How much gas in case of accidental deco.

[TSandM]

I think it is fair to point out that the Suunto RGBM algorithm is both on the very conservative end of things, AND is well known to penalize divers for deep stops. I think it's quite possible that another computer (say one running V-planner) wouldn't have racked up the amount of deco you saw on the Vyper, and would have begun to credit you for decompression as soon as you passed the offgassing ceiling of the controlling compartment.

To the OP -- the very fact that Andy and I can get into this discussion is a beautiful example of why you should treat no-decompression time with a great deal of respect. There is much that is not actually KNOWN with certainty about decompression. The models that are used for recreational diving are subjected to a fair amount (and in some cases, a great deal) of validation, because a) it's easy to do, and b) the liability of selling a dive computer with a faulty algorithm is pretty major. Once you exceed the limits of the model, you have entered a world where far less is known, and far less has been validated. The consequences of a misstep, especially with recreational-type dives, can be very high, as DCS in recreational divers is more often neurologic than joint pain. So Andy is quite right (and I agreed with him) that inadvertently going into deco is a major error that should be a strong wake-up call about your dive planning AND your situational awareness in the water.

Situational awareness is something that isn't strong in new divers, because they are challenged for bandwidth in just managing the mechanics of the dive. That's one of the reasons that OW divers are encouraged to respect the 60 foot limit -- it's difficult to get yourself into trouble from a decompression standpoint when staying above that depth, and given the gas consumption rates of most new folks. (This is no longer as true if you begin to do multiple dives/multiple days.)

But I will still applaud the OP for being aware that not having enough gas is the worst factor in having made an error in managing his decompression status.

 

[ianr33]

I'm not sure quite what you mean by that, but I can assure you that the event described was very real. I'm not in the habit of posting BS for the sake of it, especially when it's an admission of my own fallibility.

I'm not questioning your computer requested a lot of deco. Just pointing out that a more capable computer that was not way out of it's comfort zone would not do that.

As I posted. I've done a series of dives where V planner wanted 10 minutes deco and my cheap rec computer wanted an hour. I trust v planner on that one.

ianr33... I had about 4x your experience when that happened to me. I thought I knew a lot then. I managed to learn something. I'm still learning... so should you.

O.K. Dad, thanks for the advice.

 

[redacted]

i suspect that with the right profiles, your deco requirement on a recreational dive computer can go from one minute of ndl to a number of minutes [not one or 2] of deco very quickly. the problem occurs with multiple days of multiple deeper dives all approaching ndls. with the earlier dives on the first day, it is a fairly fast tissue compartment regulating your dive. these fast compartments load and unload rather quickly [half times in the 5 to 20 minute range] and their saturation depths are deeper [eg, in the 70 to 90 foot range]. i am doing this off the top of my head with one hand tied behind my back so values are rough guesses. these fast compartments cl;ear rather quickly and start off-gassing at greater depths so any obligation is often worked off during a slow ascent.

but, with mult day, multi dive scenario, the slower compartments start to take control. they have half times in the 3 to 12 hour range so it takes a bunch of diving to put them in control. but once they are in control, it take a lot more time to accomplish a given level of off-gassing. and their saturation depth limits tend to be relatively shallow [30 to 50 feet] so that same slow ascent that cleared your deco requirement on the first day has you continuing to on-gas the controlling slow compartment on the 4th day. then, in stead of having cleared you deco en-route to your 10 ft stop, you may be adding minuted of additional stop time for each minute you spend ascending before the controlling compartment starts off-gassing. this is a time when a 60 fpm ascent rate is better for you than a 30. and a 10 or 20 fpm ascent rate can bring on a big problem.

 

[DevonDiver]

I'm not questioning your computer requested a lot of deco. Just pointing out that a more capable computer that was not way out of it's comfort zone would not do that.

As I posted. I've done a series of dives where V planner wanted 10 minutes deco and my cheap rec computer wanted an hour. I trust v planner on that one.
.

Are we talking about technical divers using V-planner... or are we taking about recreational divers who 'don't want to be fearful' of going into decompression?

Which computer models do they use?

Hint: the ones I've used to make an example, not ones I could have used to show off about. I don't need to swing that..

Also: you seem to have some mis-appreciation of dive computers. The cost value of a computer isn't representative of the 'quality' of the algorithm. It's about the user.

Put 'Joe Noobie' on an aggressive computer, throw deep stops and multi-speed ascent rates at him... BENT

Stick 'Jonny Tech' on a plain 'ole' RGBM machine... frustration, long stops...grrrrrr

Not better or worse... just tailored for the market demographic that should be using them.

