Going into deco

[cloudboy55]

Okay . . . It's confession time. This came up over the weekend, where my husband did a repetitive dive and racked up what his Mosquito told him was 22 minutes of deco (which is kind of absurd on a dive with a max depth of 90 feet, but where the vast majority of the dive was spent around 50 to 60, but that's what the instrument said). Since it wouldn't give him any credit for time served below 20 feet, he ended up with about a ten minute hang at 10 feet, which he did. Gas was no issue.

Yeah, I know, I know, you shouldn't do decompression diving unless you're deco certified and are diving doubles and have appropriate decompression gases and do your gas management ahead of time. But I suspect that Peter's not the only one who's ever done this. In fact, I know Catherine does deco from time to time.

My question is: Who has deliberately gone into deco on a recreational dive, and how did you figure out how much deco to do? Did you do what your computer asked for? Did it make any sense?

I go into deco all the time on recreational dives without separate deco gasses. I don't really see that as a problem provided you have ample gas and you plan the decompression appropriately.

My Suunto Vytec really adds a good deal of deco time for repetitive decompression dives, even after a two hour surface interval.

I am a technical diver also, so take my comments in the proper perspective.

 

[MXGratefulDiver]

I never had a deco obligation and now...for the confession part, I'm not sure I would be able to read it on my computer if I did. I have an Uwatec. Would it tell me, 10 minutes at 20 feet or something like that? I have no clue. I've occasionally thought about the fact that I don't know what the computer will look like during a deco obligation, but never thought to try it out or ask someone, or look in the manual.

The important thing is to understand WHAT the computer is telling you if you should see the numbers. It will usually flash some part of the display ... which is to get your attention that you have gone beyond NDL. It will then display two numbers ... one which is the "ceiling" (usually 10 feet), and one which is the deco time (usually displays where your NDL is typically displayed).

It means ... "don't go above 10 feet until you have stayed there for this many minutes". You should generally, at that point, begin your ascent in an orderly manner. Depending on the computer's algorithm, it may start to credit you with offgassing time after you've reached about 50% of your max depth ... or it may continue accruing deco time until you've reached a relatively shallow depth (20-30 feet). Either way, there are two important things you should do ...

1. Communicate to your buddy that you have a deco obligation ... do this by tapping your computer, holding your hand up with pinkie finger extended (ASL sign for D) and then use your fingers to signal how many minutes of deco obligation you have. Then you must ...

2. Keep a close eye on your available air supply ... running out of air is worse than getting bent. Let your buddy know how much gas you have ... in fact, the two of you should each know how much the other has, because chances are if you're low, so is your buddy.

Do not hurry to your safety stop depth ... unless your gas supply mandates it. If you have sufficient air, remain at safety stop depth until your computer "clears" which means it will go back to the display you're used to seeing at your safety stop depth. Then surface normally .... actually, this would be a very good time to practice surfacing from your safety stop as slowly as possible ...

... Bob (Grateful Diver)

 

[Charlie99]

We were fine, had a good long dive. Computer was miffed. So what? The dive rocked.

From what TS&M posted, I don't think the computer was miffed at all. It just said that Peter had a deco obligation; and then he met that obligation.

Deco isn't a problem. Being in deco and not having the gas to do the stops IS a problem.

I don't see NDL as a sharp line, and don't overly obsess about the relatively fuzzy distinction between an NDL dive and one with a few minutes of deco obligation. I'm pushing things whether my computer says I have 4 minutes of NDL left or whether my computer says I have a few minutes of deco obligation. Anytime I'm heavily loaded (doesn't matter which side of "NDL" it's on) I'll have lots of gas and lots of time for a slow ascent and stops.

Since I'm diving a relatively liberal computer, I go into deco only once in a while. More often, though, I'll have a buddy using a more conservative computer that will be showing 5 or 10 minutes of deco. No problem -- by the time we do a slow ascent and hangs at 40' and 25' the deco stop time is either already met, or down to just 3 or 4 minutes.

One nice thing about the Pelagic/Oceanic/Aeris line of computers is the graphical display of N2 loading on the bargraph. I pay less attention to NDL than I do to the bargraph and what my depths have been during the dive. After a while, I got a pretty good sense of how long of an ascent it would take to get the bargraph back to the green (or nearly so). It turns out that unless we have been diving a reverse profile or short SI, what it takes to get my Oceanic back near green is what it takes to clear the deco obligation on a Suunto.

Charlie Allen

 

[TSandM]

We looked at the profile when we downloaded the dive, and the computer continued to accrue deco time until Peter got to 35 feet. He didn't get much credit for the time he spent at 20, and the ceiling was 10 feet.

