120/20 rule or a 130 rule?

[ppo2_diver]

Given that this is the DIR forum, shouldn't the general attitude be that you plan your dive and dive your plan?

Personally, I take the attitude that you either do plan your dive and dive your plan or you strap on a computer. Trusting your brain to be able to get the limits right always seems like an accident in waiting.

But trusting an electronic device that can fail at any moment is more of a concern. When you go through the fundies courses, you learn to become a thinking diver. I'd rather trust my own brain than a dive computer program with gradient factors that are out of my control. Just look at the recent recalls at UWATEC with dive computers mis-calculating the dive profiles. The more you learn about decompression theory, the more comfortable you'll be at determining your own NDL limits.

 

[JessH]

Why is 240 minutes at 30' more aggressive or ridiculous than
80' for 40', 90 minute SI, followed by 80', 30 minutes?

I can't answer for him, but I think it is obvious that the second profile is much more aggressive. That being said, I think what he was getting at was that blindly following the tables without thinking is ridiculous, not the profile in and of itself.

BTW, if you are going to say "It's OK because of the slow ascent and stops, please tell me what they are so that you find the 80' 40min, 90 SI, 80' 30 minute profile reasonable.

***WARNING: The following is my own opinion and not fact. I have not been trained by GUE. Much of this is simply my own personal conclusions and as such may be incorrect. DO NOT TRY THIS WITHOUT PROPER TRAINING***

Most tables would actually say that you can't do this profile. But in certain contexts this profile MIGHT be even less likely to bend you than diving the tables in a traditional maner. From what I understand of the minimum deco style profile that GUE teaches, you should do a 10fpm ascent from roughly 1/2 your max depth and then starting somewhere around 30ft you should come up even slower in order to shape the curve better. This is often achieved with a series of stops at various depths along with slow moves. This ascent profile will decrease the formation of bubbles which leads to more efficient offgassing. You will also offgass more before leaving the water. This slow ascent will also alow you to withstand higher nitrogen loads without getting bent since the same nitrogen load will be less likely to cause significant bubbling (is this a correct assumption?)

I believe that these aggressive profiles will not bend you as long as you follow all of the rules. Traditional tables assume much less ideal ascent profiles (60fpm straight to the surface) and as such penalize you for repetative dives much more than necessary when you are doing a minimum deco ascent(this is my own personal assumption). My only concern with using this aggressive of a profile is that after a number of repetative dives you may be able to do a minimum deco ascent perfectly safely but not a straight ascent to the surface. While you wouldn't normally want to do that anyway in an emergency it may be necessary. Of course that may not actually be the case, but I don't currently have enough information at my disposable to be sure about the matter and as such add a good level more conservatism when doing repetative dives in situations where this issue could come up (such as diving with a single tank with a buddy that I don't know very well).

~Jess

 

[Charlie99]

Indeed, what you describe is the logic some people use to say that residual nitrogen can be ignored and SI shortened to less than standard.

It is rather strange though, that it is claimed that the "bubble models" support these assertions, since RGBM and VPM object strenuously to some of these "DIR Approved" profiles.

Take for example the following profile:
100' for 30 min on EAN32.
20 min SI,
then repeat with another 100' for 30 minute on EAN32.
Another 20 minute SI and
repeat 100' for 30min again for 3 and 4th dives, 20 min SI between them.

For the ascent after each dive, starting at about 80% ATA, say 70' for this example, slow the ascent from 30' a minute to 10' a minute, or 30 second pause followed by 30 seconds to go up another 10'. Then increase the pauses to 1 minute at 30', 20' and 10'. And for 3rd/4th dive start the 1 minute stops at 40'.

Is this truly a DIR profile?

Is that slow ascent and stops of 11 or 12 minutes after each dive truly enough to allow one to repeat the 100' 30 minute dive after just a 20 minute SI?

This sort of claim is often made. Has there really been any study of this?

 

[limeyx]

Indeed, what you describe is the logic some people use to say that residual nitrogen can be ignored and SI shortened to less than standard.

It is rather strange though, that it is claimed that the "bubble models" support these assertions, since RGBM and VPM object strenuously to some of these "DIR Approved" profiles.