I wear my 'cheap computer' when I shepherd novice divers. It keeps them safe...it keeps their dives simple... and has done for nearly 10 years at a dive pro. When I plan tech dives, the 'ole faithful Vyper becomes a back-up timer... and I get to choose which of the lovely desktop software toys I will trust my life to. Which one doesn't really matter, because I'll tailor the parameters to what I want anyway.

Proplanner on MSDOS anyone?

 

[Bob DBF]

Divers have computers which gives the remaining NDL, but they go into deco.
Divers have SPG's, but they go OOA.
Divers have depth gauges, but go deeper than plan.

Does anyone see a pattern?

As an OW diver, you are flying on instruments to avoid deco and other problems. Not because deco is bad, as others have mentioned, but because it is not in your dive plan an therefore you are probably not properly equipped with training or gear and the concequences can be catastrophic.

As a diver your first priorty should be on your instruments and keeping yourself safe, and secondarily on the pretty critters, wrecks, and treasure chests; because if you don't get out of the water safely, you won't be going back. Redundant gas is fine, but it won't (and shouldn't) be necessary if you watch your instruments and follow your plan.

Sure anyone can come up with exceptions, and they might be valid, but the concept is to avoid the exceptions.



Bob
-----------------------------------------------

That's my point, people, by and large, are not taught that diving can be deadly, they are taught how safe it is, and they are not equipped with the skills, taught and trained to the level required to be useful in an emergency.

 

[tracydr]

I agree with TSand M here. I don't think the deco in Devon Divers post was "real"

I have an Aeris computer and have found a foolproof way to throw it for a complete loop: Do a regular dive first ,maybe 60 feet. Then do a deco dive to perhaps 130. The computer will rapidly come back with insane amounts of deco. (V-planner wanted maybe 10 minutes, computer needed maybe an hour) My assumption was the computer didn't know what to do with those profiles ,became massively conservative just in case.

Now, if I hadn't planned these dives first on V- Planner I would have been very concerned about this.

Deco will not go instantly from nothing to 20 minutes on any "normal" profile. (But it's still a dumb idea to go into unplanned deco )

I would suggest anyone regularly doing dives that push NDL do an Advanced Nirox course. You will learn lots of deco theory and become a much safer diver . (But you may get hooked and end up spending thousands on new gear.......)

Very interesting. Now I understand how I incurred about 25 minutes of deco by going 1-2 minutes over my NDL on a multiday dive trip.
I have been reading Deco For Divers, great book. Just order " The Six Skills" yesterday.

 

[lowviz]

...//...I incurred about 25 minutes of deco by going 1-2 minutes over my NDL on a multiday dive trip. ...//...

OK, please elaborate.

I simply cannot make your or DevonDiver's fantastic obligations occur with non-deco diving, now matter how I try. Obviously I am missing something very important and won't quit until I get this sorted out.

(V-Planner v3.89)

---------- Post Merged at 04:21 PM ---------- Previous Post was at 02:57 PM ----------

Just downloaded v3.91. What conservatism level are we using?

---------- Post Merged at 07:11 PM ---------- Previous Post was at 02:57 PM ----------

...//...If you were on a no deco dive and for whatever reason (inattention, dealing with a situation, etc) ran your NDL down and clipped the edge of the deco envelope, how much gas should you have to safely clear your obligation without pushing an out of air situation? ...//...

OMG freeclimbmtb, I think that the answer is: "screw you, you shouldn't have done that."

 

[TSandM]

Lowviz, you CAN'T get V-planner to do what Andy is describing, because V-planner will give you credit for the offgassing that occurs as soon as you ascend past the offgassing ceiling of the fastest compartment. The models used by recreational computers, and in particular Suunto, are very Buhlmann-based, and don't begin to consider you as decompressing until you get very shallow. Therefore, deco continues to accrue, sometimes rapidly, throughout what other models would consider part of your ascent and decompression. That's what somebody above has said that their technical diving computer has called for 10 minutes of deco when a recreational computer taken on the same dive was demanding an hour. It's pretty clear that both of them can't be "right" about how much decompression is actually needed.

Andy's point, though, is a good one -- which is that BECAUSE recreational divers who inadvertently go into deco are typically using recreational computers that will accrue unrealistic amounts of deco very quickly, one cannot say that the amount of gas required to satisfy the computer is minimal. If you have done a single deep dive and violated parameters by very little, you will get an 8 minute stop at 10 feet from a Suunto; but if you have been doing repeated deep diving over several days, as Andy pointed out, you may be shocked at the amount of deco you're suddenly requested to do, and it won't decrement during your ascent to your stop depth.

