Ratio Deco

[MXGratefulDiver]

... it's been around long enough now that if it's apt to get someone hurt, it will have done so.

Has it?

... Bob (Grateful Diver)

 

[Kevrumbo]

... it's been around long enough now that if it's apt to get someone hurt, it will have done so.

Has it?

... Bob (Grateful Diver)

The same rhetoric above can be said for any of the current dual phase deco algorithms or model strategies in use.

Objective reality and practical to the point: Even if following & apparently completing a correctly prescribed deco profile, you may still end up surfacing with anything from delayed sub-clinical to immediate acute DCS type I symptoms. This especially becomes evident after several consecutive days and weeks of mandatory decompression, "expedition" type technical diving.

You have to take into account many other environmental & physiological risk factors along with following the decompression schedule as calculated by whatever deco strategy & breathing gases you choose to implement.

(i.g Possible risk factors: dehydration & insufficient "acclimatization" to a tropical environment; and no prior "work-up" practice deco dives to sensitize the body's immune/inflammatory response system to inert gas loads & micro-bubble formation in tissues & venous blood vessels)

21 consecutive dive days completed here at Truk, including 10 straight days of two deco dives per day with an average 3hr SIT. Except for the North Pass site of the Oite Destroyer at 57m average depth, all deep morning dives were mostly on the wrecks of the Fourth Fleet Anchorage (San Francisco Maru, Aikoku Maru etc) with ave depths of 45m to 51m with 45min to 60min Bottom Times, and total run times of two-and-half to over three hours. All but two deep dives were on Air bottom mix, the other two using 20/20 "Tropical Economy Trimix" (for reel-line penetration of Aikoku Maru's engine room at 60m max), with 50% and 100% O2 for deco; and Nitrox30 for the repetitive dives in the afternoon with O2 deco only- all on Open Circuit. No prompt or delayed acute DCS symptoms/signs post-dive this time compared to last year Oct-Nov, with only a few upper arm/shoulder "niggles" felt overnight once. (Air & water temperatures 27 deg C, wind chill Winter conditions with NE winds 8 to 12 knots, 1m to 2m surface water chop with scattered rainshowers inside the atoll/lagoon).

The disadvantage of tactically compensating for the deep stop slow tissue loading with elective extra O2 time of around 10 to 20 minutes maximum was expected: an uncomfortably high CNS OxTox figure result of 300 to over 500 max as tracked by the Petrel dive computer on 30/85 GF. By the start of this last week, I discarded the Ratio Deco Profile (along with Nitrox50 intermediate deco S-curve profiles emphasizing the high ppO2/"Oxygen Window" at 21m & 18m, and only slowing the ascent rate from the bottom at 10m/min to 3m-6m/min, at where that first required Ratio Deco/One Minute Deep Stop would have been), and instead followed the Petrel computer at GF's 30/85 with further conservative resetting on-the-fly of the Surfacing GF to 70 or 60, in order to extend the O2 deco profile (I really like and found this feature of the Shearwater Petrel Dive Computer most useful along with the @+5min/"predicted deco time remaining to surface staying at current depth for 5 more minutes" function). The CNS loading in this instance never went beyond 250 max.

Anecdotal Impression: I did not notice or feel any difference qualitatively post-dive using either Ratio Deco w/ Deep Stops, or Buhlmann GF's 30/85 as calculated by the Petrel Computer -both with using high N2 fractional bottom mixes of Air, 20/20 Trimix, or Nitrox30 & extended O2 profiles. The disadvantage of using elective extended O2 profiles to conservatively compensate & eliminate slow tissue loading is noted above with excessive CNS/Oxygen Toxicity rating factor, especially with deco profile implementation of the Ratio Deco Algorithm with Deep Stops.

NEDU Deep Stops Study

Use and apply the best practices & deco algorithms that work for you, hopefully with minimal trial & error/lessons learned mistakes. And always have an optional IWR contingency plan ready to use immediately if necessary. . .

 

[PfcAJ]

... it's been around long enough now that if it's apt to get someone hurt, it will have done so.

Has it?

... Bob (Grateful Diver)

Speak of the devil...

---------- Post added July 22nd, 2015 at 05:51 PM ----------

This especially becomes evident after several consecutive days and weeks of mandatory decompression

This. Because you carry gas loads across multiple days.

Surface time matters. If you don't have enough, you're gunna have a bad time.

To suggest that you're 'clean' after a certain ascent schedule is jiggery pokery and pure applesauce.

 

[LiteHedded]

... it's been around long enough now that if it's apt to get someone hurt, it will have done so.

Has it?

... Bob (Grateful Diver)

yes it has

 

[decompression]

The stuff UTD is peddling is make-pretend. You can see it for your self when looking at the PADI dive tables. Capital baloney, and its apt to get someone hurt.

Don't get me goin' on his 'ratio deco' for proper deco dives. Absolutely preposterous.

Using a simple set of rules to come up with an ascent schedule that's close or the same to an established algorithm is one thing. Ignoring the algorithm and suggesting that the ratio is the 'gold standard' is beyond the pale.

Explain?


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[MXGratefulDiver]

yes it has

... applied as taught?

... Bob (Grateful Diver)

 

[decompression]

yes it has

Who? How many?


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[PfcAJ]

Explain?


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Explain what? Look at a table.

According to AG, if the table doesn't equal ratio deco, the table is wrong. To the rest of the world, if the table doesnt equal RD, RD is wrong and we do what the table says.

Think that idea through for a moment... The table is based on math, RD (as AG teaches it) is based on....? I mean, there's a prime example in this thread. Kev wrote about how diving for multiple days using AG's methods will result in bent.

Its unacceptable to peddle ideas that get people hurt. You can't "ignore" the previous day's dives, or "ignore" a deco schedule because it doesn't like up with your pretty little ratio. Just like you can't "ignore" breathing different gases or diving to a different depth and expect to have the same likelyhood of DCS. It all matters. Some thing matter more than others, but it all matters.

 

[decompression]

Explain what? Look at a table.

According to AG, if the table doesn't equal ratio deco, the table is wrong. To the rest of the world, if the table doesnt equal RD, RD is wrong and we do what the table says.

Think that idea through for a moment... The table is based on math, RD (as AG teaches it) is based on....?

Let me sincerely challenge you for and answer to your own question, what is ratio deco based on? Please don't be flippant and say "nothing, see, I'm right".

Further, in hopes of learning more, who has been hurt solely attributable to using ratio deco?


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[boulderjohn]

I only know of 6 cases of DCS in the UTD group with which I used to dive. Of course, I was told that none of them count as examples of people getting DCS while using ratio deco, because in each case, there was some other reason for it. What were those other reasons? Nobody knows, but it had to be something else. Why? Because you don't get bent using ratio deco unless some otehr factor is in play, so something else had to be going on. Maybe a PFO.

BTW, I mentioned that in a SB thread a number of eyars ago, and I received an email from a UTD represenative saying that what I wrote was disparaging of the agency, and if I did it again I would be reported to PADI for violating that agency's standard prohibiting saying something disparaging about other agencies. The assumption was that PADI would then sanction me for violating that standard.