Deep Stops Increases DCS

[Dr. Lecter]

Good so don't "pontificate" on something y'all absolutely know nothing about.

You aren't doing these dives consecutively like the Truk Dive Guides over a month's time (and myself on Ratio Deco with non-standard Deep Air since 2007) --so wtf do you all know?

I know multiple days of at least one and usually two 200'-240' air dives (often longer than 50 minutes you mentioned) is nothing particularly impressive, Kev. You're hardly the only one in this thread with experience doing that, and the difference between you and me of a year or two ago is that you only did that stuff a couple weeks a year. The other guys in here may never have dove air past whatever magical limit DIR imposed on them, but that ain't me.

And what I'm telling you is deep stop profiles for such dives produced for me similar, though less objectively bendy, results as you're reporting. I had two choices: slap a ultra low surfacing GF on top of the deep stop model's output, or, try something different. Both "worked," but having tried each way I think less time (not zero time) on deep stops that aren't nearly as deep is the way to go. YMMV.

 

[C Dub]

/popcorn

Kev needs a rebreather, so he doesn't have to keep posting scans of his gas bills.

/beer

 

[victorzamora]

Admission: I'm not Trimix trained, but do believe myself to be a slave to logic. Let's break this down here.
Statement1:

Because nobody else other than the Dive Guides at Truk Lagoon are doing years of consecutive day/continuous month-long Deep Air Deco Profiles on accelerated 50% and 100% O2 (and they are using dive computers LV X1, DR Nitek Q, and Suunto Vytecs with VPM, Buhlmann GF's and RGBM algorithms --and even they are getting "niggles").

Statement2:

I choose to stick with what I know now, and that's RD with DeepStops and extended O2 Profiles to eliminate slow-tissue residual N2.

Statement1 makes a few claims.
1a) "Nobody other than the dive guides at Truk Lagoon are doing years of consecutive/continuous day/month long deep-air deco profiles with EAN50 and O2. What this implies is, to me, is that for long-term/continuous deco diving conclusions to be drawn from, these guys are the best. Right? So if we're to make ANY sweeping statements about deco algorithms....these guys are the best model.
1b) These guys, the "optimal models" for deco algos, are diving computers running Buhlmann, VPM, and RGBM (really? Suunto Vytec to 200ft?)
1c) The worst these guys get are "niggles" diving these profiles. Which algos are producing what is not said, but I'd be curious to know.
1d) By elimination, we can assume these guys aren't diving Kev's Ratio Deco.

Statement2 makes it very clear that Kev will continue diving with his Ratio Deco, which has bent him multiple times of his own admission.

Non sequitur, much? These guys are proof you can do these dives safely and they're using one solution. I'm proof that you'll get bent all the time if you dive with this other solution. Clearly, I like my other solution better.

 

[Kevrumbo]

I know multiple days of at least one and usually two 200'-240' air dives (often longer than 50 minutes you mentioned) is nothing particularly impressive, Kev. You're hardly the only one in this thread with experience doing that, and the difference between you and me of a year or two ago is that you only did that stuff a couple weeks a year. The other guys in here may never have dove air past whatever magical limit DIR imposed on them, but that ain't me.

And what I'm telling you is deep stop profiles for such dives produced for me similar, though less objectively bendy, results as you're reporting. I had two choices: slap a ultra low surfacing GF on top of the deep stop model's output, or, try something different. Both "worked," but having tried each way I think less time (not zero time) on deep stops that aren't nearly as deep is the way to go. YMMV.

Great Dr. Lecter . . .you're being objective and contributory with your own anecdotal experiences. But I'm not trying to "impress" you or anyone with these Deep Air Profiles in Truk over multiple month-long trips per year since 2007 (four separate trips in 2012-13 with a Bikini Atoll Trip back-to-back); I'm simply a tourist Tech Diver historically interested in WWII Indo-Pacific Wrecks.

What truly is impressive and telling are the Truk Stop Dive Guides -especially the native Chuukese Divers- who've been doing these long Deep Air deco profiles for consecutive days per month over the years with clients for a living, and what they've been doing all along: Doing long O2 or 50% clean-up profiles to eliminate residual N2 slow-tissue loading as necessary before going on at least a week-long no-diving activity break.

Anyway, that's similar to the prescription that I'm going to start using for these types of dives: Long O2 deco profiles on top of Ratio Deco, with a Petrel Computer ZHL-16C algorithm showing a surfacing Gradient Factor of 40% to 50% -and take a day-off after four consecutive days (or 8 consecutive Deep Air Deco Dives). . .

---------- Post added December 17th, 2014 at 03:04 PM ----------

Admission: I'm not Trimix trained, but do believe myself to be a slave to logic. Let's break this down here.
Statement1:
Statement2:

Statement1 makes a few claims.
1a) "Nobody other than the dive guides at Truk Lagoon are doing years of consecutive/continuous day/month long deep-air deco profiles with EAN50 and O2. What this implies is, to me, is that for long-term/continuous deco diving conclusions to be drawn from, these guys are the best. Right? So if we're to make ANY sweeping statements about deco algorithms....these guys are the best model.
1b) These guys, the "optimal models" for deco algos, are diving computers running Buhlmann, VPM, and RGBM (really? Suunto Vytec to 200ft?)
1c) The worst these guys get are "niggles" diving these profiles. Which algos are producing what is not said, but I'd be curious to know.
1d) By elimination, we can assume these guys aren't diving Kev's Ratio Deco.

