Deco with too less air, options from the book

[crpntr133]

Just want to drop back in and say thanks to a lot of knowledgeable people. This thread has gone from tar and feathers to calm and collected. I've learned a bit along the way. Just starting my deco adventures it never hurts to learn more or at least plant the seed. And if it does hurt then hang till it stops.

 

[MXGratefulDiver]

Ahh, i see now where the bus comment came from. I can't speak for Pete, but the way we use RD is not just in case of emergency. we use it to plan the deep stop and deco portion of the dive from beginning to end while we are on the surface and then adjust it underwater if need be.

The way RD was taught to me included a very comprehensive overview of decompression theory from its inception through the various models up to present day. Haldanean, Neo-Haldanean, Bulhlmann, VPM, RGBM, micro-bubble theory, bubble gradient mechanics, oxygen window, exponential curves, s-shaped curves, deep stops, etc were all discussed at great length.

When i compare RD with V-Planner for instance, there are similarities in run-times but differences in the shape of the deco curve. also V-Planner doesn't give deep stops, at least to my knowledge the way i've been using it. i use V-Planner because it's fun to compare schedules. in practice i have only used RD.

the planning is done with paper and pencil (at most) and i use an aladdin tec2g or suunto vyper in gauge mode. i like the tec2 bc it has a nice depth averaging feature.

the beauty of RD is that we dive the same standard gases and the same profiles over and over so you get to monitor how your body reacts to the dives while keeping variables such as gas and schedule to a constant. of course, if something isn't working then you play around with adding time here and subtracting there, etc. it also makes dive planning very easy and quick on the surface for the whole team.

having an idea of how deco *should* work, in an emergency RD will get you out of the water faster and safer (hopefully) if the fit hits the shan. this means knowing where you can shave off time, where it's best not to, etc. i have never had to do this and hopefully i will never have to but that is how it was presented to me.

RD has been used for simple "no-deco" dives and it has been used for dives to 590' and anything in between...

hope this answers your questions.

best,

Ari

That's a pretty good summary of my experience as well, although I use a Liquivision X-1 running V-Planner as my primary dive computer, and a Tec2G in gauge mode as backup. Nonetheless, I do not use the X-1 to determine my deco profile ... that's determined beforehand by running tables on a desktop, then using RD to shape the curve to my liking.

... Bob (Grateful Diver)

 

[Shearwater]

My answer would be different.

There was a Deep Stops conference last summer, and the proceedings came out this week. There were several studies done to try to establish the usefulness of deep stops on air dives. One of the studies was by the guys at NEDU. They were expecting to show that deep stops like what would be produced by a bubble model would be an improvement over an existing Buhlmann style profiles. As a side note, they generated the profiles by modifying existing Navy models and didn't use VPM or any other commercial model in the study.

In any case, by the end of the week, there was no consensus, and at best conflicting results among the studies. The more I study deco, the less I know for sure.

So I would pretty much ignore the changes in decompression risk and concentrate on operational risk. Often in emergencies the diver takes several minutes after the incident to recover their breathing rate. Running out of gas deep would be a disaster.

So I would start a slow ascent while concentrating on getting myself relaxed. I would probably skip the first stop then slow down. I would be judging my breathing rate and gas left. If possible, I would stop at 9 meters. I would certainly want to come to a complete stop at the 6 meter stop.

My thinking here is that continuous ascents tend to be curves and most physiological processes are curves rather than squares. It makes sense to me.

On the other hand, Hill (I think) tested continuous ascents to the surface with poor results.

So I would modify that with the logic that, if I have bubbles, I want them to shrink. I don't see how existing bubbles could shrink without stopping the ascent. So at some point I would stop the ascent.

Now that I am at 6 meters with quite a lot of gas left (and I am sure I have found the boat), I am going to evaluate my options. Is there someone else in the water that I can use to communicate? Could I blow my bag and start pulling on it wildly to attract attention?

