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Thread: Diluent / Bail-out / Deco Line gas choice

  1. #31
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    Re: Diluent / Bail-out / Deco Line gas choice

    Quote Originally Posted by hoppyinca  View Original Post
    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
    Hello Mate,

    My bailout is planned from the worst possible moment, i.e. after total planned bottom time. With regards to loop floods, I believe that point the Padowan was making is that a flood is likely to occur under two scenarios - tear in the loop, possible but not that likely or through an error in assembly. With the latter it would be normal to expect that the failure would occur early on in the dive.

    However, both mine and Janos's experience have been floods well into the dive.

    Cheers

  2. #32
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    Re: Diluent / Bail-out / Deco Line gas choice

    Quote Originally Posted by hoppyinca  View Original Post
    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
    The reason that the worst case scanario is not my modus-operandi for (self carried) bailout is that for the majority of bailout reasons I feel my plan will be sufficient, for the 1 in 100 bailouts that I do where my plan is not sufficient, I accept the risk that I may need to call for boat support, take gas from a team member, risk getting back on the loop or surfacing and getting bent. In my opinion, the only time where I am screwed like this is if I flood my loop after a significant bottom time at a depth of over 60m, I have lost my buddy, can't get back to the shot and have to bag off and ascend alone, and can't get any drop tank support from the boat - IMHO the chances of ALL these things happening is so slim, I'll accept that risk.

    It's my way of compromising between Alpinism and Seige Tactics for bailout. I'll cover a certain amount of scenarios with what I carry, and accept the risks that in certain cases I may have a problem.

  3. #33
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    Re: Diluent / Bail-out / Deco Line gas choice

    Quote Originally Posted by wondersea  View Original Post
    Hi all,

    Just wondering about your choice in matter of diluent / bailout and Deco line for let see :

    1 / Dive at 40 m (130 ft)

    2/ Dive at 60 m (196 ft)

    3/ Dive at 100 m (328 ft)

    Same or different gas for diluent / Bailout / Deco line (gas/depth) ?

    Heliair / Trimix / Heliox / Triox / Nitrox ?

    I presume that we are with CCR and we don't take all decompression bailout gaz onboard but just enough (with security) to join the Deco line if need.

    Can you argument your choice :)

    I think not all of you as the same strategy and it's will be great to compare it.

    Thank's for your cooperation.
    Antoine;

    To participate in your original query, I present how I would plan my bail out strategy, and I invite corrections/improvements please.

    These are bail-out plans (not dive ones). I use 1 offboard tank for both bailout and ADV, hence dil = bail-out gas, and can carry whatever else is needed by plumbing in my onboard to OC. I can also strap-on 80 cu-ft (maybe even larger) as onboard to my Meg, + side-mount another pair.

    There seems 2 opposing schools of thought about diluent choice.

    1) Keep the PO2 about 1.0 on botttom to facilitate effective loop flush to reduce PO2 quickly (for hyperox and HCAP issues).

    2) Avoid hypoxic mixes wherever possible, and make dil PO2 higher to faciliate bail-out avoiding hypoxia, and speeding up deco issues.

    I lean towards 2) and make my bottom dils with a PO2 of 1.3 nowadays. I've got a good facility and access to cheap gas and I can make any kind of mix.

    On the 100m dive (which I don't do yet), I switch diluent to keep the dPInert to within 0.5bar.

    All bailout plans are at nominal conservatism settings, and I expect I would spend more time (especially at the shallows) if actual volumes permitted.

    In these plans, I assumed no time spent on bottom searching for the up-line. In reality, one should plan to spend the time necessary to find the up-line from the farthest point (i.e. planned turn around point) using a high (stressed out) RMV (RMV=40L/m). On ascent, I assume an average of 20 (L/m), as I know I'm making progress once I get my hands on the line and maybe the attention of buddies.
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    Last edited by Gilles; 14th June 2007 at 16:05.

  4. #34
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    Re: Diluent / Bail-out / Deco Line gas choice

    Quote Originally Posted by hoppyinca  View Original Post
    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
    agreed! if u don't assume that u end up dead i think

  5. #35
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    Re: Diluent / Bail-out / Deco Line gas choice

    Quote Originally Posted by jiseson  View Original Post
    agreed! if u don't assume that u end up dead i think
    If you want to base your bailout strategy on absolute worst case failure mode, on your own, at the end of your bottom time, with the biggest SAC rate and still condust a conservative deco schedule then that's fine - but for my average dive ~70m for 40mins bottom time I'd need to be carrying at least 3x 80cuft cylinders, more if the dive is much deeper. I'm not prepared to do that, so I accept an element of risk and have a strategy that I feel covers the most likely scenarios.

