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Thread: Favourite bailout gases

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    Question Favourite bailout gases

    Note this is not about the "best" gases - since that is so subjective and Coolaid flavoured.

    But I would love to hear what people feel is their favoured bailout mix (s). Tell us what you carry for what type of diving - I'm most interested in logistics for the 50m -80m range but feel free to comment about how your planning changes for deeper stuff.

    I have until recently been mostly diving to no deeper than 60m and carrying air as bailout. I typically dive 10/50 (and heli-air dilutions of that) as my on-board diluent. For further background I use off board inflation and assume full dil at the start of any deeper dive. I have been playing with the numbers and trying to consider several scenarios such as optimal OC deco, optimal SCR gases, and optimal logistics in terms of not having to change mixes in bailout slings too often for a range of different diving. I think I have settled on the following:

    For 50m and shallower (no significant penetration) dives I carry a sling of Nx40 and plan to use my dil as first bailout mix. In an emergency I would breathe it on the bottom and it also makes a nice semiclosed gas should that scenario arise. The one thing I'm not totally thrilled about is the significant reverse gradients for He and N2 in the case of a long BT and bailout right at the end...but I'm not sure these depths warrant the hassle of introducing a small fraction of He...but say maybe 20% might be a good thing - what do you think?

    For up to 80m (again no significant penetration) I plan to add a second sling of 21/35. Again I plan the first sanity breath and early ascent off my dil but in a pinch I'll breathe the 21/35 on the bottom. This also is a good SCR mix for the depth (better than 17/35) and on bailout deco gives a good gradient for both He and N2.

    If considering penetration I'll take the 21/35 for shallower dives and for penetration at 80ish I'll swap the 21/35 mix for something more friendly at depth like 10/50.

    So to summarize: On any given weekend trip I'll have 3 cylinders with me:
    1. a 12L of 10/50 from which I'll top off my onboard (and have to take with if it's a penetration at 80m).
    2. a 7L of 21/35
    3. a 7L of Nx40

    I'm pretty new to the Tx bailout scene and trying to figure out what is most flexible...so I'd appreciate you comments and notes from the real world.

    Cheers
    AB

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    Re: Favourite bailout gases

    Quote Originally Posted by Underwaterbear
    what do you think?
    I think you better stay real friendly with your buddies if you plan on doing 80m dives with just a 7 of 40% and a 7 of 21/35 as bailout...

    For 50m stuff I have been carrying a 5l of air and a 3l of O2 - and then I use the 3l of O2 on the rebreather and just carry the 5l of air for shallower stuff the next day. Makes the logistics easy for places like Mt G.
    Alternately a 5l of 50% and plan on getting shallow on dil is ok out to about 30min at 50m.

    Deeper than that, I like air/light trimix and 60% for bailout - keeps the volumes reasonably balanced and is OK in 7's for 25min @70m.

    All the above means a lot of bailout tanks, or dumping mixes. I've done a few single tank dives on 50% in the last year...

    As you can see I don't have a clue what the best approach is and should shut up.

    Mike

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    Re: Favourite bailout gases

    This is a whole new world for me. On open circuit, I used mixes that have become pretty standard: 100%, 50%, 21/35, 18/45, 15/55, 10/70. I have no idea how you RB divers have come up with the combinations you use for bailout.

    Not that I am there yet. However, it is an intellectual curiousity for me at this point.

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    Re: Favourite bailout gases

    Quote Originally Posted by Mike
    I think you better stay real friendly with your buddies if you plan on doing 80m dives with just a 7 of 40% and a 7 of 21/35 as bailout...
    Sorry, you're quite right, a 7L of Nx40 just scrapes in for 20min at 80m...actually I have my 12L being filled with Nx40 by the gas fairy tonight...:D

    Cheers

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    Re: Favourite bailout gases

    Quote Originally Posted by Underwaterbear
    I'm pretty new to the Tx bailout scene and trying to figure out what is most flexible...so I'd appreciate you comments and notes from the real world.

    Cheers
    AB
    Hi Andrew. good question. I don't expect that you will get a very 'typical' answer here as there are too many variables. For what it is worth here is my take on your question.

    I think you are on the right track on one side of the coin in thinking about what tank will get you to where. This is essentially no different to OC trimix planning. Lots of what ifs etc. I don't like one thing you hinted at though. That being SCR bailout.

    I hold a dim view of this as a bailout planning option on deep wreck diving (shallow cave is a different matter) for a couple of reasons. SCR bailout is a pretty tough skill to do well on ascent and unless you are keen on keeping your skills up and practicing this often, I would wager if your Prism shat itself at 80m you would be a little concerned possibly even wearing brown derps. I think that due to the difficulty of doing this skill during a brown derp moment possibly isn't the time to be relying on this skill.

    Secondly, lets say you are a gun at this sort of skill and bailing out to SCR is a piece of the proverbial. You have skilfully kept your pO2 in the range you are happy with and now the kicker...........what is your deco obligation? You need more higher O2 gas now. Surely it is preferable to take more of the bottom mix(es) to ensure an easier time of things.

