Standard Bailout Mixes

jradomski

Due to the Pms I have been getting I see some clarification is necessary..

As to what the diluent/bailout PO2 should be..

If you are running a 1.0 SP then a gas that you can verify this point is fine, although its not an ideal choice since this is a cal point, and all you can verify is that the cells agree with each other and come back to ~1.0.. This is the only point you can be sure of.. a leaner gas would allow you to verify the linearity of a cell up to 1.0 so now you can know if the cell is good up to 1.0.. you still have no idea if its ok above this point..

If you are running a 1.3 SP and you have questions about the cells if you verify it to a 1.0, you can only be sure that its ok at a 1.0, and it may be used to verify if 1 cell is disagreeing consistently with the others which cells might be correct.. if some verify to the cal point and other do not, then you have a reasonable guide.. If you have cell questions and can only verify to a 1.0 that should be you new setpoint...

If you use a low setpoint then bump it up for deco when you get shallow, you should only bump it up to whatever po2 you can verify to.. That might mean waitning until you get to a depth that you can use an offboard deco gas..


I am happy being able to flush down ~1.3 po2, I dont see a need to go lower.. and this is at max depth, once I'm shallower I can flush down much farther..

Cell verification is also not the only reason I prefer to have a richer bailout/diluent.. If I have to bail onto OC (or scr) I don't want to make my required deco any worse than its already going to be.. for example say an easy 60m dive for 45 minutes using a 10/85 GF.. using 10/50 as dil/bailout +50% vs using 21/50 + 50%. (I kept the He the same to just compare the differences in o2) If having to bail to OC the dive using 10/50 requires about 20 mins extra deco.. That might mean carrying a larger or extra cylinder to cover the bailout... for someone carrying 10/50 vs 21/50 and o2 instead of 50%.. the difference is 90 minutes.. (both dives the bailout is longer than using 50%)

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Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

silent running

Hi Steve, I'm pretty sure NAUI recomend standard mixes, can't remember exactly which ones, I'll have to check my course materials when I get home. They advocate team BO strategies and an absolute minimum of gas switching, so I think that's probably part of the reason for standardization and a pretty good argument for it, at least the minimum gas switching idea. Much of the tmix course was written by a retired Navy diver, so that might also have something to do with it being standardized and team oriented.

I guess another factor would be whether or not SCR is part of your BO plan. If it is, then you'd want as hot a mix as you dare at depth to keep your emergency deco to a minimum. Being a new tmix diver, I'm still tryting to sort out the easiest, most flexible way for me to plan, so this is a good topic to have discussed.

Do any agencies teach SCR as a first option in a BO short of total loop flood?

kieranu

If I remember correctly, Mr Radomski's does thats for sure.

jradomski

Almost correct..

SCR skills are taught starting with the first class..
On No stop required dives where there is adequate OC bailout to make it back to the point of entry safely then a Bail to OC would be preferred for newer rebreather divers, but where margins need to be extended SCR would be the first option, this doesnt preclude the diver from switching to full OC at a later point..
On dives near the recreational limits a mix of the two works well,, DO SCR in the deeper portions to save gas (to build some safety margin) and then switch to OC once you get shallower..
On deco dives SCR is a better first option since it give the diver alot more time and margin to safely end the dive..

We try and teach the diver there is not one answer to all situations, and try and give them all the options.. The only Intro level class we do not push SCR skills as strongly is for the megladon since that is ISC's philosophy..

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

Abbo

In all honesty, I haven't dived air deeper than 60m and don't want to have to try. I used to frequently do solo OC at 60m on air. I once thought that anything higher than a PO2 of 1.6 and you immediately start breakdancing, but that's clearly laughable.

To be fair, the person who was showing me this idea of PO2=2.0 at max depth had a reg attached to his dil, so the intention was to breathe dil if possible up to the first stop. He was, however, prepared to go straight to the sling tank at 2.0 if he couldn't access the dil tank. I would have thought that the time spent on PO2=2.0 would be quite short on the way to the first necessary stop at around half the max depth. It also occurs to me that the most likely reason for going to BO would be hypercapnia, so a rich mix wouldn't be a bad thing...but it would be a bad thing if I were bailing from an ox tox problem.

If I took air and O2 in 7 litre sling tanks to 85m, bailed at 85m to air and swam to 50m for a first stop I would risk ox tox at the start, but would thereafter benefit from having the gas on me to get me through deco. Serious question to deeper divers: is this unnecessarily risky?

decoweenie

Ascend from 85m to 50 using a normal deco ascend rate of 10m/min only takes 3.5 mins normally. And the PO2 is dropping constantly (from 2.0).

Anecdotal comparison, I had an incident where my PO2 was 2.45 for close to 3 mins (just don't ask me how ) at 65m between periods of checking the handset when I immediately flushed the loop and ascend to lower the PO2.

No sign of impending ox-tox, but I think I was lucky too...

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jradomski

When I was young, bold and stupid I did a 100m OC AIR dive (about 10 mins on bottom) and had no otox symptoms but in that case it was probably the lack of n2 that helped me out..

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

JonORunde

I would not worry about a couple of minutes at high ppO2 -that should not be a big issue for the most of us.
But, going from a fat trimix-bottommix to _air_ at great depths would probably feel like a hammer in the back of your head. *that* is what worries me about such a strategy.

To the question, i also try to keep gases pretty standard, with ppO2 less then 1.4 at planned bottom, and _plenty_ of He -normaly about the same as DIL.

100%
50%
30/20ish
21/35
18/45
12/62

Theese in different sizes, from cu40 to cu80, I bring as many as I need for as deep/long as I plan -or mostly, a bit _more_ then I plan to need.

Yes, I have a lot of tanks

Jon O

wedivebc

So are you concerned that a cell can current limit during a dive and therefore must be validated regularly even though it made 1.6 at the start of a dive?
What I am reading here is you select your gas on the basis of cell validation ability. In my mind other than validating the cells at a known gas pressure to ensure they are all still functioning I can't see why a high PO2 flush is needed. I was not aware cells would drop out at the high end that fast.

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Cheers,

Dave....

Man is the only animal burdened with the knowledge he will eventually die

Fun Under Pressure

i think standards gases don´t bring any benefit. The DIR guy´s use it to have the best END´s and MOD´s . But for my (only air diluent dive´s at this time) a use gases that i can breath at my max. deep.
Ali 80 21/00 ; Ali 80 50/00 ; Ali 7L 100/00

For deeper dive´s i think one bailout tank with a gas i can breathe at the MOD and one or two tank´s for deco on OC and one tank with 100 % for last deco. I think that´s a lot of tanks, and i must do any training dive´s befor i do deeper dive´s, but i have children´s and the safety is importend for me.

Cheers Markku