Info Why are tables not taught in OW classes anymore?

[boulderjohn]

How did people dive in Cozumel pre-computers?

The same way I did before I got mine (which didn't take long). They trusted the guide. There are still lots of operators there at do not require computers, and I'm sure their divers just trust the guide, too.

On several occasions when I was teaching the tables version of the class and we were going over the tables over and over and over again, students told me that their friends who were already divers told them you only had to do the table stuff in class. Once you were diving in the real world, the DM did all that stuff for you, and you just followed along.

 

[boulderjohn]

I was talking to what Dan's spokesman said, and you deleted that part of my post:

Are you sure? Here’s an explanation by DAN of a dive resulting in decompression sickness, without exceeding the computer’s algorithm.


I am not against computers; I use one. But I do want divers to know more about their limitations. I worked in high tech, which allowed the chips that make them possible to be built.

SeaRat

Decompression algorithms, whether tables or compujters, are not perfect, and they never have been. A very small percentage of divers get bent even though they are within limits, and that has always been true.

I got bent after a 2-tank NDL dive to a wreck, so it was pretty much a square profile that would have been within NDLs on tables as well as the computer. I happened to have a deco bottle of oxygen with me, and I used it on the safety stop, just because I had it.

It happens.

 

[tursiops]

From The Validation of Dive Computer Decompression Safety:

"When dive computers were first introduced, many dive physicians believed that the DCS incidence would increase drastically. This did not happen, and there is no evidence of any more DCS for dive computers than for dive tables, although the proportion of AGE among injured divers appears to have decreased." -- Richard Vann​

 

[tursiops]

An interesting read: Historical Perspectives on Dive Tables and Decompression Models – Divers' Blogs

Historical Perspectives on Dive Tables and Decompression Models​

June 4, 2012 by Bret Gilliam

 

[scubadada]

An interesting read: Historical Perspectives on Dive Tables and Decompression Models – Divers' Blogs

Historical Perspectives on Dive Tables and Decompression Models​

June 4, 2012 by Bret Gilliam

Written in 2012, surprised DSAT, PADI RDP and DSAT computer algorithm was not mentioned, especially with regard to recreational repetitive dives.

 

[Superlyte27]

The U.S. Navy tables are built upon a lot of chamber and real world diving tests. The computer algorithms are not. From what I have read, the computer software is not produced to any standard, and not tested in chamber tests. They are also proprietary, and therefore each one manufacturer's algorithm has a slightly different approach, which is why some allow more bottom time than others. I can find no scientific literature that shows tests being done by the manufacturer, although the manufacturers probably do these tests. They just don't publish them. So when you use a computer to what we used to call the "knife edge" of the NDLs, you really are trusting that testing has been done, and that the algorithms are correct. Here's another evaluation:

The issue is the actual testing and refinement of the algorithm used to determine the decompression limits. This is an interesting study, and anyone using a dive computer should read the entire document.

SeaRat

The U.S. Navy tables are built upon a lot of chamber and real world diving tests. The computer algorithms are not. From what I have read, the computer software is not produced to any standard, and not tested in chamber tests. They are also proprietary, and therefore each one manufacturer's algorithm has a slightly different approach, which is why some allow more bottom time than others. I can find no scientific literature that shows tests being done by the manufacturer, although the manufacturers probably do these tests. They just don't publish them. So when you use a computer to what we used to call the "knife edge" of the NDLs, you really are trusting that testing has been done, and that the algorithms are correct. Here's another evaluation:

The issue is the actual testing and refinement of the algorithm used to determine the decompression limits. This is an interesting study, and anyone using a dive computer should read the entire document.

SeaRat

Chamber rides based on 20 year old navy divers in peak physical condition. That’s correlates perfectly to todays average diver, lol

 

[steinbil]

I got bent after a 2-tank NDL dive to a wreck, so it was pretty much a square profile that would have been within NDLs on tables as well as the computer. I happened to have a deco bottle of oxygen with me, and I used it on the safety stop, just because I had it.

Wow. Sounds like you were well within the limits considering the O2 would have increased the efficiency of your safety stop. Do you mind sharing the profile and bottom mix, if you have it? Were there any other factors you could identify? What’s your take on what happened? What symptoms did you have, and when did they appear?

 

[BRT]

Oh, there’s more than one. Here’s an example:

Ultrasound in the diagnosis of acute-phase decompression sickness

A 53-year-old man, who performed a 44-minute dive to a depth of 21 meters, felt severe abdominal pain with dyspnea after surfacing. An ultrasound stud…

www.sciencedirect.com

In 2010 DAN published an article titled “The Validation of Dive Computer Decompression Safety,” in which they stated:

But on the other side, you’d think that the incidence of decompression sickness would decrease with dive computer usage; it hasn’t. Apparently, unless something has happened since 2010, there is no standard for validation of dive computer algorithms. Please read this article, and the expert commentary toward the end of the article.

The Validation of Dive Computer Decompression Safety

There is a lack of hard data on the validation of decompression safety and the intersection of dive computers. Read more.

dan.org

SeaRat

I would not expect DCS incidents to go down with computers. Computers are a way to get closer to the limits. 60 feet for 60 minutes vs 60 feet for 70 or 80 minutes with computers.

 

[BRT]

There was a computer years ago that was malfunctioning and was bending divers. It was recalled. Can’t remember the name or model but it did happen.

It assumed the surface interval was done on bottom gas (nitrox)?

 

[Bigbella]

I would not expect DCS incidents to go down with computers. Computers are a way to get closer to the limits. 60 feet for 60 minutes vs 60 feet for 70 or 80 minutes with computers.

There seems to be good deal of variability among dive computers, not only in terms of their chosen algorithms, but also myriad excuses why there hasn't been more exhaustive testing, as mentioned in an old 2010 DAN article, "There are at least two reasons for this: 1) dive computers are not regulated; 2) validation of decompression safety is complicated and expensive. Thus, in most cases manufacturers do not have the data necessary to support claims of risk control or risk reduction — an important issue for divers."

I dove a Suunto Solution for decades, without any issue -- still have two of them, fully functional, in my collection, and whose default setting happened to be, paradoxically, a bit more conservative than my NAUI tables, which had allowed for example, a maximum of 22 minutes at 30 meters, while the Solution only allowed for 17 before the onset of decompression.

From 12-15 meters, there was a ten minute difference, with the tables allowing more time; only four at 18 some odd reason; nine at 21 meters; seven at 24; 2 at 27 through 36 meters; and it only switched-out at forty, where the computer allowed for an additional minute.

As an aside, the Suunto Solution also allowed six minutes at 46 meters -- which was really something for the books, back in 1992-3 . . .