Take for example the following profile:
100' for 30 min on EAN32.
20 min SI,
then repeat with another 100' for 30 minute on EAN32.
Another 20 minute SI and
repeat 100' for 30min again for 3 and 4th dives, 20 min SI between them.

For the ascent after each dive, starting at about 80% ATA, say 70' for this example, slow the ascent from 30' a minute to 10' a minute, or 30 second pause followed by 30 seconds to go up another 10'. Then increase the pauses to 1 minute at 30', 20' and 10'. And for 3rd/4th dive start the 1 minute stops at 40'.

Is this truly a DIR profile?

Is that slow ascent and stops of 11 or 12 minutes after each dive truly enough to allow one to repeat the 100' 30 minute dive after just a 20 minute SI?

This sort of claim is often made. Has there really been any study of this?

I would certainly not do those profiles as a general rule.
The guidelines I use for these kind of profiles are (using very similar tables to the above posts).

1 hour SI -- double the 30, 20, 10 stops on subseqent dives
90 min SI keep them at 1 min (but do slow ascent from 20 feet)

always shoot for 60 min SI. Maybe I'm just a chicken tho

I would probably do two 100 foot dives with 20 min SI, but not 3 in a row like that.

However, just because I wouldn't do it doesn't mean others wont/cant/arent

And it's always 1 min stops from 50% max depth for me, so 50 feet is the first stop for a 100 foot dive.

This is essentially what was covered in our DIR-F class. Does that mean someone with a "more complete" view of decompression wouldn't do the above? no. maybe they would.

EDIT: I have used the above rules for up to 7 dives in a day, average depth 80 feet (over all dives) starting on 32% for dives 1-2 and gradually diluting the fill to air for dive 7. With no ill effects. Obviously 1 data point does not a general rule make tho

 

[limeyx]

...

BTW, if you are going to say "It's OK because of the slow ascent and stops, please tell me what they are so that you find the 80' 40min, 90 SI, 80' 30 minute profile reasonable.

Sounds like a perfectly reasonable profile to me on 32%.
On Air, I'd rather make it 30 min and 30 min, but at a push I'd do it on air.

Here's something close (ish)

and these two were after a 40 min dive at average of 60 feet (yeah yeah, the gods of "reverse" profiles are going to come down and kill me dead)

Note: I'm not counting the ascent portion in the avg depth.

All dives on 32%.
If we'd have had time, we would have done a fourth also.

I think some people get too caught up in the details of ths algorithm and that compartment and those mm of mercury, and make things more complex than they really need to be.

The "right" ascent can help a lot, and everyone's limit is different. I think the 60-90 min SI is a good compromise such that for a day of recreational diving you are not going to build up too much N2, and by day 2 you are essentially "reset" (although you might to 2 min stops on subsequent days)

 

[JessH]

The tables that are based off of the bubble model, such as the tables that gue and naui provide say that the bubble formation will exist much earlier during the ascent and accounts for that by making multiple deep stops instead of a single stop. This allows your lungs to purge the inert gases from your body more effectively than a disolved gas model.

I was under the impression that GUE has not actually published any tables,. Please correct me if I am wrong. Most of the generally used tables actually agree rather well on single dive NDL times. The only real difference is the conservation factor applied. The NDL times don't really change depending on the model, what changes is the ascent and how repetative dives are treated. I have been told that GUE teaches a 120/20 rule, my 130 rule is simply a simplification of this process.

Some of the disolved gas and bubble models may have similar numbers when it comes to depth/bottom time, but their application of the tables are different. Using a minimum deco table, but using the rules from the navy dive tables aren't what the tables were designed to do.

The 130 rule matches Peter Steinhoffs tables reasonably well. I am not aware of any other minimum deco tables in existance. NAUI's RGBM tables are the closest I know of but they are only advocating a 1 minute stop at half depth and the usual 15ft safety stop; this is bubble model but I don't think I would call it minimum deco.

If you want to memorize a table then memorize the tables that you are using and apply them how they were meant to be applied. Correct me if I'm wrong, but it almost sounds as if you are trying to take the features from each table that you like and apply it in a manner that it wasn't meant to be applied.

