decompression

[FMT]

Pages 61-65 of TDI Trimix speaks only to the times of deco
stops and not to their effectiveness. Yes the times are
close (deco program settings dependent of course) between 80 and 100% but this manual does not speak as to the offgassing gradients of one verses the other (aka oxygen window). Yes high ppO2 does induce vasoconstriction but it takes time.
So if your O2 stop is short then so what, if it is long then this is where back gas breaks come in to refresh the lungs from the high O2 effects. In summing up on page 65 the author speaks about "goofing around with stage bottles" as a reason to get shallow and this, echoing DRE, really speaks to poor diving skills. Trimix diving is serious stuff and one should be committed to practice to eliminate these poor diving skills. Some people might think it looks stoopid to dive square lake in doubles with a stage but I have done it many times to improve my skills and you'll see me there still improving. I hope I remembered my flame-retardant drysuit underoos. haha
Todd

[beeger]

I have to side with the 100% O2 crowd here. In addition to what is mentioned above there seems to be some evidence of that the presence of any inert gas in the breathing mixture used for deco defeats the physiological purpose of using oxygen in the first place, above and beyond any considerations around PP02 (I can't find the information I'm looking for right now, but the source is, I believe, the Physiology and Medicine of Diving). Further, ascending from 30 (or 20) feet to the surface is where your greatest pressure change for the entire dive will occur - it is here where exposure to pure O2 would really seem necessitated. These last 20 feet should be treated as part of your decompression, as this is where sub-clinical DCS could become a real issue. However the PPO2s of 80% are negligible in this range and will make for inefficient off-gassing.

[DRE]

[quote='wazeediver link' dateline='1043036211']
David David David
You have been DIR brain washed

First of all, I'm not DIR brainwashed - if you've read any of my other posts you would have immediately noticed that. BTW, I'm the one who coined the term Holistic Hogarthian in order not to be confused with DIR mentality. I think for myself and try out the things which could improve my diving - decompression being one of them, and I can guarantee you that a lot of my knowledge comes from personally trying what works and what doesn't.

\"First off you can run your dive on v-planner with 100% then plug in 80% it's the same run time........\"

There is a huge difference between what a deco progarm tells you and what your body tells you. I used EAN80 in the past until I made the switch to O2, the difference was tremendous: no more post-dive fatigue, and ready to go right away. Run times don't mean anything for the O2 portion of the dive anyway: if you haven't been doing proper deep stops, have been using too high a bottom PPN2 or PPO2, too fast an ascent, etc., you can use whatever gas you want in the 20ft range and still will not decompress properly.

\"Second the 100% o2 induces vasoconstristion and that counters the real off gassing\"

As FMT already mentioned, if you have to stay a long time on O2, you take backgas breaks. For every 10 minutes on O2 I go 2 minutes to my backgas. TDI, I believe, tells you to switch
after 20 or 25 minutes and not to count those minutes toward deco. Guess why I get out of the water 15 minutes sooner than then ones using their EAN80 and not doing backgas breaks. BTW, the backgas breaks reset the lungs so you can use O2 for extended periods of time. Otherwise, explain how there's cave divers doing dives with a total bottom time of 300 minutes at 300ft, doing more than an hour on O2 and still being able to go for a run after a 14hour dive? So what is the real offgassing?


\"Third check out pages 61-65in your TDI trimix diver manual\"

It's the typical BS of the ignoramus - every little kid can play at home with a PC program and come up with some results to show their superiority. Did TDI publish the Doppler studies, whcih compare subclinical or silent bubbling when using O2 compared to EAN80. No! Again, diving is a reallife sport, not one that's done behind a computer or from a manual.


















[/quote]

[DRE]

"Side note- who the heck wants to do cold water deco :o."

Dive the Kamloops - 260ft to the sand at the bow. 20 minute bottom time, total dive time 70 minutes, using EAN50 and O2 for deco.


"Anyway, I would think useing EAN 80 would be advantagous because you could start much earlier ie at 30 ft instead of 20 with 100% O2. Furthermore wouldn't your allowable exposure be lower with 80%?"

First of all, at 30ft your PPO2 of EAN80 is 1.53, O2 @ 20 is 1.6 - already there is a benefit for using O2 @ 20. Second, you don't stay @ 30, but most people will go to 20 and then 10, which will lower the PPo2 even more, thus reducing the deco effectiveness even more. Third, EAN80 still has N2 in it, which means that the pressure differential between inspired and arterial gas in't optimal. An analogy: you want to cut bourbon with soda: what's more optimal: to cut it with pure soda or a mixture of soda and bourbon; what will give you the better result?
Fourth, allowable exposure should be thrown out of the window when using correct gasses. Most people advocate the use of fairly high PPO2's for bottom gas (TDI recommends 1.4ATA). This will do much more damage to your CNS clock than using high PPO2 deco gasses, which is where you really need them. Using a backgas with low PPO2, as in the 1.0-1.2 range, will give you the possibility to switch back and forth between your deco gas and backgas during deco, thus constantly resetting the CNS clock (actually you reset your lungs - the CNS clock is a concept that dates back to the 1960's and was so poorly understood that it led to ultraconservatism, kinda like modernday dive computers)

[DRE]

Both IANTD and TDI recommended the use of EAN80 or even EAN75 as a deco gas in a class setting because they were worried that student divers could not maintain their boyancy @ 20 with O2, thus risking the chance of an oxtox hit. That's why EAN80 even @ 30 deosn't even give you a 1.6PPO2. This is the one of the biggest goofs in tech training ever imaginable - a mix diver not being able to maintain proper boyancy (LOL).

[LKunze]

Man that must be an awesome dive! I've heard a few stories about that wreck. Still bodies inside it right?

[DRE]

one of the best I've ever done. I wrote a trip report on this dive and posted it to . Look under under Trip Reports and Kamloops - steel cave.

[freedivernd]

Dre,
that was a nicely written article on the Kamloops.. but I'm afraid the only way I'll ever see it is by pictures, a submarine, or maybe some day.. a sled ride. Just dreamin'.

Fred

[LKunze]

Great review Dre...I enjoyed it.

[wazeediver]

David ,your the man .You brought this site to life,in the middle of winter....Keep up the posts......

I dive an Inspiration, so my opinion doesn't realy count.

Thanks Al