Hello and welcome to our community! Is this your first visit?
Register
Page 1 of 45 12311 ... LastLast
Results 1 to 10 of 446

Thread: Deep Stops

  1. #1
    New TDF Member
    Join Date
    Nov 2017
    Location
    cornwall
    Posts
    1
    Likes (Given)
    0
    Likes (Received)
    0

    Deep Stops

    I was told a few days ago that for Tek diving PADI are not in favour of deep stops anymore. Is this true? If it is what research is this based upon please?

  2. #2
    Established TDF Member
    Join Date
    Feb 2013
    Posts
    734
    Likes (Given)
    109
    Likes (Received)
    224
    Deep stops became fashionable when bubble models gained traction as preferable decompression models a fair few years ago. The theory was that allowing absorbed nitrogen to disperse slowly would prevent micro bubble formation at depth and thus larger damaging bendy bubbles would not form in the shallows.

    The problem was that deep stops allowed continued on-gassing of the more absorbent ("faster compartment") bits of the body like the blood, and, more significantly, the slower absorbing bits ("slow compartments") like your bones which then take longer to decompress, so bends became more, rather than less, likely.

    The only empirical evidence for this was in a US Navy experimental diving unit study that was conducted by the US Navy who compared deep stop strategies against "traditional" gradient models of which Bühlman 16c is the most common. The results suggested the bubble model resulted in more bends, hence the US Navy rejected a bubble model as a basis for future dive tables.

    That probably sounds like gobbledygook so listen to a guy who can actually explain this stuff:

    https://www.youtube.com/watch?v=HU04JhXggPg
    Last edited by Tewdric; 21-11-2017 at 09:11 PM.

  3. #3
    Established TDF Member nigel hewitt's Avatar
    Join Date
    Sep 2013
    Location
    Brighton, at the Marina end.
    Posts
    2,762
    Likes (Given)
    501
    Likes (Received)
    2016
    The deep stops enthusiasts had 'get you out faster' profiles and the USN tested them properly and they failed dismally.
    I think they pulled the test as not safe before they finished the planned dives.

    Then a pretty good hatch job on the theory was done by Simon Mitchell, my favourite deco guru.
    So we dialled up 40/75 GFs on our computers, did Bühlmann plus a bit and all lived happily ever after.

    It's probably 100 times more complicated but that's my reading of it.
    Last edited by nigel hewitt; 23-11-2017 at 10:00 PM.
    Helium, because I'm worth it.
    Waterboarding at Guantanamo Bay sounded like a radical holiday opportunity until I looked it up.

  4. #4
    Gone diving back later Vanny's Avatar
    Join Date
    Jan 2013
    Location
    Essssssex
    Posts
    1,002
    Likes (Given)
    356
    Likes (Received)
    245
    I'm guessing that link goes to Prof simon Mitchell. He's the guy to watch/listen to. But yes deep,stops have generally fallen out of fashion. You'll prob find comments around where divers talk about changing their gradient factors to mive away from deep stops , preferring longer shallow stops.

  5. #5
    Established TDF Member Energy58's Avatar
    Join Date
    Jun 2014
    Location
    Oman
    Posts
    1,512
    Likes (Given)
    245
    Likes (Received)
    385
    Quote Originally Posted by nigel hewitt View Post
    The deep stops enthusiasts had 'get you out faster' profiles and the USN tested them properly and they failed dismally.
    I think they pulled the test as not safe before they finished the planned dives.

    Then a pretty good hatched job on the theory was done by Simon Mitchell, my favourite deco guru.
    So we dialled up 40/75 GFs on our computers, did Bühlmann plus a bit and all lived happily ever after.

    It's probably 100 times more complicated but that's my reading of it.
    Deep stops/bubble models always were deco woo - there was no actual evidence that they did what they were supposed to do (which is something to do with the assumed maths of bubble growth) but they got you out of the water faster - the NEDU trials simply proved it by bending a bunch of divers!

  6. #6
    Established TDF Member
    Join Date
    May 2014
    Location
    Colchester
    Posts
    1,313
    Likes (Given)
    1727
    Likes (Received)
    326
    Quote Originally Posted by Energy58 View Post
    the NEDU trials simply proved it by bending a bunch of divers!
    To be exact, they did 20 profiles across the test group on Buhlmann with no bends.

    They got to 18 profiles with bubble model and stopped after the 2nd bend.

    *edit - "exact" appears to be a poor choice of word. Those results are from a different presentation

    This study was pretty brutal and roundly rubbishes bubble model theory (at least for the bubble model in question):

    On Thalmann (gas content) - 192 dives resulting in 2 pain-only bends and one with spinal symptoms

    On BVM (bubble model) - 198 dives resulting in 11 bends, including pain-only, skin & neurological.

    Ultrasound scans also observed a higher instance of large bubbles in the BVM dives.

    Would have been nice (for us) if they'd done Buhlmann vs. RGBM
    Last edited by PhilPage; 22-11-2017 at 11:31 AM.

  7. #7
    Established TDF Member
    Join Date
    May 2014
    Location
    Colchester
    Posts
    1,313
    Likes (Given)
    1727
    Likes (Received)
    326
    Quote Originally Posted by Penny View Post
    I was told a few days ago that for Tek diving PADI are not in favour of deep stops anymore. Is this true?
    Yes, and not limited to PADI - everyone has been forced to re-evaluate their deco approaches (unless they'd already binned deepstops). The only thing that's remarkable is that it's taken this long to get decent traction.

    Quote Originally Posted by Penny View Post
    If it is what research is this based upon please?
    2011 NEDU study: http://archive.rubicon-foundation.or...pdf?sequence=1

  8. #8
    Established TDF Member Wardy_uk's Avatar
    Join Date
    Jan 2016
    Location
    NW Leicestershire
    Posts
    530
    Likes (Given)
    495
    Likes (Received)
    92
    at a risk of going slightly off topic - what's the thinking on how this extends to the "deeper" stops being added to no-deco dives? a fair number of computers stick a stop in at 10/11m when you get close to NDL's, and I've found adding a stop in at 9m seems to reduce the feelings of fatigue I get on longer 20/25m dives... is this thinking still valid, or debunked like "proper" deep stops?

  9. #9
    Established TDF Member
    Join Date
    Jan 2013
    Location
    NE UK
    Posts
    552
    Likes (Given)
    7
    Likes (Received)
    110
    I was alway a little puzzled that the studies were of just deep stops against just shallow stops and (when I looked at the ages ago) not deep stops with extra shallow stops as well.


    Sent from my iPhone using Tapatalk

  10. #10
    Established TDF Member
    Join Date
    Jan 2013
    Location
    East Midlands
    Posts
    2,883
    Likes (Given)
    829
    Likes (Received)
    1109
    Blog Entries
    2
    Quote Originally Posted by Wardy_uk View Post
    at a risk of going slightly off topic - what's the thinking on how this extends to the "deeper" stops being added to no-deco dives? a fair number of computers stick a stop in at 10/11m when you get close to NDL's, and I've found adding a stop in at 9m seems to reduce the feelings of fatigue I get on longer 20/25m dives... is this thinking still valid, or debunked like "proper" deep stops?
    The study didn't address them in any way if I recall correctly.

    If you think it makes you feel better, why change it? I tend to do them if I remember and the profile lends itself to doing them, but then again I also feel less tired diving nitrox and that's a myth too apparently, so what do I know?!


 
Page 1 of 45 12311 ... LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •