Average depth finder

[CAPTAIN SINBAD]

This thread and others like it bring to mind the current anti-science attitude in America. So what if all those decompression scientists who did all that research that led to the dive theories those computers and dive tables are based on. I can tell just by looking around that they are all wrong and must have done terrible research!

​

Those decompression scientists who did all the decompression research did not have the same religious faith in the dive computer that that you have John. Listen to this guy ...

“Decompression is an area where you discover that the more you learn, the more you know that you really do not know what is going on. From the “black and white” exactness of table-entries, the second-by-second countdown of dive computers and beneath the mathematical purity of decompression models lurks a dark and mysterious physiological jungle that has barely been explored.”

Karl E. Huggins PhD – Decompression Theory, University of Michigan.

When scientists state their view, they are pretty open about the inconsistency of models and their 'not knowings.' We divers on the other hand are in need of Perdix assurances and Buhlmann therapy.

None of the above should be taken to mean that tables and computers should not be used. What else do we have? A true scientific attitude would be to openly acknowledge that these computers and tables are putting a very tiny black dot in a very large grey area. We do not have science on our side when we argue for the completeness of that tiny black dot that the computer and table generates while we conveniently ignore the large grey in which it is placed ... for our own therapeutic reasons.

 

[boulderjohn]

What he is saying is that there is still much we don't know. That is certainly true. ON the other hand, saying there is still much we don't know is not the same as saying we don't know anything. In logic that is called the appeal to ignorance fallacy.

 

[tbone1004]

@CAPTAIN SINBAD and what makes you think that AG knows better than the guys that developed the algorithms, or that your brain is reliable enough to run the calculations when subject to inert gas narcosis and all of the other stresses of diving?

 

[boulderjohn]

what makes you think that AG knows better than the guys that developed the algorithms

It is a line of thought similar to the vaccination controversy. People know that all the scientists say that there is no credible evidence linking vaccinations to autism, but they assume a former Playboy bunny must be a more credible source than all the world's scientists.

 

[scubadada]

Those decompression scientists who did all the decompression research did not have the same religious faith in the dive computer that that you have John. Listen to this guy ...

“Decompression is an area where you discover that the more you learn, the more you know that you really do not know what is going on. From the “black and white” exactness of table-entries, the second-by-second countdown of dive computers and beneath the mathematical purity of decompression models lurks a dark and mysterious physiological jungle that has barely been explored.”

Karl E. Huggins PhD – Decompression Theory, University of Michigan.

When scientists state their view, they are pretty open about the inconsistency of models and their 'not knowings.' We divers on the other hand are in need of Perdix assurances and Buhlmann therapy.

None of the above should be taken to mean that tables and computers should not be used. What else do we have? A true scientific attitude would be to openly acknowledge that these computers and tables are putting a very tiny black dot in a very large grey area. We do not have science on our side when we argue for the completeness of that tiny black dot that the computer and table generates while we conveniently ignore the large grey in which it is placed ... for our own therapeutic reasons.

Best of luck

 

[CAPTAIN SINBAD]

@CAPTAIN SINBAD and what makes you think that AG knows better than the guys that developed the algorithms, or that your brain is reliable enough to run the calculations when subject to inert gas narcosis and all of the other stresses of diving?

Given the fact that scientific community is extremely divided on the issue of nitrogen build-up, a scientifically honest dive computer would be something like this:

DIVER: Computer, what is my NDL?


COMPUTER: There is no such thing as NDL. You have bubbles in your body as of this very moment!


DIVER: Really? But my old computer always tells me that I have a few minutes left before I reach my NDL.


