Deco without deco training

[Slamfire]

The big challenge with recreational divers and "oops I screwed the pooch" deco is having the gas to do it. Divers who don't pay attention to their depth or bottom time generally don't pay much more attention to their gas...

I totally agree with you, that's why in my hypothetical scenario I was referring to recreational divers that consciously decide to go a few mins into deco, which goes along with having the appropriate gas supplies.

Let me take it a step further, and say that even staying within the NDL could still be putting the diver at higher risks than purposefully taking the computer into deco for a few more mins...

I think, in a lot of cases, a little "unintentional" deco may just mean that they didn't necessarily plan for deco on that dive but they have thought things through to the point of knowing what their options are.

Exactly. Let me move on from hypothetical divers into my own personal experience. I doubled my tanks and started very closely measuring my SAC rates for every dive well before getting formal deco training. It may sound silly but I measure SAC rates to 3 decimal places. For an individual dive alone, 3 decimal places don't mean squat, but after having a couple 100 dives measured like this, individual data point errors start averaging out to the point where I've detected small leaks and regulator maladjustments just because my SAC rate climbed slightly for no apparent reason -- no, I have never used an air integrated computer.

I also started doing dives with small deco obligations before formal deco training (this does not constitute an endorsement for diving beyond your capabilities -- I am no instructor nor dive professional so take whatever I say with a grain of salt. I do not assume liabilities). At that time a typical diving day for me included two dives. The vast majority of small deco dives I did like this were done on the first dive of the day -- following the common recreational advise that your most aggressive dive should be done first. I always aimed at getting out of the first dive with half or more than half of the doubles gas supplies because this was what I would use for the shorter, more conservative 2nd dive. If I got delayed or overextended my plan on the first dive, it just meant I was going to have a very short 2nd dive, or no 2nd dive at all. It would not mean I would run out of gas to do deco for the 1st dive.

The one time I was surprised with gas supplies, was when I did take the second dive into deco. I had done the first dive by breathing out a slinged Al 80 I wanted to drain, and then moving into the doubles. Consequently I had more than usual gas in the doubles after the first dive. After a 2 hr SI I thought nothing of taking the 2nd dive into a small deco obligation. Unexplainably at the time, my second dive profile generated more deco obligation than I had expected. I did have to tap into my reserves to finish the deco obligation, but all the while I was annoyed and pissed off at the computer for "malfunctioning" on me and giving me longer than expected deco.

So when I get back home I go to the manual to see if I can find anything that explains my computer's bad behaviour. I found it near the end of the manual under a section of detailed technical specifications. The computer is built to change gradient factors (M-Values) to more conservative settings when you do repetitive dives. I had just never encountered this situation before because my 2nd dives had always been more conservative due to lower gas supplies.

 

[ianr33]

Unexplainably at the time, my second dive profile generated more deco obligation than I had expected. I did have to tap into my reserves to finish the deco obligation, but all the while I was annoyed and pissed off at the computer for "malfunctioning" on me and giving me longer than expected deco.

So when I get back home I go to the manual to see if I can find anything that explains my computer's bad behaviour. I found it near the end of the manual under a section of detailed technical specifications. The computer is built to change gradient factors (M-Values) to more conservative settings when you do repetitive dives. I had just never encountered this situation before because my 2nd dives had always been more conservative due to lower gas supplies.

Thats a pretty good reason why not to use a recreational computer as the primary planning tool for deco dives.

I've seen something similar with my Aeris computer on a couple of occasions. If I do,say,a 60 foot dive thats well within NDL, then a 130 foot dive that goes into deco the computer gets very upset and starts asking for huge amounts of deco.

These dives were sketched out beforehand with V-planner so I knew the computer was giving me garbage. It was probably still wanting 40 more minutes in the water when I surfaced. Figure I was using it way beyond what it was designed for so the CYA mod kicked in!

 

[Doc Intrepid]

For you guys who may not have had a chance to work with V-planner, here is what Ian is using to cut his tables. (I use the same software.) There are others, but Ross Hemingway's product works real well for a lot of divers. By simply trying different profiles and gasses, etc. you can learn a lot about how different variables will impact your dive planning.

