Place of dive tables in modern diving (Split from the basic thread)

[dmaziuk]

Once again, if we look at the actual math, we will see a strong correlation between No-Fly time recommendations, and the residual supersaturation times.

You are trying to justify the cause with a result, but the presumed cause (excess multi-day residual tissue pressure buildup) is not present in the amounts you implied, or amounts that are significant.

Sorry (this being basic forum and all), I have to ask: what is residual supersaturation times and how is it (un-) related to excess multi-day residual tissue pressure buildup?

 

[stuartv]

Regarding the discussion of gradual accumulation of residual nitrogen over multiple days of multiple dives, which has a direct bearing on general recommendations to take some kind of break every 3 or 4 days:

I think this statement (bolded, to preserve context) is the fundamental issue:

The point in discussion, is the long held belief that we divers accumulate some excessive tissue saturation over several days, and that directly causes injury. But that acumulation is not the case. If the basic on / off gassing formula are to be trusted, then they show the build up does not exist.

The fact is, those formula are NOT to be trusted. They are to be accepted with high confidence, but not complete 100% confidence.

The formulas are a mathematical model intended to predict inert gas buildup in a diver's body. But, every person's body is different. Some people's bodies exactly match the model's predictions. Others' bodies don't match very well at all. Some people will match the formula well on one day, but not match well at all on another day. As one example, they may match well when they are well hydrated and not match well at all when under-hydrated.

If a particular individual varies from the model by retaining 10% extra nitrogen (I'm speaking in very simplistic terms here - this is Basic), then, at the end of 1 day, they aren't that far off from the model's predictions and are probably not going to experience symptoms of DCS. But, when you compound that personal variation over multiple dives per day for multiple days, then the difference between what the model PREDICTS and the actual state of the person's residual nitrogen load is going to become larger and larger. To the point that they could become very susceptible to DCS.

It's like being off in aim by 1 degree. If you're shooting at a target that is 10' away, you will still hit the bullseye. But, if you're shooting at a target that is 100 yards away, you're going to miss. The end of your first dive is the target that is 10' away. The end of your 20th dive in 5 days is a target that is 100 yards away.

I think recognition that the "formula" are just estimates - educated guesses, if you will - is key to understanding why it is important for divers - and especially divers on the less experienced end of the spectrum - to give themselves a break every few days. Even though the "formula" may predict that it is not necessary.

There is only one time when a dive computer OR TABLE has it's maximum accuracy and that time is when you have not been diving for a while - i.e. greater than 24 hours, AT LEAST. Taking a break every few days lets your body and dive computer both reset back to a known "good" state - to the state where body and computer match most closely. Your body gets back to (more or less) "zero" and the computer does the same. In other words, the break is when your body "walks forward" and gets up to 10' away from that target that was 100 yards away.

 

[dmaziuk]

I still think you can't have it both ways: either you trust the model, buy the most liberal computer you can find, dive to its NDLs, and fly home 6 hours later. Or don't trust the model, don't dive every third day, and wait 24 hours before boarding an airplane.

It seems to me the way modern diving is taught -- tables or not -- is that both are true at the same time.

 

[lowviz]

Sorry (this being basic forum and all), I have to ask: what is residual supersaturation times and how is it (un-) related to excess multi-day residual tissue pressure buildup?

Jeez.

OK, my take on it. If you dive too much on vacation you can get bent. If you get bent but don't dive too much, then it must be something else...

Where the hell is the 'stick your tongue out' emoji???

 

[rossh]

Sorry (this being basic forum and all), I have to ask: what is residual supersaturation times and how is it (un-) related to excess multi-day residual tissue pressure buildup?

Do the math, and you can see for yourself. Or use a planning tool that has all this inbuilt (MultiDeco). The multi-day residual assumptions do not accumulate in the ways they are often implied. It's all proportional.

.

 

[Kevrumbo]

Once again, if we look at the actual math, we will see a strong correlation between No-Fly time recommendations, and the residual supersaturation times. The idea behind no-fly times, is to get every recent diver passenger back to the same baseline as the non-diver passengers.

You are trying to justify the cause with a result, but the presumed cause (excess multi-day residual tissue pressure buildup) is not present in the amounts you implied, or amounts that are significant.

