How do you manage decompression

[fsardone]

Hello there,
I see this sub forum has almost no traffic and I believe Decompression is central topic in Tech Diving. I am also curious on how people do things in this area. I have been into decompression diving since 2003 (air only) and into trimix and rich EAN Deco since 2012. I am wondering how people do manage their decompression plan and execute it, since in my personal experience I have seen many variation. In my mind there could be nobody not planning the dive on a computer (diving or otherwise) else they could not know how much gas is needed but ... maybe I will get a surprise here (in fact, I recently met someone that did not have the faintest clue on how much deco he would incur, but he was happy that an EAN50 S80 and OXY S40 would surely be sufficient....)

Just trying to get some insight, voters will not be exposed

Cheers

Fabio

 

[Diver0001]

I dove tables for years when I first started diving (from 1984 to about 1998). In that period of time I made on the order of 600-700 dives using them. When I first started technical diving (2003-2004) I didn't have a mixed gas computer so I went back to using tables. I combined what I knew with the tables and developed some ascent strategies that allowed me to use tables without fussing too much about the exact run-times. It worked but it wasn't optimal, to say the least. I guess you could see it as a bit of a roll-your-own bare-back riding ratio deco but it was rough cut and only applicable to dives fairly similar to ones I was sure about.

I bought a mixed gas computer in ... I want to say 2004 and since then I've used it for calculating the shallow stops. I still use vplanner (used to use a spreadsheet) to make a rough navigation/gas plan. Principles I learned from guys who had gone before me (guys like Steve Lewis) allow me to make fairly care free nitrox dives up to the limits of depth, time, and gas supply that I work with. Learning these skills and especially the addition of a computer, freed me from a LOT of time-pressure that used to distract me during dives. As I said, I usually refer to the computer for the shallow stops. Deeper than about 12m I dive using the same principles I would use if I were diving on tables.

Recently I took a trimix class and again I don't have the right computer, so I'm back to tables again. I now know a LOT more about deco theory than I did during previous courses but having dived with a computer for 10 years I'm experiencing the limitations of tables in a different way. A recent experience (that you will know about, fsardone), convinced me that we really should be viewing a computer as mandatory equipment at this level. The problem was precipitated by communication problems, but not having a computer made me feel that "time pressure" again, when in reality options were available by which diving tables made following up difficult.

R..

 

[TSandM]

I haven't done a huge amount of staged decompression diving, but it's all been planned and executed using Ratio Deco.

 

[boulderjohn]

I think I have tried almost everything.

I did a lot of dives using Ratio Deco. I have stopped doing that for several reasons. One (and only one) of them was the experience some friends had getting bent doing it. They were using a computer on gauge mode as a bottom timer, and its log showed that they had made three separate errors in their calculations. It made me concerned about my ability to make similar miscalculations.

I was trained throughout my trimix training and subsequent dives to use V-Planner and a bottom timer. I was comfortable making the contingency plans and didn't have a problem, but I wondered about my ability to make appropriate decisions in case something really unusual happened that made me depart far from the plan. That is what happened to Rob. It also happened to two friends of mine recently.

Then I did some dives using V-Planner and contingency plans, backed up by a computer. I liked that better, because if the plan went too far astray, I had something reasonably reliable to fall back on.

Then I started using a Predator (and now a Petrel) to preplan the dive and make contingency plans. I followed the plans as I had with V-Planner, and I used the Predator for backup.

On my last dives, I did the preplanning on the Petrel and wrote those plans down. I then just followed the Petrel, using the written contingency plans for backup. My buddy did the same thing, so we were using identical computers with identical settings to be able to check against each other.

 

[TSandM]

I have always let V planner run on my X1 -- it has always been happy with the profiles I've come up with using RD. I view it as a "brain fart" insurance policy.

 

[PfcAJ]

I create tables for a range of depths and times and stick them in my wetnotes.

For short things I use GUE's ratio deco method.

 

[fsardone]

Great, folks this is what I was hoping for! People discussing how they do things and why.

I think I have tried almost everything.
I was trained throughout my trimix training and subsequent dives to use V-Planner and a bottom timer.

This is how I dive: Plan on V-planner, print tables, laminate, dive the plan, in case of deviation from the plan follow multi gas computer and use ratio deco to check multi gas computer. Why mnemonics? To kill the time during deco I am deviating so I am in a "I have messed up something" mode and I am doing a non planned dive.

Being able to calculate is much more important with no direct access to surface (cave-no DSMB) otherwise computer is good enough: if you are deviating (unless you are rescuing somebody ...) you are also aborting straight to deco and computer calculated TTS should suffice. But it also works as computer sanity check.

