If you had to choose, 80% or 100% for deco gas and why.

[jadairiii]

And there you have it. Opinionated, inflexible a-holes like you are the reason I will never have anything to do with DIR, GUE, UTD, etc. It is those instructors that have always regaled me with the "we do it this way just because we all do it the same" rather than having a justification. ....

When I took my first Tech classes in 1995, from one of the founding Board of Directors of IANTD, the MAIN reason taught for 80/20 at that time was ability to get a complete fill and issues with buoyancy in open water. That was taught in both my Tec Nitrox class and my Tech Deep Air.

That was the justification back then, cant tell you what they claim now.

 

[lowviz]

Twenty feet. I just enter a lower partial pressure limit so my gas-switch suggestion ends up where I want it. I like 20' better than 15 as I get to do a longer *slow* final ascent.

 

[TONY CHANEY]

These days with boosters you can always get oxygen at 3,000psi, pumping O2 higher is crazy talk.

Not attacking but do you not find it funny which rules / guidelines we except to disreguard and others we hold in the highest degree. So I have a question. Why do you feel that it is OK to fill 600 psi over what the guidelines tell us but feel that it is "crazy talk" to boost it higher. Just asking.

 

[Errol Kalayci]

Someone mentioned filling O2 to 4500psi which prompted the comment.
Most of the shops I have seen bank and fill to 3,000psi which would give 40cft in an Al40. Does filling to 3,000psi generate the same issues as filling to 4,500psi? Why would you need to ever fill higher pressure? I would only fill an al 40 to 3,000psi to get the 40cft, otherwise I bring a diff cylinder and no need to pump it that high. Then again, I sometimes exceed the speed limit but don't speed when it appears risk outweighs the benefit. I do not drink and drive, ever. Maybe my logic is flawed but there you have it.

 

[kwinter]

I will start with my 80% (not 80/20) at 9m/30 ft. But keep in mind that the 30 foot stop is much shorter than the 20 and 10 foot stops, so overall exposure is much less.

And Tony is absolutely correct. You can't say that pumping O2 to 3000 is safe, but anything more is crazy. Risk goes up exponentially after 2400. There is no cliff to jump off that says one pressure is fine while an extra 100 psi is deadly. But that's just DIR thinking, I guess.

 

[100days-a-year]

You can buy HP 02 locally,better tell Airgas and Praxair they are not DIR.And wasn't that GI3 quote off the internet?

I don't dispute the contributions that DIR has made but they have a PR problem because of the attitudes of many of it's proponents.

 

[Errol Kalayci]

DIR thinking is to think things through and understand. Decompression is up to the individual and team. Kwinter states that he has a PFO and thinks that continuing to decompression dive is a good idea. Hmmm, I will go with thinking things through.

 

[100days-a-year]

Errol,a high pressure (3000+)T make it easier to get full fills in deco tanks.I don't have a Haskel,only met 1 guy in Jax who did.I use the HP tank to fill deco tanks and when it gets low I use it to PP blend.

My personal T is LP but it's nice to have the others available when I do want to dive mix or do accelerated deco.

 

[Errol Kalayci]

100days, I don't disagree. My comment was directed at someone saying they dove with 4,500+psi of oxygen. Storage and filling is not the same issue and my comment was not directed at that.

 

[Michael Guerrero]

In Deco for Divers, Mark Powell said in the bluntest possible terms that the O2 window theory as being discussed in these pages is flat wrong.

I'm seeing a pattern that suggests why software programs generally do not include it.

My understanding of the theory is that aside from total tissue pressure (a la ICD), partial pressures of differing gases don't have an affect on each other. The whole 1.6 ppO2 thing is just to get you on a low (or in the case of O2 zero) inert gas as quickly as is safe from and Oxygen Toxicity perspective (i.e., 1.6 ata). The gradient between the inspired inert gas and the inert gas loaded into the tissues is what affects off-gassing (and bubbles). That gradient is controlled by the fraction of inspired inert gas and depth. The fact that 80% has nitrogen in it makes it inherently less effective than O2 in terms of creating a maximum inert gas gradient (assuming an air dive). However, it can be breathed sooner (i.e., deeper) than pure O2 according to our standards, which means that the large shift in gradient not controlled simply by depth is achieved sooner in the dive.

Anyway, you guys already knew all that, so consider it for posterity.