"Riding your Computer Up" vs. "Lite Deco"

[stuartv]

Each table has a clearly defined line that I see. I wouldn't expect them to be the same because they all use a different algorithm, even if just slight.

Most cars engines are based on an Otto cycle, yet they don't all put out the same hp per litre.

Do you understand that I was responding to a statement that "THE MODEL" dictates a clear, definitive line?

Any table is a specific implementation of the model that it is based on. So, yes, your table has a clear, definitive line. The model that it is based on does not.

 

[Scuba J7]

Do you understand that I was responding to a statement that "THE MODEL" dictates a clear, definitive line?

Any table is a specific implementation of the model that it is based on. So, yes, your table has a clear, definitive line. The model that it is based on does not.

I know you were referring to the model, but that's not what is being used, an altered version of it is. The base model is theory anyway, which is why there is no hard line for everyone (even if all physiology was the same).

 

[redacted]

We are talking about limits, specifically NDL
Yes more nitrogen in your body = higher risk of DCS even if it's negligible it is still more.

More nitrogen, yes. More risk of DCS, not necessarily. It is absolutely nonsense to teach a student diver that he faces a higher risk of DCS when he exits the water in PG B rather than PG A. Elevated levels of N2 are simply that until they approach a level where DCS may occur; i.e.NDLs.

 

[KenGordon]

Can you explain that? Can you provide any supporting data on the different risk levels?

Read this Development of Iso-DCS Risk Air and Nitrox Decompression Tables Using Statistical Bubble Dynamics Models.

It is about developing replacements for the navy tables and attempting to make all the plans have similar risk. See Table 7, page 25 in section 4.2.1. Compare the calculated risks at 50ft and 150ft, surprisingly it is higher at the 50ft NDL than at the 150ft NDL.

 

[stuartv]

I know you were referring to the model, but that's not what is being used, an altered version of it is. The base model is theory anyway, which is why there is no hard line for everyone (even if all physiology was the same).

Let me be more clear. An earlier post said that the [decompression] model dictates a clear, definitive line for NDLs. That statement was foundational to then accuse some people of "second-guessing their agencies."

Now, if you were trained on tables and diving using tables, then yes, you have a clear, definitive line. If you are PADI-trained, then you should be using PADI tables and any given NDL is clear and well-defined. But, if you are PADI-trained (only) and decide to use NOAA or SDI or whatever tables, then you are violating your training. And that is not the subject of this conversation.

Things are not so clear (despite earlier posts) for people diving with computers. As far as I know, @DevonDiver was right in saying that all agencies tell divers to dive conservatively. But, also as far as I know, none of those agencies define what "diving conservatively" means. Staying within your NDL is not a matter of being conservative or not. That is simply following your training.

A diver could be wearing their regular computer and a new computer that they are just taking along to try out and see how it works. If they get down to 1 minute of NDL on their regular computer and the "test" computer is showing a deco obligation, is the diver under some obligation by their training to follow the test computer and do the deco? I would say no. Their training is to follow their computer. The agency does not tell them what computer to buy, what algorithm to use, or what settings to use. So, if they are following the computer they chose, they are within their training, whether there happens to be another computer hung on their arm that says something different or not. It's a choice that is up to the diver. It is a grey area, not a clear, definitive line. Even though the diver is still strictly following their training. So, accusing them of second-guessing their agency is just flat wrong, in my opinion.

 

[Scuba J7]

More nitrogen, yes. More risk of DCS, not necessarily. It is absolutely nonsense to teach a student diver that he faces a higher risk of DCS when he exits the water in PG B rather than PG A. Elevated levels of N2 are simply that until they approach a level where DCS may occur; i.e.NDLs.

Lets ask the experts!

Common sense dictates that the closer you are to the cliff your chances of falling over it increase.

 

[dmaziuk]

It exists only to allow students understanding of the core concepts, uncluttered by irrelevant complications.

My cert only really says that the guy who trained me has been known to some people to do a decent job of training divers. Dive shops seem to trust that. Getting those some people to get the instructors to get the students to buy a specific model of a relatively expensive device is too way much of a stretch I think. Or to get the instructors to buy enough of those to rent them out to the entire class.

A club that could expel you if you don't meet its standards would be in a better position to do something like that. It would also be in a better position to send a rep to, say, Heinrichs Weikamp and ask them to develop special firmware for that reference training algorithm, promising sales to all club members in return. I doubt that would be a wise move, and besides the club in question is already way ahead of the curve and we're not talking about they should do.

The point being, teaching core concepts of a dive computer algorithm is a nice idea but having an actual dive computer for that sounds like a complication that makes it, very relevantly, impractical.

 

[boulderjohn]

There is still a line, what you describe is the manufacturer and end user moving the line. Maybe we should FORCE all manufacturers to use the same algorithm and then follow up with training agencies.

That would be similar to someone in the 1950s wanting to require all doctors treating polio victims to use the same iron lung protocol and requiring all iron lung manufacturers to use the same methodologies for manufacturing iron lungs. If we did that then, we would still be using iron lungs today. If you are going to stifle research and innovation, you should have a pretty darn good reason. I have for the life of me not seen any reason for doing this, let alone a good one. Yes, different algorithms produce somewhat different results. So what? Can anyone identify a problem that has resulted from this that requires such a drastic solution?

 

[boulderjohn]

In the table I included, the DSAT NDLs at all depths are all 7-8 minutes shorter than the USN 2.3% DCS values.

Remember there is more to tables than NDLs. The PADI NDLs are shorter than the old Navy ones in large part because they wanted to shorten the surface intervals before subsequent dives.

 

[scubadada]

This thread had gone off into the ludicrous