Is "bailout stashing" a thing?

[PEDiver]

Another question, while I have you all here, is how feasible are bailout rebreathers? In what little research I’d done into them, I’d heard that you had to worry about the bailout rebreather flooding when not in use, but I don’t have the context to know how likely/problematic that would be.

The cross section of divers utilizing bailout rebreathers is very small - it is mostly used by a handful of individuals doing very extreme dives (either super deep or long penetration in caves) where staging or carrying enough OC bailout is not an option. You will see this being used by groups like KUR, Wet Mules, some explorers in France/Europe, etc. Bringing a second rebreather for bailout has its own unique challenges, including maintaining unit integrity throughout the dive, making sure there are no floods (this is bad for any rebreather), and making sure all electronics are functioning properly (if an eCCR - some divers opt to use mCCRs or PSCCRs which are functionally simpler but also have their own issues). This is obviously not an exhaustive list and maybe someone with experience with bailout rebreathers can chime in.

 

[AeroSpartacus]

Here's an article from In Depth a few months ago about bailout rebreathers that probably covers a lot of questions you might have: Our Journey Into Bailout Rebreathers

 

[SouthernSharktoothDiver]

@AeroSpartacus thanks for the rec, I’ll give it a read

 

[SouthernSharktoothDiver]

I know a few guys using them and I’m looking in to acquiring one myself, yeah flooding is the main issue (worry) but then you really should vent the expanding gasses in that loop as you ascend, as much as there will be an OPV that’s still a difference of a few kg potentially if your lazy and don’t do it,
I’m of the mind I’d only take one if I had more than say 1hr of deco,, as why load up the lime and gases etc when an ali80 or a couple of Ali 40,s would do without the extra hassle, their place imo is really with the 80m+ stuff,, and on that note I’ll explain my personal take on it,

If I’m say doing a 100m dive with a fair chunk of bottom time my worry isn’t necessarily with the amount of gas I can carry (3 Ali 80,s I can cope reasonably well with, 4 I’m maxed out) but if I were really put in to a situation with 4hrs of deco my worry would be decompressing safely after breathing for 4hrs in the cold Atlantic in uk waters. I think the cold would be really taking it’s toll,
My next point is that to carry adequate bailout to the 120-170m depths out there (which some do as there are cracking wrecks) you cannot honestly carry enough personal gas in the event it goes wrong at the bottom,,, where as a cylinder of deep bail and a bailout unit offers an acceptable safety margin ,,, I must stress the depths and dive times I’m talking about are all up to the individuals level of risk acceptance,,, as you quickly realise your “definitely not in Kansas any more Toto”

170m, is that even possible? I thought at a certain point you had to worry about CNS toxicity of helium?

 

[runsongas]

HPNS, not helium toxicity. but it is mitigated in trimix vs heliox. its also why the research into using hydrogen in place of nitrogen is ongoing.

High Pressure Neurological Syndrome - DIVER magazine

Diving Medicine By Dr. David Sawatzky In the last two columns I reviewed inert gas narcosis. High Pressure Neurological (Nervous) Syndrome (HPNS) is a similar problem that is experienced on deeper dives. It is a difficulty that recreational divers will never experience but advanced technical...

divermag.com

High Pressure Problems on Über-Deep Dives: Dealing with HPNS

If you’re diving beyond 150 m/490 ft you’re likely to experience the effects of High Pressure Nervous Syndrome (HPNS). Here InDepth’s science geek Reilly Fogarty discusses the physiology of deep helium diving, explains the mechanisms believed to be behind HPNS, and explores its real world...

indepthmag.com

 

[AeroSpartacus]

170m, is that even possible? I thought at a certain point you had to worry about CNS toxicity of helium?

The Wet Mules have been to about 245m in New Zealand. And as far as hydrogen goes, there's also an article about some recent testing (N = 1) they did on that: Hydrogen, At Last? (they also use bailout rebreathers). That being said, they did more recently do some more hydrogen dives in Boesmansgat cave in South Africa and had problems with DCS

 

[SouthernSharktoothDiver]

Yeah...good for them but I'll pass. I have a bucket list item or two at 100m or so, but that's probably deep enough for me

 

[Alex Ouroboros]

170m, is that even possible? I thought at a certain point you had to worry about CNS toxicity of helium?

Yeah empress of Britain is deeper than that, and she’s been dived a few times

 

[Alex Ouroboros]

Yeah...good for them but I'll pass. I have a bucket list item or two at 100m or so, but that's probably deep enough for me

Oh hey, your absolutely right, only do what your comfortable with at any point, 100m is still damned deep, the reality is that after 60m if you had a real catastrophic be it psychological or physical your unlikely to survive an almost direct ascent anyway, once a person has fully absorbed this sort of reality and is accepting of it you see the depth as importantly as the bottom time if you know what I mean, i only become aware of it when giving advice in this sort of circumstance when it’s been discussed and you think “wow,,, I’ll bite off 4hrs of deco and it’s just exactly that, 4hrs, your not thinking wtf happens if whatever occurs, you’ve planned your contingency so you know your all good and enjoy the dive,,, if you thought about it all negatively for quite a while I dare say you wouldn’t bother… funny thing the brain.

Bear in mind there will be people reading this that are thinking “4hrs? I don’t really worry about 8 what’s this guy talking about”, and I’ve been on more than a couple of trips where I’m the baby diver not having a 150m behind me… but that’s major experience and ability… so few do it.

 

[mr_v]

Not sure if that matters, but here is how I think of gas tanks for CC, cave diving:

- Bailout bottles are on you - you have access to them at all times; you use the bailouts to calculate your radius.
- Safety bottles are left in the cave as your extra margin of safety.
- Deco bottles are left at appropriate depths in case if you switch to OC and must deco; 50% and 100% O2 are the norm.

I am nitpicking here, but technically CC divers do not rely on "stage" bottles; I see cave staging as an OC concept. If my dives require more than two bailouts, I'll get a DPV and a backup DVP so that I can get out faster without racking up deco.

Bailout rebreathers are tricky due to operational overhead. When I inquired about diving with one, the person who has done BO CCR dives strongly discouraged me from going that route.