Place of dive tables in modern diving

[MrVegas]

In reading some of the threads where people have described their experiences getting the bends without appearing to go over their NDLs , it looks like the profiles posted were all fine by the computer, and much more experienced people than me indicated that the profiles should have been fine. But when I look at the tables, it seems like in some of those cases, people would have either been pushing very close to the limits or would have been over. I do realize that the tables only provide square profiles and that the computers probably provide much more accurate information. Still, maybe the tables are worth taking a look at before hand to get a rough idea of where things stand rather than just relying on the computers.

I'm saying this cautiously and certainly do not have the experience to be critical (nor would I want to be). All the dives I have done so far have been fairly shallow single tank dives and I'm pretty sure if I looked at nothing other than the pressure gauge it wouldn't matter much. We were not taught the tables in my certification class, but I certainly have taken the time to try understand them. (The NOAA tables have a pretty good presentation, I think.) Of course, the tables from different agencies have different information, too.

 

[CT-Rich]

It is SB, what were you expecting? The inquisition? (Crap, that is Mel Brooks...... )

The Inquisition was Monty Python, as was the parrot sketch....

 

[CT-Rich]

I am wondering how many of you have used or heard of "Depth-Averaging Tables?" I know that UTD has these and in the UTD curriculum, they are called "Min-Deco Tables." I must state that my own knowledge of these is very minimal as I have not used them much except for a few test dives. They are supposed to give you your NDL based on average depth rather than max depth. Here is what they look like

To be used for Standard Gas of Nitrox 32 with UTD Min Deco Ascent Schedule:

60 ft = 60 mins
70 ft = 50 mins
80 ft = 40 mins
90 ft = 35 mins
100 ft = 30 mins
110 ft = 25 mins

The above depths are average depths, so you could be going up and down saw toothing through the dive but if you average depth is accurate then those limits are supposed to work. UTD Ascent strategy is something that looks like this:

View attachment 447233 View attachment 447234

Unlike conventional tables these limits are explained to be "repeatable." By repeatable, it means that if the surface interval is 60 minutes of more you repeat the same table for up to three dives and no adjustments will be needed. If your surface interval is less than 60 minutes then you will repeat the same table but double the stops on the way up.

Anyone using these?

I think they are fine as long as you are calling the deepest depth “the average” and your computer doesn’t beep...

 

[tridacna]

The Inquisition was Monty Python, as was the parrot sketch....

Oy vey. Not even close. Let me help you. And yes I know MP’s “nobody expects...”. Enjoy.


And let’s leave Norwegian Blues out of this.

 

[Storker]

let’s leave Norwegian Blues out of this.

Why? They've got wonderful plumage, you know.

And just FTR:

 

[lowviz]

...//... I do realize that the tables only provide square profiles and that the computers probably provide much more accurate information. Still, maybe the tables are worth taking a look at before hand to get a rough idea of where things stand rather than just relying on the computers. ....

If this thread accomplished nothing more than what is quoted above, then it was most worthwhile. (we all had some fun along the way, but you will learn to ignore that or join in)

I'll offer some generalizations for your further consideration. People who dive tables tend to be conservative divers. Tables force you to mind your depth profile, but not outrageously so. You get used to it. It really isn't that bad. Best part is, over time, you become predictable as to how you dive and comfortable with respect to your imagined gas loading.

You are not locked to tables. Go dive a PDC, your choice.

A PDC is a wonderful thing. It tells you how much more fun you can have if you let loose. But it can be set incorrectly and give you bad advice. It is up to you, and you alone, to set it. The manufacturers won't share any blame if you set it poorly, so just take their suggestion for a conservative setting as a start. However, it is pretty hard to really screw up (lasting physical damage) with a PDC. I've experienced minor physical damages from diving and they aren't worth the fun I had in any dive I ever did.

That being said, you can dive any wonky profile you want and your PDC will keep on guessing as to your gas loading. It will be far closer than any tables, but you need to realize that by doing so you turned your back on basic understanding and are willing to trust your physical well-being to your PDC. People do it far more often than not. I have no problem with that either.

