CCR Bailout Planning

[Dive Africa]

I do an actual bailout every once in a while, normally from sub 100m to start - see what my actual gas consumption was (per gas) obviously very different for O2 at deco than for a 6/75 at depth) - ad a 50% factor for stress etc - then apply rule of enough gas for 1.5 divers, you do this regularly enough you know exactly how much gas you need - tends to works out at about double the gas you would require for easy breathing exit.... and for a crazy (in my head at least) dive I'll add an extra bottom cylinder just because its fun to drag 6/7 ali 80's around - I do stage the gas as I go in and depending on the dive. Our dives tend to be deep and not to long in horizontal distance...

We all where taught gas planning as part of cave diving and CCR diving courses - use those rules.

[rddvet]

We all where taught gas planning as part of cave diving and CCR diving courses - use those rules.

You'd be surprised what's not taught, or taught based on the instructors' choice as opposed to being semi-standardized. Same thing with DPV. I've yet to hear 10 instructors be exactly the same on DPV gas planning. And generally you have some pretty crazy variation that aren't even in the same ball park (and some don't seem too safe).

[Nitrogenius]

https://www.spareair.com/

Found that to be sufficient for any dives above 300'

An second one of these for any up to 600' .. and that's depth of course !

[Nitrogenius]

So then why wouldn't you treat the rebreather has the first third, and the bailout as the other 2/3rds? That scheme seems more analogous - you're carrying twice the gas needed to exit from max penetration.

Agreed.. in general except that it is only 200% needed for yourself and exactly 100% in a team which is likely where Forrest math stems from..
so it depends whether you are planning solo or team.. min gas as in the rule of thirds is the minimum.. add more conservatism for more challenging dives..
Whether this is done by raising SAC, reducing planned exit speed etc. etc. don't matter..
For reasons of comparability I use real life "proven and known" SAC and swimming rates for the math and then apply the intended safety factor..


I also on top of the "regular bailout gas math" I add "CO2 hit bailout gas" my math on that one stems from real life experience and aftermath from the incident. For three minutes I plan an SAC of 2,5 cft/min at max depth.. When that calculation exceeds an AL80 then I just calculate 1 AL80 for that incident. Reasoning here is, if I did not manage to get my breathing in control yet before I depleted the tank, then I am f..ed anyways and will not make it. In deep diving then I increase my safety factor for the next 10 min by 50% cushion then back to normal planning..
Havent done it ion cave yet, but this is how I would approach it..

[JoeyP]

One problem planning bailout on CCR, is the fact that your SAC rate gets worse the longer you dive CCRs.

That should not happen because there is NO reason to change your breathing pattern because you are on a CCR. Most folks that say their SAC went to hell because of the CCR probably never had a good rate to begin with. If you allow your SAC rate to deteriorate because you are on CCR you are not breathing properly and are more predisposed to a CO2 event.

[JoeyP]

1. Hinkle, twin 85's. Anytime I am going beyond the hinkle I start dropping stage bottles.

2. Depends on the time we expect it'll take to move through that tight silty section. If it's going to take 40 minutes to negotiate I bring more than an hours worth of gas for that section.

3. Enough to get you out, cover your deco, and give you a little extra in case.

You know, there are instructors that teach this stuff and have experience doing this type of diving. I'm one of them. Let me know if I can help.

What Ken said and I'll add that while calculations are great, you need to *really* do a test run of these b/o swims to know for sure what you can do with a given quantity of gas. There is no substitute for knowing that you've done it before.

[Nitrogenius]

That should not happen because there is NO reason to change your breathing pattern because you are on a CCR. Most folks that say their SAC went to hell because of the CCR probably never had a good rate to begin with. If you allow your SAC rate to deteriorate because you are on CCR you are not breathing properly and are more predisposed to a CO2 event.

I agree partially, but in my opinion if there is a difference in breathing pattern and SAC due to diving CCR, then the breathing pattern during doing lots of OC (and back in the OC times) was the "unnatural" pattern and hence predisposed to CO2 retaining.
As you have no "incentive" to breath "unnatural" in order to save gas it is very unlikely that one breathes unnatural on a rebreather..
But yes especially in OC folks should maintain a natural breathing pattern and not "save" as this can end bad..

What Ken said and I'll add that while calculations are great, you need to *really* do a test run of these b/o swims to know for sure what you can do with a given quantity of gas. There is no substitute for knowing that you've done it before.

In my opinion the "knowing that you have done it before" and potentially using such values/volumes for Bailout planning as also risky as it might provide a false sense of safety.
It is extremely unlikely that one will use as "little" gas on a tested bailout vs a real one!
So if the "done it before" method is chosen one should make sure to add proper safety margin to those volumes as well. It might make a huge difference mentally though..


Disclaimer: No/very limited CCR cave experience, but lots of similarities to OW deep Bailouts though..


Best eye opener in regards to CCR BO planning though is a CO2 event.. Difficult to train/simulate though!