Diluent / Bail-out / Deco Line gas choice

jptaylor9

Having bailed from a 60m dive on a cold Febraury dive in the channel when my loop flooded, I know how tight the gas supply in 7L is.

Talking practical experience here rather than computer models

However, if I'd aborted dive at the bottom of the shot line when the loop breathing felt odd rather than pressing on with the dive, I'd have been able to make a leisurely ascent... I think there is a lesson there!

JT

jiseson

as i am reading this thread it seems to me that the limiting factor to a dives' duration is not scrubber time but how much bailout u can carry. doean't this effectively severely reduce the arguments vs Extend aire, ... or for that matter OC?

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Jonathan D Iseson

RichClark

Absolutely, what limits my bottom time is the amount of bailout I'm either able or willing to carry.

Cheers

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Mark Chase

Yes and no.


Bailout is the limiting factor but I cant see how it affects the argument with OC as you only use bailout in an emergency not every dive. An incident at depth on a working CCR is still 100times safer on CCR than on OC. Helium usage on CCR is still a tiny fraction of OC?? theres just no comparison.

We have found we still do similar run times to the old days of deep OC diving but now we dont leave bottom at 70 with 30 bar any more and if we do its realy not an issue

Extend air has no great run time advantage over conventional scrubber materials but it may or may not allow for smaller scrubbers (depending on who you believe)

ATB

Mark Chase

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jiseson

as far as the Extend Aire - i was just inquiring re those commnets i read knocking it's use due to it's shorter duration as compared toMeg , APD.... larger capacity scrubbers-seems all mute then no?

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Jonathan D Iseson

Mark Chase

To the best of my knowladge the extendair cartridge in the inspo I looked at was aparently offering 6 hour run times but this was later refuted and pulled back to the standard Inspo 3 hours.

I persoanly managed 4-5 out of an inspo scrubber anyway and know several people who considered six hours on a standard inspo scrubber to be about right in 15c+ water at least.

What ever push it past the manufacturors recomendations at your perrel and if you do it unnecessarily then your mad. My average scrubber usage at home is about 2.5hour then bin it, as its only £7.50 a fill so why try to push a second dive and risk a breakthrough.

ATB

Mark Chase

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Padowan

Personally for dives over 60m I like to carry enough gas to get me back to the shallows, and not necessarily conduct all my deco. My assumption is that once there, I should have people around me with gas, access to gas staged on the station, or dropped from the boat, and in the event that the bailout was a scrubber breakthrough, rather than a total loop flood (the only 2 things I see causing me to permanently bail onto OC at depth) I would take the risk that if I ran out of carried OC gas, the drop in gas density, and reduced workload with being on deco in the shallows, I would seriously consider going back on the loop as I feel it would still perform. So an 80cuft of bottom mix, and either a 7L or an 80cuft of a mid-water mix (up to perhaps 50%) should get me back to the shallows, blowing some deep stops, where I do as much deco as I can, before calling for drop gas, using gas from a buddy or the station or switching back to the loop again.

In Janos's case, he had a loop flood, so had no choice but to conduct the whole deco on OC. The interesting thing about this is that the flood happened (or was noticed) at the end of the bottom time, my assumption on loop flood has always been that a misplaced o-ring or other significant leak would result in a flooded loop early on, maybe it's time to re-evaluate that assumption. However I know that my Inspo is more tolerant of water in the loop than the KISS, and I have easier options of getting the water out.

Food for thought for sure.

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RichClark

A bit of a hijack, sorry.

That's probably true, but I wonder if an inspo (or any other OTS cunterlung Rebreather for that matter) is more prone to flood because extra breaks in the loop Not trying unit bash!

I flooded my loop, through user error / poor maintenance on about minute 75 of a 65m training dive so its probably worth considering that a loop flood isn't always going to occur early on in the dive.

More food for thought....

Rich

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Mark Chase

I have to say i got a hell of a lot of water in my inspo on two occasions. Having the large counter lungs it was not an issue to have half the exhale lung full of water. I ended both dives on loop.

It was amusing to take the inject button off and see a steady jet of water poor out.

The KISS just doesn't have the potently to handle that much water. You would have to bailout. It is it's biggest failing IMHO.


As for failure points on the KISS? I don't think number of failure points is at all important its how likely they are to fail that counts. I have read about a few KISS floods and experienced a fair bit of gurgling my self QED there has to be Ingres possibilities in the design that apparently can elude normal preview checks.

Personally I find it hard to do good YBOD quality positive and negative tests on the KISS. The OPV blows much too easily to hold a good positive and I am almost frightened to do a negative test due to the design of the ADV.

On the other hand i don't worry about it so long as i have adequate bailout. I did some silly 60m Alpinist dives on the YBOD but there is no way id dive alpinist on the KISS to any depth below 20m.

ATB

Mark Chase

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hoppyinca

okay, newby here, but why would you not assume the "worst case senario" when planning bailout to be at the end of the planned bottom time?

worst case in my mind would be break through or complete flood (and cocktail) at the end of bottom time. Really what ever it takes for your rig, or for you to consider your rig, no longer usable...

I agree with several view points on amount of gas to carry, where to carry it, and access to that gas (e.g. on board/ off board), but in my mind the starting point for bailout would be the "worst case" which is at max N2 loading... i.e. end of bottom time...

just my newbly 2 cents...
hoppyinca