Technical diving with oc versus ccr gas requirements

[divezonescuba]

Hello:

Soliciting input on a question.

it seems that to do a deep dive say 100 m on ccr would require a diver to carry much of the same oc gasses as an oc diver or even more in the event of a bailout. That could mean possibly cylinders with a bottom gas, a travel gas, and two deco gases for example. You wouldn’t have to carry as much bailout bottom gas since you would ascent directly. Of course, those cylinders would not be needed to be used unless a bailout was required.

Am I understanding this correctly?

 

[tursiops]

It is not uncommon.

 

[grantctobin]

Yes. That’s minimum backgas + 3 deco bottles on OC or CCR+deepbailout+ 3 deco bottles on a rebreather. 100M is on the cusp of needing a fourth deco mix depending on bottom time and gas calc conservatism.

If the unit remains operational, one would use <10cuft O2 and similar diluent volumes for this dive and not burn through any bailout gas.

 

[GF99/99]

Yes. That’s minimum backgas + 3 deco bottles on OC or CCR+deepbailout+ 3 deco bottles on a rebreather. 100M is on the cusp of needing a fourth deco mix depending on bottom time and gas calc conservatism.

If the unit remains operational, one would use <10cuft O2 and similar diluent volumes for this dive and not burn through any bailout gas.

Yup you need to carry enough bail out gas to get you safely to the surface and as grantctobin has mentioned 3 bailouts at 100m is kind of the limit (and of course this is all depending on your bottom time) Yes you can do team bail out planning down to about 130m-140m but honestly if you already have 3 stages a 4th does not really matter so why not take it. You can never have to much deco gas. After about 130m-140m'ish this is when you start to need support divers with extra deco gas at least in my opinion. I have found that people that are doing sub 100's all have very very different styles of diving. Its actually quite interested to compare dive planning with other people that do sub 100's

Also yes you are correct the bail outs never get used. Some people have several year old bail outs.

 

[helodriver87]

Yup. You don't really get away with carrying much less gas. You just get to use less. And of course, you have the luxury of time in any situation short of a full bailout.

 

[DiveTucson]

I would argue that 3 BO bottles on a 100M CCR dive would barely be adequate especially as the two main reasons you would have for bailing out and staying off the loop at these depths would be hypercapnia and complete catastrophic flood. I think most CCR divers carry an inadequate amount of BO to surface safely. For me a 100M dive is at least 4 possibly 5 bottles.

 

[kensuf]

I would argue that 3 BO bottles on a 100M CCR dive would barely be adequate especially as the two main reasons you would have for bailing out and staying off the loop at these depths would be hypercapnia and complete catastrophic flood. I think most CCR divers carry an inadequate amount of BO to surface safely. For me a 100M dive is at least 4 possibly 5 bottles.

Hypercapnia is bad stuff, you'll go through reserves quickly. At those depths, AL40s of deep gas isn't appropriate either.

 

[tbone1004]

Hello:

Soliciting input on a question.

it seems that to do a deep dive say 100 m on ccr would require a diver to carry much of the same oc gasses as an oc diver or even more in the event of a bailout. That could mean possibly cylinders with a bottom gas, a travel gas, and two deco gases for example. You wouldn’t have to carry as much bailout bottom gas since you would ascent directly. Of course, those cylinders would not be needed to be used unless a bailout was required.

Am I understanding this correctly?

all the CCR does is replace one of the backgas bottles. Everything else still has to come with.
Deco Planner with 60/80 GF's, 330ft for 15mins, on 10/70 which is about what I'd run with a CCR and 35/25, 50%, and O2 deco gases. It calls for 22cf of the deep deco, 42cf of 50% and 41cf of O2. From that the O2 and 50% are automatically 80's, the deep mix COULD be an AL40, but then you'd still need a bottom mix to get to 70ft, and that damned well better be at least 80cf. Cue why I dive a rack when in the ocean as the double 50's give me more than enough to get there. At 100m you're going to consume 10cfm to move around and somewhere well over 20cfm if you go hypercapnic. AL40's are idiotic.

 

[GF99/99]

Hi guys sorry in advance if this is going to far off the OP subject but figured it has alot of value as to how many bail outs you have.

Just curious what others thoughts are on appropriate bail out RMV for your dive planning?

 

[tbone1004]

Hi guys sorry in advance if this is going to far off the OP subject but figured it has alot of value as to how many bail outs you have.

Just curious what others thoughts are on appropriate bail out RMV for your dive planning?

on a CCR, no less than 2cfm for 10mins at the bottom to deal with hypercapnia. 1cfm for everything else. NO LESS unless you are actively diving open circuit. A lot of CCR divers stop diving OC regularly and still use 0.5-0.7 to plan dives because that's what they used to do. They get used to breathing as much as they want and can't keep it below 1cfm