how to kill yourself on a twin Rebreather, lesson 1

Drmike

So you have a nice twin Rebreather and a nice twin bov. You switch back and forth between the main unit and the bob during a dive. You stop switching/checking for quite a while, to carry out some tasks, staying on your primary unit. You are of course checking your primary unit ppo2 as you have done millions of times before. Everything is fine. After sometime you think about switching back to your bob to check it and as you go to do so you realise all this time you were still breathing off your bob loop!! -

You have been breathing down the bob ppo2 but monitoring the main Rebreather ppo2!!!!

Easily done - Ive discovered - easy way to kill yourself

I now believe there needs to be a common ppo2 in both loops at all times OR a fool proof way to see only your loop ppo2 that your breathing - a way to not make the mistake of monitoiring the wrong loop.

One thing I may have a look at is having two huds (one for each loop) and having the huds on a linkage so that when you turn the bov to the other loop the hud for the loop you are leaving goes out of view and the hud for the one you are going to comes into view.

This was one lesson that could easily have been learnt the hard way!

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Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

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dave t

Glad you survived that Mike

fwiw I belive backup Rebreather should be instantly ready, that means maybe electronic control to keep the po2 steady/ready all the time. I believe the back up Rebreather should be as capable if not more so that the primary Rebreather.

keep you experiences coming Mike

best

Dave

paulraymaekers

hello mike,

in the setup of the exploration breather the idee is having hud's (as we have 2 huds for each breather in the rEvo-setup), on each side of the mouthpiece

the hud's can be mounted on a baseplate connected to the BOV swivel

when you turn the BOV swivel from one position to the other, you 'flip-up' the active hud's of the breather you start breathing, and 'flip-down' the breather you just left

not tried yet, but is easy to accomplish

regards
paul

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Drmike

yup thats what I had in mind.

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

Drmike

I dont think the staring ppo2 is important or detracts from readiness (seeing as in almost all dils likely to be used the dil will be breathable at depth and it only takes a few secs to boost it up manually. You bail and step one is to establish same ppo2 as primary unit then you turn the dive.

But reading the wrong display, as we have seen, could get yah killed prity damn quick so there must be a foolproof way to ensure that doesnt happen. Habit (or always looking at primary display) is against us.

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

johnv

Mike, surely this the same as requiring a way to make sure you have the correct diluent at the right depth - Label the tanks, label the whips, be careful Job Done. As ever it's down to the diver, greater complexity of equipment requires greater awareness. especially at the bleeding edge.

My system is fiendishly simple and foolproof. I pack the secondary display away when the secondary CCR is not in use - I only have it on my arm when I'm breathing from it. Problem solved. An emergency switch is to O/C or to backup CCR Semi closed while I ready the display (takes only a few seconds).

Label your loops carefully, Pick your primary CCR, stick with that for the bulk of the dive and only use the bailout unit to check loop & ADV integrity at suitable points. Looking at the wrong display should simply not be an issue.

With respect, If you really need a technical solution for ensuring you look at the correct display you might want to re-consider using 2 CCR's as there are lots of other potentially fatal problems that can bite just as easily if you are not very aware.

good luck with it.

John

johnv

This is quite wrong. you _must_ be sure that the gas in the secondary is breathable at the depth you are at.


If you are swapping CCRs, lets say you have PPO2 in the backup loop at 20M of 1.4 and the bag is full, then decend to 40m, you now have a loop of 2.8 when you swap onto it. That's not ideal to say the least.

If you inject extra O2 into the loop (say your are using CMF and forget to turn your KISS Valve off after swapping) you could end up with a loop full of O2 at depth.

These things aren't like the boris, you have to be on top of them as you probably won't get alarms and prompts from a homebuild.

decoweenie

ADV will add diluent on descend so the PO2 could drop depending on the diluent mix.

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johnv

Agreed, but I suggested a full bag, so my example is correct.

Most people exhale when swapping (to ensure no water goes into the loop, so the bag is often full or close)

Feel free to pick holes in the examples, but the point still stands, you need to make sure the loop Po2 is breathable at the depth you are at.

Padowan

To me this is a case of relying too much on the HUD and it not giving the diver enough information rather than checking primary numerical displays (occasionally). The Boris HUD tells the diver that the loop PPO2 is on setpoint, whereas when looking at the cell readouts you're able to see the small fluctuations in PPO2 that you get when you breathe out, and when the O2 is injected - I know I'm only dealing with one loop with my Inspo, but even though I have a (Shearwater) HUD that tells me the PPO2 or each cell (to the nearest 0.1) - I still look at the handsets regularly to watch for this fluctuative (if that's a real word) behaviour, that the HUD does not have the granularity to display.

Good lesson to have learned though - keep up the good work on the dual unit, I've been following it's development with interest.

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