You could see it that way, but that is far from what I am actually doing. I have been looking at various tables in order to get a better idea of the safe limits for NDL diving. I have basically been trying to get a better idea of the big picture. If you do the same you will probably realize just how much this is not an exact science. You will also notice that the numbers are all suprisingly similar. Some add more conservatism by giving less time, but the shape is still the same meaning the same simple rules apply. The NAUI air tables for example can be rememberd by starting with 115 instead of the 120 used with the Navy tables. Another difference is the accuracy of the numbers. Some tables will use numbers such as 22 and 8 for NDL times(NAUI) while others chose to instead simplify things by sticking to multiples of 5(Navy). The fact of the matter is that there is no magic number where you will automatically get bent when you pass it. Instead there is a very large fuzzy area where the likelyhood of getting bent increases as you stay down longer. The fact of the matter is many people have been bent while diving within the NDL. That is why I feel having a good understanding of the tables and the ability to control the conservatism factor yourself based on your own present conditions is preferable to blindly following a table.

As for people questioning the way that I am currently diving. What I am actually currently doing is using a memorized version of the NOAA tables. This is basically the 120 rule for air and the 130 rule for EAN32. For repetative dives I have been getting a good feel for how much I should subtract from my starting number in order to be within these tables limits. That being said I do actually look at the tables to see how close my estimates are. In addition to that I have been shaping my ascents to be similar to a minimum deco profile. This is not part of the NOAA tables but I feel that it doesn't harm their integrity and instead adds an extra level of conservatism to them. I am also conservatively playing with depth averaging. This definitely violates the tables but I do feel that it is a safe tool if used properly. If you think that I am crazy and am going to kill myself than you are welcome to go on thinking that, I am not telling anyone else that they should dive this way. If you have actual constructive criticism than I will gladly listen to it.

~Jess

 

[MonkSeal]

Given that this is the DIR forum, shouldn't the general attitude be that you plan your dive and dive your plan?

No, it's not DIR attitude. DIR attitude is to be able to adapt your plan during the dive according to situation.

Personally, I take the attitude that you either do plan your dive and dive your plan or you strap on a computer. Trusting your brain to be able to get the limits right always seems like an accident in waiting.

This is totaly opposit to DIR attitude.

 

[Charlie99]

I think some people get too caught up in the details of ths algorithm and that compartment and those mm of mercury, and make things more complex than they really need to be.

Au contraire, I use the example of series of 100' 30 minute repetitive dives, 11 minute ascent, 20 minute SI as merely a specific example of the philosophy that "residual nitrogen doesn't matter if you do a slow ascent"

What some divers are learning in DIR-F is that slow ascents and deep stops are magic bullets that eliminate the need to account for residual nitrogen, either for repetitive dives or for fly-after-dive. That isn't just a "detail of the algorithm", but instead is a basic philosophical difference.

The specific 4 repetitive dive profile I posted above, 100', 30 minutes on EAN32, 20 minute SI, with complete details on the ascent were reviewed by a GUE instructor, and his comment was "The profile that he mentioned below is quite right."

---------------------

The profiles you posted, more or less 90', 31 minute, 17 minute ascent, and 80 minute SI are very reasonable profiles. Whether or not you think in these terms, your 1 hour 20 minute SI allows for offgassing of dissolved gas. It looks like you are using something similar to the 5th-dx min deco rules, which look pretty reasonable to me. If you took a dive computer along for the ride, it would be happy.

There is a big difference between your profile and one that does just 1 minute at 30/20/10' for the first two dives, and 1 minute at 40/30/20/10' for 3rd and 4th dives, all after just a 20 minute SI. In addition, the ideal ascent profile was described as slowing to 10fpm at 80%ata. To my understanding, with EAN32/68% inert gas, even a saturated compartment/tissue would be at less pressure than ambient at 80%ata, so starting deep stops there would be counterproductive. Again, the 5th-dx sort of profile you describe, with deep stops starting aaround 50% depth makes a lot of since to me, but the 80% ata profile being taught in some GUE DIR-F classes seems a bit out of whack.

yeah yeah, the gods of "reverse" profiles are going to come down and kill me dead

Well, according to some DIR-F grads, what is being taught is that, even in min deco diving, that reverse profiles are preferred. Not merely acceptable, but actually the preferred method of diving, and that forward profiles are inferior. Again, not just a minor difference in algorithm, but an entirely different philosophy.

