Would you really know what was going on if your computer went into Deco...?

[rcohn]

Let me ask every one something...

Using a haldanian model computer what's the differene in gas loading when you are at the leading compartments critical tension after 5 minutes of required decompression and being in the same situation after 30 minutes of required decompression?

Which holds more risk and why?

I assume you mean two different dives, the first with a required 5-minute deco and the second with a required 30-minute deco, and both deco stops have been completed.

The leading compartment should have reached 100%. I would think that the dive with higher N2 load (longer required deco) carried greater risk because the higher gas load may have led to higher gradients during ascent that could/would result in greater bubble growth depending on how the ascent was conducted.

Remember a necessary caveat is 100% of what? Most recreational computers have reduced M values so their 100% compartment gas load is less than some of the tables and deco software programs. For example, the Suunto algorithm (first dive) reaches 100% in a compartment in 17 minutes at 100 ft. The US Navy tables (from memory I might be off) allows 25 minutes at 100 ft. Gas load is also exponential in nature, most of the load in the critical compartment occurs within the first few minutes of the time at depth. The difference in critical compartment gas load (assuming the same compartment) between 17 and 25 minutes is rather small.

Ralph

 

[rcohn]

Where did I say that advanced decompression gas is required to dive to 100 ft?

I think it was when your said:

Personally (and you can do what you want of course) but it would be a rare occassion that I venture very deep for very long without a decompression gas.

In my opinion (underline that if you wish) standard recreational equipment and the methods commonly taught are NOT suitable for dives to 100 ft and beyond.

Also I’m assuming the deco gas you’re referring to must be 100% O2 (only a st**ke would use anything else) which would have severe consequences if accidentally misused.

Actually the recommendation to do this can also be found in the PADI nitrox text.

I'm only familiar with my YMCA training, a few years ago, where the standard was direct ascent.

I don't need to show proof of anything. The classes that I mentioned are designed just exactly for what I recommend them for and teach the skills that those agencies believe that a diver should have to do dives of that level. I'm not trying to really change anything. I'm just encouraging that option.

If you want to keep making extraordinary claims, while maintaining a shred of credibility, you need to present some form of proof. No one else I've ever heard of, including working divemasters I talked with at very active vacation dive spots, has claimed to have seen anything like the number of accidents you seem to have witnessed. Most statistics I've seen estimate diving to be a relatively safe sport. Your continual assertions, that all sport divers you've watched are incompetent fools, lacks credibility.

Using the IANTD advanced nitrox class as an example because I'm most familiar with it...the class envolves diving to a max depth of 130 ft and a max manditory decompression of 15 minutes. Isn't that the kind of dive we're talking about pretty much?

But...the focus of the class is the skills that serve a diver doing deeper recreational dives.

I thought we were talking about what to do when a dive, planned to remain within the NDLs, goes awry and a small unanticipated decompression obligation occurs. This never occurs with most divers and, with the considerable conservatism in most sport diving computers, can be handled with relative safety by following the computers deco plan. Thousand of dives are performed when recreational diver intentionally incur a deco obligation with satisfactory results. It is certainly an adequate plan for a rare emergency that most divers will never experience.

Ralph

 

[Genesis]

Mike, you need to be more specific, or you're not going to get straight answers

I wrote up a somewhat-longish answer to your question, but I'm going to hold off posting it for a bit and see if there are other's taking a crack at it.

Ralph, which diver are you betting on? I can't tell - Mike didn't specify the starting or total obligations of either diver.....

I (think) I understood what he was asking and the process he was thinking through - we'll see later when I post my answer..... correct me if I'm wrong Mike, but your question intentionally did not specify which diver started with the greater total deco obligation or even where (out of that total) he is now - just that one diver has doen 5 minutes of deco, the other 30, correct?

The answer I wrote up made few assumptions for the unspecifieds (e.g. I did NOT assume that the diver with the 30 minutes of deco "served" had the higher original obligation); the question still can be answered without knowing the other facts, but it cannot be answered with certainty (e.g. the diver who has done only 5 minutes of deco might have done all of the required deco!); therefore, there are some assumptions we must make (e.g. that both divers still have required deco time ahead of them when they "break" the schedule.)

 

[Laser]

No one else I've ever heard of, including working divemasters I talked with at very active vacation dive spots, has claimed to have seen anything like the number of accidents you seem to have witnessed. Most statistics I've seen estimate diving to be a relatively safe sport. Your continual assertions, that all sport divers you've watched are incompetent fools, lacks credibility.

I dive in a few spots where Mike does and I see some of the things that he sees. While there may not be " accidents " as termed by someone getting injured, there are a plethora of people with tanks on their backs but they're not necessarily divers. Things such as treading on the bottom, getting lost from their group, can't hold a stop, on and on. As an example, last year in my dirf class at one of the quarries that Mike frequents, we were at 30 ft conducting drills ( neutrally buoyant ) and a diver came crashing down right in the middle of our group, hitting the bottom and stirring up the silt. Then a binder ring of instruction cards came down...followed by an instructor crashing to the bottom. This instructor was teaching an AOW class. Very nice.

