Please help me stop!

[Kern]

But what do you do if the voices in your head conflict with your counselor?

Chemical intervention may be required!

Must dash, it's a long drive to the nearest wreck.

 

[DaleC]

Except that...

Those NDL dives with the same deco have been extensively studied with many test subjects and peer reviewed articles. That research indicates that the stop is not really necessary, but it can be helpful. It is not necessary because the diver has not built up enough of a nitrogen load to need more than that. Divers can be very confident that what they are doing will work.

In contrast, the decompression diver knows he or she has built up enough of a nitrogen load to form a very real danger. In order to deal with that danger, the diver follows a very precise protocol, a protocol that is highly theoretical and has not had anything like the testing for NDL profiles.

There are all sorts of theories, and they don't agree. Two different divers following the same bottom time profile will use different decompression schedules, and neither one has been more thoroughly tested than the other. Some of the most popular decompression systems being used today have been barely tested at all.

This past October my buddy and I followed the exact same profiles through three days of decompression diving, and we talked openly and with some concern about the theory and the lack of testing for what we were doing in our planning quite a bit. The next day I felt great, better than I have felt after such a series of dives ever, probably.

He was in the chamber.

I accept all that and understand decompression theory is just that; theory, but so is non decompression diving. People still get bent within the limits. Here's a question though: 20 minutes at 100 feet and supposedly I can ascend directly to the surface with or without a safety stop. 21 minutes and I have a manditory deco obligation. Did something demonstrably different happen in that one minute and is the diver ascending directly to the surface after 19 minutes in a safer position than the diver doing manditory deco after 21 minutes.

That was the gist of my question at the time.

 

[Slamfire]

I think I understand your point here.

Just a while ago I postulated as to whether a diver doing a planned deco dive was safer than someone simply diving within NDL limits. My thinking was that a deco diver chose a model and calculated his off gassing according to his actual dive profile where as a NDL diver does the same deco (3 minute SS) whether they spend 1 minute at 100ft or 19 minutes.

Not just that, but I also wanted to point out that a deco dive doesn't have to be a complex super long, super deep dive.

Two weeks ago Dale and I were on the same boat dive trip. We were not buddied together that time. Because of the boat and ferry schedules, my buddy and I were notified we could not be longer than 1hr per dive. This was a 2 dive trip. On both of our dives we went into deco. On both of our dives we complied with the time restrictions. Dive 1 was to 131' max depth 52 mins run time and dive 2 was to 92' 44 mins run time. These are not inordinately deep dives. In fact it could be debated that they qualify within the realm of recreational diving, at least in terms of depth and time. The first dive was in full compliance with Mares RGBM deco schedule. On the second dive we carried an AL 40 with 50% nitrox. The computer screamed at me because it believed I surfaced with 7 mins of remaining deco obligation. I knew better because I was using 50% and my computer only handles 1 gas.

What I want to point out here is that in addition to keeping it short and shallow, we never allowed ourselves to be rushed into an ascent by an imminent arrival of the end of the NDL. We went up at our planned pace, we had plenty of bottom time, and remained in compliance of a conservative algorithm. We had the initiative in our dive profile. Relinquishing the initiative of your dive profiles to a computer is not necessarily the best idea.

 

[Slamfire]

I accept all that and understand decompression theory is just that; theory, but so is non decompression diving. People still get bent within the limits. Here's a question though: 20 minutes at 100 feet and supposedly I can ascend directly to the surface with or without a safety stop. 21 minutes and I have a manditory deco obligation. Did something demonstrably different happen in that one minute and is the diver ascending directly to the surface after 19 minutes in a safer position than the diver doing manditory deco after 21 minutes.

That was the gist of my question at the time.

Exactly. What would be safer -- to stay with NDL after 19 mins and go directly to the surface or to stay 21 mins and comply with the mandatory deco stops? Often times experienced recreational divers will ride the NDL to the very edge all the way to the surface. Breaking the NDL becomes such an unnecessary taboo that when they want to stay down longer, they are willing to buy new, less conservative computers just to have the new machine tell them that they are not taboo breakers. Not the safest diving progression. Just take it into deco and do the time.

 

[RJP]

Did I miss something, or are you self-identifying as a fool? This thread has become richer than I could ever have hoped for...

That's the difference between you and me... self-awareness.

