DECO StOPs

[GDI]

:doctor:
I know we have visited this topic many times on this board.
The topic point this time is to explain why a diver would need to do a stop half the distance from their deepest depth to their first required deco stop depth. (If I understood the question asked of me)

Example (hypothetical) The dive plan calls for a max depth of 300 ft, based on the BT The first stop required for deco is 100 ft BUT the half stop point then would be at 150 ft for 1-2 minutes before ascending to the 100 ft deco stop.

Are there any Opinions and reasons for doing this half stop - on this approach to deco dives?

 

[MechDiver]

If I was doing a 300' dive I'd be stopping way before 100'. I don't know what you're basing your "profile" on, but it ain't very good.

As you said, yes we've visited this same thing many times and your answers are already here.

I would suggest if you want to learn about deco diving and profiles you take a class that will address all the issues and not just piecemeal items.

MD

 

[Doc Intrepid]

Here is your answer, in brief:
http://www.abysmal.com/web/library/articles/the_importance_of_deepstops.html

For a broader coverage of the topic, I suggest you print off, three hole punch, put in a 3 ring binder, and study all the articles found here:
http://www.abysmal.com/web/library/index.html

While its only a beginning lit review, Abyss offers one of the better collections of journal items and articles available. It will certainly provide a decent foundation for future questions.

Doc

 

[Karl_in_Calif]

BRW, the author of RGBM, has said here on this board that for NDL diving, a first deep stop at 1/2 max depth is "usually" ok.

For deco diving, however, he warns that there are complex interactions that determine what the first stop should be. Apparently RGBM factors all these considerations into its own calculation of what the first deep stop should be.

I think the answer is: get the RGBM software and run the profile.

Then it will crank out what the first deep stop should be for you, based on depth, mix, time at depth, etc. I dont know. I have not bought it and used it yet.

That is my non-technical summary of what I got out of his very technical advice.

This board is a gold mine of cutting edge diving technology, and BRW is one of the reasons why.

 

[Karl_in_Calif]

MechDiver once bubbled...
I would suggest if you want to learn about deco diving and profiles you take a class that will address all the issues and not just piecemeal items.

MD

This is the best advice MD has ever given. I completely agree.

 

[pdoege]

That is a great dive. Just for funsies I ran it through V-Planner using hypoxic trimix. (Why not? Its fun!)

The loss of gas scenario is pretty fricking terrifying. About 460ft^3 of trimix...

The all-goes-well profile still uses 280ft^3. Time for the cave filled 120s...

I'll need some AL80s for the travel gas and deco gas too....

Anyway, the 1st stop is at 200' and total deco time is around 80 minutes for 15 minutes of bottom time.

The actual inputs are left as an exercise for the reader.

Peter

 

[GDI]

:doctor:
I was able to read the articles you provided DOC thank -you they are good and very much in line with what I was thinking. pdoege, although I didn't give any specific BT I am glad you ran this profile. I also ran a similar profile on one of my software programs. I admit that none of my programs required me to conduct any deco stops before 100 ft with only a 15 min BT. I used both a 16/40 and a 15/45, remember all theoretical. I even ran a 18/40 mix and that didn't require a deco at 100 ft but the ppO2 was higher than I would like a 1.8. Also I did not mention what my travel gas would be, travel gas has a lot to do with determining as to what your deco stops and times would be
I encourage my students to ask WHY? and not just blindly accept things, this way I learn as much as they do (teaching is often the best way to learn) I wanted to give the best answer to my student as to why one would conduct a short stop halfway from their deepest depth to the first deco stop and as a habit if I don't feel that I will give them the best answer at the time I go looking for the best answer. On my deep dives I have not experienced any real increase in fatique or any other symptoms that would cause me to question my habits. I may not be susceptable to these affects due to my personal fitness level. I am considered very physically fit. Physical fitness and personal habits plays a big role in on and off gasing functions
Sorry MD did I not mention I am an instructor

 

[patmandu]

Hi GDI,

There's alot more to proper decompression than just inputting the numbers into a deco program and running the tables. Unfortunately the programs don't do a good job at reflecting the recent knowledge/experience that is coming out practically daily in this realm.

Deeper stops are starting to, well, get deeper as the understanding of bubble formation, etc increases. I know of many divers that are making their first brief stops at 80% of their maximum depth and then making 'quick stops' or rolling stops through these deeper depths to their first required stop.

I think we've all seen the 'bend and mend' deco schedules that call for a diver to get shallow, and then spend an inordinate amount of time at the shallower stops in order to off gas all the bubbles that are flying around the bloostream from the quick ascent.

Coming up slowly and gradually (i.e. rolling stops) starting at 80% of the max depth allows you to slowly off-gas and 'stop' (for lack of a better word) the rapid release of bubbles that you get if you just simply go up to the first required stop and then have to wait..... If that makes any sense.

Decompression diving is more art than science when put into 'real world'.

While being in good physical shape, is certainly a good thing in decompression diving. I would hesitate to be convinced that you're not doing some type of damage to your body with poor decompression techniques.

 

[pdoege]

about GDI's comment about 100' (or so) being the first required deco stop.

In particular, I was wondering what kind of 1/2 *ssed table would start the stops at 100' on a 300' dive.

So I went looking through the Navy Extreme Exposure tables and well, a 300' dive on air for 15 minutes gives about 62 minutes of deco starting at 50' (!!!)

I can see where the term bend and mend comes from.

The same dive gives V-Planner fits (1100% CNS) and the stops start at 140'. Adding some conservatism to the mix results in the stops moving down to 160'. The deco time runs around 90 minutes.

This sounds a whole lot better to me. (Well, other than the entire nutso 300' on air without a deco gas thing.)

Peter

 

[GDI]

:doctor:
I agree with what you are saying. My personal habits for deco diving include if required a deep stop and I tend to work on a running time scenario. I do not rely solely on software tables. Why I asked my question was that I have a student to whom I explained that deep stops really give the body a better chance to off gas. The process of deco diving is to reacclimate back to the surface and prevent DCI. My student wants even more information then what I've given him. Sometimes you just can't explain things to everybody and this student is one of them. If deco diving was an exact science/art we would not be having this discussion. All I want is another explaination as to why deep stops may be required and how we go about calculating them. the info I have from DOC's reply may just work for my student. But if any of you want to discuss your logic rhyme or reason as to why we should or should not do deep stops then lets hear it. I believe in deep stops when required and using a running time method to conduct deco dives. Having more than 10K logged dives in my lifetime and never a incident I am still open to suggestions and to learning.