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

[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.

[patmandu]

GDI,

If I came across as accusatory or anything of the like, my apologies. I'm here to learn and try to share what I've been taught. That being said.

I think any discussion on decompression between divers is a wonderful thing, and should be looked upon as an educational opportunity as well.

I don't doubt that your deco works for you and it's what you believe is right for you. My reservations are that: Maybe someone will read your post and decide that your deco approach is the right for them too, and go out and get hurt (I know they shouldn't do that from reading stuff on the internet, but there are alot of people out there...). Anyways, my second reservation is that decompression theory is an evolving one, and even if something works well for you, maybe it's not 'best' for you, if that makes sense.

I'm more than willing to discuss deep stops (with my limited knowledge) and why I think they make/do not make sense. I try to look at decompression with a common sense approach.....i.e. deep stops and slow ascents seem to make sense if you want to limit cascading of bubbles coming out of solution.

As for your student, have they read the bubble mechanic stuff that erik baker has written?

Here's a few links that may help to at least describe/introduce the notions:

ftp://ftp.decompression.org/pub/Baker/Deep%20Stops.pdf

http://www.decompression.org/maiken/VPM/Bubble_Model_Program_Info.htm

http://www.decompression.org/maiken/Bubble_Decompression_Strategies.htm

[GDI]

:doctor:
Patmandu and the rest of you I am sorry if my words are coming accross as harsh, that is not my intent. Deco diving is a very wide based subject with so many avenues to look at. By no means should this board be the sole source of information. patmandu I too continue to learn so much more about deco each and every time I look at it. I have seen alot of changes in the various techniques since my first work with bubble studies at DCIEM (now DRDC) We have not even touched the surface. The navy tables have been a base for many years for many divers BUT the navy also has a large man pool to complete their task and they also have the chambers on site or close by. I see the differences in V-planner, Z-Planner, Voyager, GUE and a few others out there. Some are similar more so than others and I suspect that the program designers each have influenced the parameters of their respective software.
However this thread like so many has given me the method to which I will be able to answer my students question. I enjoy students like this. If we do look back at my original question it had nothing to do with using tables/software but rather technique and reason. The Question(s) again is WHY do we do deep stops and why are they a good thing to do and how do we know when to do them or not to do them? Note that in theory I could go into decompression in only 33 ft if I had the gas. I can do the same at 130 ft and so on. All of this can be done by diving by tables. The purpose of deco diving is to "under control" reduce the gases pressure gradiant on the various tissue groupings of the body and to release these gases through the bodies own physiological means - diffusion out through the skin and respiratory system for example. IMO we do deep stops to allow the body to have a pressure gas tension release resting phase during the ascent reacclimating the body back to acceptable surface tension tolerances. These tolerances of course are particular to the individual and can vary from day to day. Dive tables at any level cannot factor the individual diver let alone on a day to day basis. They are designed to accomondate the average population characteristics of divers. Case in point the US Navy tables are suited for young very fit divers and a man pool of resources and really shouldn't be used for the average civilian diver. Now Why do you do or not do deep stops?

[IndigoBlue]

patmandu once bubbled...

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.


Why do you believe it is 80%?

Is this an empirical finding? By whom?

[GDI]

:doctor:
Welcome Indigoblue and thank you for asking "WHY"
and what is your opinion on deep stops?

[IndigoBlue]

GDI once bubbled...
:doctor:
Welcome Indigoblue and thank you for asking "WHY"
and what is your opinion on deep stops?

I am still getting caught up on all the major posts on this site over the past 3 years. These contain some very interesting information.

I do not really have a personal opinion of deep stops. From the sound of the previous posts here, that subject is in flux. So I want to know what particular study helps Patmandu to settle upon 80%.

I have heard 50%, which Pyle made famous for deep air and collecting fish. I have also read that nitrogen and helium act differently, so it seems difficult to postulate one rule for all gas mixes, offhand. That is also why I ask.

I am curious to read Patmandu's sources.

[patmandu]

IndigoBlue once bubbled...


Why do you believe it is 80%?

Is this an empirical finding? By whom?

Good question, and I'm not sure I have a good answer for you. 80% certainly isn't a hard and fast rule for deep stops, and no I don't have any 'hard copy' studies of findings that 80% is THE place to start deep stops. Pyle stops at 50% may be the answer....I don't know.

