DIR recreational deco?

[FreeFloat]

Perhaps those items were covered in your classbooks and handouts even though the instructor never mentioned it.

Surely there is some hardcopy info you take away from the class to help refresh your memory later.

No..... I don't recall anything in hardcopy from DIR-F.

 

[MikeFerrara]

Lamont,

We'll address some of the issues you raise but right now my wife is waiting for me to take her to dinner.

Also I'm going to start another thread outside of the DIR forum...probably in the morning. I can give you my take on it but it may or may not be consistant with DIR so it's best we do it elsewhere. ok?

There have also been a number of other threads where we have discussed this same stuff but I'll be darned if I remember which threads it was in.

 

[Uncle Pug]

One of the reasons, "Take the Class" is repeated so often is that the decompression content is only a portion of what comprises the GUE approach... the skill set must go with it and that cannot be learned on the internet. So don't be offended when folks say, "Take the class."

 

[Charlie99]

There have also been a number of other threads where we have discussed this same stuff but I'll be darned if I remember which threads it was in.

Perhaps one of those threads is this thread.

The only response that had info on GUE's teaching was:

In my GUE Tech class we were NOT taught this. We were taught to double the shallow stops for a repetitive dive.
GUE, read DIR, does not really seem to care if you do reverse profiles or not but they certainly don't say you have to.

 

[MASS-Diver]

Perhaps one of those threads is this thread.

The only response that had info on GUE's teaching was:

PM MHK.

 

[Whirling Girl]

Okay, maybe I just shouldn't even be trying to do this, but I'm trying to sort out what GI3 says about decompression diving and apply it to diving within the NDL limits.

Well, as a variation on the "take a class" theme, you should go to the George Irvine lecture at 5th D in September. I was at the last one and George discussed this issue in detail.

The gist of what he said (and please be tolerant, it was a while ago and I didn't take notes) was that diving deeper on the second dive will clean out any bubbles you might have accumulated on the first.

He also said that if you follow the correct deco profiles, using deep stops and a graduated ascent, you should come out clean as a whistle. This renders a surface interval irrelevant for the purpose of offgassing, so you can treat your second dive as a standalone rather than a second, for purposes of setting your profile.

What he also said, however, was that this discussion was pointless in the context of recreational diving without gas switches. Unless you're breathing 50/50 at 70' and/or pure O2 at 20', you're not going to come out clean. Backgas, no matter what the mixture, though He does help on the cleanup, is not going to clean you up like high O2 mixes at deco stops.

If I'm misrepresenting any of this, feel free to correct it; like I said, it has been a while.

Hope that answers your question at least in part. But go get it from the horse's mouth. It's a great opportunity to meet the man in person and ask all kinds of questions!

 

[lamont]

What he also said, however, was that this discussion was pointless in the context of recreational diving without gas switches. Unless you're breathing 50/50 at 70' and/or pure O2 at 20', you're not going to come out clean. Backgas, no matter what the mixture, though He does help on the cleanup, is not going to clean you up like high O2 mixes at deco stops.

Ah, thanks. That makes sense and is some of the kind of info that I was looking for...

If I took a spare air of 100% along with me would that work for a 'recreational' deco stop at 20 fsw?





(kidding... just kidding...)

 

[Albion]

sorry if im getting the wrong end of this, or even if this is correct place to discuss.

Why would you plan to be diving deeper on second dive to clean out from the first surely you should be clean as possible from first dive. I was thinking along the lines of what if something prevented you making a second dive. Or is he saying that, if making a second dive then it is important to go deeper to compress any bubbles back before making the second ascent?

I have been trying to follow the DAN theory on this, where they checked accident statistics in recreational diving to see where the "deepest first" came from and if it had any basis. So far they are saying there are no statistics to indicate deepest first in and it seems to have just been "good idea"

By deepest first i mean first dive deep then second shallower not meaning reverse profiles on single dive.

 

[RichLockyer]

is he saying that, if making a second dive then it is important to go deeper to compress any bubbles back before making the second ascent?

I have been trying to follow the DAN theory on this, where they checked accident statistics in recreational diving to see where the "deepest first" came from and if it had any basis. So far they are saying there are no statistics to indicate deepest first in and it seems to have just been "good idea"

You got it. Recompress and reabsorb any bubbles remaining from the first dive.
Going deepest dive first, if there are any bubbles remaining, the second dive may not fully recompress them to the point that they can be reabsorbed. IF they get through the lungs, back into the arterial side, they can cause a type-2 hit. Even if they don't cause a hit, they will be the nucleii for bubble formation during the ascent from the second dive.

Basically, George is treating the second dive as a preventative IWR from the first, and like a chamber treatment, you need to recompress to a depth below the original dive.

Keep in mind that his reference is on deco dives (even minimum deco), and deco is not done on air, "because it doesn't work".

As far as where deepest-first came from, it's how the tables were developed. I don't know what it is in the algorithm, but that's the answer I've always been given by instructors. "It's a table issue, and if you're diving on a computer, it doesn't matter."

Personally, I do deepest first simply because of the bottom time penalties.... or deepest EAD first if diving a mix of nitrox and air (which is rare).

 

[Albion]

Personally, I do deepest first simply because of the bottom time penalties.... or deepest EAD first if diving a mix of nitrox and air (which is rare).

So first the disclaimer, im just thinking this through and will discuss it with an instructor. also not trying to stear away from topic but we are headed that way now.

An operator i use make regular trips out to one of the nearby wrecks (max bottom 60M) but plenty to see at recreational levels. Normally because many novice-ish rec divers are on these trips so they normally do a check out dive at one of the reefs. I have always used this to get deep initially then work back up reef face so as not to get too much loading. Then have a 2 / 3 hour surface interval out to wreck. so from what you are saying i could do a 30M non deco dive using say 35% nitrox (EAD23M) on the reef then safely (within trianing) do a 45M deco dive on trimix 25/30 (just enough helium to get me to 21M ead, Obviously more is better but just looking at the theory here


Please dont say take a class, i havent done the trimix card yet, im just seeing how it could benefit me on trips like this