Min Deco for 30/30

[mikeny9]

Wow, how did you get access to my dive log and history with UTD? You are some kind of magician that's for sure. You certainly exude the personality that would make people want to sign up with GUE don't you. Oh wait, they can't, because they are not as good as you? Keep at it man, you're doing wonders for your credibility.

 

[PfcAJ]

Well, how about you enlighten me?

So far it's a rec course from UTD, fundamentals, and a few hundred dives.

 

[mikeny9]

I've said my peace, I think I'll end it there. Have fun, troll on

 

[LiteHedded]

I've said my peace, I think I'll end it there. Have fun, troll on

Thought you might

 

[boulderjohn]

UTD has no recorded medical incidents and has been diving the way they do for years.

Six cases of DCS in the UTD group with which I dived. One required helicopter evacuation and recompression. One sought out the chamber on his own and went through a series of treatments. The rest were resolved through IWR in some cases or surface oxygen in others.

We were diving at altitude (4,600 feet), and Andrew had said that altitude did not matter for recompression. I asked him how he knew it did not matter. He said that he knew for two reasons: 1) he dives at Lake Tahoe and does fine and 2) No one has been bent using UTD's RD at altitude. When I asked about the people in our group who had gotten bent, he said he did not include them because they don't count. Why don't they count? Because something other than their ascent profile caused the DCS. What was it? He didn't know, but it had to be something else, because the ascent profiles wouldn't have caused it.

So those are the cases I know of, but I only dived with one small UTD group for a few years. Are there any more? How can we know, since if they do happen, they don't count?

 

[boulderjohn]

One more thing--in my numbers I did not count the fatality in that UTD group or the 3 months pf paralysis of his buddy as a result of his DCS. (I do not know for sure what they were doing for their ascent profile or how they derived it, and they never did find the body of the fatality.)

 

[rjack321]

I actually dive with a couple of UTD instructors fairly often and I’m not sure where this notion that 25/25 = 32% is coming from. I occasionally DM with them too. While there is some odd concepts about helium being better than N2 taught at the agency level, at a practical level that is not what we are doing.

Air = 21/35 = 18/45 (the latter is getting iffy for me but ok)
25/25 = -10% EAD (and almost always used with O2 for deco which “fixes” many discrepancies)
32% = -20% EAD

We don’t dive at altitude, and to completely blow off altitude is not a good idea. For many recreational dives on 32% altitude is not very relevant. For deco dives you want to have some padding, how much I leave for you to research using real science.

 

[RainPilot]

The UTD Min deco tables clearly state what gases they are for. The 32% one also says 25/25 on it.

Whether actual dives are being conducted this way is a different issue.
The deco tables are a different story.

 

[rjack321]

The UTD Min deco tables clearly state what gases they are for. The 32% one also says 25/25 on it.

Whether actual dives are being conducted this way is a different issue.
The deco tables are a different story.

I know its been a debated issue which has gone back and forth. As others have pointed out, there is no actual science to support the current choice (but AG doesn't seem to care what the science says about most things). We use -10% EAD which there is evidence to support. i.e, on a total inerts basis 25% O2 is about -10% EAD compared to air. Seems to work for us, we have no DCS history like boulderjohn has, but we also don't use 25/25 deeper than about 130ft, there is one wreck that we use 25/25 on (the Diamond Knot) which dips to 140ft but we never end up that deep for more than a minute. Most of it is between 120 and 75ft and 25/25 plus O2 for deco works pretty good.

I have to admit I have not used 30/30 in almost a decade as its pretty much useless here. When I did use it (with a MOD of 120ft) -20% EAD was fine for recreational no deco or min deco dives. I have done a bunch of deco dives on 30% EAN however (it's what we had) and I will warn the OP that a 2% difference in O2 content isn't all that relevant for a recreational dive. But a 4 hour dive on 30% is not the same deco as a 4 hour dive on 32%.

 

[mikeny9]

For what its worth, UTD uses 25/25 for the 100' - 130' range as well. Past that it's 21/35 or 18/45.

Regarding EAD, the only formula I've seen is for nitrox only and only examines the nitrogen component. One of the many things debated in this thread is whether Helium should be considered just as bad as Nitrogen in terms of EAD, and if not, by how much? If you completely ignore Helium, then 25/25 at 100' has an EAD of 51'. If you consider Helium just as bad as Nitrogen, 25/25 at 100' has an EAD of 93'. For comparison, EANx 32 at 100' has an EAD of 81'.