I think there are more (unexplained physiological effects) as the leading causes to multi-day DCS injury than what has been presumed in the past.

Do the math, and you can see for yourself. Or use a planning tool that has all this inbuilt (MultiDeco). The multi-day residual assumptions do not accumulate in the ways they are often implied. It's all proportional.

.

Once again Ross:

The second, I think, is simply part of a general recommendation to avoid diving right up to the no decompression limits (or computer ceiling), along with the observation that none of our predictive algorithms have been adequately tested over multiple consecutive days of multiple dives per day. Having a day off periodically in such a sequence is a common recommendation perceived to be likely to increase safety.

Simon M

 

[dmaziuk]

Do the math, and you can see for yourself. Or use a planning tool that has all this inbuilt (MultiDeco). The multi-day residual assumptions do not accumulate in the ways they are often implied. It's all proportional.

I'm actually not arguing that: even without doing the actual numbers I can't see the slowest TCs on-gassing significantly over my usual dive trip. But if that's the case, then you have to agree that the 24-hour no-fly period is not supported by the math either. Yet you say

Once again, if we look at the actual math, we will see a strong correlation between No-Fly time recommendations, and the residual supersaturation times. The idea behind no-fly times, is to get every recent diver passenger back to the same baseline as the non-diver passengers.

I'm just trying to parse that, and I'm asking what the words actually mean. Once I know that I'll be able to put them together and hopefully understand the sentences.

 

[AfterDark]

No. But the Twilight Zone, quite possibly...

rossh's response was clearly tempered for newbies in Basics.

I live in the Twilight Zone. A problem? No just chain yanking Carry on!

 

[AfterDark]

Nope, no such thing exists. No deco here, move along now...

Well I just didn't know what else to call it. Theories about the human body's physiological response to gas breathed under pressure and after the pressure is relieved? Better maybe?

 

[Dan_P]

For the "Basic" section:

Look, as far as "Basic" stuff in relation to Ratio Deco goes, I think we can all agree it's well within the realm of Min Deco (recreational diving) rather than actual decompression diving (technical diving).

With regards to the current debate around deep stops, the issue generally at the core of discussion, is on-gassing at (deep stop) depths during technical dives.
However, in terms of matters Basic; as recreational dives are in that regard of a different nature in terms of exposure, I think it's fair to assume some deep stop emphasis would be relatively more benefitial in a recreational setting, compared to a technical one.

So, are DAN wrong when they say that deep stops are benefitial in a recreational setting?
Personally, I doubt it.

Let's say there are three major ways to go about it (recreational):

1) Tables - They take some time to learn but don't need batteries for you to browse through them. But you need to bring them. And they're poor for adaptation
2) Computers - Easy, but can be expensive (though not the basic ones, to be sure!), they may run on differing algorithms within the team and they may make the diver complacent.
3) Ratio Deco/Min Deco (RD/MD) - Easy (particularly at entry-level) and adaptable, more training required than computer

Personally, I use RD/MD, most prefer computers.
I think the use of traditional tables will expire in favor of those two categories, as tables lack the adaptability of Min Deco and computers, require probably as much (or more) training than both MD and computers and really won't be much cheaper anymore.

For the "Advanced" section:
In regards Ratio Deco, if the issue is altitude diving within the realm where you'd consider asking NASA for a consultant in order to do it, okay;
You got me. I'm not an astronaut.
There is no fluid water at those altitudes on the continent I inhabit, only ice.
If the issue is "total debunking" of deep stops, anyone is free to plug in 100/100 and dive that if one believes that's more safe.

In either case, the major categories within the topic at hand (tables), remain:

1) Tables - Before mobile apps, divers huddled around the Personal Computer at Bob's place to compute dive profiles which would then be written off and brought diving. This was normal even in the 2000's, but at least people had laptops, plus Aqua and Spice Girls had worn off.
2) Computers - Better than tables. Expensive, but you kind of still need to run "tables". Danger of complacency.
3) Ratio Deco - Better than tables. Inexpensive, adaptive, but inaccurate.

With the introduction of mobile apps that more easily allows cutting tables, and a natural place for "sanity checking" against them when planning a technical dive with computer, I think these "tables" (I suppose it's fair to call them that) will continue to have a place among tech divers in the future.
Granted, some divers use Ratio Deco, but the majority do use computers.