I really don't know why his computer was so annoyed with him. Ascent from the first dive was along terrain and eventually a controlled minimum deco ascent; surface interval was generous, and as stated, the average depth for the second dive was about 47 feet on my computer (we were not diving in the same team, so his might have been a little different). I was figuring a 60 foot average depth, which should have given us 50 minutes with a minimum deco ascent with the shallow stops doubled, and in fact, the dive was 68 minutes, but that included 15 minutes of shallow hang with Peter. (He joined us for deco.) The one thing that was a bit unusual was that we did 32% on the first dive, and air on the second -- Maybe Suuntos don't like that?

Anyway, Ken nailed it -- The dive was awesome, and everybody came out fine; no issues with deco, no issues with gas, just this long hang to keep Peter's computer functioning.

And Walter, the reason for all the disclaimers in the original post was just to save people the breath of telling us that you shouldn't do deco unless you have the training, the equipment, and the gas, 'cuz I knew that was coming.

 

[evil_xander]

On a couple of occasions, Aladin Tec would signal me mandatory stop of 3 mins @3 meters, top was 2 minutes @6 meters, but it all usually goes away with the slow ascent.

Running out of air was never the possible scenario, even with those stops. I do like to have at least an idea to which depth we're going and for how long, so that I might consult the USN diving tables before the dive, in case the computer fails. At least I err on the conservative side that way... Never happened though.

 

[DandyDon]

I dive two Oceanic computers - and while any electronic gadget can crash or give caca readouts, as long as they agree - I feel I am diving within standards approved by all major agencies. Don't have any respect for the more conservative brands...

I never had a deco obligation and now...for the confession part, I'm not sure I would be able to read it on my computer if I did. I have an Uwatec. Would it tell me, 10 minutes at 20 feet or something like that? I have no clue. I've occasionally thought about the fact that I don't know what the computer will look like during a deco obligation, but never thought to try it out or ask someone, or look in the manual.

Doesn't sound safe.

I run simulations with my computers, so I can see exactly what they look like when demanding deco, etc. - and I encourage my buddies to do the same. I drill my home buddy on his.

TDI has a course called "Decompression Procedures", which is separate from the advanced nitrox. So, yes, there is such a thing

Got that card. Didn't learn anything I didn't already know, but I went to the effort...

And don't fault the Inst. I just already knew all that.

Deco isn't a problem. Being in deco and not having the gas to do the stops IS a problem.

:blush: Been there once. Still owe a NC diver some Nitrox - glad he had it to spare on the deco line.

On a couple of occasions, Aladin Tec would signal me mandatory stop of 3 mins @3 meters, top was 2 minutes @6 meters, but it all usually goes away with the slow ascent.

Are you sure that was Deco Obligations or Safety Stop INdicated...?

 

[Peter Guy]

OK, since I'm the one who "did the crime so I did the time" I want to give the other side of the story.

First of all, my team had discussed the possibility (probability!) that we would "go into deco" per my Suunto on both dives -- which we did. We also had planned on doing minimum deco profiles on both dives -- which I believe we did.

Second, after discussing the "possibility" of going into deco, we discussed the issue of having enough gas -- and we decided that wasn't an issue.

Third, and last, since both dives were rocking, we decided to "do the crime" with the (correct) belief that we'd do enough shallow to clear any obligation. Yes, we deliberately went into "an overhead environment" without doubles, but the team had plenty of gas.

Here are the profiles of both dives:

Dive One -- I surfaced with 600+ PSI or about 24 Ft3 remaining.

Dive Two -- I surfaced with 600+ PSI or about 24 Ft3 remaining.

I loved the time I spent hanging -- did some drills with HBDivegirl, looked at the Garibaldi, had a wonderful time.

TSandM just said, these dives are a perfect example of why new divers shouldn't have big tanks!

 

[PalatkaBoy]

I never had a deco obligation and now...for the confession part, I'm not sure I would be able to read it on my computer if I did. I have an Uwatec. Would it tell me, 10 minutes at 20 feet or something like that? I have no clue. I've occasionally thought about the fact that I don't know what the computer will look like during a deco obligation, but never thought to try it out or ask someone, or look in the manual.

If you have an Uwatec SmartCom, it will tell you depth and time of stop. Once that stop is complete it will give you the next stop required.

Before anyone digs into my profile, yes, I know what deco stops on my computer should look like but no, I have never seen one.

 

[Blackwood]

I thought I was breathing the stage, but I was actually breathing my backgas.

Yikes.

Like: wow.


Edit: Never mind, I read the rest of your post. When I first read that I was thinking along the lines of a deep diving backgas (lean O2).

 

[Wildcard]

It's a rare weekend my Vyper is talking to me at the end. Even here in the shallows of the caribbean chasing divers up and down realy POes it. I have deco obligations all the time. It's just far to conservative of a algorthem. In hawaii on the deep stuff I get bent almost every dive Im leading due to again having to chase divers around, boouncing for the mooring and such. My puter would be much happier if more people would work on there dive skills some.