rebreather loops?

[milldog]

just a quick question, if the INSPO fucks up and you have to bail out to cylinders can you use the loop in an OC capacity ??? working from the Dil cylinder or is there another way ??

Graham

[jptaylor9]

Originally Posted by milldog

just a quick question, if the INSPO fucks up and you have to bail out to cylinders can you use the loop in an OC capacity ??? working from the Dil cylinder or is there another way ??

There is a technique called "open loop", discussed in detail on RBW.

JT

[milldog]

Originally Posted by jptaylor9

There is a technique called "open loop", discussed in detail on RBW.

JT

so could you use that method to go OC and reduce bail out IE use that to get to say 21m for the switch to 50% instead of carrying bottom and deco bail out ???

[Scuby]

Originally Posted by milldog

so could you use that method to go OC and reduce bail out IE use that to get to say 21m for the switch to 50% instead of carrying bottom and deco bail out ???

Why not just stick a reg on the dil cylinder (assuming you don't like the inflator-reg thing)?

David

[DannyB]

Originally Posted by milldog

just a quick question, if the INSPO fucks up and you have to bail out to cylinders can you use the loop in an OC capacity ??? working from the Dil cylinder or is there another way ??

Graham

Depends on how it goes. If the electronics go then you can go to SCR mode, that effectivley turns your 3L dil into a 12L. If the scrubber is getting breakthrough you can flush and then see if it's got enough life in it to cope in SCR mode, it often will. If you get a complete loop flood then it's off the loop onto OC bailout. Either using an aftermarket DSV or by reg swapping.

HTH

Danny

[Ken]

Originally Posted by milldog

just a quick question, if the INSPO fucks up and you have to bail out to cylinders can you use the loop in an OC capacity ??? working from the Dil cylinder or is there another way ??

Graham

One of your options is to go to semi-closed mode after sorting thing out. By sorting things out I mean either use your BOV, do a closed loop drill, or go to bailout to get some sanity breaths in there.

What mode you go to is dependent upon the severity of the problem and your level of conservatism. Whatever it is...your dive should certainly be over.

[milldog]

Originally Posted by DannyB

Depends on how it goes. If the electronics go then you can go to SCR mode, that effectivley turns your 3L dil into a 12L. If the scrubber is getting breakthrough you can flush and then see if it's got enough life in it to cope in SCR mode, it often will. If you get a complete loop flood then it's off the loop onto OC bailout. Either using an aftermarket DSV or by reg swapping.

HTH

Danny

this is what i wanted to know cheers

[Mark Chase]

Originally Posted by milldog

just a quick question, if the INSPO fucks up and you have to bail out to cylinders can you use the loop in an OC capacity ??? working from the Dil cylinder or is there another way ??

Graham

Open loop uses the ADV so it assumes you have one.

If the loop is still working and your bailing out the only reason will be C02 or lack of 02.

Co2 from all the people i know who have had a hit means your RMV will be massive. Open loop and a 3ltr is unlikely to be enough to save your arse all the way up to 21m.

With C02 its Much Much better to bail OC and immediately start getting C02 free gas. Better still is have a BOV and just switch to OC.

Lack of 02 shouldn't be a major problem and you can just go semi closed but one would hope you had at very least a hose on your shallow deco that you could plug in to the unit and run it on that instead. You can run manual addition using 50% and keep it ticking over assuming the narcosis isn't an issue.

Semi closed as a bail out for a C02 hit has (I am told) been dropped from the IANTD training program. I think this is very sensible and I hope that it will be dropped from TDI as well if it hasn't already. Personally I would rather bailout than run the unit semi closed. I tried it once for practice and done for any significant length of time it is uncomfortable. I ended up with a sore nose and throat and a headache. If you have bailout gas use it and if you havent then why not?

Personally I believe that an integrated BOV with off board gas in suitably sized tanks is a significant safety advantage. I watched someone bail on to OC because they couldn't get a breath on their unit and it wasn't a pretty thing to watch. Hes alive but it wasn't something you would want to do to often.

ATB

Mark Chase

[NotDeadYet]

Originally Posted by milldog

so could you use that method to go OC and reduce bail out IE use that to get to say 21m for the switch to 50% instead of carrying bottom and deco bail out ???

As Gordon Smith used to famously say, diluent is not bailout. That's the same attitude I take with my rebreather. Dil drives the rebreather, that's it. I have the standard KISS DSV which I only ever use for taking a few breaths as a tranisition stage to bailing out to a separate bail out supply. I never rely on onboard gas as bailout because it isn't. Not carrying a gas breathable at depth is a good way to become dead.

If you sit down and do a proper fault tree risk analysis on rebreather diving the one thing that becomes very clear is that most of the major (i.e. fatal) problems on a rebreather become minor (or are eliminated completely) by the addition of solid, reliable bailout.

Cheers,

Stuart

[Muddweller]

When I was making some OC bailout tables I quickly came to realise that my 4 litre dil would not be enough to get me for e.g. from 50m to 21m for the switch to 50% even if it was full. This was based on an ascent of 9m/min and a SAC rate of 30ltr/min.

As others have said it's not a good idea to have dil as your only bailout for that depth, however at present that is how I dive. The max depth I chose to use my unit is based on a basic formula to calculate my air consumption for the duration of the ascent to 18m. I should have 60 bar left at 18m then I switch to a 5ltr 50%, this limits the max depth I can use my unit as it is to 40m.

Maybe I should go back to twins

Regards
Karl