BOV/gag strap vs. OC second stage on bungee necklace

[doctormike]

Hi,

Newbie JJ diver here. I'm starting a new thread about a topic that came up tangentially elsewhere. Maybe better to start on Rebreather World? Wasn't sure if there were more CCR divers here or there...

My instructor (and the JJ distributor) both feel that an OC regulator on a bungee necklace, plugged into an off board gas source (side mounted AL 80) is the best bailout configuration. I also know that JJ used to have a BOV, but they don't offer one now under the current CE. I'm actually comfortable with this configuration, having bailed out several times with this setup in training. I also really instinctively like the idea of a completely redundant system, separate from the rebreather.

However, I have seen a lot of talk about the benefits of a BOV used with a gag strap in cases where a quick switch to OC is necessary (specifically, suspected hypercapnia). One article sent to me was particularly interesting (see attached). Basically, this was a review of rebreather accidents in French military divers, with 54 cases of loss of consciousness but only 3 deaths. Since a loss of consciousness at depth is normally rarely survivable, a 94% survival rate is very impressive. The raw data isn't available, but they do note that a retaining strap for the loop was standard practice.

I wouldn't want to use a strap without a BOV since that it would make it more difficult to quickly get off the loop, so I was thinking about adding an aftermarket BOV to my JJ (i.e. Golem Gear Shrimp). I was also thinking of putting an OC regulator on my bailout tank in addition to the hose to the BOV, stowed like on a deco tank with a bungee, to provide redundancy in case of something like a damaged loop or lost mouthpiece.

What do you experienced CCR divers think about this question?

Thanks in advance!

 

[Basking Ridge Diver]

I am not a rebreather diver - yet

All I can tell you is every one of my "better" instructors have told me - "Do not change the configuration I am teaching until you have 50 dives on it."

At first this can seem a bit "put-offish" - but the ultimate goal is to get the diver/student comfortable with the configuration before adding additional 1) complexity and 2) areas that can throw a monkey wrench into the configuration that was taught.
My advice is dive the configuration until you have it down cold - then start to add additional "options" once you understand the impacts...

Good Luck -

 

[doctormike]

Thanks for the response. I don't want to come off as if I don't trust my instructor. He's awesome, which is why I did advanced wreck tech, and CCR training with him. In fact, he is one of the main reasons why I chose the JJ. But most instructors do recognize that there are more than one way of doing things, and it ultimately comes down to me doing the analysis of the costs and benefits.

I don't think that a BOV really counts as much additional complexity - some would say it's a simpler protocol than getting off the loop and onto a separate regulator, but I guess that's semantics. Take a look at that paper... I believe that this was also a conclusion at the latest rebreather forum. Of course, it's controversial, which is why I'm asking for opinions...

 

[Basking Ridge Diver]

Indeed, 2 preventive measures are mandatory: ( I) systematic linking of divers in pairs, so that a diver can find his buddy regardless of diving conditions (particularly if visibility is poor) and can lend assistance in the event of rescue; (2) using a strap to hold the mouthpiece in position, along with a lip guard, so that an unconscious diver can still breathe without risk of drowning. The rescuer can then concentrate on the quality of assistance and respecting the diving parameters for regaining the surface.
A great majority of these biochemical troubles were encountered by student divers in whom the intensity of physical exertion (sustained finning), difficulty to adapt breathing to the device at the start of the course, and the long duration of training dives led to an imbalance between CO^ production and elimination with subsequent arterial CO^ build-up. Additionally, excessive work of breathing and exercising for any length of time are prone to make a diver less tolerant to high oxygen levels,^ and consequently, acute hyperoxia was also predominant in CS student during the initial part of their course. The association between hypercapnia and susceptibility to CNS-O^ toxicity was ascribed mainly to the vasodilatory effect of CO^ antagonizing the protective O^-induced cerebral vasoconstriction,*' thereby increasing delivery of O^ to neural tissue, resulting in increased production of deleterious reactive oxygen species.

I found this to be interesting - but I would ask :
Are you pushing yourself to the military level of CO2 build up? That seems to be the biggest cross section based on the three areas of Gas Toxicity 68% - of which Hypercapnia 60%, CNS oxygen toxicity 25% and Hypoxia 15%.