 

[The Chairman]

... and some get their fun by shooting their mouth off on Internet forums. They're mostly losers ...

I don't know if I would go that far, Bob. People are looking for passion, and many of us find it in Scuba Diving. Hell, it's just so far out there for us and it's as amazing as hell. I have yet to see some one NOT light up when they start to tell others what they saw underwater. Their whole demeanor changes and they often become quite the evangelist.

But, if you mess with HOW they dive, that passion can quickly be redirected. Their mission can quickly become trying to convert the world to the way they dive, the way they train and to use the gear that they use. To be sure, I have seen this at many LDSs when it comes to what they have to offer. Of course, there is this phenomenon to contend with as well:

 

[boulderjohn]

Here's a question though: 20 minutes at 100 feet and supposedly I can ascend directly to the surface with or without a safety stop. 21 minutes and I have a manditory deco obligation. Did something demonstrably different happen in that one minute and is the diver ascending directly to the surface after 19 minutes in a safer position than the diver doing manditory deco after 21 minutes.

I assume you are quoting the PADI RDP with the quoted time. That system is designed to do no decompression diving only. It has no capacity to measure decompression dives. Whatever the research of Powell, Spencer, et. al, showed, , they had to draw that NDL line. That extra minute does not bring a lot of deco time at all. It just does not show up on the chart.

If you were to use a computer, you would go over the magic number for no deco just as much, but it has the capacity to tell you what to do. You would probably clear it with a good ascent alone. Otherwise, you would probably just have a mandatory safety stop.

There has to be a hard number somewhere. How else could you do it?

On the second dive we carried an AL 40 with 50% nitrox. The computer screamed at me because it believed I surfaced with 7 mins of remaining deco obligation. I knew better because I was using 50% and my computer only handles 1 gas.
...
Relinquishing the initiative of your dive profiles to a computer is not necessarily the best idea.

If you are going to use 2 gases but use neither 2 gas decompression tables nor a computer that can handle 2 gases, then you have relinquished your dive profile to guesswork.

Exactly. What would be safer -- to stay with NDL after 19 mins and go directly to the surface or to stay 21 mins and comply with the mandatory deco stops? Often times experienced recreational divers will ride the NDL to the very edge all the way to the surface. Breaking the NDL becomes such an unnecessary taboo that when they want to stay down longer, they are willing to buy new, less conservative computers just to have the new machine tell them that they are not taboo breakers. Not the safest diving progression. Just take it into deco and do the time.

First of all, one minute of deco will not lead to "deco stops." At most it will lead to a mandatory safety stop, possibly with an additional minute or so.

I agree that if people are going to use computers, they need to know how to do use them. I also agree that one should know how to deal with basic deco issues such as you describe. That is not the case, though. There was a recent thread in which a diver described his panic when he went into deco by one minute and did not have any idea that his computer could guide him through the ascent. He had also forgotten that he had been taught what to do on tables in that case in his OW class.

The solution would be for agencies to teach how to use a computers as a part of their OW instruction. SDI does that now. PADI now offers it as an option. Mention that in a thread on SB and watch how people recoil in horror that students are being taught how to use a dive computer. Another sign that the apocalypse is upon us!

 

[Walter]

First of all, one minute of deco will not lead to "deco stops." At most it will lead to a mandatory safety stop, possibly with an additional minute or so.

A safety stop is, by definition, optional. If the stop is mandatory, it is a staged decompression stop.

 

[boulderjohn]

A safety stop is, by definition, optional. If the stop is mandatory, it is a staged decompression stop.

Gee, thanks.

Of course that is true. I was trying to simplify a more complex explanation. The truth is that 1 minute of deco will probably be satisfied by a normal safety stop. It might be satisfied before the normal safety stop, provided a good ascent profile.

 

[MXGratefulDiver]

Gee, thanks.

Of course that is true. I was trying to simplify a more complex explanation. The truth is that 1 minute of deco will probably be satisfied by a normal safety stop. It might be satisfied before the normal safety stop, provided a good ascent profile.

This is true. On a typical profile at my local mudhole ... a visit to a bottle field at 75-95 fsw ... my dive computer will often go 2 to 4 minutes into deco before I start heading up. And most times it will have cleared before I ever make it to safety stop depth ...

... Bob (Grateful Diver)