decompression

[DRE]

I've noticed that some people had different conceptions on how to do deco, what is considered DIR deco (or as I like to call it: proper deco), what gasses to use, what protocols to follow, etc. I was wondering if we could start a discussion about deco, how people do things as it seems that this topic continually is misunderstood or clouded by a priori assumptions, many stemming from OW training. So let's start by asking how y'all plan a deco dive and how you go about it and take it from there.

[nomads]

DRE, Rather than asking us to ask, why don't you just tell us? If you plan to use this forum as a vehicle to domonstrate your knowlege I am not interested. There are other sources that I would prefer to use.

[DRE]

I'm not trying to tell you what I think you should do, I'm just interested to start a debate on decompression since I know there are a lot of different opinions about this topic. If you don't want to discuss that on this forum, that's fine with me. There's enough other forums where this stuff does receive quite a bit of attention and informative discussion.
Joel (in a post about DIR) pointed out that there's more to DIR than just gear config, so I was interested to approach other topics. If you'd like to start talking about physical conditioning for diving, proper scenarios for doing boat diving, proper gas management scenarios in overhead environment or whatever, start a new topic yourself and I'll participate in the discussion.
Otherwise, if you prefer giving some negative attitude, I can point you to some other forums where that's how they do things.

So here's a specific question: do you use 100% O2 or EAN80 for your final deco gas (or any other mix), and why?

[DanL]

The only decompression I do now is a drink or hot tub - or both - after work. I'll be watching this thread to learn more. Rec trimix, decompression, etc all sound intriguing. Always something to look forward to...

[crunchyfrogs]

DRE;

In response to your question, I'm using 100% O2 @ 20 ft. The reason is I off gas nitrogen faster then if I was using 80% EAN, in other words I can do a better job cleaning out my body using pure O2. IF I were to use anything less, my off gassing would be slower because the gas would contain nitrogen.

Cruchyfrogs

[DRE]

That's a very good point you made there - not only does the nitrogen takes up space that otherwise could be used by the O2, it also doesn't optimize the oxygen window, ie the pressure differential between the partial pressure of arterial inert gas (nitrogen and/or helium) and the partial pressure of inspired O2. If you consider the oxygen window to be at 100% at 20ft on pure O2, doing the math for EAN 80 @ 30ft, which will roughly give you the same PPO2 as O2 @ 20ft, will give you a less than optimal oxygen window, hence you're doing inefficient deco. This I consider the main reason why not to use EAN80 for deco purposes. All of the arguments why you should use it (such as it's safer to mix, you can get more in a tank, it's safer because maintaining proper boyancy sin't as critical, etc.) can all be reduced to poor diving skills (if you can't maintain proper boyancy @ 20ft you shoudn't be tech diving in the first place - in fact, you should redo your OW class and get it right).
Also, nitrogen is probably the worst gas to deco from - it damages your red blood cells when inspired at higher PP's (deep air diving is as stupid as drunk driving in that regard), it cannot flow through cell walls, so your chances of subclinical DCS inrease exponentially, so why would you put in a deco gas in the first place? - especially when O2 is so readily available and you don't have to deal with the mixing nightmares (what's easier than topping off O2 with O2???).
Helium on the other hand has all of the posiitve aspects for deco that N2 doesn't have - so it's definitely the gas to use (case in point: DSAT - Padis's tech branch, or what's in a name - just launchd their trimix program).
I welcome anyone who has any arguments pro using EAN 80 to join this discussion - maybe we can get started having a real debate then.

[tbrown]

Well, I'm not a tech diver, but I did stay at Holiday Inn Express, and I'm sort of bored, so even though I may not be the most effective advocate for 80% here goes. Side note- who the heck wants to do cold water deco :o. 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%?

[FMT]

Why do cold water deco? A good question considering
the extra difficulties and planning involved.
Ask around about the difference between deep cold
water wrecks and shallow wrecks that have been stripped
of everything in the pre-"take only pictures" days.
That I think is the biggest reason.
Todd

[wazeediver]

David David David
You have been DIR brain washed

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

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

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

Al

[tbrown]

Out of my own curiosity, what does your mix have to do with bouancy, or lack of?