We actually went through this on a dive in Southern California. We had five divers who did three dives together. On the third dive, two of them ducked about 20 feet deeper than the rest for a couple of minutes to look at a ray. We had two Aeris computers, a Vytec that didn't do the duck, a Vytec that did, and myself running RD. Nobody had any deco except the guy using the Vytec that did the brief deep segment -- and he had TWENTY MINUTES of it. Since he didn't want the computer to lock up for a later dive that day, or for the following day's diving, he had to satisfy the thing. Luckily, he had plenty of gas to sit for twenty minutes at 15 feet, but we were sure annoyed to have to do it with him.

Whose model was "right"? The bottom line is that nobody knows, but you may need more gas than you think, if you go over your limits, especially if you don't have any basis on which to question the output of your dive computer.

 

[lowviz]

I read his bio. He is a local diver with a straight-forward, pertinent, and quite reasonable question.

Really, does anyone think that he is diving in five day stretches to the limits of NDL? He asked a simple question and, IMHO, should have received answers in the context of his question.

We can all come up with scenarios that make a mockery of "what you should do if...", or macho deco divers know that you are close to killing yourself because of what you don't know.

Yeah, I know all about the liability issues that we as posters all face...

I'd rather give good generic advice that speaks to the bell-curve in an attempt to help someone who is rightfully concerned rather than firing FUD missiles while establishing superiority of one's past experience. I'm permanently fixed somewhere between "Joe Noobie and Jonny Tech" (DevonDiver's terms, not mine). I learned conservatism indirectly though Lamont and then quite directly through Doppler. With divers of that caliber striving to remain safe and sane, the message sunk in to my very core, I'm a believer.

My diving world is just a tad past NDL limits. It is the North East Atlantic after all. We are a highly under-represented lot on SB, really starting to understand why...

 

[dumpsterDiver]

Lowviz, you CAN'T get V-planner to do what Andy is describing, because V-planner will give you credit for the offgassing that occurs as soon as you ascend past the offgassing ceiling of the fastest compartment. The models used by recreational computers, and in particular Suunto, are very Buhlmann-based, and don't begin to consider you as decompressing until you get very shallow. Therefore, deco continues to accrue, sometimes rapidly, throughout what other models would consider part of your ascent and decompression. That's what somebody above has said that their technical diving computer has called for 10 minutes of deco when a recreational computer taken on the same dive was demanding an hour. It's pretty clear that both of them can't be "right" about how much decompression is actually needed.

Andy's point, though, is a good one -- which is that BECAUSE recreational divers who inadvertently go into deco are typically using recreational computers that will accrue unrealistic amounts of deco very quickly, one cannot say that the amount of gas required to satisfy the computer is minimal. If you have done a single deep dive and violated parameters by very little, you will get an 8 minute stop at 10 feet from a Suunto; but if you have been doing repeated deep diving over several days, as Andy pointed out, you may be shocked at the amount of deco you're suddenly requested to do, and it won't decrement during your ascent to your stop depth.

We actually went through this on a dive in Southern California. We had five divers who did three dives together. On the third dive, two of them ducked about 20 feet deeper than the rest for a couple of minutes to look at a ray. We had two Aeris computers, a Vytec that didn't do the duck, a Vytec that did, and myself running RD. Nobody had any deco except the guy using the Vytec that did the brief deep segment -- and he had TWENTY MINUTES of it. Since he didn't want the computer to lock up for a later dive that day, or for the following day's diving, he had to satisfy the thing. Luckily, he had plenty of gas to sit for twenty minutes at 15 feet, but we were sure annoyed to have to do it with him.

Whose model was "right"? The bottom line is that nobody knows, but you may need more gas than you think, if you go over your limits, especially if you don't have any basis on which to question the output of your dive computer.

Really? I use a typical recreational nitrox computer. I often do a 180 ft dive and get 8-15 minutes of deco on that first dive and then 90 minutes later do another pretty long dive in 80 or 100 feet and approach deco limits again with a rich nitrox mix and somethimes do another dive too, with a little deco.

This weekend (in a priod of 6 hrs or so) I did 4 dives with depths between 165 and 135 on light nitrox and went into deco on 2-3 drops, I forget actually. My Oceanic computer has little trouble with a first deep deco dive and then repet dives less than 100 afterwards. It only really gets mad at me when I do repetative dives past about 120 feet.

To make a general statement that mainstream recreational computers give unfair amounts of deco for small transgressions into deco, is not necessarily true in my experience. What people need to be aware of is that.... staying 2 minutes past the no-deco limit at 100 feet on the first dive will give you minimal deco.... doing the exact same 2 minutes past the no-deco limit on the 3-4-5th dive can casue the computer to really spank the diver with a lot of deco. This is an important distinction...