If none of that worked, I would go to my 3 meter stop. Again, do any other opportunities present themselves. At this point I should have enough air for quite a long stop if I'm careful and relaxed. If I still have 10 minutes of air left I would surface and yell out my predicament, then go back to 10 feet and wait until I was nearly out of air. I would surface with some air in my tank, and immediately go on oxygen and start drinking water even if I had no symptoms.

I'm not recommending this, but it's what I would do. YMMV

Bruce

 

[Chatterton]

Ari,

This is where I get a little confused. Can you explain to me, what you mean by planning the dive with a "pencil and paper at most"? What do you go into the water with, a written profile on a slate? A collection of tables, or what?

Cheers

JC

Ahh, i see now where the bus comment came from. I can't speak for Pete, but the way we use RD is not just in case of emergency. we use it to plan the deep stop and deco portion of the dive from beginning to end while we are on the surface and then adjust it underwater if need be.

The way RD was taught to me included a very comprehensive overview of decompression theory from its inception through the various models up to present day. Haldanean, Neo-Haldanean, Bulhlmann, VPM, RGBM, micro-bubble theory, bubble gradient mechanics, oxygen window, exponential curves, s-shaped curves, deep stops, etc were all discussed at great length.

When i compare RD with V-Planner for instance, there are similarities in run-times but differences in the shape of the deco curve. also V-Planner doesn't give deep stops, at least to my knowledge the way i've been using it. i use V-Planner because it's fun to compare schedules. in practice i have only used RD.

the planning is done with paper and pencil (at most) and i use an aladdin tec2g or suunto vyper in gauge mode. i like the tec2 bc it has a nice depth averaging feature.

the beauty of RD is that we dive the same standard gases and the same profiles over and over so you get to monitor how your body reacts to the dives while keeping variables such as gas and schedule to a constant. of course, if something isn't working then you play around with adding time here and subtracting there, etc. it also makes dive planning very easy and quick on the surface for the whole team.

having an idea of how deco *should* work, in an emergency RD will get you out of the water faster and safer (hopefully) if the fit hits the shan. this means knowing where you can shave off time, where it's best not to, etc. i have never had to do this and hopefully i will never have to but that is how it was presented to me.

RD has been used for simple "no-deco" dives and it has been used for dives to 590' and anything in between...

hope this answers your questions.

best,

Ari

 

[Chatterton]

Bruce,

The last time I saw Richard Pyle, about a year ago, he complained to me that the one thing in diving to bear his name simply does not work? I have never liked deep stops (Pyle, Microbubble, WKPP, whatever) however, the point is that today's Gospel is not necessarily what we will be diving tomorrow. Some theory is sort of trendy, like fashion. This whole Deco science thing is kind of dynamic.

Cheers

JC

My answer would be different.

There was a Deep Stops conference last summer, and the proceedings came out this week. There were several studies done to try to establish the usefulness of deep stops on air dives. One of the studies was by the guys at NEDU. They were expecting to show that deep stops like what would be produced by a bubble model would be an improvement over an existing Buhlmann style profiles. As a side note, they generated the profiles by modifying existing Navy models and didn't use VPM or any other commercial model in the study.

In any case, by the end of the week, there was no consensus, and at best conflicting results among the studies. The more I study deco, the less I know for sure.

So I would pretty much ignore the changes in decompression risk and concentrate on operational risk. Often in emergencies the diver takes several minutes after the incident to recover their breathing rate. Running out of gas deep would be a disaster.

So I would start a slow ascent while concentrating on getting myself relaxed. I would probably skip the first stop then slow down. I would be judging my breathing rate and gas left. If possible, I would stop at 9 meters. I would certainly want to come to a complete stop at the 6 meter stop.

My thinking here is that continuous ascents tend to be curves and most physiological processes are curves rather than squares. It makes sense to me.

On the other hand, Hill (I think) tested continuous ascents to the surface with poor results.

So I would modify that with the logic that, if I have bubbles, I want them to shrink. I don't see how existing bubbles could shrink without stopping the ascent. So at some point I would stop the ascent.