V-Planner VPM-B dive decompression software - download

V-Planner VPM & VPM-B & VPMB & VPM-B/E dive decompression software


Basic explanation of VPM = "Varying Permeability Model" -
Reduced gradient bubble model - Wikipedia, the free encyclopedia


Other information sources re: Reduced Gradient Bubble Model (RGBM) -
http://www.archeonet.org/sub/biblio/Wienke. RGBM Overview and Update.pdf

RGBM Papers | www.gapsoftware.com

 

[HowardE]

I use MV Plan - MV-Plan the Java Dive Planner

It uses Gradient Factors,(based on Bühlmann M-Values) like many tech computers (like my Shearwater Predator), and I can more accurately predict what my computer will assign me on any given dive.

And - it's free.

 

[NAM001]

As stated above it is "just a tool" how you choose to use it is up to you. By understanding your puter you will better understand where you "really are, in relation to nitrogen loading".
I said earlier that if your unit is not set up to handle deco it is just punting you out of the water, a simple default setting if you will. Most rec units are verrry conservative, but the owner needs to know how much so to be able to proccess the information it gives you in "real time-real world. All this takes effort while not diving and promotes the tennant of "the thinking diver".
I would suggest that the moment you become the thinking diver and get some mental input from somewhere you are no longer a stumbler and these questions will easily be resolved by your organic puter.

There is no substitute for:

dive planning
gas management
bail out planning
organic puter

As a side note I cut tables for every dive. I have puter a for another opinion. My choice of standard op. Some of my buddies dive thier puter and have cut tables for another opinion. It all boils down to organic puter choices, based on information and education. Darwin usually does not allow substitutions.
Eric

YOU ARE RIGHT Because the puter is conservative is the reason why I do not have a panic problem when the puter yells deco. Another is i dont run in 1.6 atm. I could but i dont. I also run with a conservitive setting. The few times i have hit deco i was the first to get there. Kind of like not panicing when the gas gage says empty. you know there is still a couple of gallons left before oyou really have problem.

 

[NAM001]

You know, I often see references around here to the superiority of the "organic computer". And while of course generally speaking that's true, nevertheless between organic and digital, one of them is KNOWN to start having problems at depth due to narcosis, even before the diver is aware of the effect, while the other is immune.

So, the organic computer is not always supreme. You may think your organic computer is always correct - but then, think about it, who's whispering that in your ear?

i wont gie up my puter. its only a rec puter aeris t3 elite for one, but doing the mental calc and havng the puter to compare gives me to options and i can pick the level of conservitism i want or feel i need. besides i seldom get below 80-90. Im not in the tech league. I just prefer to use practices that are founded on fact and common sense.

 

[lamont]

You know, I often see references around here to the superiority of the "organic computer". And while of course generally speaking that's true, nevertheless between organic and digital, one of them is KNOWN to start having problems at depth due to narcosis, even before the diver is aware of the effect, while the other is immune.

So, the organic computer is not always supreme. You may think your organic computer is always correct - but then, think about it, who's whispering that in your ear?

The problem is that the Buhlmann-based algorithms in recreational computers are no longer used in technical diving because bubble-model/deep-stops models produce less DCS. So, a naive diver following a recreational computers recommendations for decompression stops will be at a higher rate of DCS than a technical diver blindly following a computer that implements VPM or RGBM. The difference between that recreational diver and the technical diver in this case is that the technical diver knows enough at 1 ATA END to be able to select a proper decompression algorithm.

Trying to turn it into a human vs. computer argument is avoiding the larger problem that recreational divers that don't know anything about decompression while on the surface are only going to be asking for trouble by naively trusting their computer while underwater.

 

[Kern]

So when I get back home I go to the manual to see if I can find anything that explains my computer's bad behaviour. I found it near the end of the manual under a section of detailed technical specifications. The computer is built to change gradient factors (M-Values) to more conservative settings when you do repetitive dives. I had just never encountered this situation before because my 2nd dives had always been more conservative due to lower gas supplies.

Not knowing how the machine works is user error. I'v also seen users make some interesting errors with their desk top deco software too. To me, anyone who uses a vanilla, neo Haldanian bend & mend algo for anything but the most minor oops deco infraction, is well into user error.