 

[Genesis]

Well, both student and instructor did dive "deep" - into the mud!

 

[MikeFerrara]

Mike, you need to be more specific, or you're not going to get straight answers

I wrote up a somewhat-longish answer to your question, but I'm going to hold off posting it for a bit and see if there are other's taking a crack at it.

Ralph, which diver are you betting on? I can't tell - Mike didn't specify the starting or total obligations of either diver.....

I (think) I understood what he was asking and the process he was thinking through - we'll see later when I post my answer..... correct me if I'm wrong Mike, but your question intentionally did not specify which diver started with the greater total deco obligation or even where (out of that total) he is now - just that one diver has doen 5 minutes of deco, the other 30, correct?

The answer I wrote up made few assumptions for the unspecifieds (e.g. I did NOT assume that the diver with the 30 minutes of deco "served" had the higher original obligation); the question still can be answered without knowing the other facts, but it cannot be answered with certainty (e.g. the diver who has done only 5 minutes of deco might have done all of the required deco!); therefore, there are some assumptions we must make (e.g. that both divers still have required deco time ahead of them when they "break" the schedule.)

Sorry. Both divers have completed their required decompression. One had a total of 30 minutes and the other 5. In both cases their computer/table has cleared them to surface.

 

[MikeFerrara]

Originally Posted by MikeFerrara
Where did I say that advanced decompression gas is required to dive to 100 ft?

I think it was when your said:

Personally (and you can do what you want of course) but it would be a rare occassion that I venture very deep for very long without a decompression gas.

In my opinion (underline that if you wish) standard recreational equipment and the methods commonly taught are NOT suitable for dives to 100 ft and beyond.

Also I’m assuming the deco gas you’re referring to must be 100% O2 (only a st**ke would use anything else) which would have severe consequences if accidentally misused.

Again I pointed out that I never said that is's required. All I said was that that's what I choose to do based on what I know. Make your own choice but I think it's best to do it from an informed position.

I don't need to show proof of anything. The classes that I mentioned are designed just exactly for what I recommend them for and teach the skills that those agencies believe that a diver should have to do dives of that level. I'm not trying to really change anything. I'm just encouraging that option.

If you want to keep making extraordinary claims, while maintaining a shred of credibility, you need to present some form of proof. No one else I've ever heard of, including working divemasters I talked with at very active vacation dive spots, has claimed to have seen anything like the number of accidents you seem to have witnessed. Most statistics I've seen estimate diving to be a relatively safe sport. Your continual assertions, that all sport divers you've watched are incompetent fools, lacks credibility.

Again, the training/skills that I recommend a diver having for dives to those depths is consistant with the recommendations of the agency that I teach through. IANTD has a number of texts on the subject and I highly recommend them for inclusion in your own reference lib. What do want proof of? That the agency is right?

As far as accidents/incedents, some of those that have happened at Gilboa are documented right here on this board. The most interesting one this past year was an AOW student lost a fin a 80 ft. He sunk deeper and ended up in panic. After a rapid ascent was not breathing and if I remember right there was no pulse. They were able to revive him luckily.

deep diving without prereq skills...You all do what you was ok?



[/QUOTE=me]
Using the IANTD advanced nitrox class as an example because I'm most familiar with it...the class envolves diving to a max depth of 130 ft and a max manditory decompression of 15 minutes. Isn't that the kind of dive we're talking about pretty much?

But...the focus of the class is the skills that serve a diver doing deeper recreational dives. [/QUOTE]

I thought we were talking about what to do when a dive, planned to remain within the NDLs, goes awry and a small unanticipated decompression obligation occurs. This never occurs with most divers and, with the in most sport diving computers, can be handled with relative safety by following the computers deco plan. Thousand of dives are performed when recreational diver intentionally incur a deco obligation with satisfactory results. It is certainly an adequate plan for a rare emergency that most divers will never experience.

Ralph

A couple things here. The training/skills that reference above are those that I think a diver should have prior to doing dives where there is a significant risk of incurring a decompression obligation. Period

The statement you mane that recrestional computers have considerable conservatism is something we could debate. While they may have conservative NDL's the models commonly employed and the schedules generated for manditory decompression may not look so conservative when compare to a more modern model like VPM, RGBM or even Buhlman with gradient factor control. In an earlier post I described the situation where a freind was badly bent while his computer was very happy. He even did more decompression than his computer recommended. After comparing his schedule to those that I generated for the same dive I would not say his computer was conservative. I'd say it bent him on the initial ascent and then failed to treat him enough. It worked for his buddy though and maybe it would work for you...or not.

Your statement that

It is certainly an adequate plan for a rare emergency that most divers will never experience.

refering to the computer generated emergency decompression is based on what exactly? It's not a PLAN at all and that's the problem. It's a feature of the computer to bail you out after your failure to plan. The simple act of having to use it is a good arguement in favor of divers getting the training/skills that I recommended prior to doing those dives so that they can choose the way they want to decompress and have the skill and gas to execute the schedule.

