Deco while cave diving

Got a question for everyone,

I recently got my discretionary apprentice and I'm looking to do lots of cave diving. - Which has got me thinking.... I've always used dive tables in my OW diving and I'm a little confused about how to use them correctly in cave diving. When planning a dive in the open water, using tables is pretty straight forward. You a pick a max depth and a max time and stick to the plan. In the OW, if you're diving a square profile - it's easy to plan ahead of time.

Cave diving is somewhat different I've learned, many sites (not all) have wildy varying depths throughout the dive. When using tables, how do you plan for the depth of the dive if the dive's profile varies from one moment to the next? Do you pick the max depth of the site or is there an averaging system used to find what depth you should be using in your plan? It would seem that picking the max depth of certain sites would give you ridiculous levels of conservatism on dives that only go deep for a few feet and then go shallow again for hundreds of feet. Finally, most confusing to me is deco diving in a cave, how do you plan for exact mixtures of deco gas and the amount you'll need, if you'd don't have an exact depth to work with? Thanks for any aid to my confusion!!

Should I just buy a computer? :D
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Does anybody know of a shorter word for yes?

I use a computer and back up with a bottom timer and tables based on worst case bottom times. It's super conservative if you have to go to the tables but it's safe.

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Originally Posted by andrebasso

Do you pick the max depth of the site? It would seem that picking the max depth of certain sites would give you ridiculous levels of conservatism on dives that only go deep for a few feet and then go shallow again for hundreds of feet.

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The Cave Diving Manual discusses various situations for diving and deco but max depth + time is the general rule when using the Navy tables.

Padi tables are multilevel capable but are incompatable with deco or any extreeme diving. The Bheulman tables may have a multilevel proceedure and is compatable with deco. Various dive table software programes allow you to specify an expected multilevel profile and will give a deco schedule to your specified conservatism.

The easiest solution is to buy a dive computer - but it is not a complete solution as you should have the capabiliy of estimating your deco ahead of time and/or having a backup method in case the computer deco looks weird or the computer fails. Some people use 2 computers so the can check against each other and a convienient backup in case one fails.

Most software programs that provide deco also can predict and track deco gas volumes which can be a useful feature as dives grow more complex - or just longer and deeper. Always a problem if you have a deco plan but not enough gas to accomplish it. ;)

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Originally Posted by Gary

Some people use 2 computers so they can check against each other and a convienient backup in case one fails.

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That is my solution. 2 multi-gas computers.

I am intro and this opinion might be worth the paper it is written on. Ahh..... the disclaimer is now out of the way.

This seems like a situation I shouldn't be diving until I have been specifically trained for it. Becuase we might be allowed to do something in the guidelines doesn't in any way mean that we should do it. Diving outside our training limits is one of those magic rules, yes? My understanding is that this is handled in full cave by the instructor and materials. Is this correct?

I think in this situation, I would call my instructor or go to dinner/lunch with him and ask him what he thinks. I expect to stay with him for all of my cave training. So we talk regularly to montior my progress, my decisions and of course my questions.

I am sure this didn't answer your question, the answer to you question is that I use a vr3, a watch, a cobra is guage mode and a set of navy tables. I monitor my depth and my time so in the event I have to switch to tables I can.

Hans

Have you had a decompression class yet? If not I strongly encourage you to take one, either in conjunction with your full cave class or before it with a local instructor. It'll be worth the money spent.

Good Luck!

All of the above posters are correct.

The path I followed was using a single gas computer and then started cutting tables at max depth using D-planner. I was being terribly punished with deco time but was learning. I learned how different tables worked and watched what others were doing with their various computers. I was doing Ginnie stuff, etc. I still did not 'really' understand deco procedures but was doing my best. The next step was to take an Extended Range or Advanced deco procedures type class IN ADDITION TO reading as much literature I could to better understand what is currently understood about decompression and the models. If you can understand the models, then you can better pick which computer will work for your type of diving.

You'll learn why diving on run time is far more sensible than stop times, etc. particularly when you are REALLY racking up the deco in a multi-level situation.

Finally I bought a multi-gas computer to help me follow a deliberate deco schedule / profile. The computer is a helper, especially for multi-level dives. Knowing the tables, what they mean and what to do with them is your backup and can save your butt.

It took me two years to work through this. I dive one weekend a month.

That being said - I now carry the multi-gas computer as primary and use my single gas computer as a bottom timer. Backup tables are always in my pocket. Yet I'm sure there are still more things to learn about deco procedures.

Just my 2 cents.

Back in the old days when I had a choice of air & US Navy tables, we'd stop at 40' and calculate deco based on max depth and run time to that point.

Multi gas computers are the best thing to happen to cave diving since.... well, the old days.

Here's my two cents:

I'm 47 years old and don't want to get bent. I have no interest in something that will "get you out of the water faster." A reasonably conservative multi-level computer is as fast as I want.

That said, I use two different computers (a Nitek Plus and a Nitek HE), and stay three minutes past when the slower one cleared.

