Staged Deco

[Jay Roy]

So according to what your saying, you cant do staged deco if you keep your deco bottles clipped on...

So you're right and everyone else is wrong.

As you say they can be use to increase push on the way in but the OP specifically asked about "staged deco" and leaving bottles for use on the way back or up is at least as common.

If you run a search on any of the specialist sites including cave & rebreather, the references to staged bottles for use on the way out is common.
The following phrase appears often on rebreather discussions:
"Came out on OC bailout including using staged deco tanks left in situ on the way in."
One would hope that these people know what they are talking about.

There are many references to "staged deco" on the BSAC forums - and they also pride themselves on their training standards.

If you look at the Divernet site there is a description of an Advanced (TDI) wreck course where they leave their (staged) deco cylinders outside the wreck.
http://www.divernet.com/cgi-bin/articles.pl?id=2302&section=6&action=display&show=

There are many similar references.

 

[rjack321]

Planned seperation still doesn't make it a team IMO. To each his own though.

 

[rjack321]

So according to what your saying, you cant do staged deco if you keep your deco bottles clipped on...

Rather than jumping all over the semantics why not try to understand the OP's questions? Ummm maybe by asking for clarification if you don't get it or providing your personal dictionary - which may or may not be how someone who's 1st language isn't English may see it.

 

[electric_diver]

Hi all,

, and what the most used gas for staged deco is, whether is be 100% O2, or an EAN mix. And does this mean that you stage the bottles at a specific point on a line?

Also, is staging bottles a generally accepted practise, or do mose divers prefer to carry the stage bottles on a sling?

My experience is whatever gas is available is used. You mentioned Bikini Atoll. The surface supplied deco gas there is 74% or 75% because that is what their equipment can reliably produce in the volumes needed.

In Truk Lagoon, we used 50% because a higher mix would not have been ready in time for the dive given the number of deco bottles that needed to be filled.

There was a recent thread debating 80% versus 100%. Look around for it. Read it and decide for yourself.

Personally I prefer approximately 80% because the dive shops near me can fill my AL40 to 3000psi with 75% to 80%. They can only get 2000psi or so with pure 02.

Note that Bikini is surface supplied and deco bottles are neither slung nor staged. On some dives in Bikini the DMs did have stage bottles but they recovered them at the deco bar.

Personally I much prefer slinging my deco gas and keeping it with me.

 

[beejw]

Thanks all for your POV. I never thought a simple question would stir up such a silt storm

I know have a much greater understanding of what deco is. i cant wait

in reference to electric_divers immediately previous post, wouldnt pure O2 give you a shorter deco time, meaning you need less gas anyway, or is 2000psi still not enough. i suppose it depends on what your MOD and BT were?

 

[rjack321]

in reference to electric_divers immediately previous post, wouldnt pure O2 give you a shorter deco time, meaning you need less gas anyway, or is 2000psi still not enough. i suppose it depends on what your MOD and BT were?

Its not that simple. You need to carry the backgas to get up to 20ft for instance and do additional time between 80ish and 20ft.

2000 psi in an AL40 is typically quite adequate. Its lower percentage of O2 deco gases (e.g. 50%) where having full fills is important since you are using it deeper and consequently use more of it.

 

[miketsp]

So according to what your saying, you cant do staged deco if you keep your deco bottles clipped on...

As far as I'm concerned if your deco gas is in a separate cylinder that's a stage deco cylinder irrespective if you carry it with you or drop it off for later recovery.

Example of items from some advertised technical courses

"All divers will be taught with a stage cylinder of bottom mix or with a stage cylinder of decompression mix if the Instructor elects not to incorporate stage dives into the Program."

"A stage decompression cylinder containing oxygen or an EAN mixture with at least 50% oxygen, and appropriately labeled. (Technical Cave Diver Program only)."

"Demonstrate either on a cave dive or confined water the ability to drop and recover a stage cylinder. This may be the tank used as a decompression tank or an actual penetration stage cylinder."


And finally, much as I hate to quote it, Wikpedia has a nice definition:
"Divers doing technical diving often carry different gases, each in a separate cylinder, for each phase of the dive:

travel gas - a cylinder holding gas for use during the descent - typically a nitrox with a medium oxygen partial pressure
bottom gas - a cylinder holding gas for use at depth - typically a helium-based gas with a low oxygen partial pressure
stage - a cylinder holding gas for use at the decompression stop - typically nitrox with a high oxygen partial pressure."

 

[ianr33]

in reference to electric_divers immediately previous post, wouldnt pure O2 give you a shorter deco time, meaning you need less gas anyway, or is 2000psi still not enough. i suppose it depends on what your MOD and BT were?

Pure O2 will most likely not give the quickest deco time.50% or 80% often work out faster as you switch to them earlier.

80% can be err.....,shall we say controversial

IMHO the phrase "staged deco" is somewhat misleading. As far as I am concerned it means a dive that does not use backgas for deco,irrespective of wether the deco tanks are dropped somewhere or carried by the diver.

 

[rjack321]

So the final word is... the definitions change depending on who your talking to. You need to be clear about what you are asking about.

Deco proceedures? or cylinders?

"Staged deco" is really a mismash and it not at all clear if thats a question about gear or proceedures.

 

[ianr33]

My TDI card states

"Qualified to conduct dives for planned staged decompression to 150fsw" the only time on that course we took the tanks off was on an initial skills dive.