After I posted a link to an old PDF explaining how to calculate Ratio Deco, a fellow SBer was kind enough to forward a very interesting rebuttal,
Decompression Myths and Mistakes. Naturally, I wondered what the rest of SB has to say on the subject. Alas, while a quick search for
Ratio Deco on Scubaboard gives
254 results, a search for
Decompression Myths and Mistakes gives just
one result.
Has this been discussed in a thread that doesn't show up in my search? If so would someone be kind enough to PM or reply with a link to the thread? Thanks in advance...
That isn't really a terribly good "rebuttal" and I think it could be cleaned up a lot more if rossh took Sherwood's Tech1/Tech2 course (although I'd love to sit in on the discussion between bob and ross for the oxygen window section, that'd be a hoot...).
A lot of it is either outdated or irrelevant:
- deeper stops, more time spent deep: the recent blurb on the GUE website accelerating the tech1 deep stops for short dives addresses at least some of this. reading between the lines it looks like they investigated their tech1 practices against what decompression science was suggesting and made some adjustments.
- % of ATAs versus constant ATAs for start of deep stops: hey, i agree with rossh on this one and disagree with GUE, but for Tech2 dives where it matters more GUE and rossh agree more -- its on 100 fsw dives where it gets really silly -- and again GUE seems to be slowly evolving. even for recreational diving they went from pause at 80% of max depth and 1's from 50% of max depth to pause at 50% of max depth and 1-1-1 from 30 fsw, which is much more in line with rossh's 2.0 ATA suggestion.
- slow ascent off the bottom: this seems to be a GUE fundamentals level problem. most tech2 divers i've seen get the hell of the bottom when its time. i remember as an impressionable newbie being alarmed by how fast the tech2 guys would go from thumbs up to sailing through the water column to the first deep stop. now my suunto ascent alarm (27 fpm i think?) often screams at me about ascent rates during the initial portion of an ascent, particularly if i'm running a scooter up slope.
- the other issue in there that affects DIR is the O2 window issue -- i don't think the rest are really DIR related (that page isn't really a rebutal of DIR or Ratio Deco and rossh is being pretty evenhanded in spreading the love around). and i'll agree that GUE is almost certainly wrong about the physiology of the O2 window issue, but what they teach based on the O2 window is O2 deco at 20 fsw and accelerated deco by pushing the gradient, both practices which rossh actually supports in that paper (with caveats in the case of accelerated deco). that doesn't require any changes in the way GUE divers dive, it just requires changes in the voodoo incantations required to explain why the practices work to decompress you...
that page was more interesting as a rebuttal a few years ago before GUE cleaned up a few of the sillier recommendations for fundamental and tech1 (and keep in mind that GUE is a slightly ass-backwards organization that was conceived of as an organization to create tech2/cave2 divers for the WKPP and the further you get away from those origins towards tech1->DIRF->recreational diving, the rougher around the edges it actually gets not vice versa).
