Going back on the loop ?

colinicky

This question relates to a vision with trimix software

On a 50m dive you have a problem ,it is serious enough to bailout (or in a moment of panic you think it is !)you abort the dive & start your ascent .At some point on the way up you decide to go back on the loop as you worked out it wasn't that serious .
Now the big question is how ? #
obviously you switched the onboard computer to oc so that dissabled the O2 injector so if you have ascended to your 10m stop the ppo will have dropped a lot ,as soon as you switch the computer back to cc it is going to dump O2 into the loop but with a time lag for it to get to the dsv is there still enough O2 to breath longenough to get the gas circulating ?
hope it makes sense

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Colin

I trust my rebreather completely ,
I just don't trust the user

onwards & downwards

Sutty

I dive a Kiss but...
Assuming your dil is breatheable at your 10m stop can you not just take an o/c breath, stick your DSV in, blow your lungful into the loop, then dump the whole content of the loop, your next breath will fire the ADV and your breath will be nearly all dil. (blowing into the loop 1st flushes the exhale hose and part of the scrubber). The unit will then inject to bring up PO2.
As I aid I dive a Kiss, but any problems with this plan?

Neil

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Padowan

If the unit was on setpoint at 50m (for ease of numbers lets say that it was at 1.2 bar) then this implies that you have an FO2 of 20% in the loop. As you ascend, the PPO2 will drop, but the FO2 will remain the same, and at 10m, you still have 20% FO2 gas in the loop, which is perfectly preathable at that depth. So I'd just go straight into the loop.

If I was at all concerned, then I would either dil flush if deeper than 6m, or O2 flush from 6m and shallower before getting back in.

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Janos

Again I dive a Kiss...

Doing the maths, you'd have to have a very low ppO2 (0.5 or so) at 50m in order for it to be hypoxic at 10, (it will drop by a factor of three). However, couldn't you do an off-loop dil flush (depending what the problem was) and then get back on the loop?

Or is there some subtlety that I'm missing about the vision?

Janos

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colinicky

Simple answer is I didn't know so I thought I ought to ask ! My course was taught along the lines of once you bailed out you stayed bailout .I am now learning differently

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Colin

I trust my rebreather completely ,
I just don't trust the user

onwards & downwards

sven

Colin,

My instructor hammered the message home to me that "the loop is your friend", so I would probably not have gotten off the loop in the first place. Nevertheless, in your scenario I would either (depending on the gases available) flush the loop (if DIL breathable at that depth), or, switch to CCR and check what is in the loop & add enough O2 to be able breathe it. More likely I would go 1) AND 2) before switching. That allows you check the loop before you breathe it (while on OC). In case you don't trust the results, you just stay on OC and follow your tables. You may have to "suck" the loop empty before you breathe the loop again. It all depends on the situation.

All this is somewhat mute, as nobody knows how we would react under stress ...

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BeachedCetacea

time to get rid of that anoying message and make my first post...

The vision actually maintains set put even when in OC mode. This is obviously great in the situation you describe but anoying when ascending on OC as the rebreather is still injecting O2. Whenever I have bailed out (practice only) and started the ascent, I switch back to CC breifly and switch to the low set point to give me better bouyancy control.

In the situation above, if you were using a setpoint of 1.3 on the bottom, the unit would maintain 1.3 all the way up (assuming its working correctly) so you would only experience a slight difference depending on what OC gas you blew into the loop when switching.

Devils Advocate

when you change the vision to O/C mode, the controller will still try and maintain the setpoint. So, if you got to your stop and went back on the loop the setpoint will be whatever you had it set to. I try and get students to switch to low setpoint before they switch the vision to O/C mode to make the ascent a bit easier.

Check out page 81-83 of the vision manual.

Regards
Aaron.

decoweenie

You KISSers are nosy bunch, even in the Inspiration forum...

Colin,

If you are worried about it, how about...

• open up your OPV (which should be at least cracked open during your ascent anyway)
• squeeze your CL as flat as possible to pump the gas in the loop out
• add a few squirts of O2
• go back on CC and let the ADV make up the rest of the breath

That should give you breathable gas if you can't see the PO2 values. And the automatic O2 injection should start immediately.

If possible, always try to breath out into the water the last breath when you decided to OC bail-out, instead of breathing back into the loop. This minimizes the gas expansion in the loop when you ascent..

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caver95

I am not by any means an experinced CCR diver. In my studies of trying to become a good CCR diver I have spoken with many people and I hold a great amout of respect for them. The one thing that is coming amoung them is don't be affraid to get off the loop, and take a few sanity breaths, why would you want to stay on something that is trying to kill you and you arent sure what the problem is. Bail, clear the old head, figure out the problem and the propper response for the problem, and if possible get back on the loop. Getting back on the loop I leearned to flush with a known gas, something that wont kill you. I am not the least bit affraid of going to OC, but I will get back on if I can.

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