I never see anybody underwater. I like it that way too. Forces you to lose the fantasy that someone will be there for you in time of need.

 

[Kevrumbo]

I am wondering how many of you have used or heard of "Depth-Averaging Tables?" I know that UTD has these and in the UTD curriculum, they are called "Min-Deco Tables." I must state that my own knowledge of these is very minimal as I have not used them much except for a few test dives. They are supposed to give you your NDL based on average depth rather than max depth. Here is what they look like

To be used for Standard Gas of Nitrox 32 with UTD Min Deco Ascent Schedule:

60 ft = 60 mins
70 ft = 50 mins
80 ft = 40 mins
90 ft = 35 mins
100 ft = 30 mins
110 ft = 25 mins

The above depths are average depths, so you could be going up and down saw toothing through the dive but if you average depth is accurate then those limits are supposed to work. UTD Ascent strategy is something that looks like this:

View attachment 447233 View attachment 447234

Unlike conventional tables these limits are explained to be "repeatable." By repeatable, it means that if the surface interval is 60 minutes of more you repeat the same table for up to three dives and no adjustments will be needed. If your surface interval is less than 60 minutes then you will repeat the same table but double the stops on the way up.

Anyone using these?

It's my opinion that this is nothing but junk science. I wouldn't trust my well being to something like that.

UTD nonsense in Basic? Dangerous advice.

Average depth tables violate physics and biology. Gas on-take is not linear with depth/time, so average depth is not average gas on-take.

Average depth tables would be fine IF the 'average depth' was the depth that would properly predict your total gas load after the dive as if the dive were done at that constant depth.

If their average depth is truly just a depth average, then they are AFU. I don't care enough to check.

She summarized and explained it very well @CAPTAIN SINBAD , as you quoted Lynne Flaherty MD (Rest in Peace) a while back in another thread:

The concept of "minimum deco" comes from the idea that there really is no such thing as a "no decompression" dive. ALL dives involve absorption of nitrogen, and offgassing or decompression. "No deco" dives are the ones where the M-value line intersects the surface, and staged decompression dives are the ones where you hit the maximum M-value before you get there. A pure Haldane/Buhlmann dissolved gas approach will drive you shallow very quickly, and have you sit shallow to offgas. "Shallow", for a no-deco dive, is the surface.

The MDL tables we are given as DIR divers are derived from Decoplanner, for the times that give an ascent profile with one minute stops from half maximum depth. Therefore, our ascents are at 30 fpm to half maximal depth (or half average depth, depending on where the ascent begins) and 10 fpm thereafter. This is often accomplished by a "thirty second move, thirty second stop" strategy . . .We often also do two minutes from ten feet to the surface, if conditions permit.

Because we have built decompression into our model, we are able to do some depth averaging to determine the total time we can spend at depth. The tables built and taught by other agencies are made with other assumptions, which is why you are taught to take the maximum depth of the dive and run your tables from there. But it has never made a great deal of sense to me (nor is it the way any of my computers has run) to consider the entire dive done to 130 feet, if we went down there for two minutes, and spent the majority of the rest of the dive above 60.

You are not required to accept this approach to diving, but there are a lot of people using it and diving actively around the world with an excellent safety record.

This is just a simple consistent and controllable ascent strategy for a recreational diver within NoStop/NDL limits, ascending 30 fpm/10mpm to half of max or average depth, and then a slowing ascent at 10fpm/3mpm to the surface, instead of doing an ascent 30fpm all the way to 15fsw and then "jam on the brakes" for a 3 to 5min Safety Stop.

Within general recreational depth Ratio Deco, 100fsw/30msw is the reference set point for the NoStop Air Table with a 20min NDL (30min NDL for Nitrox 32) with a particular theoretical tissue compartment controlling the ascent. Once again, the motivation in RD methodology is to prevent surfacing supersaturation or worst case bubbling of this leading tissue compartment caused by directly encroaching upon its M-value (such as going all the way to the surface after a Safety Stop as most conventional tables would allow with a 20min Air NDL @100fsw), which is the reason why for the stop at half-depth 50fsw/15msw, just as the compartment barely begins to desaturate/unload.