What I like to do is start 'rolling stops' (30 seconds at the depth, 30 seconds to next 10 ft increment) until I reach 10 ft below my first gas switch at which I'll spend 60 seconds to get squared away, and ready for my gas switch (of course, if the schedule I'm running requires a longer stop, I'll do that). After the minute at 10ft below my gas switch, I'll spend 3-5 minutes minimum at the gas switch (starting once I am breathing the new gas).

I'm am by no means a deco expert and I don't recommend anyone follow what I do. I look at decompression from a perspective of what makes sense to me and what seem logical. Starting a controlled slow ascent from a deeper depth (say 80% for instance) allows me to slowly increase the gradient and slowly start to off-gas.

Where did I learn this? Mainly from trying to listen and learn from folks who I respect and routinely pull insane runtimes. I listen, try to understand their reasonings, and then pass it through my common sense/logical BullSh*t meter.

I use various decompression programs, analyze where the theoritical compartment off gassing starts to occur in the compartments and then 're-shape' the curve to build in sensical deeper stops.

Does that help to answer the question?

I welcome comments/debate/ etc. This is how we are learn

[GDI]

:doctor:
So patmandu you opt to do deep stops when required and of course taking the time to enter into your gas switch depth. If I understand you, you also do running time ascents, slow ascents stopping only when the profile calls for it, other than when adjusting yourself to switch gases? OK can see that

[patmandu]

GDI once bubbled...
:doctor:
So patmandu you opt to do deep stops when required and of course taking the time to enter into your gas switch depth. If I understand you, you also do running time ascents, slow ascents stopping only when the profile calls for it, other than when adjusting yourself to switch gases? OK can see that

I would agree with that statement. The only caveat is that I tend to 're-shape' the output from the computer profile to include more time at deeper and intermediate stops and a reduction in the shallower stuff, to 'round out' or 'reshape' the deco profile. Although some of the VPM profiles are very close to what I would 'like' to see.

[pipedope]

Comes from GI3 at the WKPP.
Go to the WKPP web site and read the articles on DECO;
http://www.wkpp.org/decompression.htm

[patmandu]

pipedope once bubbled...
Comes from GI3 at the WKPP.
Go to the WKPP web site and read the articles on DECO;
http://www.wkpp.org/decompression.htm


Well, there you go. Thans for the link. If it's not obvious, I'm GUE trained and one of my instructors is a WKPP diver with whom I've had alot of diving related discussions.

[IndigoBlue]

patmandu once bubbled...


Good question, and I'm not sure I have a good answer for you. 80% certainly isn't a hard and fast rule for deep stops, and no I don't have any 'hard copy' studies of findings that 80% is THE place to start deep stops. Pyle stops at 50% may be the answer....I don't know.


I read the WKP Project discussion recommending 80%:

http://www.wkpp.org/articles/Decompression/first_deep_stops.htm

They postulate it without any discussion of where it comes from. So now we are left to guess where it comes from. An old IANTD deco manual that I have mentions a 1.72 maximum pressure change gradient for helium and 1.61 for air. The reciprocal of 1.72 is 58% and the reciprocal of 1.61 is 62%. Of course, these are old manuals from the 1990s.

80% is half way to 60% (rounded). I am therefore guessing that this is where the 80% comes from. But I do not know either.

The rest of their discussion uses these %s:

"These deep stops are equally divided at all depths up to 65 percent of the profile. At that point you begin lengthening the stops. Between 65% and 45%, the steps slightly lengthen, but max out at 10 minutes. Between 45% and 35%, the max is 20 minutes, between 35 and 25%, the max is 30 minutes, subject to certain parameters."

I have to wonder if RGBM is based on similar "reduced" gradients as well, since RGBM is reduced-gradient?

50% is the reciprocal of 2 which is Haldane. And Haldane is really old thought.

[pdoege]

The idea behind the depth percentage seems to be that there is some critical pressure differential where outgassing is fast enough for reasonable offgassing yet not so fast as to cause DCS.

There doesn't seem to be a set number, and the number probably changes a bit depending on the person, depth, temp, etc. The TDI deco manual lists numbers from 2.0 to 1.3, depending on the table/algorithm. 1.3 is around 77%, ie reasonably close to 80%.

I don't think that I would dive based on a set number. I would feel a lot better running a custom table. That being said, 80% seems like a relatively safe rule of thumb.

Peter

edit: I do not have the data in front of me. IIRC, the 2.0 number is from a Navy table. I think the 1.3 was DCIEM. No way to know for sure without checking at home.