    It's certainly not as black and white as "u end up dead i think".

  6. #36
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    Re: Diluent / Bail-out / Deco Line gas choice

    Hello folks,

    I initiate this thread because it's not really simple to find a good way in matter of gas strategy with a CCR.

    Each of you as his point of vue about how organize the bail out.

    It's interesting to know all of your approach.

    I try to find my own way put on this few thing.

    First, I want dive light ! If I choose RB its because I don't want to have many tank with me
    So, only two tank 7/10L max BailOut with me.

    Then, I want optimize tank filling. Diluent and BO1 have to be often refill (so heliair) , BO2 and deco we hope not.

    Also I want to keep BO2 and deco for next dive if not use, anyway the depth !

    And I want same simple emergency procedure whatever the mix and the depth.

    Some of you, can tell me I want the sheep with 5 legs like we say in France. :D

    But let try it ...

    I use V-planner VPM-B and VPM-B/E and excel. Sure some wrong statement that you can show me.

    In fact, I prefigure three case:

    40 - 60 m (0 - 40, simple plan with Nx)

    60 - 80 m

    80 - 100 m

    I presume that on boat there is one deco line and another ready for diver SMB signal .

    - The decoline is always the same :

    6 m - oxy
    30 m - Tx 40/20
    60 m - Tx 18/44 (for 100 m dive only)

    - No diluent change during the dive

    - onboard diluent (3L / S 19) for diluent / wing and BOV (BOV is only here for 2/3 min to answer the question, I find the problem, I return to the loop or I definitively bail out and start ascent and deco.)

    - Bailout 1 (6L / S 50) for diluent or first bailout which start at the worth time (end of bottom time at the max depth)

    So, H 10/52 up to 80m, H 8/62 up to 100 m

    - Bailout 2 (7L / S 60) to join the deco line or have time to send the alerte yellow SMB in order the boat send along a deco line.

    So Tx 18/44 up to 80 m, Tx 12/57 up to100 m

    Here is the result in details, I thing it's not to bad, take a look on it :

    May be I am wrong at all, and I am waiting for your comments and advises ;)
    Attached Files

  7. #37
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    Re: Diluent / Bail-out / Deco Line gas choice

    Quote Originally Posted by wondersea  View Original Post
    May be I am wrong at all, and I am waiting for your comments and advises ;)
    Antoine;

    The discussion would be facilitated if you re-calculate using the same bottom times I assumed in the examples I provided above (60, 40, 20 minutes for the 40, 60, 100 meter dives respectively).

    The amount of deco is normally very sensitive to the amount of bottom time.

    This way I may be able to demonstrate a more efficient choice of gases.

  8. #38
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    Re: Diluent / Bail-out / Deco Line gas choice

    OK Gilles, you're right,

    I will doing it this evening and post a new model with same parameters.

  9. #39
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    Re: Diluent / Bail-out / Deco Line gas choice

    Well ;) ,

    Here is the file with Vplanner screen. I didn't want to wait up tonight.

    Conservatism nominal, VPM B/E

    For 60 m Dive, I have almost 10 min difference between VPM B and VPM B/E not for the 2 other dive ????

    Thanks'
    Attached Files

  10. #40
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    Re: Diluent / Bail-out / Deco Line gas choice

    Antoine;

    I illustrate your version of a 100m bailout plan for all to see. I hope you don't mind.

    I am not an expert at planning 100m dives, but the topic interests me, and I hope those who know more will chime in, if/when I'm stating or .

    1) You have 5 different gases, all in strange volumes, probably needing 6 different tanks (or 1 large tank for your 3400L of 40/20 to make a total of 5 tanks for the other gases). Your creating logistics issues for yourself.

    2) What is the logic of using 8/62, other than being a convenient Heliair mix?

    3) Why the switch from 8/62 to 12/57 for 1 stop? If your going to mix 12/57, why not use this as a bottom dil?

    Look at my version above. More than all the gas I need (assuming average RMV of 20 L/m) can be carried by 4x 11.2L tanks filled to 200b. 1 of O2 and another of EAN 50 strapped on as inboard. The other 2 sidemounted with the 12/59 as bottom dil on the left, and the next richer 24/39 sidemounted on the right.
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