Access to OC Oxygen from CCR?

Ben Field

Hi All,

I've been tidying up the hoses on my SK and absentmindedly made a note that I have a free LP port on the O2 reg.... then I had a look at the gallery and a few posts people have made showing modifications they've done to various rebreathers, although its not proper survey it seemed to me that about 1/3 of people have access to their onboard O2 by an OC reg.

I can see why this might be useful, also why it might be a potential problem in the case of a free flow (for example)... but I haven't really considered doing it as for my diving I'm still in the "if in doubt, bailout" depths with no deco

Are there any pro's and con's to doing this, any big reasons why a Rebreather diver should or should not have access to their O2 via OC?

(This seems to me something that may have been discussed before but I couldn't find a thread on a similar topic, apologies if you've all been over it in the past! )

BEN

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nigelh

I have it and the only time I've ever used it was to put it in the mouth of a guy who missed some stops when the boat's oxygen was on his buddy who missed lots more. I hope it stays that way.

Some friends of mine have a similar rig but no flowstop and I saw the reg get jammed in the harness and freeflow off most of their O2 swimming to the shot while we shouted at them. It was turn round and be picked up again - no dive.

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nigelh

Padowan

This is a classic case of you needing to weigh up the pros and cons of each - as there are reasons for having it either way:

Pros:
Access to some O2 in bailout/DCS scenario, 3L @150bar at 6m @ 15SLM SAC = max 19mins at 6m - useful for sure, but based on some assumtions.

Cons:
Any sort of reg freeflow = loss of some O2. Could be mitigated by flowstop.
Any sort of hose failure, and you lose all your O2 - (no more likely than a failure of any other O2 hose you have, but more hoses = more risk)

I had one one, with a shut off, and a mouthpiece cover, never used it, decided that I would configure onboard(OB) = CCR only, so removed it. Also applied the same OB=CCR logic to dil too, and no longer have any OC option on my dil either.

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CCR900

Just a couple of points:

If you have a KISS first stage with a blanking plate which will not compensate for depth how do you intened on using it at 6m?

If you ever use an OC reg on your OC supply, what is the risk it goes into freeflow (due to lack of use) and dumps all your lovely O2. The problem then is you have not only lost your CCR but your OC deco gas too.

Maybe you are putting too many eggs in one basket and should consider using seperate tanks.

F

PS I used to put an OC on my O" but took it off 1 year later after never using it and yes the second stage was in sh*t state (knocked around).

lizardland

I don't have OC on my O2 as it is a very limited use gas and a very limited supply so why take the chance introducing something else to go wrong. With OC diving, reg problems were usually 2nd stage failures in my experience, though that's hardly a definitive sample

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Scubascooby

Surely this wouldn't make much difference at 6m (1.6bar) since the ip will be
high enough to deliver gas at the 2nd stage. It might not be the best breathe
in the world.

Peter

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Deepwreck

Interesting Question. The problem comes into pay when you are diving Deco, not when you are diving Open water. You should carry enough bailout to get you to the surface, and to aid a buddy. In Open water diving having access to the onboard O2 is not necessary, and will only add to the conplications of your Kit. Having the correct bailout, other than onboard, is the solution. If you need O2 at the end of an Open water dive your coming very close to Deco diving, and then you should have both a bottom mix bailout bottle, and a High PO2 bottle for Bailout deco.
Personally I use a mix bottom bailout bottle that is good for the max depth I plan on diving. Say 18/30 as an example. Then I also use a Bailout O2 bottle for deco. Some people will use 50% O2, and theres nothing wrong with either way.
I look at having a OC reg on my O2 as nothing but a problem. If you get yourself into such a mess that you need O2 you will most likely already also be off your CCR Csr and bailing in some form or another. In this case, like I said earler, your bailout gas should be adiquite, and you need to carry enough. The O2 use for speeding up the deco margin shouldn't be a problem as you shouldn't have much deco if any to worry about.
If all else fails then take the tank off and switch to your Dil Rig. Not easy.
Plan, Plan, Plan, and then Plan again.

Ben Field

Yeah, that had occurred to me too, although I'm sure you'd still get something out of it.

However I was interested in peoples thinking so asked anyway... as I said, I don't think its something I need, certainly not yet and I like the idea that my O2 is limited in that it can only "leak" into my rebreather!

BEN

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edster

I remember talking abouthis on a previous post - cant find it though! But I think the concensus there was much like here - too many cons to balance out the pros. I decided against it, anyway. Plan, then carry enough off board bailout / deco gas! Thats my philosophy...

Damn, did I see a ?

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PCDiver

I added a regulator to my O2 bottle. I do not rely on it for deeper dives (> 30 meters). But on shallower dives with no or very limited deco I dive alpinist. Having access to +15 minutes of good deco gas can make a big difference. I also use a flow stop and all my bottles are +200 bar on every dive.