Five minutes at 15' is a lot funner than five hours in a chamber.

And adding some sort of "deep stops" if you don't have a computer that provides them is a big plus. Lots of methods for that.

Angie,

Are you willing to post a reading list?

Hans

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Originally Posted by Gary

And adding some sort of "deep stops"

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Absolutely. Minimum of three minutes at half of max depth.

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Originally Posted by andrebasso

Got a question for everyone,

I recently got my discretionary apprentice and I'm looking to do lots of cave diving.

Finally, most confusing to me is deco diving in a cave, how do you plan for exact mixtures of deco gas and the amount you'll need, if you'd don't have an exact depth to work with? Thanks for any aid to my confusion!!

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Andre, don't mean to rain on your parade but one of the limitations on your discretionary apprentice is no decompression diving and it's on there for the simple reason that you haven't been introduced to decompression diving yet, hence this thread...

Just my O2, but the internet is not the place to learn about decompression procedures. Be careful out there :)

Safe diving,

Rich

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Originally Posted by Luxrok

Angie,

Are you willing to post a reading list?

Hans

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Nope because I agree with Rich. The internet is not the place to learn about decompression procedures. What you should research are decompression models as in understanding the Buhlmann model, how the variables work in the mathematical models. Maybe review the latest RGMB (?) theories, etc. Then you will know (mostly) what you are buying in a dive computer because each uses a different software algorithm (model) to handle the decompression profiles and each works best for a particular type of diving . So you can make an informed decision about what you are doing. I don't need to post a reading list for that. Basic internet searches will get you there.

Try to understand. I'm not being sarcastic. I truly believe that you need to work with divers that can give you the proper training/mentorship. If you have to pay for it, it's worth it. The alternative of not knowing is like firing a weapon but not knowing how it really works. Sooner or later you will hurt yourself. Not that it can't happen anyway but maybe it will improve your odds of avoiding a trip to the chamber.

Good luck.

Angie

Hey everyone, thanks for all the responses. Based on some of your feedback I feel that my original post may have been misleading. Here is a bit of a clarification on my point of view and my thought processes:

1) As a Dicretionary Apprentice, I have a BIG intention to do as much diving as possible and ask as many questions as I can think of.

2) As a Discretionary Apprentice, I have NO intention of diving beyond my limits of training... Jumps, circuits, trimix, DPV, stage use, surveying, deco diving are all beyond my level of training. That does not mean that I'm not curious about them and that I won't ask questions. When I was an Open Water diver, Cavern Diving was beyond my level of training. That did not mean that I didn't inquire or ask questions until I took the class. That would be like a 500lbs couch potato showing up to a triathlon event, don't you agree? Unprepared and oblivious. Anyhow, now that I'm getting close to Full Cave certification, these are things that are naturally popping up in my mind. Namely Deco and tables.

SO, anyhow... my question about table use.
What I've gathered from your responses is that tables should pretty much always be planned with max depth in mind, this makes sense and is easiest and most conservative for table use. This is how they are used in the OW, so this is quite familiar with me. With tables you have a disadvantage in that you may become severely penalized with heavy deco times and excessive stop times. You are bound to a distinct and unchanging dive profile that can not really be broken. It seems the ADVANTAGE however with this system of diving is that if you're doing deco diving you know exactly how much gas you will need. Mixing deco gases and selecting the correct volumes and planning for contingencies is very easy since you know to a very precise degree what your profile will be.

This then naturally leads into the conversation of computer usage. When using a computer, it will write a custom depth profile for you as you dive. This custom depth profile may possibly lead to far shorter stop times and a far less volume of required deco gas. However, now that you're not diving an exact and fixed profile - how do you determine the amount of gas you'll need for the deco obligations before starting the dive? It seems that when using a computer, the DISADVANTAGE is that you don't have a way to easily calculate required deco volumes and gas mixes BEFORE the custom dive profile is written for you by the computer. A bit of a conundrum in my mind... a computer gives you reduced deco times but you have no way of knowing which deco gases to bring beforehand.
It seems to me the only answer is a mix of table and computer use. Mix your deco gases and prepare the correct deco volumes based on a square profile and THEN allow the computer to reward you with less deco obligations if need be. This way if you must resort to tables (during the dive) - you already have the needed deco gas. However, if you end up finishing the dive using the computer only, you'll likely have plenty of reserve deco gas. That seems to be the only way.

By the way, any personal comments or suggestion on this topic will be seen purely as that, your personal comments. I have no intention of writing this stuff down and taking any of your words or advice as "the printed word." I merely intend to compare and contrast any advice here with what I already know about OW deco procedures. I have quite a few books on deco procedures and theory but none of them seem to talk about caves, which is why I'm asking here.

Oh and thank you all for the nice comments on my "Creature" image, I thought that was pretty damn funny too.

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Originally Posted by Sludge

Five minutes at 15' is a lot funner than five hours in a chamber.