COMPUTER: Well those NDL limits that you see on tables and computers were developed during the days of Dissolved Gas models. This was a strange time in the history of decompression research because Doppler technology did not exist. Scientists could not look inside the body to see whether there were bubbles in the blood stream or not. They could observe decompression symptoms in divers like neurological symptoms and skin rashes etc. They mistakenly believed that nitrogen is held in the body in the form of dissolved gas. When the diver rises to lower pressures this dissolved gas turns into bubbles which are causing the symptoms they could see. Based on this assumption they built tables that show limits at which gas turns into bubbles. When dives were done within the limits of those tables, they actually reduced observable symptoms in enough divers for tables to become the guiding factor in diving. Not everyone was saved by those tables though. There were people diving within the table limits who were still surfacing with decompression symptoms. When Doppler bubble detection technology was invented in 1960s, it enabled scientists to see inside the bodies of divers for the first time. It showed that all those divers that were perceived to be “clean” and healthy after the dive with no observable symptoms of DCS also had bubbles flowing through their blood stream. Yet these bubbles were not causing the symptoms that we call DCS. This is why, as the world’s most scientifically honest dive computer, I am telling you that you are medically bent right now though you may not have symptoms when you reach the surface.


DIVER: Holy crap! So without those end limits, where do I end the dive so that I do not have those bubbles in my blood?


COMPUTER: Well you can stop diving and take up another hobby. Have you considered ballroom dancing?


DIVER: Umm no. Does that mean there won’t be any bubbles in my blood stream if I take up ballroom dancing?


COMPUTER: No. You could still have bubbles in your blood stream if you do ballroom dancing. Doppler research showed that bubbles can form during exercise when you are hiking or skiing when you are doing physical labor. Bubbles themselves may not be a problem. In medical terms they are called “silent bubbles.” These run through your body without causing any symptoms. Under certain pressure differences bubbles either become too big or just so much that they start blocking passages and thus become “symptomatic bubbles.” That is when crap begins to happen in divers dude!


DIVER: But I really like all these fish and turtles. I would like to be a diver. How do I prevent my good bubbles from becoming bad bubbles and cause these nasty symptoms?


COMPUTER: Well I can not be sure because at the time that I was designed, people who designed me were not sure either. I do have that old research that was done prior to the invention of Doppler radar. I can project to you the table limits that were developed during the era of dissolved gas models. That table stuff they did back almost a hundred years ago did reduce visible symptoms in a lot of people. It is very possible that you could be one of them. Would you like me to project those NDL limits?


DIVER: Ummm … I think I will take ballroom dancing! Before I finally give up diving, how reliable would those table limits be?


COMPUTER: I can not guarantee total safety. Tables have been revised a lot even though the fundamental assumption behind them is known to be scientifically wrong. You see when the tables were developed, they were used in square profiles. The divers using tables never spent all their time at the maximum table depth limits and always came out with unspent time. This unspent time became the safety margin that prevented the development of symptoms in a lot of divers. When computers came about, this unutilized time was projected back to the diver as something they could use! Thus people in the age of computers began to chase those limits to their logical end. They did not understand that those end limits were causing a certain percentage to get bent even when a square profile was assumed. When you create a culture of readjusting table limits by depth and time and chasing them to their end then you are causing more people to move closer to limit where they get symptoms.


DIVER: Does this mean that tables with their square profiles are safer?


COMPUTER: Yes. If 100 people used a table and assumed a square profile and another 100 people used computers to do a multi-level dive all the way to the end limit then the latter will have greater rates of DCS incidents.


DIVER: DANG! I am throwing you away and going back to those tables.

If such an honest dive computer existed then Andrew and the UTD/GUE crowd will have no problems using it because the diver that would be born from its use would essentially be a UTD/GUE kind of diver. This would be the fellow who will have more faith in generalized tables instead of the mathematical precision that is being projected to him by his computer. Instead of coming up with a NDL (No Decompression Limit), this guy will come up with a standardized minimum decompression schedule first. Then he will come up with all the dives that would be covered by this schedule and the dives on which this schedule will be insufficient. The former will become his recreational dives and the latter will become his technical dives. Once you have the minimum decompression schedule, then you may be able to get away with average depths instead of max bottom depths that traditional tables are based upon.