 

[amascuba]

I was under the impression that GUE has not actually published any tables,. Please correct me if I am wrong. Most of the generally used tables actually agree rather well on single dive NDL times. The only real difference is the conservation factor applied. The NDL times don't really change depending on the model, what changes is the ascent and how repetative dives are treated. I have been told that GUE teaches a 120/20 rule, my 130 rule is simply a simplification of this process.


The 130 rule matches Peter Steinhoffs tables reasonably well. I am not aware of any other minimum deco tables in existance. NAUI's RGBM tables are the closest I know of but they are only advocating a 1 minute stop at half depth and the usual 15ft safety stop; this is bubble model but I don't think I would call it minimum deco.


You could see it that way, but that is far from what I am actually doing. I have been looking at various tables in order to get a better idea of the safe limits for NDL diving. I have basically been trying to get a better idea of the big picture. If you do the same you will probably realize just how much this is not an exact science. You will also notice that the numbers are all suprisingly similar. Some add more conservatism by giving less time, but the shape is still the same meaning the same simple rules apply. The NAUI air tables for example can be rememberd by starting with 115 instead of the 120 used with the Navy tables. Another difference is the accuracy of the numbers. Some tables will use numbers such as 22 and 8 for NDL times(NAUI) while others chose to instead simplify things by sticking to multiples of 5(Navy). The fact of the matter is that there is no magic number where you will automatically get bent when you pass it. Instead there is a very large fuzzy area where the likelyhood of getting bent increases as you stay down longer. The fact of the matter is many people have been bent while diving within the NDL. That is why I feel having a good understanding of the tables and the ability to control the conservatism factor yourself based on your own present conditions is preferable to blindly following a table.

As for people questioning the way that I am currently diving. What I am actually currently doing is using a memorized version of the NOAA tables. This is basically the 120 rule for air and the 130 rule for EAN32. For repetative dives I have been getting a good feel for how much I should subtract from my starting number in order to be within these tables limits. That being said I do actually look at the tables to see how close my estimates are. In addition to that I have been shaping my ascents to be similar to a minimum deco profile. This is not part of the NOAA tables but I feel that it doesn't harm their integrity and instead adds an extra level of conservatism to them. I am also conservatively playing with depth averaging. This definitely violates the tables but I do feel that it is a safe tool if used properly. If you think that I am crazy and am going to kill myself than you are welcome to go on thinking that, I am not telling anyone else that they should dive this way. If you have actual constructive criticism than I will gladly listen to it.

~Jess

I'm in no way saying that you are a unsafe diver doing unsafe profiles. The only thing that caught my eye is that you seemed to be picking and choosing which features you liked from each table and used those in your profiles. Perhaps I just totally misread the entire thing, which is always possible. If the NOAA tables are similar in depth/bt to those that you use then that's great. You have a hard copy of what you have.

I use depth averaging quiet often. I have the minimum deco tables that peter steinhoff has posted on his website memorized and that's what I use during my recreational dives. The difference is I start doing 1min stops at 50% of the max depth, I will use depth averaging to determine my MDL if I started the deepest part of my dive first, and if I have a SI that's longer than 90 minutes I will consider it a new dive otherwise I will double the time on my stops.

 

[limeyx]

Au contraire, I use the example of series of 100' 30 minute repetitive dives, 11 minute ascent, 20 minute SI as merely a specific example of the philosophy that "residual nitrogen doesn't matter if you do a slow ascent"

Well, according to some DIR-F grads, what is being taught is that, even in min deco diving, that reverse profiles are preferred. Not merely acceptable, but actually the preferred method of diving, and that forward profiles are inferior. Again, not just a minor difference in algorithm, but an entirely different philosophy.

Here's your post that I responded to:

BTW, if you are going to say "It's OK because of the slow ascent and stops, please tell me what they are so that you find the 80' 40min, 90 SI, 80' 30 minute profile reasonable.

Maybe you didn't mean to write that.

We did NOT learn that 20 min (or even zero min) SI is allowable (as I said in my other post)