 

[DA Aquamaster]

Some random thoughts acquired over 25 years of deco diving.

There is the recreational diver pushing the NDL's version. I took OW from PADI and they accommodated this to some degree with tables showing stops for "unintentional" deco. These included all the US Navy Table profiles to no greater than 140' with the deco stop depth not exceeding 10'. At "normal" recreational depths in the 60-80 ft range you could almost double your bottom time and not exceed 15 minutes of deco at 10'. That left you feeling fairly confident about blowing off the NDL's but set you up nicely for running out of gas.

In addition to a lack of gas planning, this level of training failed to take into account the hit rate on single square profile deco dives (1%) and on repetitive deco dives (4%) with fit, make US navy divers averaging 23 years of age. I'll call this Deco 100 training. It is not much but will get you to the surface in a pinch as long as it is very limited and is truly unintentional.

It is worth noting here that with the much more liberal NDLs on the US Navy based recreational tables of the day that many of those recreational profiles would be considered "deco" dives today on tables where the limits have been adjusted downward on haldane based tables due to doppler ultrasound data as well as on newer tables, multi-level tables and on computers intended for multilevel diving.

As a result of the realities in deco diving with minimal training and the fact that we were all aggressively inclined college students who were likely to do it anyway, the same instructor went overboard and taught in AOW what amounted to deco procedures building in gas planning and the dangers involved in pushing the theoretical nature of the tables, there limitations and the related need for healthy fudge factors. The major difference here was planning, increased conservatism and the instilling of the idea that any emergency must be dealt with underwater as surfacing is just not an option as it is in effect an overhead environment. I am pretty sure he vastly exceeded the PADI standards and course limits of the time. We'll call that Deco 200.

Deco 300 came a decade and a half later when higher 02 percentage deco gasses were common for "accellerated" deco. This is commonly taught now in a combination of Deco Prodecdures and Advanced Nitrox. Solid gas planning and an understanding of the math is emphasized - and is indeed now much more essential as gas planning and gas laws are all but gone from the average OW and AOW courses, as is the ability to effectively use dive tables. When I took those classes, we still used Navy tables but it was understood that they were not exactly conservative and was at best an inefficent bend and treat models. It was however used because they were still a "standard" and were common ground for discussion and table work.

Due to the limitations of the US Navy model, the instructor supplemented the course with discussion of newer models, deeper stops, etc and how that impacted the profile and the planning. The focus was still very much on developing the deco profile and gas plan with tables or software and then using a computer, if any, as a backup or as means to bailout to the surface if you abort the dive significantly early.

Deco 400 has in effect been everything else that came with doing longer accellerated deco in overhead environments and in particular;

1) offshore where conditions can go south in a hurry, where you may have to adapt to a missing ascent line, strong currents, decisions regarding whether to leave your deco gas, and if so how to leave them with maximum chance of finding them when needed,

2) In a cave where you may have very little control over the profile, where you usally have no other exit routes or faster ways to surface in an emergency due to the exceptionally hard overhead and where you may need to be strategic in where you leave your gas for a variety of reasons, and

3) lots of research and self study of factors associated with DCI such as proper hydration, water temp, work load, pros and cons of various deco models, gasses, etc.

Some of 1,2 and 3 came with instruction and some if it came from experience, but all of it is important.

In short, in my experience the major danger in doing deco diving comes in those phases where a diver knows enough to get into trouble at his current level but not enough to fully understand or appreciate how little he knows and/or the magnitude of what he does not know.

It is a continuous learning process so regardless of where you are in the Deco 100 to Deco whatever series, procede slowly and incrementally (even with instruction as instruction means very little until you also have enough experience to fully understand and integrate what you have learned) and always be aware that there is always something you do not know that could potentially kill you. And be aware that deco theory is just that - theory. Your best indicator of what is not enough deco will be how you feel after the dive, so learn to be very aware of the subtle signs your body tells you and then adjust accordingly.

 

[waterpirate]

If someone is wispering in your ear and confusing your organic puter I urge you to get He. I did!