Statement2 makes it very clear that Kev will continue diving with his Ratio Deco, which has bent him multiple times of his own admission.

Non sequitur, much? These guys are proof you can do these dives safely and they're using one solution. I'm proof that you'll get bent all the time if you dive with this other solution. Clearly, I like my other solution better.

Simple logical & practical answer Vic . . .go to Truk, interview and dive with them. See what you learn and do what's objectively best for you. Doesn't that make sense?

 

[Akimbo]

High Oxygen levels have been the secret sauce since the 1930s, even before pure O2 was formally used for treating bends. There were tons of “secret” mixes starting with the Keller and Albert Bühlmann deep experiments in the 1960s. That lead to almost as many proprietary HeO2 decompression tables as oilfield diving companies.

I have seen the Keller/Bühlmann (1000’ dive in 1962) and maybe 15% of the proprietary commercial tables and they all pretty much boil down to very high PPO2s — like up to 3.2 ATA. Suck enough Oxygen at the end of a dive and you can even make otherwise crappy tables work.

You really can end a deep dive with, theoretically, the same or less inert gas loading than when you started — especially if you have a chamber for administering O2. That in turn eliminates residual gas concerns for repeds.

 

[Kevrumbo]

High Oxygen levels have been the secret sauce since the 1930s, even before pure O2 was formally used for treating bends. There were tons of “secret” mixes starting with the Keller and Albert Bühlmann deep experiments in the 1960s. That lead to almost as many proprietary HeO2 decompression tables as oilfield diving companies.

I have seen the Keller/Bühlmann (1000’ dive in 1962) and maybe 15% of the proprietary commercial tables and they all pretty much boil down to very high PPO2s — like up to 3.2 ATA. Suck enough Oxygen at the end of a dive and you can even make otherwise crappy tables work.

You really can end a deep dive with, theoretically, the same or less inert gas loading than when you started — especially if you have a chamber for administering O2. That in turn eliminates residual gas concerns for repeds.

Well that was the initial scary part about going to 9m on O2 -and doing over two-and-a-half hours IWR therapy: The CNS loading readout on my Petrel computer topped out at "999" at the end of the session. But I was effectively "de-nitrogenated" by the Petrel's tissue loading bar graph at the end of the IWR treatment, as well as more importantly relieving the Right upper arm/shoulder type I pain for the last week of my Truk trip.

CNS exposure tolerance/Ox-tox with the longer O2 profiles (along with rare unknown cause, late onset of type II DCS signs/symptoms) are my concerns now.

(Much safer to do as a US Navy or COMEX Diver with a dedicated Recompression Chamber waiting for you exclusively on the surface)

 

[Akimbo]

Well that was the initial scary part about going to 9m on O2 -and doing over two-and-a-half hours IWR therapy:…

It is a lot less scary when you consider that the Brits raised the floor for combat swimmers from 60' to 33' in the 1940s and that held for decades. The USN’s floor was 25' for a very long time. Obviously, a combat swimmer is under much higher workloads and stress than a diver decompressing. This thread might add perspective for others reading this: http://www.scubaboard.com/forums/diving-medicine/440726-oxygen-toxicity-limits-symptoms.html

 

[WhiteSands]

_t

i think you all could benefit from reading all of dr. doolette's responses to questions like these about the methodology in that big thread on rebreather world.
he was good enough to spend a lot of time explaining the study there.

Would someone be so kid as to PM me the link to RB world, if its against TOS to post here?

 

[Kevrumbo]

_t
Would someone be so kid as to PM me the link to RB world, if its against TOS to post here?

David J. Doolette, co-author of the NEDU Deep Stops Study, and his introductory & first initial post in that controversial Rebreather World Thread:

Rebreather World - View Single Post - Deep stops debate (split from ascent rate thread)

. . .The more important issue is that technical divers do not do air decompression dives, they use oxygen-accelerated decompression. If decompression stops are conducted using a breathing mixture with a low inert gas fraction, then, of course, there is less gas uptake into the relatively slow compartments. The effect of this is to increase the depth at which stops become “bad” deep stops.

David Doolette

To reiterate: Look at the Bottom Mix Gas used in the NEDU Study link (essentially Deep Air):

(Abstract, p.i). . .Divers wearing swimsuits and tshirts, breathing surface-supplied air via MK 20 UBA, and immersed in 86 °F water were compressed at 57 fsw/min to 170 fsw for a 30 minute bottom time during which they performed 130 watt cycle ergometer work. . . Results indicate that slower tissue gas washout or continued gas uptake offsets the benefits of reduced bubble growth at deep stops. . .

(Conclusion p.18) . . .The practical conclusion of this study is that controlling bubble formation in fast compartments with deep stops is unwarranted for air decompression dives.

This is the simple main practical point IMO/IME, to take away from the study:

Of course you're going to have significant residual inert Nitrogen and potentially on-gas N2 at your deep stop & perhaps even possibly at intermediate deco stops on Eanx50 which may encroach on critical slow tissue M-values as well --if you were using a working bottom mix with a high fractional N2 content to begin with like Air. Plan accordingly, use a computer to track your inert tissue loading (i.g. Shearwater Petrel) and be prepared to extend your 6m depth 100% Oxygen deco profile along with a stand-by IWR contingency protocol.

 

[Omisson]

Dang lost my popcorn