Time adjustment for deco stop on 100% O2 vs. air (21%)

[vicp]

I remember hearing or reading somewhere (but can't find it now) on how much to cut down time for deco stops at or above 20' that are planned on air but using 100% O2 instead.

For instance, if using Deco air tables but plan on using 100% at 20' or above, how do you adjust the times for those stops?

Or if using V-Planner in evaluation mode which does not allow 100% until you buy the key (you can use up to 50% in evaluation mode but then all the other deco stops (to 40') will use the 50% deco gas). Suppose you are diving on air and you set your shallowest deco stop to 20' (or even 10'), how do you adjust the air deco time for 20' if you plan on using 100% there?

If someone even has formula or algorithm for this, it would be greatly appreciated!

- Thanks

 

[boulderjohn]

Your profile does not list the training/courses/certifications you have for decompression diving. I mention this because you will find a lot of people who could answer your question will be hesitant to do so for fear of helping an untrained diver get in over his head.

 

[Divin'Papaw]

Your profile does not list the training/courses/certifications you have for decompression diving. I mention this because you will find a lot of people who could answer your question will be hesitant to do so for fear of helping an untrained diver get in over his head.

+1 get the training and you'll know. That's what tech courses are for. You clearly haven't gotten the proper training or you wouldn't need to ask the question.

Moving into decompression diving without proper training is incredibly foolish. It's just not worth the risk. If you going to move into that type of high risk diving, do it right. Your life is far too valuable.

 

[vicp]

Thanks for all the admonition guys - appreciate the concern but this is not proprietery knowledge. Didn't realize I needed to prove my creds to get a question answered. I do not typically update profiles.

FYI I am finishing Advanced Nitrox/Deco Procedures (2 more dives) and starting full cave this weekend. I am certified also for VIP, O2 service, reg rebuilds, Nitrox and Trimix blending, DiveCon, Divemaster, cavern, intro to cave, etc., as well as have a degree in Ocean Engineering.

The reason I ask this is that i have been doing practice deco dive planning for my class, but do not have the full version of V-Planner yet and am using the air tables along with the demo/eval version of V-Planner. We have been setting the shallowest stop at 20' and have been doing it on 100% O2. We have gotten the profiles from the instructor's full V-Planner but he is not available at the moment.

The questions remains, what do you use to adjust air deco time to 100% for planning purposes, other than relying on software or just diving your computer. I can probably dig through the back of Mark Powell's book for an appropriate algorithm to program, but was also trying to find out what other people use.

Thanks

 

[mathauck0814]

I am certified also for VIP, O2 service, reg rebuilds, Nitrox and Trimix blending, DiveCon, Divemaster, cavern, intro to cave, etc., as well as have a degree in Ocean Engineering.

None of these are decompression or technical diving certifications; which explains why you're asking the question.

The questions remains, what do you use to adjust air deco time to 100% for planning purposes, other than relying on software or just diving your computer. I can probably dig through the back of Mark Powell's book for an appropriate algorithm to program, but was also trying to find out what other people use.

We use v-planner and the knowledge we received in our training. Speak with your instructor.

 

[Superlyte27]

Roughly 1/2. 14 minutes on Air, figure 7 minutes on O2. But it would be stupid (possibly deadly) to not verify this with tables.
Who's your AN/DP & Cave Instructor?

I ask because if you haven't learned how to do this yet, or if he hasn't provided you with tables to do this yet, I want to be able to warn other students.

 

[Divin'Papaw]

FYI I am finishing Advanced Nitrox/Deco Procedures (2 more dives) and starting full cave this weekend. I am certified also for VIP, O2 service, reg rebuilds, Nitrox and Trimix blending, DiveCon, Divemaster, cavern, intro to cave, etc., as well as have a degree in Ocean Engineering.

So you've spent all that $$$ on training and gear and now you can't afford $85 for a registration key to V-Planner??? Register the software!

 

[Superlyte27]

I wouldn't. There's better stuff out there. Just buy a Predator or Petrel and be done with it.

 

[Ste Wart]

Try this:

MV-Plan the Java Dive Planner

It's free Dive Planner. I have it but I don't use it. No real reason the profiles are the same as any other. Have a play.

 

[vicp]

Roughly 1/2. 14 minutes on Air, figure 7 minutes on O2. But it would be stupid (possibly deadly) to not verify this with tables.
Who's your AN/DP & Cave Instructor?

I ask because if you haven't learned how to do this yet, or if he hasn't provided you with tables to do this yet, I want to be able to warn other students.

Thanks Peter, roughly half is what I remember from one deco ground school. I just wanted to corraborate this from others rules of thumb, tables and/or calculations.

I actually took the ground portion twice with two different instructors, did not dive with the first, am diving with the second. In the first class we used the air tables, added deep stops and cut the stop time in half when using 100% at 20' and above. For Nitrox, we used EAD, rounded up in the air tables and cut 20' deco on 100% in half. In the second class we used V-Planner. The only tables that I have seen and that are in the TDI books are the air decompression profiles, including the TDI plastic table that I carry. I have not seen the IANTD tables, but they may have the information I am looking for. Maybe you can tell me what other tables list bottom and deco gasses with varying FO2s.

As far as what instructors I have used, that does not matter, as all are very well known in cave diving circles and I have no desire to cast aspersions on any of them.

None of these are decompression or technical diving certifications; which explains why you're asking the question.



We use v-planner and the knowledge we received in our training. Speak with your instructor.

Sounds like you don't have a clue.

So you've spent all that $$$ on training and gear and now you can't afford $85 for a registration key to V-Planner??? Register the software!

DH - you can also stick your advice "you know where." I did not ask anyone's opinion what I should spend my money on.

I am waiting on the Dive Rite Workbench software, having bought a DR Nitek Q, and evaluating V-P, which I most likely will purchase. I ask questions to acquire information and to find out what others do. Any conclusion I come to and folliow will be vetted somewhat scientifically (my profession) to my satisfaction. I have enough education (PhD, etc.) to do research and can write my own software if neccessary. Yours and other's self righteous, "snarky" comments only show how limited your knowledge really is.

---------- Post Merged at 05:26 PM ---------- Previous Post was at 05:01 PM ----------

For others with helpful replies, thank you. My interest is not just a software solution, but also the models, rules-of-thumb used, and the reasoning behind them.

I'm sorry, but instructors are not really the definitive authority on things as they can have very divergent opinions and usually teach the agency bottom line, if they remember it.