Now that I am at 6 meters with quite a lot of gas left (and I am sure I have found the boat), I am going to evaluate my options. Is there someone else in the water that I can use to communicate? Could I blow my bag and start pulling on it wildly to attract attention?

If none of that worked, I would go to my 3 meter stop. Again, do any other opportunities present themselves. At this point I should have enough air for quite a long stop if I'm careful and relaxed. If I still have 10 minutes of air left I would surface and yell out my predicament, then go back to 10 feet and wait until I was nearly out of air. I would surface with some air in my tank, and immediately go on oxygen and start drinking water even if I had no symptoms.

I'm not recommending this, but it's what I would do. YMMV

Bruce

 

[Chatterton]

R,

I have already posted that I have never trained in RD, and never used RD on a dive. I might have massive misconceptions about RD, and how it could cure all my diving ills. I am more than willing to have you end my confusion. Can you start with two questions?

What are the advantages over a dive computer?

What do you take in the water with you other than a depth gauge and a timer?


Cheers

JC

Hi John-
Would you be willing to please share your understanding of RD since you've recommended against it here. I get the sense you've certain ... confusions. Thanks.

 

[Rainer]

Sorry if I misunderstood your earlier warnings against using RD. I had assumed you had some understanding of it before making these claims. As for your questions:

(1) Advantages: It's much cheaper (free), forces a diver to keep constantly engaged during the dive, won't lock me out, won't leave me high and dry in an emergency, is running what I consider a better algo than most computers, affords (along with standard gases) feedback about personal conservatism, has all similarly trained teammates running the same algorithm, and won't fail due to low battery or flood.

(2) My brain.

Again, I'd be happy to discuss any possible misunderstandings you have. You might not have any, I don't know. Why don't you go ahead and tell me what you understand RD to be?

Cheers.


Edit: Let me also just add, like orange_diver, I don't give one hoot how others choose to dive (as long as it doesn't affect me). If that means rocking five dive computers, go for it. That said, I *am* curious why people suggest others avoid certain strategies as you did earlier, John.

R,

I have already posted that I have never trained in RD, and never used RD on a dive. I might have massive misconceptions about RD, and how it could cure all my diving ills. I am more than willing to have you end my confusion. Can you start with two questions?

What are the advantages over a dive computer?

What do you take in the water with you other than a depth gauge and a timer?


Cheers

JC

 

[orange_diver]

Ari,

This is where I get a little confused. Can you explain to me, what you mean by planning the dive with a "pencil and paper at most"? What do you go into the water with, a written profile on a slate? A collection of tables, or what?

Cheers

JC

the rules of RD are simple enough that basic math is used to create your deco profile. once the profile is planned you can put it in your wetnotes if you want but if you run that profile a few times it becomes easy to remember.

changes are easy to make underwater if you were at depth for shorter or longer periods of time, because of the simple math formula we use. changes are made in your head to the running tally of stops/times you need to do.

i know it may sound like voodoo but i assure you it's not! and it's not complicated but there are strict rules in using it and i'm hesitant to be specific in an online forum because it may lead someone to dive that way, not knowing that there is more involved than what they read here.

if you are ever in the socal region it would be my pleasure to chat about it in person and i'm sure i can bring a few much more experienced divers as well to that table. and if you ever find yourself in monterey, CA an RD seminar from Andrew Georgitsis would be the best source for enlightenment on the subject.

best,

A.

 

[crpntr133]

Is there any place to read about ratio deco? I'm not interested in practicing it just understand more of what everyone is talking about. I did a google search and came up with a few things but nothing worth reading.

 

[Rainer]

For $75 (much less than a new VR3, Shearwater or X1) you can learn all about it here:

Ratio Deco Class - $75.00 - Unified Team Diving

It really doesn't make sense to discuss this openly in detail on the web, as without a full understanding, people are going to hurt themselves (I don't know anyone who thinks learning deco on the internet is a good idea; I'd feel the same way about openly discussing VPlanner schedules). If you want to learn more, take a class or talk in person with someone who has. For a more general discussion, however, feel free to ask any questions.