Calculating deco and mix

[limeyx]

How do you know when the window is open and when it is closed?

Based on experience, guesswork and hand-waving

But the O2-window is completely separate than air-breaks on O2 (which again are simply experience and seeing what works and what doesn't -- that's where the 12/6 or 10/5 came from, what the WKPP found worked "best" for 6+ hours on O2 where they have if you listen to conventional wisdom, exceeded multiple times the current 100% CNS limits)

Fact is, that at 70 feet and 60 feet, you are offgassing some and ongassing some even with 50% nitrox, you are also breathing down your deco gas pretty quickly, so the strategy is

1) deep stops to in theory discourage expansion of bubbles (who the heck knows what really works here -- again, it's based on experience of how people felt after big dives)
2) what GUE calls "O2 window" -- whatever the heck that is, which we can really think of as a gas-switch to 1.6 PPO2. Here they used to use S-curve, where you spend a longer time at the deepest 2 stops to get the benefit of the higher PPo2, then less time in the middle where neither the PPo2 or gradient is really helping much, then longer at the shallower end where the gradient helps you
3) "deco segments" are usually approx 5 stops of 10 feet, so generally you extend the first 2 and last one, and the middle ones are short
4) based on experience, the final 100% segments are 12 on 6 off where some people have suggested that the air breaks are as effective as time on the O2 bottle, so count them in the deco time.

I dont honestly care that much if you can take every component of that and relate it to a physcial process in the body. What I care about is that it "works" and is easy to calculate and modify on the surface and under water.

 

[Bismark]

Okay Dave, if you wait until Monday I should have a pretty succinct summary put together by then. In the meantime you can google the article "Gas Exchange, Partial Pressure Gradients, and the Oxygen Window". I think you can download and print it from somewhere on the net. If not I could probably fax it to you.

Are you having trouble with the big words in a GUE Explanation........? ha, I had to say that, hope you aren't the insecure type. As far as I knew it wasn't a GUE thing and was just plain science. Hang in there until Monday. In the meantime keep the window closed, it is supposed to rain this weekend.........

PS: Dave if you don't already know the whole deal with Ratio Deco, I can provide some sources for you as well. Whether you use it or not or just plain disagree with it, I look at knowledge as pretty much value free. That's why I have manuals and books from just about every agency that I could find on these subjects. Then I make an informed decision and voila..........too scared to actually get in the water......

best,

 

[TSandM]

Bismark, I'm seriously looking forward to your report on your weekend's research!

 

[Gene_Hobbs]

Bismark, I'm seriously looking forward to your report on your weekend's research!

So am I, should be entertaining.

Please let me know if you need help finding any of the background references I put here.

 

[Bismark]

Thanks Gene. I had some of them but an exhaustive literature search can be just that.......... haven't done this since grad school. Not sure if I missed it or not........ Very interested in your foundation.....might be able to offer some help from the PNW. Can you think of anything you would be of timely and particular value? I will be contacting you by PM.

best,

 

[JS1scuba]

Actually, Joel, I think the OP wanted to know if he could reduce surface interval or no-fly time by doing his ascents on enriched mixes, which he probably can, since the same time spent underwater breathing backgas or deco gas will result in different tissue N2 tensions on surfacing. But it isn't worth it, in terms of expense, hassle factor, or the very real risk of oxygen toxicity.

Hi TS --

The simplest way for him to do that then is not by in-water 50/50 but by surface oxygen. For example if you used EAN 36 for a 100 fsw dive for 40 min you have a 3 min stop / saftey stop -- if you then did 30 minutes of pure o2 on the surface you desaturate to a level where you can now make an ascent to 9000 foot elevation. Even as little as 10 minutes allows your cieling to move up to 4000 foot elevation. This is how we are able to do some dive days and fly the same day or out here in Calif make the drive over the mountain range without getting bent.

The same concept applies to repet dives. By desaturating using surface O2 breathing you can eliminate the residual inert gas load.

For example that same 100 fsw dive for 40 min which is no stop if you do a 30 min SI your repet to the same depth / time will now require 23 minutes of stop time. If however you did that SI with 100% oxygen you can now make a repet with only 13 minutes of stop time on the repet. It's pretty agressive and while i would not suggest it be done for a variety of reasons, the math does work out for it.

US Airforce and EDU have done studies on flying after diving using oxygen breathing to lower the inert gas load quite sucessfully to get the divers to be able to fly sooner after diving. The concept works.

But in the OPs idea as you indicate doing it in-water provides other issues that may not warrant the benefit.

cheers
JDS

 

[Gene_Hobbs]

<OFF TOPIC>

Very interested in your foundation.....might be able to offer some help from the PNW. Can you think of anything you would be of timely and particular value? I will be contacting you by PM.

Thanks! We can always use help! The list of things to add grows much faster than we are able to add them these days (all of us have real jobs too). Help adding items is GREAT and does not take much time.

We also just started our first fund raiser to reach '$5k for 5k' since we have over 5,000 items in the database now. We hoped to add that to our grant from ONR so we would be able to fix some usability issues with our site as well as get some part time help from a grad student in library science. The support has been coming in slowly with 5 donors getting us 30% of the way to our goal. The next fund raiser is being planned and help with the mailing list is welcome also.

We have also hoped that we could get more divers, shops, and clubs to add our site to their web page. We have not really paid attention to our web stats (mainly because we don't know what to do with them) but we hope that our search rankings will come up this year as more people find out about us. (NEDU is even putting a poster up in their booth at 'Beneath the Sea' to show off the work we have done in collaboration with them.)

That pretty much sums up our top three priorities for this year. I look forward to your PM.

We now join you regularly scheduled thread, already in progress...