Decompressing under GF ceiling rather than set depth?

[mrki]

mrki, what I was asking was if anybody does their deco following the GF ceiling rather than the customary 20 ft and 10 ft stops, in order to minimize the 1.6 ppo2 at 20 ft. I personally don?t, and many times finish all my deco at 20 ft. However, in places where is easy to move up and keep a shallower depth (like JB for example), I do move up to finish deco there. Sorry my post wasn?t clear but I wasn?t thinking following the GF ceiling literally every foot to surface, just getting out of the 1.6 ppo2.

I was suggesting that setting last stop to 10ft and then having the choice to finish deco at either 10 or 20ft was (at least in my case) a beter alternative to having it set to 20ft and then watching those blinking red digits for the last stop.

[michael-fisch]

After a few runs involving hours of 2.8Bar O2 with 5 minute air breaks after every 20 minutes of O2, I've kind of lost any fear of doing Deco at 1.6 O2.
Sure I would not do a long dive at Ginnie on a 36% because others have tried it and died, but doing deco on 1.6 or for short periods higher is not something that I feel uncomfortable with.
What I don't like are shoulder, elbow and hip pains along with skin bends or exaustion, so if I have to run the O2 a little bit higher in order to feel great after the dive that's ok.

Michael

[Nitrogenius]

All I know is that doing the 10 foot stop gets me out of the water faster, without needing to click off that I didn't complete a stop that my computer wanted me to do. I am sure I will never know enough details about the models to know if it's OK to short change my 20 foot stop or not, but I presume there is a reason it is calculated the way that it is.

That's why I meant within the model.. That is what your computer is showing. The question I have is really if especially to that question hi PO2 + lower gradient or lower PO2 and steeper gradient is the most efficient way to spend a given time for deco.


Your computer would also let you out of the water earlier if you would instead of going to 10' at that moment e.g. change your GF hi..


The real question is: If you run into constraints that you can only spend a set amount of time between 20' and surface on oxygen where and how is that exact same time spend best from a decompression perspective. The models answer is easy that would be as soon as possible get to 10' but is that true in reality given you loose PO2 ? I doubt it.
On the other hand the question would be, what is your constraint: it has to be something like thermal stress or exhaustion etc., cause if it is gas on OC there would be additional incentive to get to 10' as you will be able to increase overall deco time that way..


Intersting one to look at from comparing it by exact same time.. Maybe some of those heat maps from the infamous deep stop discussion several years ago on RBW could give some insight. It would still stay "within" the model, but it would at least show the stress on ALL compartments, while the computer will only always have assessed on the leading compartment..

[TotDoc]

Maybe some of those heat maps from the infamous deep stop discussion several years ago on RBW could give some insight. It would still stay "within" the model, but it would at least show the stress on ALL compartments, while the computer will only always have assessed on the leading compartment..

Maybe...but you can also see the saturation of the compartments used in the computer calculation on the shearwater...it's able to be selected during the dive, and is a cool thing to watch during deco, especially after a deep dive like eagles nest, where you really get some loading in the slower tissue compartments.



This obviously provides no clear answer to the question at hand, but I didn't know if you were aware the computer had that feature or not


Here's the Shearwater video of the graph:

https://www.youtube.com/watch?v=O81vX79X_mA

[Dsix36]

Food for thought:

I understand that there are several documented cases of O2 seizures at 20'. Are there any documented cases at 10'? Is there any chance that the lessened depth (read as water pressure) would have any significant impact of it. I know that on the surface one can get away with a lot more, but is this only because of immersion and just having your face wet would have the same effect? The PO2 would be lower but it would still be O2.

[Nitrogenius]

This obviously provides no clear answer to the question at hand, but I didn't know if you were aware the computer had that feature or not

I am aware. Thanks. While this provides you some info in that regards it does not really Provider the same insight as those heatmaps in the sense of "overall" stress..

[fno]

All, I routinely race tractors with my neighbor and good friend of many years, Erik Baker since neither of us can cave dive anymore. He has forgotten more about deco than most people know. (not really, he forgets nothing). He was also my go to deco planner for many years as I was his worst case scenario tester for his models. All that being said, no matter if your last stop is 20' or 10' make sure those 20' of ascension is done in a very slow manner. In other words, Erik's advice was to move up a foot at a time by the minute. He explained at the time that the pressure gradients at these depths are the most influential on your lively hood than anywhere else in the water table. To further the point, his advice about tables was to follow whatever table or computer you want as long as you pay attention to the 20' and above stops and keep them slow, slow, slow.

[Kelly Jessop]

Sure I would not do a long dive at Ginnie on a 36% because others have tried it and died, but doing deco on 1.6 or for short periods higher is not something that I feel uncomfortable with.

Funny, 36% at Ginnie used to be standard, and that is when Ginnie really pumped. We since have gotten smarter,but remember lots of dives there, and many other people, without symptoms.

What I don't like are shoulder, elbow and hip pains along with skin bends or exaustion, so if I have to run the O2 a little bit higher in order to feel great after the dive that's ok.

If someone is having the above they are bent. Skin bends which we have blown off as nothing is actually a type 2 hit.

[mfascuba]

I set my computer (shearwater) for last stop at 10 feet, regardless of whether I'm in the ocean or in a cave. In the cave I will do my 10 foot stop at 10 foot, in the ocean I go to around 12 to 15 feet depending on how much "texture" there is on the surface. I used to have a VR3 that prominently displayed %CNS on the home screen. At 1.6 PPO2 the clock goes 2.5% per minute. It is like a freight train, 1% every 24 seconds. People have died from O2 tox/seizure, it's something I have strived to avoid. Even in Ginnie once I clear the 20 foot stop I may go to 18 feet, that reduction in depth is enough to slow down the CNS clock, the goal is to clear the 20 foot stop and get up off of the 20 foot depth. There are few absolutes in the world - My personal tolerance to oxygen seizures is unknown, but there is a limit to it. I don't want to find it.