So in an example from 100fsw for any bottom time up to 20min Air NDL, the stops are at every 10' up starting at 50fsw, with a 30second hold & 30second move for a 10fpm ascent rate to the surface. For UTD Table NDL repetitive dives less than minimum 60 minutes SIT, they also double the stops to 2 minutes each at 30'/9m, 20'/6m and 10'/3m for conservatism.

 

[The Chairman]

This is just a simple consistent and controllable ascent strategy

It's a strategy to be 'different' and look cool to everyone else using this fraudulent system. That's my opinion and I have seen no real science to change my mind. In fact, in talking with DAN behind the scenes, they don't like it either. While the rest us, following tables or PDCs get bent so rarely as to DAN referring to these incidents as being mere "noise", it's not so with ratio deco divers. They get bent to the point of it being alarming to DAN.

To quote the venerable Dick Rutkowski who popularized NitrOx: "Science over Bullshite". If you can't produce the science, then don't feed me the BS.

To put this in perspective, I know of only 4 people who got bent diving within their NDLs. All of them were on Ratio Deco. All of them. None of them blame ratio deco... they blame themselves for not averaging correctly, making mental mistakes and what not. This is why PDCs are so good. They never get distracted from their one job of making sure you're not a DCS statistic. Within NDLs, they are amazingly effective. Get into deco and especially multiple days of deco and then things start to slide a bit. But not nearly as bad as Ratio Deco. I love you Kev, but that RD crap scares the bejesus out of me. I won't go there. I won't.

 

[boulderjohn]

To put this in perspective, I know of only 4 people who got bent diving within their NDLs. All of them were on Ratio Deco. All of them. None of them blame ratio deco... they blame themselves for not averaging correctly and what not.

All 8 cases I know of personally were on Ratio Deco. Those cases lead me to point out two interesting uses of logic related to the explanations of them.

1. The reason to use Ratio Deco, we were told, was because it is possible that the computer could make a mistake,so it is better to trust "the computer between the ears." In several of the cases I know, divers made mistakes, mistakes that were revealed because they had a computer in gauge mode for a bottom timer and were able to check the log for the dive and find what they actually did rather than what they thought they did. When people make mistakes calculating average depths, miscount their deco times, etc., then it is their fault, not the fault of Ratio Deco. So apparently Ratio Deco is better than a computer because the human brain never makes mistakes, but when it does make mistakes, the brain is suddenly no longer an integral part of Ratio Deco.
2. All the cases I know of occurred at altitude--not quite 5,000 feet. We were told not to adjust Ratio Deco in any way for altitude, because altitude does not matter for decompression. Since that contradicts what everyone else believes, I asked how they knew it was safe to use RD at altitude without adjustment. I was told two reasons: 1) Andrew dives at Lake Tahoe without adjusting, and he is fine. 2) No one has ever been bent at altitude using RD. I responded that all the people in our group who had gotten bent were using RD at altitude. I was told those did not count, because there was some other reason for their being bent. I asked what those reasons were. They didn't know--maybe PFOs, maybe something else. How did they know it was not Ratio Deco? Because no one gets bent diving at altitude using RD, so therefore it had to be something else.

I find it interesting that when some people follow procedures that are different from everyone else and unsupported by any scientific studies, they are automatically assumed by some to be superior to everyone else. I was recently part of a FaceBook discussion in which PADI was mocked because it was still teaching traditional decompression approaches and not teaching this "more sophisticated" approach. When I pointed out that there was no science supporting it, I was removed from the discussion.

 

[The Chairman]

they are automatically assumed by some to be superior to everyone else.

No John, they are assumed to be superior only by themselves and those who also believe the fraud. Everyone else rolls their eyes and hope that they don't get hurt too badly.