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Now, that, I would write down as the being "the printed word." LOL

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You could just guess...

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Originally Posted by andrebasso

What I've gathered from you responses is that tables should pretty much always be planned with max depth in mind, this makes sense and is easiest and most conservative for table use.

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It's really more about the limitations of how the tables were designed. The Cave Manual discusses the Navy Tables as the default for most divers of the time and the Navy Tables have no approved multi level dive procedure - therefore: max depth and time is the assumption.

Various deco programs and method will have various limitations on how they are used. I think most advanced deco procedures classes these days are going to suggest not using the Navy Dive Tables because of the limitations of the Navy Tables and because of the many newer models and tools that provide both better deco and better tools for planning and accomplishing it.

What tools you will be subjected to will depend a lot on your instructor / training agency.

With most dive computers getting into more intense decos you will probably find that your planning tools will have you making deeper stops for shorter times and get you of the water faster then your dive computer. This is largely because making the deeper stops doesn't follow the computer's model and the computer will penalize your deco accordingly. On other profiles the computer will give you so much less deco time that the plan will require stops your computer doesn't and it may clear before your 10' stop. ;-)

Or you can spend the extra planning & bucks for a dive computer that incorporates a dive model similar to your planing tools so they are reasonably similar in basic assumptions. Which will still not make them match perfectly on every dive but will make them closer.

Even the best tools can't make deco 100% safe or do thinking for you. Seeking a good understanding of the principals (like you seem to be) is your best bet.

The old "Haldanian" US Navy Tables (and earlier) were later largely usurped by the Bheuhman Models which generally had safer supersaturation values and considered more and longer on/off-gassing halftimes. Those are now being generally replaced by Bubble Models which provide shorter, safer decos by doing deeper stops on the way up.

The best reference I know of was John Lippman's (of D.A.N.) "Deeper into Diving" (not "Deeper Diving" which he also wrote) which goes into the details and safety analysis of each set of tables and many dive computers in use up to that time. Unfortunately it is decades out of date and doesn't address the newer bubble models at all. There is information all over the web on these subjects. A few from my old bookmarks:

http://www.decompression.org/maiken/...ogram_Info.htm
http://www.decompression.org/maiken/...blications.htm
http://www.rgbmdiving.com/
http://www.cisatlantic.com/trimix/tools.htm
ftp://ftp.decompression.org/pub/Baker/


It's not about how any of these models computes their decos but how the general methods have evolved to provide safer decopression when we use them. Understanding the mathematical models themselves is unnecessary (Haldanian Models can produce the same deco profiles as the Bubble Models by choosing the right values) but making an informed choice and employing good general practices is the goal.

A good deco proceedures or trimix class will present more of this in a useful, hands-on way (and in a shorter peroid of time) then you can get by reading the net. Extra reading won't hurt you but won't present the information in as usable a format.

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Originally Posted by Gary

I think most advanced deco procedures classes these days are going to suggest not using the Navy Dive Tables because of the limitations of the Navy Tables and because of the many newer models and tools that provide both better deco and better tools for planning and accomplishing it.

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Yes, this seems to be the case based on what I've read, especially with the new RGBM tables that have come out in recent years. Seems that very few people still rely on the Navy tables, RGBM's ability to supress micronuclei formation via deep stops seems far superior to excessive shallow stops..

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Originally Posted by Gary

Or you can spend the extra planning & bucks for a dive computer that incorporates a dive model similar to your planing tools so they are reasonably similar in basic assumptions. Which will still not make them match perfectly on every dive but will make them closer.

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Okay that's the smartest thing I've heard so far. Definitelty a good move, especially if you're cutting the initial plan with tables/software, you'd want the piece of mind that the computer will have SOME KIND of core similiarity to the tables/software you started the plan with. Do you have any recommendation on combinations of tables and computers that would do as you described? For example, I know that SUUNTO also makes RGBM tables that incorporate (to a degree) the same RGBM deco model as their computers. PM me with any recommendations.

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Originally Posted by Gary

A good deco proceedures or trimix class will present more of this in a useful, hands-on way (and in a shorter peroid of time) then you can get by reading the net. Extra reading won't hurt you but won't present the information in as usable a format.

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Absolutely, a deco class will be my next investment but I still have lots of questions until then.... :twisted:

Very informative post Gary, THX.

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Originally Posted by andrebasso

Do you have any recommendation on combinations of tables and computers that would do as you described?

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I think the older (non-VPM) VR3 computers are probably the most prefered dive computer with intrinsic deep stops - not cheap though. If I had no limit on spending I'd go with that I think.

There was a discussion on Ross's Vplanner yahoo group about a year ago on the latest implementations of RGBM VPM and dive computers utilizing a (crippled/poor) version of the RGBM for their model. I don't remember a good solution to your question being presented there but it was very informative. I think it was about the time GAP was introduced and was part of the discussion. Maybe newer stuff as well: http://groups.yahoo.com/group/vplanner/