Having said that, I am not convinced on a lot of things that UTD does ... yet. Those ultra-deep, deep-stops being one of them. I think that the point that you make with deep stops being calculated using pressure (ATA) instead of depth (feet) makes more sense.

 

[tbone1004]

uhhh what?

you do realize that the NDL is essentially the same as "your stops have cleared" right? I.e. I dive to some point and my NDL is based on a theoretical tissue loading of 90. I can do the same dive, but do it 10 minutes longer where I have a 5 minute decompression stop but that 5 minutes is determined by how long it takes for my tissues to calm down to 90, and I am surfacing with theoretically the same amount of nitrogen in my body.

your argument above makes literally no sense.

If we stay with Buhlmann, which btw is what made of your DIR crowd uses to validate their decompression schedules so we will continue to use that because it's what most of us actually use. If you set the GF hi to 90, or some arbitrary number, then your NDL is calculated based on you making a direct ascent to the surface *no stops at all*, and you surfacing with no compartments exceeding 90% of theoretical loading. If you go into deco, and your GF hi is 90, it tells you to stop until you have offgassed to the point that when you make a no-stop ascent *on a shearwater that's either from 20 or 10ft*, you will not have a compartment exceed 90%. Ergo, all diving is calculated based on the tissue loading, and the NDL just means you have a no-stop ascent.

All you are arguing is that instead of calculating the NDL based on a true no stop ascent, you are just factoring in stops for your ascent to accomplish the same thing. If you adjust the algorithm for the computers to factor in these stops, all you do is extend the NDL from what they are factoring in based on an unimpeded ascent and arguably reducing the safety factor in that algorithm. By adding in planned stops, you don't get the luxury of skipping them if something happens because they are now mandatory stops to your ascent profile. On top of that, you have no real ability to quantify any adjustments to your diving profile based on various conditions. I.E. my suit flooded and now instead of being warm on deco where I know I can come out at a GF-Hi of 85 which is a known good variable for me, I need to lower it down to say 60 because I know that I am not offgassing as efficiently. All you can do with your model is just add time and pray because there is nothing there to go on other than something that was developed by cave divers as a "close enough" model

 

[stuartv]

this guy will come up with a standardized minimum decompression schedule first. Then he will come up with all the dives that would be covered by this schedule and the dives on which this schedule will be insufficient. The former will become his recreational dives and the latter will become his technical dives. Once you have the minimum decompression schedule, then you may be able to get away with average depths instead of max bottom depths that traditional tables are based upon.

We already have that. The standardized minimum decompression schedule is "ascend steadily at 30 fpm". There are tables that already give you the schedule of all dives covered by this standardized min deco schedule - including pressure groups and what-not for determining what dives are "min deco" according to this standardized schedule even when it's the 2nd, 3rd, etc. dive of the day. And there are computers that work like the tables, only with much finer resolution, and save you from doing the lookups, tracking pressure groups, etc..

All the dives not covered by those tables and/or computers (giving that standardized min deco schedule) are the technical dives.

Even with that, it does not allow you get away with average depths. No amount of mental gymnastics changes the fact that on- and off-gassing is not linear.

 

[stuartv]

uhhh what?

you do realize that the NDL is essentially the same as "your stops have cleared" right? I.e. I dive to some point and my NDL is based on a theoretical tissue loading of 90. I can do the same dive, but do it 10 minutes longer where I have a 5 minute decompression stop but that 5 minutes is determined by how long it takes for my tissues to calm down to 90, and I am surfacing with theoretically the same amount of nitrogen in my body.

Not really. In theory, you would surface with more nitrogen in your body, in the slower compartments. Only your leading compartment would theoretically be the same in both cases.

 

[tbone1004]

theoretical tissue loading being the percentage of any one compartment not exceeding that value. obviously the total nitrogen in the system is higher, but nothing about any sort of min deco or ratio deco or whatever is going to solve any of that. In fact, because of their favoritism of deep stops, you would have more tissue on-gassing in the slow tissues and have more total nitrogen with that profile.