Open circuit at first sign of trouble?

schford

This has turned into a great thread.

I am wondering if we should start a new one discussing the best strategy for each Rebreather...As this convertsation is moving away slightly form original topic of whether it shoudl be taught or not ;-)...

the way i see it

Megalodon - definatly open Loop
Kiss - Would seem to be using the mouth piece as you cant crush lungs and hit ADV / Addd button in one movement.
Inspiration with ADV - open loop?
Inspiration without ADV - open loop still?
Prism Topaz - Stef what do ya think?

what do you guys think? someone start a new thread!

Stuart

Divechick

I have got in the habit (in my admittedly meagre number of dives on the Meg) of having the ADV on when descending and then isolating it to prevent it firing unexpectedly and then cracking it open briefly if I need to increase loop volume at any time.

It occurs to me reading this thread that this adds a further hurdle to doing a dil flush and going to open loop, because rather than simply crossing arms and pulling to chest, you would have to fiddle around trying to un-isolate the ADV before purging. This seems particularly unattractive given what people have been saying about loss of motor skills from a CO2 hit. It would also mean that if I were to simply go to open loop by breathing out through my nose immediately, the ADV would not automatically fire to replenish the loop, as it would be isolated, so I would end up scrabbling to un-isolate it with an empty loop.

Is isolating the ADV at depth such a bad idea? Appreciate any thoughts!

Sarah

ROB DAVIE

Sarah,

Tom Mount dives the Meg a LOT and his practice is to use the ADV on descent, and then shut the trombone valve.

Rob Davie

__________________
"CC Rebreathers will become a viable part of tech diving WHEN PIGS FLY!!"--GI3

caveseeker7

Absolutely, I believe it to be an essential skill.

An OC/DSV is a very nice feature to have, but open loop is an important skill to have.
Big difference. And on KISS, CIS, Rebreather-80 and custom DSVs you have the choice of either.
But if you're diving with minimal loop volume, as you should and likely will after a little while, open loop should work as well with backmounted lung(s) as it does with o-t-s bags.
There should be no need to squeeze the bags, unless your breathing has become so shallow as not to empty the bag on a single breath (which I understand is the reason for the squeezing).

Without an ADV it's just a skill that's more involved, and a skill that may well be harder to execute than turning a knob.

I like the idea of an OC/DSV a lot and bugged Pete Readey about it.
He shares Leon's view that it's not worth it, though he believes that OC-integration just adds to much bits, pieces and failure points to what should be a very simple part of the loop.

Still, adding one is one of the few mods I'm considering for my own Rebreather when I get it. One advantage I see is that when you're incapacitated enough to have trouble with either skill or equipment a buddy can easily enough turn the knob to OC, especially if combined with a FFM.

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

schford

Excellent points Stef - I really like the one about your buddy being able to open it - I had not considered that one.

have some green

Stuart

caveseeker7

Very much so indeed.

I like that Freudian slip, if you don't believe in open loop you will by the end of this thread.
Maybe it's shifting away from the question because there is simply no good argument not to teach, practise and have that skill.
And I don't think that we need separate threads, just makes it harder to find what you're looking for down the road.

As I said in the previous post, I consider it an essential skill.
Now on a Meg and SportKiss (maybe others, I don't know them all well enough) the dil injection is on exhale side, so going open loop means you have to clear everything between the valve and the DSV. So taking a deep sanity breath or two on OC might be a good idea even if you want to handle any problems open loop. Something to consider, and one reason why I believe that an OC/DSV comes in handier on those units.

On the PRISM, as well as the Inspiration, diluent addition is on the inhalation side, so going open loop means you bypass the loop immediately. It also means you will have to clear the bad gas in the loop later.

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

caveseeker7

Isolating the ADV at depth is a standard procedure for many divers and instructors. When practicing open loop drills I suggest you practise both opening the isolator as well as replenishing the gas in the bag with the manual dil add valve (same as units without ADV).

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

schford

Thats probably why we are taught to crush CLs and fire ADV - in a few milli seconds you are breathing clean fresh gas - and you can do it with no need of those fine motor skills!

Stuart

Ken

Hi Fellas,

Thanks for the green blobs. I was just kidding...but I feel a whole lot better! Green is good.

I think any Rebreather instructor has a duty to teach critical diving skills specific to their units as well as offer and allow students to practice alternatives. Since every rebreather has unique qualities it's incumbent upon the user to also learn these skills. At least one thing is for sure these days, you don't see too many alpinist RB divers.

This forum certainly has brought up some interesting perspectives and sound suggestions. It's also great that people are willing to share experiences. Curious, is there a link to Dr. Mike's experience? I know that when I got past my CO2 hit that I felt remarkably weak. It was like the aftermath of hiking (with a full backpack) without food for twelve hours. In the midst of my CO2 hits I was able to move my hands, grab things shakily and think - albeit not too well. What saved my ass was just stopping everything and focusing on breathing, and then sorting. Remarkably ugly when it happens in an overhead environment.

decoweenie

I beg the difference.

If you do actually dive MLV, there is one breath (plus a tiny bit). So I could and do teach people to completely empty the loop volume with one breath out. No need to do any "cross your arm, squeeze your CL" bit. It is that simple to breath out thru the nose (or what you guys call Open Loop). I could trigger the ADV if I exaggerate the exhalation breath

I dive the Insp as well which isn't much different than the Meg. And I could do the same with MLV.

The problem is people think they are diving MLV and they are not if they have to squeeze gas out from the CL to empty the loop.