You seem to be argueing in favor of divers ridin the edge of the "NDL" and relying on the computer to bail them out while I advocate the diver understanding the situation that they're in on such a dive and making informed decisions and being in control.

Do have some kind of proof that what you suggest is better? Are you suggesting that divers are better of at 100ft + without the trianing/skills I'm recommending?

What exactly is your motivation here?

You're using resort DM's as your knowledge base? Thats a joke right?

Trust me dives any one?

 

[Genesis]

Sorry. Both divers have completed their required decompression. One had a total of 30 minutes and the other 5. In both cases their computer/table has cleared them to surface.

Ok, here's my analysis:

My answer is that the diver who has undergone 5 minutes of deco is in more
danger.

The reason is that the diver who has undergone only 5 minutes of deco
almost certanly has his "leading" compartment as the fastest (one or
two, excluding his blood) compartments in the body - which are unfortunately compartments that can really f#$@ you - the "fast" compartments include the tissues that produce neurological bends, as "faster" tissues are (generally) those that are best-perfused - neurologically-related organs, of course, are among the best-perfused organs of all. (Actually, blood is probably the "fastest" tissue, and bubbling on the arterial side of the circulation will severely hose you.)

The diver with 100% loading in his leading compartment after 30 minutes of
deco PROBABLY has a "slower" leading compartment - he has LESS overpressure in the "fast" compartments, because slower compatments tend to control the shallower stops, and you've specified that the diver has already done 30 minutes of stops - which would be the deeper ones. If you were to look at that diver's fast compartments, they would be WELL below critical tension.

The slower compartments are less likely to produce a Type II hit.

Therefore, using only the Haldanean approach, the diver who has done only 5 minutes of deco is more likely to take a Type II hit, while the diver who did 30 minutes of deco is more likely to take a Type I hit.

This is with all other things being equal, which of course they never are, and this also assumes no PFO - if a slow compartment bubbles into the venous circulation it may not produce a hit at all (the lungs are a pretty decent filter, and aleovi can obtain oxygen by direct gas exchange with the air in the lungs), provided there is no shunt.

If there IS a PFO, then slow compartments can easily produce a Type II hit, since bubbling into the venous circulation can cross over - in this case there is may be little or no difference in risk profile.

(BTW, the true "answer" for the diver who had 5 minutes of required deco is to do another 5 minutes, so as to allow those fast compartments to desaturate - because those are the ones you REALLY don't want to have a problem with.)

So how'd I do, teach?

 

[ArcticDiver]

Posted by Mike Ferrara: "Once they do they may decide to decompress exactly as their computer says to. Then again they may not but until they make the decision they're letting some one else make the decisions for them and it isn't me."

Thanks for your reply Mike. Now I think I better understand your posts. I suspected you were an engineer or something similiar, so I looked up your public profile. Sure enough. As an engineer I bet you have very definite views that are never in doubt to those around you. That carries over into diving if I understand your posts correctly.

What does surprise me considering your occupation is the illogic portrayed by your posts. I've snipped one quote to illustrate. It rather directly says that if they follow their computer they are letting someone else make decisions for them. Implied is that if they don't follow the computer; but follow something else they aren't letting someone else make the decisions.

In fact, whether a diver follows tables, or a computer they are trusting someone else to establish the parameters of their decisions. The only difference is whether the presentation in an electronic display, or on paper.

Now much of your posting, and others, comments on whether this or that computer is too conservative, or too aggressive. Putting that kind of subjective information in this discussion just fogs the issue instead of putting light on it. What is too conservative for one person may not be for another. That perspective has little to do with science and a lot to do with personality and personal experience.

Anyway, thanks for the insight so I can better evaluate how much of what you post to accept and how much to chuck. Especially since you are exceptionally outspoken about your views.

Thanks

 

[Gary D.]

Posted by Mike Ferrara: "Once they do they may decide to decompress exactly as their computer says to. Then again they may not but until they make the decision they're letting some one else make the decisions for them and it isn't me."
________________________________________________________________

In fact, whether a diver follows tables, or a computer they are trusting someone else to establish the parameters of their decisions. The only difference is whether the presentation in an electronic display, or on paper.
________________________________________________________________________________________________________________________________

We trust others making decisions in life threatening stuff every day so why should diving be any different.

Years, make that decades and decades of research have gone into the tables and computers. So no matter how you look at it your still counting on someone else to get it right.

How we survived as long as we have is a wonder. I for one have to totally rely on the computer and pay attention to it. I've been doing that for the past 10 or so years. I just don't have the luxury to do it another way.

I've been in 2 groups now where we were well within the no deco limits and a bunch of the group had DCS hits. I've had the longest and deepest profile and been fine. I've been with divers that have had hits that missed me. Why?

It's a weird sport that doesn't work the same for everyone. Over the years I've had 2 confirmed hits. One in each wrist after real long deep chamber rides. Both times I was hit within 30 minitues of surfacing. None of the other 3 got a hit. Back down 20 feet and I was fine so we restarted the count down from there. Weird world. BAck then computers were still the size of a semi trailer.

Gary D.