    I do practice it from time to time, but it will only ever come out as a last resort. I just take enough OC gas. If you put it into tanks that swim well it isn't too much bother.

    Last edited by Steve; 9th February 2006 at 09:34.
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    Re: Favourite bailout gases

    Down to 40mt. i would take just a 7lt. EAN32.
    at 50mt. i would take a 7lt. 15/55 and a 7lt. EAN50.
    at 70mt. + i would take a 7lt. 10/80 a 7lt. EAN50.
    at 80mt. i would take a 7lt. 10/80 a 7lt. EAN 50. and a 5lt.O2

    Note that the choice in the deco bottle sizes is governed by that which i have lying around at home but think that the 7lt. is a good size for quite a good range of depths and RT's. :)

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    Re: Favourite bailout gases

    Quote: (Originally Posted by Underwaterbear)
    what do you think?



    I think you could always do a trimix ccr course and find out how to plan and do these dives safely that way.

    Oh I forgot theres nothing to learn on the Trimix ccr course.....that cant be learnt free off the net? .....you'd better hope
    Last edited by Drmike; 9th February 2006 at 09:25.

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    Re: Favourite bailout gases

    7 ltr 21/35 down to 50m with a hose to plumb in semiclosed if needs be and a drop tank of 80 on the boat. If planning a bigger dive at 50m ill also carry the 80% in a 7


    down to 80m 21/35 in a 7 80% in a 7 drop 10ltr drop tank on the boat

    Bigger dives to 80m al80 21/35 al 80 of 80%

    80m + Al40 15/45 Al80 32/20 Al80 80%


    80m would be max depth so its unlikley id be at max depth whe I bail. Initial bail will be onto inboard 3ltr whilst i deploy the hose for the 21/35 and Id be heading up at that time.

    ATB

    Mark Chase

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    Re: Favourite bailout gases

    Quote Originally Posted by Steve
    . I don't like one thing you hinted at though. That being SCR bailout.

    I hold a dim view of this as a bailout planning option on deep wreck diving (shallow cave is a different matter) for a couple of reasons. SCR bailout is a pretty tough skill to do well on ascent and unless you are keen on keeping your skills up and practicing this often, I would wager if your Prism shat itself at 80m you would be a little concerned possibly even wearing brown derps. I think that due to the difficulty of doing this skill during a brown derp moment possibly isn't the time to be relying on this skill.

    Secondly, lets say you are a gun at this sort of skill and bailing out to SCR is a piece of the proverbial. You have skilfully kept your pO2 in the range you are happy with and now the kicker...........what is your deco obligation? You need more higher O2 gas now. Surely it is preferable to take more of the bottom mix(es) to ensure an easier time of things.

    .
    Personally I dont find SCR bailout on a deep wreck dive difficult at all. I maintain min loop as I ascend (as I would do anyway) by venting and when I reach the stops I empty the loop inject dil and sit there running scr until the end of my stop - rinse and repeat. I dont try to run proper scr as Im ascending between stops its too hard I just empty the loop prior to beginning to ascend to the next stop and if its further than 3m (ie from the bottom to first stop) I will evacuate and fill again using nose and ADV as Im ascending several times - waste a bit of gas - it doesnt matter - its not accurate between stops but by breathing out mopre than the loop is expanding I will be firing in plenty of fresh dil to keep it high. In other words I dont actually run scr during the ascent phase between stops - more like OC.

    Deco planning is easy - just switch to (or carry tables) for OC with a FO2 slightly lower than your dil FO2.......now where did I learn that from?, and where did I practice it to determine what my reduction in FO2 would be?...ah yes a trimix ccr course :D

    If anything I find it easier doing this bail out deeper.

    The drop in effective FO2 is not that huge to make the amount of extra O2 excessive - and besides you govern the drop in FO2 anyway.

    You can also run SCR off the bail gas which I usually select to give a FO2 that will give me a decently high SCR ppo2 at depth - say the same (usually higher) than my setpoint........useful things CCR Trimix classes arent they.

    To me SCR on a deep dive is more valuable at the bottom and during deep stops where any delay or increased breathing rate is going to eat faster into your OC gas (assuming an OC bail) For this reason I would suggest SCR at the bottom and up to the first gas switch would be a better and safer option, especially if your one of those people who kid yourself that you only need to assume 20lpm for bottom bailout RMV.

    How hard is it to count breaths......?
    Last edited by Drmike; 9th February 2006 at 12:08.

  10. #10
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    Re: Favourite bailout gases

    Actually Mike, I was looking for discussion and ideas rather than critism and cynicism... back at you mate. Here was me thinking you were usually a generous sort of fellow. Maybe you're having an off day.

    I agree with you in regard to SCR bailout technique. Of course I learnt that on my SCR course (also useful). Of course I feel Steve's point regarding deco is well made, I guess one might carry a plan for that eventuality but he's right in saying that making things simpler is always prefferable.

    Btw, for what it's worth Mike, I've done a CCR tmx course and am in the process of getting my head around some ideas. Forgive me for posting neophyte questions in your esteemed presence.

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