I think - the real issue you are trying to solve for is the Gas Toxicity and I get that - but if you add up the total Gas Toxicity = 104 and divide by 30 years = 3.47 deaths per year. What I don't know is how many dives were done in that period of time? That to me would indicate the likelihood of this statistically occurring... and of course this is only one navy that did this count.

You are the one diving the unit - so I would not talk you out of your thought process - for me the odds seem low even for a navy. But if in the back of your mind you are thinking you need a BOV used with a gag strap - then so be it. But next you need a buddy that will be there to drag you up...

 

[PfcAJ]

I think a bov is indispensable.

It allows you to get on oc quickly without having to hold your breath and it provides a method for your buddy to put you on oc if need be.

 

[rjack321]

I wouldn't want to use a strap without a BOV since that it would make it more difficult to quickly get off the loop

This isn't really the case. I have maybe 60 dives with a standard DSV, gag strap and a 2nd stage clipped off on a ring of bungie around my neck. The ring of bungie is better than a necklace per se as its donatable just unclip and donate. As long as the gag strap isn't super tight you just pull it down and the reg can reach. Not super comfortable but you got gas and can loosen the gag strap further once you have started to leave (up or out or both)

I was also thinking of putting an OC regulator on my bailout tank in addition to the hose to the BOV, stowed like on a deco tank with a bungee, to provide redundancy in case of something like a damaged loop or lost mouthpiece.

You need to have an alternative to the BOV in case (for instance) your mouthpiece/loop is full of caustic nasties. or failed mouthpiece, or leaky exhaust diaphragm etc.

You also need to have something to donate, preferably on a 5 or 7ft hose. Its better having this at your neck so you only have one and only one place to reach and donate. Stuffed on the tank is ok, but then you need a shutoff to avoid losing gas when you bump the reg etc. And a shutoff on a donated reg to an OOA diver is not a great idea. This is a bigger compromise if you dive in mixed teams. If you are only with CCR buddies then you're pretty far down the incident pit when you are donating bailout. But there have been A LOT of accidents where buddies tried to donate bailout and the recipient refused and eventually died/drowned. Think through this donation scenario carefully since when you need it you really need it.

 

[RainPilot]

@Simon Mitchell was kind enough to send me a report on a CCR accident. One of the issues encountered by the diver experiencing CO2 bypass was extreme reluctance to let the DSV out of his mouth to bail out even when presented with a reg in his face by his buddy. There are many anecdotal accounts of this sort of behavior, a large part of why the BOV came into being I suspect.

Caustic cocktails are, as far as i can tell, extremely rare these days. Flood resistant units and better training seem to have reduced them enough to, for me, make them irrelevant for my choice of BOV or not. I carry a separate BO cylinder with 2 x second stages anyway so IF I needed to get off the loop due to a cocktail I would have no issue switching over.

That also means I have OC gas to donate to an OC buddy, RB buddies are carrying their own anyway. I dive with the BO turned on and no shutoffs. I keep the regs where I will see any bubbling easily and checking the SPG on the BO is part of my scan (Buddy, Bail, Breathe) which I do every couple of minutes.

 

[doctormike]

Yeah, having never trained with or used a BOV, I wasn't sure what people did for backup to a loop problem (caustic cocktail, lost mouthpiece, torn hose, etc..). I guess the design could be such that the OC reg was really isolated from the loop everywhere except the mouthpiece. However, I have been the OC buddy of a CCR diver who lost his loop mouthpiece, so it's probably not that rare.

Simon was the one who sent me that French article as well, and my concern about a gag with no BOV is exactly what RainPilot said - it's easy to go to OC bailout in training, my concern is how easy it is if you are hypercapneic. I suspect that it's a very different situation.

Didn't think that I would need a shutoff with the bailout valve in plain view on a sidemounted tank. I also check the BO SPG pretty frequently, and I don't think that a free flow would be unnoticed.

 

[PfcAJ]

I have a bungeed backup and a long hose. Even with stage bottles being used to drive the rb I don't find a need for any shutoffs on any of the regs. And there's a bunch!

 

[JohnnyC]

BOV on the loop. Second stage on the B/O cylinder(s) on a long hose. If you want to plumb your offboard to your BOV, that's totally cool, but if you're only diving within recreational depths I wouldn't have a problem running the BOV off of onboard dil since for me it's an intermediate step until you can get on a normal second stage on your bailout.