I haven't done a huge amount of staged decompression diving, but it's all been planned and executed using Ratio Deco.

I think I have tried almost everything.

... but I wondered about my ability to make appropriate decisions in case something really unusual happened that made me depart far from the plan. That is what happened to Rob. It also happened to two friends of mine recently.

.....
On my last dives, I did the preplanning on the Petrel and wrote those plans down. I then just followed the Petrel, using the written contingency plans for backup. My buddy did the same thing, so we were using identical computers with identical settings to be able to check against each other.

BoulderJohn, did you have a bottom timer or if your petrel went belly up you would rely on your team mate for time/depth?
In my view, two points here: doing math in the water and under pressure and team based redundancy .

When things are fine we handle task loading better but if you are under stress can you count on getting ratio deco sorted out? Do you have a sanity check?

Team redundancy on critical items (gas you breathe) to me is not a great option (I know and I am looking into rebreathers, that rebreather divers do it). For less critical items it might be an option but what if your team mate was shallower (it already was out of position ...) dives a different computer (are you already intimately confident on how yours works and you learned his) and you are absolutely sure he did not change any critical parameter because you went through the computers setup together ...

Recently I took a trimix class and again I don't have the right computer, so I'm back to tables again. I now know a LOT more about deco theory than I did during previous courses but having dived with a computer for 10 years I'm experiencing the limitations of tables in a different way. A recent experience (that you will know about, fsardone), convinced me that we really should be viewing a computer as mandatory equipment at this level. The problem was precipitated by communication problems, but not having a computer made me feel that "time pressure" again, when in reality options were available by which diving tables made following up difficult.
R..

I do agree that having a (or two?) computer able to calculate the dive profile you plan should be on the Minimum Equipment List for the dive ... I also strongly believe that you should be planning the dive and have backup tables, having two computer of the same brand model might not be backup but risk being two failures of the same kind (a software bug triggered by same sequence will be probably triggered in both) when it hits the fan you need to be able to come up with something sensible, and team sometime do break down.

In my view being able to dive with a fool proof dive timer (simple, robust and sealed) and tables, being able to calculate ratio deco and having a dive computer along gives me 2 depth timers/2 way to calculate deco according to profile I dove plus my plan ...

How much self sufficiency would you like to have in tech diving? And particularly for deco planning and execution?

Cheers

Fabio

 

[boulderjohn]

BoulderJohn, did you have a bottom timer or if your petrel went belly up you would rely on your team mate for time/depth?

I have a bottom timer I can always use with the tables I wrote down prior to the dive. Because my buddy had the same computer with the same settings, it served as another reality check. If our computers were not telling us roughly the same thing (there will usually be minor differences on a dive because of minor differences in our dives), we know something is wrong. We both had the same table-based backups.

In my view, two points here: doing math in the water and under pressure and team based redundancy .
When things are fine we handle task loading better but if you are under stress can you count on getting ratio deco sorted out? Do you have a sanity check?

I'm a relatively bright guy who can handle basic math. In the case of my friends who made the calculation errors and got bent on their Ratio Deco-based dive, one was far beyond me in that area, finishing his Ph.D in a field requiring high level math. It challenged my personal sense of fallibility.

 

[fsardone]

I'm a relatively bright guy who can handle basic math. In the case of my friends who made the calculation errors and got bent on their Ratio Deco-based dive, one was far beyond me in that area, finishing his Ph.D in a field requiring high level math. It challenged my personal sense of fallibility.

Understood and agreed: making mistakes is easy and possible for everyone even the brightest. Thats why I advocate not reeling on complex mental skills nor memory in high stress or narcosis.

As you probably know from another of my posts, I fly. Used to fly high performance: Something that does at cruise speed 7 Nautical miles per minute and occasionally supersonic. I am used to do math on the fly (pun intended ) and also have an aeronautical sciences degree (requiring lots of math plus another one unrelated in political sciences).
Nevertheless when I did math in hypoxic (altitude chamber) and high pressure/Nitrogen narcosis (depth chamber at 30 metres) environments I DID prove my fallibility.

I stopped relying solely on my mental capability out of normobaric/normoxic conditions ... If you have a chance do a fly and a dive in a chamber. You will be surprised about you do and what you cannot do. It was an enlightening experience for me.

Cheers

Fabio

 

[Subcooled]

Tables + two bottom timers

I have at least two computer generated tables: for 2/3 bottom gas and for 3/3 bottom gas. I also calculate the stops for lost deco gas. These fit on a slate, but later I plan to move on to wetnotes to have more depths and options. Deco seems to roughly equal the bottom time. The deep theoretical motivations for not using a trimix computer can be seen in my wallet.