Considering a Rebreather....

[RainPilot]

I also have both. BOV off the dil and a s40 or 80 stage depending on depth and gas sharing requirements for OC teammates.

There is a lot of evidence of how hard it is to take the DSV out of your mouth during a CO2 hit. A BOV to get your breath back and then switch to a SSAA makes sense to me.

 

[doctormike]

I also have both. BOV off the dil and a s40 or 80 stage depending on depth and gas sharing requirements for OC teammates.

There is a lot of evidence of how hard it is to take the DSV out of your mouth during a CO2 hit. A BOV to get your breath back and then switch to a SSAA makes sense to me.

Interesting, that was the sort of information that I was looking for. Thanks!

Is that just general experience/knowledge, or is there some sort of accident analysis report for that evidence..?

 

[RainPilot]

I'll have to hunt down the links but if you have a look at the proceedings of RF3.0 there's a lot of studies and anecdotal evidence alike. The consensus was that BOV and gag straps should be a recommended item for all RB divers.

I'll drop some of the RBW links here. I believe @Simon Mitchell had some good info on this as well.

 

[doctormike]

Interesting, thanks! Will look into this...

Was a bit concerned about the downside of gag straps (in terms of going to OC bailout as a separate regulator), but I guess they should be used in conjunction with a BOV.

 

[The Chairman]

Sometimes. Sometimes I have two bail outs and both can plug in. I am thinking about putting an inline valve on the regs... just in case. I like having options on a rebreather.

 

[RainPilot]

A proper gag strap will come off when you need to bail out. Most of the CCR failures are not immediately fatal but if you lose the mouthpiece eg oxtox etc then it's game over.

I dive a FFM with the RB exclusively.

 

[Dr Simon Mitchell]

Is that just general experience/knowledge, or is there some sort of accident analysis report for that evidence..?

Hello,

The stories of difficulty removing a mouthpiece during a CO2 hit are inevitably anecdote, but some are published, for example:

Trytko B, Mitchell SJ. Extreme survival: a deep technical diving accident. Diving Hyperb Med 35, 23-27, 2005

If you PM me an email address I would be happy to send you the paper.

On the issue of gag straps there is quite compelling circumstantial evidence that they are effective in reducing drowning events after loss of consciousness underwater. A French group recently published a series of ~50 loss of consciousness events underwater during military rebreather diving. There were only two deaths. All were wearing a Drager-type gag strap. There were other risk mitigating factors involved in most of these cases (like the presence of a buddy) but even so, only two drownings in 50 LOC events is fairly compelling evidence of airway protection by the gag strap.

Ref: Gempp E, Louge P, Blatteau JE, Hugon M. Descriptive epidemiology of 153 diving injuries with rebreathers among French military divers from 1979 to 2009. Mil Med. 2011;176(4):446-450

I use the Drager gag strap for all my rebreather diving. As Rainpilot says it is not a problem to remove it if you really do need to get the rebreather mouthpiece out quickly.

Simon M

 

[Diving Dubai]

This is almost a universal issue. BOVs should be available if not a standard. I went with Cooper hoses when I added my Shrimp. That was a good move as far as I'm concerned.

Can you speak "English" so I can follow? Remember the OP (me) is a layman (although I've heard of a Shrimp BOV - no idea how it differs from others

 

[RainPilot]

BOV = Bail out Valve. Its a lever on the DSV (RB mouthpiece) that allows switching from the loop to an OC gas source. It will allow you to have a RB loop and an OC second stage on the same mouthpiece.

If for some reason you need to get off a compromised loop, a single twist / pull will put you on OC. Often these are connected to the diluent cylinder which is usually pretty small so may not offer much time depending on depth and breathing rate. Thats why some / many users plumb an off board gas cylinder to the BOV so that they have a larger reserve to use.

Shrimp is a brand of aftermarket BOV for many rebreathers, many of the new RB have an integrated BOV. Any RB that wants to meet the PADI etc R-CCR (recreational rebreather) standard MUST have a BOV

 

[bl6394]

Can you speak "English" so I can follow? Remember the OP (me) is a layman (although I've heard of a Shrimp BOV - no idea how it differs from others

Just to complicate things, that what I called an OCB - Open Circuit Bailout Valve. It's APDiving's implementation of a BOV that has an integrated Open Circuit second stage. Allowing one to go from CCR to OC - without removing the mouthpiece.

OCB - Open Circuit Bailout Mouthpiece | AP Diving