Rise and Fall of the Bubble (Model) ?

[Carlos Danger]

During the intermission I just wanted thank those who helped contribute to the informative content here. While I am not a technical diver, I have found this to be a fascinating thread. I learned so much from Dr Mitchell's presentation, as well as many of the subsequent postings. This has brought clarity to some murky areas of my understanding of the history and the science, and as a recreational diver I feel much better informed on the subject.

 

[Jay]

I learned a HUGE amount from the tangential stuff on those threads, it may not be the most pleasant reading experience but patience in wading through the threads is quite rewarding.

Agreed and from a newbie’s (to algos) perspective I learnt a lot when Ross was here.

 

[lermontov]

a deco model is like a school of fish all gathered close together to avoid a predator, the bigger the number the better statistical odds you have of not getting eaten and when one does get eaten we can keep adjusting just being grateful it wasnt me

 

[J-Vo]

I'd like to think this perspective makes it into a 3rd edition of "Deco for Divers":

Delving deeper into deep stops

 

[tridacna]

a deco model is like a school of fish all gathered close together to avoid a predator, the bigger the number the better statistical odds you have of not getting eaten and when one does get eaten we can keep adjusting just being grateful it wasnt me

Thank you Professor Darwin.

 

[boulderjohn]

I'd like to think this perspective makes it into a 3rd edition of "Deco for Divers":

Delving deeper into deep stops

That's a nicely written summary of what I think appears to be current thinking.

 

[dmaziuk]

Doesn't you body use oxygen faster than it can bubble out of solution?

Are there deco tables for oxygen?

1. Maybe, but it only uses X amount of it, usually quoted number is "about 5%". And I don't believe it goes up with pressure, it's still "about 5%" at 40 metres down.

The model doesn't count everything you have in the mix: if it's 21%, the model says there's 79% of "inert gas" that bubbles. In EAN32, there's 68% "inert gas". And it is multiplied by the pressure in the equations, so at 40 m your body is "using up" all of (32*5)% O2 if you believe the model.

2. I was able to find one paper from last century that claimed oxygen seems to be a little "less bubbly" than nitrogen. Nothing else.

 

[rjack321]

Doesn't you body use oxygen faster than it can bubble out of solution?

Are there deco tables for oxygen?

Yes for all practical purposes metabolism takes care any O2 bubbles which might actually form. If that wasnt the case then the hours and hours spent in a chamber at 3ata for a Table 6 extended (on oxygen) would get you bent - but they don't. Getting bent from O2 is like getting bent from IBCD. It theory it can maybe happen in extreme or convoluted situations, but its not something you need to plan for in scuba diving.

(IBCD is real for commercial divers in helium atmospheres or if maybe you decided to do a OC switch to air as a deco gas far deeper than anyone dives air anymore)

 

[dmaziuk]

... the hours and hours spent in a chamber at 3ata for a Table 6 extended (on oxygen) would get you bent - but they don't.

And people would get bent on nitrox left and right. And if the "wrong Helium physics mattered", they'd get bent on trimix all the time too. That's the point: a model isn't the real thing, it just models relevant aspects of the real thing close enough for the purpose. Which in our case is not getting bent, and relevant aspects are time and pressure and breathing mix.

 

[GJC]

1. Maybe, but it only uses X amount of it, usually quoted number is "about 5%". And I don't believe it goes up with pressure, it's still "about 5%" at 40 metres down.

The model doesn't count everything you have in the mix: if it's 21%, the model says there's 79% of "inert gas" that bubbles. In EAN32, there's 68% "inert gas". And it is multiplied by the pressure in the equations, so at 40 m your body is "using up" all of (32*5)% O2 if you believe the model.

2. I was able to find one paper from last century that claimed oxygen seems to be a little "less bubbly" than nitrogen. Nothing else.[/QUOTE
I thought you use all of the O2 dissolved in your body and all that is bound to hemaglobin in about 5 to 10 min if you stop breathing

Yes for all practical purposes metabolism takes care any O2 bubbles which might actually form. If that wasnt the case then the hours and hours spent in a chamber at 3ata for a Table 6 extended (on oxygen) would get you bent - but they don't. Getting bent from O2 is like getting bent from IBCD. It theory it can maybe happen in extreme or convoluted situations, but its not something you need to plan for in scuba diving.

(IBCD is real for commercial divers in helium atmospheres or if maybe you decided to do a OC switch to air as a deco gas far deeper than anyone dives air anymore)

What is IBCD?