You offgas faster at 5m depth than on the surface

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

Subcooled

ScubaBoard Supporter
ScubaBoard Supporter
Scuba Instructor
Messages
2,067
Reaction score
1,199
Location
Finland
# of dives
200 - 499
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

Contributor
Messages
2,759
Reaction score
2,326
Location
Arizona
I need to take a picture of my Shearwater after a long, high O2 deco showing on-gassing on the surface (fast tissues)
 

boulderjohn

Technical Instructor
ScubaBoard Supporter
Scuba Instructor
Divemaster
Messages
28,905
Reaction score
23,844
Location
Boulder, CO
# of dives
1000 - 2499
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

ScubaBoard Supporter
ScubaBoard Supporter
Messages
1,094
Reaction score
737
Location
North Central Florida
# of dives
200 - 499
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

Technical Instructor
ScubaBoard Supporter
Scuba Instructor
Divemaster
Messages
28,905
Reaction score
23,844
Location
Boulder, CO
# of dives
1000 - 2499
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.
 

Wibble

Contributor
Messages
3,084
Reaction score
2,563
Location
UK
# of dives
500 - 999
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

Contributor
Messages
94
Reaction score
178
Location
SoCal
# of dives
I just don't log dives
The only real difference, one is recommended while the other is required.
 

dmaziuk

Contributor
Messages
8,940
Reaction score
5,316
Location
Tanoa
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.
 
https://www.shearwater.com/products/perdix-ai/

Top Bottom