• Welcome to ScubaBoard


  1. Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

    Benefits of registering include

    • Ability to post and comment on topics and discussions.
    • A Free photo gallery to share your dive photos with the world.
    • You can make this box go away

    Joining is quick and easy. Login or Register now by clicking on the button

Perdix Ndls

Discussion in 'Shearwater Research' started by Bigeclipse, Apr 20, 2016.

  1. Jax

    Jax Deplorable American ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: AZ TX
    25,459
    7,133
    113
    I absolutely reject this NEDU study for any indicator of deep stops or the effect in decompression.

    Why? The emphasis in the title is mine:

    Redistribution of decompression stop time from shallow to deep stops increases incidence of decompression sickness in air decompression dives

    The divers went to 170 FSW on AIR. They had continuing increase of N2 Loading because they were on EAN21.

    Given that technical divers choose gasses for the best mix for the dive they are doing and their decompression plans, the NEDU study does not apply.
     
    rongoodman likes this.
  2. Jax

    Jax Deplorable American ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: AZ TX
    25,459
    7,133
    113
    I cannot recommend "Deco for Divers" strongly enough. It is a very easy-reading book, and will take you as far technically as you want to go.
     
    wetb4igetinthewater and dberry like this.
  3. Kevrumbo

    Kevrumbo Banned

    # of Dives: 1,000 - 2,499
    Location: South Santa Monica Bay/Los Angeles California, USA
    5,659
    1,343
    113
    I agree; using a high FN2 bottom mix like Eanx21 will definitely supersaturate those slow tissue and load them with enough residual N2 that can produce DCS symptoms with air decompression. It's been my anecdotal experience though that if you do four consecutive days of two dives per day Air bottom mix at a an operating depth range of 45m to 60m, even with 50% & 100% O2 deco gases, you will have the the same residual N2 loading of the slow tissues generating the niggles or overt type I symptoms. To compensate on subsequent dives I changed the GF99 on the Petrel from 85 to 60 during my O2 stop at 6m to extend the profile time out on the third and fourth consecutive day (and took a day off after that). . .

    Dr. David Doolette gave a good overview of the implications of the NEDU Study to Deep Stops & Bubble Counter Models in this presentation (fast forward to time index 25:10 thru to 39:00 in the link below).

     
    Last edited: Apr 30, 2016
  4. rongoodman

    rongoodman ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Albany, NY
    4,938
    1,598
    113

    As I recall, their "deep stops" were ridiculously long and they shortened the shallow stops to compensate, so the profiles were nothing like those generated by VPM or standard Buhlmann GF combinations. This, in addition to the crazy choice of gases.
     
    Jax likes this.
  5. Kevrumbo

    Kevrumbo Banned

    # of Dives: 1,000 - 2,499
    Location: South Santa Monica Bay/Los Angeles California, USA
    5,659
    1,343
    113
    Of course no recreational sport technical diver does a profile like that in the NEDU Study for a single dive.

    But once again, it is this similar pattern of supersaturation of the slow tissues seen in the NEDU Study applied to Dual Phase Bubble Models (RGBM, VPM) or Buhlmann GF's with an emphasized deep stop component (30/85 for example): even with deco gases Eanx 50 and O2 following a prescribed Deep Deep stop algorithm, there is potential of residual inert N2 loading of those slow tissues still causing DCS symptoms --especially over several consecutive days or weeks of diving these decompression profiles.

    See links from Deep Stops increases DCS thread:
    Surface/Post-Dive Decompression on Air
    The Typical Profiles for Sport Expedition Diving
    Opinion that Deep Stops still produce Venous Gas Bubbles
    Extending O2 Stops vs de-emphasizing Deep Stops
     
    Last edited: Apr 30, 2016
  6. Jax

    Jax Deplorable American ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: AZ TX
    25,459
    7,133
    113
    There is a potential for more N2 loading in the slow tissues, but good algorithms work for that.

    upload_2016-4-30_14-7-3.png
    Source, Deco for Divers, 2nd ed., Mark Powell
     
  7. Kevrumbo

    Kevrumbo Banned

    # of Dives: 1,000 - 2,499
    Location: South Santa Monica Bay/Los Angeles California, USA
    5,659
    1,343
    113
    Simon Mitchell's recommendation (as he first told me in 2013 as my attending & treating Physician on the Bikini Atoll Expedition), in light of the NEDU Study is a Buhlmann ZHL-16 GF Lo/Hi of 40/70 as a starting reference base -although he primarily dives CCR for his Expedition Dives.

    Kevrumbo said:
    The best most prudent compromise to practically apply from the NEDU Study & discussion, is to do the Deep Stops, and extend out the O2 profile at 6m such that you have a surfacing Gradient Factor of 60% or less (per the readout of a Petrel Computer upon surfacing from your O2 deco stop) --to ensure inert gas elimination from those Slow Tissues. This is especially warranted if you're doing multiple deco dives per day for a week or more -and I would also recommend taking a day-off/break after three consecutive days of multiple deep deco dives per day. . .

    Simon replies:
    I would agree that this is a workable compromise. Deep stops can be safely incorporated into a dive profile if you want to use them. However, there is no evidence that you gain anything by doing so, and the available evidence suggests that their use is not the most efficient use of deco time. Thus, if you have a fixed amount of decompression time, the decompression will become less safe if you over-emphasize deep stops.
     
    Last edited: May 1, 2016
  8. Gaucho223

    Gaucho223 Nassau Grouper

    # of Dives: 500 - 999
    Location: Washington, USA
    196
    6
    18
    Ditto on comparing tables to computers. On suggestion w/r/t to understand your specific dive profiles/patterns: I used the petrel in parallel with my previous oceanic plus for about 30 dives. I wanted the actual data regarding ocean vice cavern or training profiles. The data and actual tissue loading made a big difference and bow I might GFs during future dives where I conscientiously made a decision to extend my bottom time into Deco and/or during CCR. Second, you might as well read and educate yourself prior to future technical classes/training--less making actual deco dives. Iow; make everything third nature through preparation, education, and using data to help you make informed decisions. Just one view of the world. btw: there is a lot of good medical and applied research coming out of the Rebreather Forum annual meetings--good stuff!
     
  9. jeanluc37

    jeanluc37 Garibaldi

    # of Dives: 50 - 99
    Location: Saint-Pierre-des-Corps
    1
    0
    1
  10. lucasvr

    lucasvr Garibaldi

    # of Dives: 100 - 199
    Location: Netherlands
    1
    1
    1
    Hi included are the NDL limits from the perdix compared to the Suunto and padi tables.
     

    Attached Files:

    outofofficebrb likes this.

Share This Page