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Increasing conservatism with Decoplanner/VPM

Discussion in 'Advanced Scuba' started by Tortuga68, Jun 11, 2011.

  1. Tortuga68

    Tortuga68 Divemaster

    # of Dives: 1,000 - 2,499
    Location: Puerto Galera, Philippines
    4,104
    842
    I have come to the conclusion that I have experienced some symptoms of DCS following some technical dives I've done in the past

    Symtptoms were: tiredness, minor shoulder pain & 'hotness' on the back of my hands. At the time I wrote them off to other causes (denial) but now think otherwise

    Typically I will do 1-2 tech dives a day, or 1 tech dive plus 1-2 rec dives. Rec being usually 20-30m and tech 45-65m

    30m rec dives have usually been on EAN32, for all other dives backgas is air. On technical dives I switch to 50% at 21m and O2 at 6m. Following the completion of the 6m stop on tech dives, I switch to back gas for the 3 minute ascent to the surface

    My runtimes are cut on Decoplanner 3.1.4 using VPM on '2' conservatism

    I have a few ideas on making them more conservative:

    1. Switch conservatism on Decoplanner to 3 or 4

    2. Add deep stop(s)

    3. Stay on O2 to surface

    I already plan to breath O2 on the boat for 5-10 minutes after tech dives (it's there in my stage so why not), and use nitrox more for rec dives - also to avoid doing reverse profiles (which I haven't done previously, per my other recent thread)

    Any thoughts on which to do and/or what do you do?

    Thanks
     
  2. down4fun

    down4fun Solo Diver

    # of Dives: 500 - 999
    Location: Fort Lauderdale
    1,170
    182
    Why add deep stops? It's my understanding that the use of deep stops have not been proven to be beneficial.

    Also a word on the surface O2. In talking with Dr Pollock during the DAN study at Innerspace the use of O2 at the surface for periods as short as 10-15 minutes is of little benefit. If you were to use it for 30+ minutes you may receive some additional deco benefit. But 10-15 minutes duration you are only affecting the fast tissues which have already off gassed. I am not quoting him, but trying to relay my understanding of what he said.

    Don't get me wrong. I applaud your trying to make changes to your deco regime to lower your DCS risk and s/s. Just not sure all the changes you are making are the ones I would make.
     
  3. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, Washington State
    11,038
    5,709
    If you still insist on diving air...
    The deep stops are not the way I would address your symptoms which are all "slow" tissue symptoms. Deep stops are intended to address "fast" tissues and/or helium offgassing. I would be moving the boat O2 time to 20ft, skip the 10ftstops entirely and replace them with a 6-8min ascent from 20ft once you are already "done". Bascially you need more time shallow to get rid of that annoyingly slow N2. So consider switching to a friendlier backgas with less N2 and more He.
     
    limeyx likes this.
  4. Tortuga68

    Tortuga68 Divemaster

    # of Dives: 1,000 - 2,499
    Location: Puerto Galera, Philippines
    4,104
    842
    Thanks guys, very good points


    So basically I would be doubling my current ascent time from 20' - I will implement this next month (my next dive trip)

    To clarify, would you stay on O2 all the way to the surface, rather than switching back to air?

    The main reason for switching to backgas at the completion of the deco schedule (apart from being the way I was taught) is to have the stages all stowed and clipped together, ready to be handed up to the boatman - but since it's pretty rare that we have heavy seas or need to get back on the boat quickly, there's no reason why I can't change this and do it on the surface, or at 1m for that matter
     
  5. SuPrBuGmAn

    SuPrBuGmAn Solo Diver

    # of Dives: 500 - 999
    Location: Tallahassee, FL
    12,436
    290
    Stay on O2 to the surface, but take a 5 min air break every 15 minutes on O2.
     
  6. Tortuga68

    Tortuga68 Divemaster

    # of Dives: 1,000 - 2,499
    Location: Puerto Galera, Philippines
    4,104
    842
    Thanks

    I usually plan my bottom time to limit O2 exposure at 6m to 10 minutes max (maybe 12 minutes if it's the second dive in a series)... so I'm thinking that doubling the ascent time to 6 minutes (ie max O2 16 minutes) will be okay, given the reduced PP during the ascent. But a good reason to switch to backgas at 1m and stow everything then, which should work well - total 15 minutes exposure, no need to take a break. One minute will be enough to stow the stage reg and switch

    I'll post on the results

    A related question: I try to avoid working after the dive (carrying gear etc) although I am going to be more diligent about it in the future than I have been (sometimes carry my gear off the boat, which I believe may have contributed to the shoulder pain)... Anyway, my question is: what's worse, climbing the ladder, or 'bench pressing' yourself up over the side of the boat? (our dive boats have low gunnels so it's not that hard). Maybe it'll be better for my shoulder and give me pain in the butt instead :p
     
  7. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, Washington State
    11,038
    5,709
    How long is a typical O2 stop now and what are you doing between the end of that time and the start of feeling iffy?
     
  8. Tortuga68

    Tortuga68 Divemaster

    # of Dives: 1,000 - 2,499
    Location: Puerto Galera, Philippines
    4,104
    842
    My O2 stops are between 6-12 minutes, depending on depth, BT & whether it's the first or second dive in a series

    A typical runtime would be something like this:

    55m for 20 minutes
    +2 minutes to first stop
    1 minute @ 24m
    2 @ 21m (switch to EAN50)
    2 @ 18m
    2 @ 15m
    2 @ 12m
    4 @ 9m
    10 @ 6m (switch to O2)
    3 minutes to surface

    Dive time 53 minutes, deco 28 minutes

    After surfacing, I hand the stages to the boatman, take off my double AL80s & help him lift them (push from below) & get on the boat using either the ladder or bench press as above. Then I'll basically relax on the boat ride (usually only ~10 minutes), drink some soluble aspirin, stow my SMB. When we get back I typically carry my AL40 stages (crew take my doubles) all of 10m to the shop. I'll wash my gear, have a cold shower, drink a gatorade, get changed. Maybe have some lunch or a lie down. That's about it

    Symptoms have typically occured within 60 minutes of surfacing & mostly gone within 2-3 hours
     
  9. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, Washington State
    11,038
    5,709
    10mins on O2 seems short to me. I don't have any software to validate this opinion, call it a gut reaction. I would say the 50% is a good idea to have as a 2nd gas (its a long way from 55m to 6m) but its not getting you much offgassing. The "real" offgassing is at 6m and you aren't there long enough.
    So same suggestion as before:
    Keep same 50% profile
    extend the 6m time to say 15mins
    5mins up to surface
    skip the boat "deco" time/gas/breathing

    Its not going to be any "worse" trying it.
     
  10. Tortuga68

    Tortuga68 Divemaster

    # of Dives: 1,000 - 2,499
    Location: Puerto Galera, Philippines
    4,104
    842
    I'm not overly keen on spending 15 minutes on O2 at 1.6 PP... and taking a 5 minute air break isn't going to fit the overall schedule very well IMO. I'm thinking I'll try a few things:

    a. extending the O2 stop (12 minutes max?)

    b. slowing the ascent for the last 6m

    c. staying on O2 for the ascent

    I'll mix & match until I find something that works both in eliminating any symptoms & being practical. Might be hard to know what works since most of my dives have been asymptomatic... actually I believe the schedules I use are "okay" but maybe on the edge of what works for me - so that if I'm not fully hydrated, or doing multiple dives, or carrying gear etc, I get a problem
     

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