?

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.