Use a gag strap?

[JohnnyC]

The BOV is for me, the gag strap is for my buddy. If I can't fix it myself, the gag strap is to give my buddy a chance to fix it for me. That's all it is. Just one more potential intervention before becoming shark bait.

 

[rjack321]

My wishful thinking was based on thinking that if you are breathing something that is not hypoxic and then it goes hypoxic, it's not going to go from, say 0.16 PO2 to 0.0 instantly. If it drops all the way to 0.12 before you pass out, it still won't require descending all THAT much to get back in the normoxic range. Well, depending on what depth you're at when it goes hypoxic, of course. Obviously, if you're already at or near your max depth, then you're screwed. The specific scenario I was thinking of was a case where my friend was in the water, descending on the shot line, paused to equalize because he had some sinus congestion, and somebody that got in after him didn't have their O2 turned on and passed out just as he passed my friend and his dive buddy. They saw the guy go limp and rescued him. Presumably, that guy's loop was hypoxic but only by virtue of being full of hypoxic dil. Which would have become breathable as he dropped. I'm not saying the guy would have come to. I don't know. I'm just saying that, in that situation it seems like a gag strap would have at least given that guy a SHOT at surviving (if there had not been anyone that saw him and rescued him).

This is all actually mostly likely (and has happened) on the surface.
Splashing with O2 off or O2 drained
Leaking ADV or ADV firing when its not supposed to
Distracted by surface currents, swimming to the shot line etc etc.
Sure you can get a hypoxic loops at depth too but its a whole lot more to go wrong. ADV firing hypoxic dil fairly shallow is the most likely way.

Breathing all the O2 out of your loop at 200ft? That takes a crazy long time compared to going hypoxic due to an ADV leaking 10/50 dil on or near the surface.

Keeping the DSV/BOV in your mouth with a gag strap can even allow the boat crew to jump in and save you in surface situations. Compared to having it fall out and flood making you sink like a stone.

 

[stuartv]

Absolutely! Not as much of a shot at surviving as using a checklist, but a shot nevertheless...



Bailout or SCR mode

MAV

Ooohh, that's a tough one. Frozen board? Hard to imagine such a wide overreading otherwise... But yup, that would be bad, and a gag strap and a buddy would help.




I think in that scenario, it would leak around your mouthpiece regardless of orientation. Highest point only an issue for dewatering, if you just have a full loop the gas is going to escape through the path of least resistance wherever it is. Which in this case would be the mouthpiece.

Yeah, my point about going hypoxic on the bottom is that you would REALLY have to be just not paying attention (or completely forget all your training). Somebody that is that dumb (or poorly trained) probably isn't going to live long diving deep on CCR, gag strap or not.

As for leaking around the mouthpiece, all I can say is that with my rEvo mouthpiece (with lip shield and gag strap), it is hard for me to vent the loop even on purpose, unless I go head up a bit. I usually end up exhaling out my nose, if I really need to vent some.

 

[rjack321]

As for leaking around the mouthpiece, all I can say is that with my rEvo mouthpiece (with lip shield and gag strap), it is hard for me to vent the loop even on purpose, unless I go head up a bit. I usually end up exhaling out my nose, if I really need to vent some.

Same on my Meg

 

[doctormike]

Yeah, my point about going hypoxic on the bottom is that you would REALLY have to be just not paying attention (or completely forget all your training). Somebody that is that dumb (or poorly trained) probably isn't going to live long diving deep on CCR, gag strap or not.

Totally agree. A gag strap is not a replacement for watching your PO2....

As for leaking around the mouthpiece, all I can say is that with my rEvo mouthpiece (with lip shield and gag strap), it is hard for me to vent the loop even on purpose, unless I go head up a bit. I usually end up exhaling out my nose, if I really need to vent some.

Really? I do loose lips when I do an O2 flush at 20 feet to check for current limitation. If you just bite the mouthpiece wings and relax your mouth, it doesn't leak?

Maybe Pete is right about the rEvo...

 

[lermontov]

iof your are

Yeah, my point about going hypoxic on the bottom is that you would REALLY have to be just not paying attention (or completely forget all your training). Somebody that is that dumb (or poorly trained) probably isn't going to live long diving deep on CCR, gag strap or not.

As for leaking around the mouthpiece, all I can say is that with my rEvo mouthpiece (with lip shield and gag strap), it is hard for me to vent the loop even on purpose, unless I go head up a bit. I usually end up exhaling out my nose, if I really need to vent some.

if your really worried about there hypoxic dil than plug in your BO and ascend on manual but wont the CMF valve cover you anyway? if you've got a set point of .7 or higher

 

[rjack321]

if your really worried about there hypoxic dil than plug in your BO and ascend on manual but wont the CMF valve cover you anyway? if you've got a set point of .7 or higher

At least on my mCCR I have to add a lot manually on ascent. It's not going to be hypoxic without manual additions on a rec dive but a deeper dive would be.

E.g. at 250ft that's 8.5 ATA. PPO2 of 1.2 = an fO2 of about 0.13
The CMF valve is at or just below my metabolic rate so if I were to ascend to the surface I would definitely be hypoxic (edit - on the surface).
E.g. at 150ft with a ppO2 of 1.2 that is 5.5 ATA which = an fO2 of about 0.21 which is breathable (barely)

 

[lermontov]

At least on my mCCR I have to add a lot manually on ascent. It's not going to be hypoxic without manual additions on a rec dive but a deeper dive would be.

E.g. at 250ft that's 8.5 ATA. PPO2 of 1.2 = an fO2 of about 0.13
The CMF valve is at or just below my metabolic rate so if I were to ascend to the surface I would definitely be hypoxic.
E.g. at 150ft with a ppO2 of 1.2 that is 5.5 ATA which = an fO2 of about 0.21 which is breathable (barely)

theoretically that may be correct but on dive of 8.5ata im hoping you'd stop for deco wouldnt that allow the cmf valve /solenoid to "catch up" to whatever set point you had

 

[JohnnyC]

A CMF will not "catch up" on ascent. Between the low flow through a CMF and the PO2 drop during ascent, you HAVE to add O2. A CMF won't even "catch up" while maintaining depth. It's below your metabolic requirement. It just delays manual addition.

 

[rjack321]

theoretically that may be correct but on dive of 8.5ata im hoping you'd stop for deco wouldnt that allow the cmf valve /solenoid to "catch up" to whatever set point you had

A solenoid would catch up
A CMF will never catch up