Open circuit at first sign of trouble?

decoweenie

This is just my opinion...

Mod-1 is supposedly the first and basic step of Rebreather certification. Shallow'ish depth and no deco -- similar to OC recreational diving. Therefore, in theory, you should be able to surface directly (after a safety stop if possible, blah blah)...

So I believe the thought is it would be simpler to teach go to OC and surface when bail-out to a relatively inexperienced diver instead of the possibility of over-complating the issue with other techniques (?)

Anyway, I teach all options in my class since I can't be sure if any particular student will go on and take Mod-2/3 before putting trimix in his diluent tank and go deep. This is especially more likely if the diver is already an OC trimix diver.

JonnyB

As a KISS owner, i would switch to OC, get a few breathes, check my displays, if hypoxia or hyperoxiia is the suspect i would calculate my diluent ppO2, go back on the loop and make a diluent flush, check my displays, see whearther or not my displays are giving me correct values, analyze again if i should stay on the loop or not, in case of breakthrough i would go OC and out of the water. In case O2 or Diluent leak i would turn of the bottle and abort dive, if it is O2 leak i will turn on and of to add O2 while acending.

/Jonny

Sue

Maybe because I'm a newbie, maybe because I have too much OC bad habits, or maybe because I'm a Kiss diver, I would switch to OC (in the mouthpeace), have a few "sanity" breaths, acess the problem, and then if I'm able to solve it, go back to the loop.

Sue

schford

Just a though for you guys with KISS OC valves in your DSV

fine motor skills are first thing to go with a bad CO2 hit - if its creeps up on you when working hard is that valve easy enough to switch over to OC?

Stuart

decoweenie

If needed, one hand is all you need to turn the switch.

What other device do you think that might be easier to get off a "bad" loop than a OC/CC DSV ?

You will find that most people who argue against a OC/CC DSV never had a CO2 hit, I tend to think.

schford

I am not arguing against it - I think it is a neat piece of engineering, was a genuinly asked question..

With a CO2 hit i heard that your fine motor skills are one of the first to go (never experinced one myself and hope to god I dont).

In terms of easyness from a lack of fine motor control I think that going closed loop by crossing arms and pressing against cheast and counter lungs thereby emptying crappy air and inserting new air is a very easy skill and it does not need any fine motor control.

But horses for courses as they say!

Stuart

decoweenie

Stuart,

If you are really worrying about fine motor skill concerning rotating a switch, what is easier than simply breath the loop content out of your nose and let the ADV make up the gas instead of squeezing your CL/etc. ?

If you are using MLV, then ~1 breath (plus a tiny bit) will dump everything from your loop out.

From the minimum exposure that I have had with CO2, the dive goes into a "hyperventilation" mode (short shallow breaths, which actually make everything much worse) as you feel as if you can't get enough O2. And the last thing you want to do is take that mouthpiece out of your mouth (since it is feeding you "air"). The motor skills are find and you are capable of doing everything else.

Mdemon

Dr Mike posted a very interesting piece which got me thinking about the whole Open Loop issue. He described how his CO2 hit rendered him unable to move - so bailout to OC or OC/DSV was impossible. He survived by breathing out through the nose until the ADV fired and then continued doing this until he was functioning - Open Loop in other words.

So, it's great having an OC/DSV for convenience (I have one myself), but to cope with the "paralysis" possibility it also seems essential to have the Open Loop drill in your back pocket.

As an aside, this also means I can have ADV and OC/DSV on different trimixes if I want to.
HTH.

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Ken

Hi Stuart,

Having had a CO2 hit at depth both on CCR & OC I can say that it is a totally disorienting and potentially debilitating experience. Fine motor skills can certainly degenerate, but before that happened I went into a weird/goofy zone. When I first experienced these strange feelings I did as I had been instructed - take a pause. You can almost feel the CO2 coming on which is lucky for me. I don't know how it affects others? The goofy feeling I experienced on my first hit was this overwhelming desire to remove my mask at 35m. Luckily, I convinced the reptilian part of my brain that this was stupid.

As Phi mentioned, the KISS DSV is certainly an easy device to close and open. It's one handed. The CIS's was nice too, just a tad heavier - one/two handed. A simple turn of the lever can certainly help to sort out things when the hit comes without the confusion of locating the bailout second stage, turning on the bailout, closing the DSV, looping the second stage around the neck, purging the bailout reg and breathing. Personally, I would go off the the loop and to the bailout only after I had sorted things during the pause. In the heat of the CO2 hit trying to go to the stage could complicate matters more than just breathing a sure, but possibly suspect gas.

On another note does the Meg allow mating to a KISS DSV?

decoweenie

I would think that Gordon and Leon might be using the same breathing hose source.

If that's correct, then a KISS DSV fitted with the new Jetsam QD should fit just fine, if Stuart wanted it...