Does defining "technical diving" serve any purpose?

[Wookie]

By that logic, a dive with 21% O2 and He up to 35% should also be removed as a mix such as that would still be the same as an air dive table wise.

I am not a helium expert, but I believe that a helium mix below 20% is not considered to be a helium dive because there isn't enough helium to come out of solution (bubble) fast enough to be considered a hazard any more than nitrogen, where mixtures above 20% get a different set of tables to account for the helium. I can stand to be corrected on this.

You are right, Thal, I would have no problem with a diver on a normoxic or hyperoxic mix with recreational helium diving air or nitrox limits on one of my charters, provided they have a card. Same with a person diving O2 mixes above 40% observing depth rules for O2 diving. But, I'm not going to provide those fills on a recreational trip, the gas booster takes up too much room on the deck, and fills would be too slow to allow the same dive times as air or nitrox fills. That's why I don't mix charter types. The objectives of a nitrox/air diver are too different than the objectives of a mix/O2 diver.

 

[markmud]

The main problem is turning out OW divers that would understand any reason for any demarcation except a rote repetition of OW 60', AOW 100', and deep 130' without having any understanding of why it may not be in their own best intrest to dive to those limits regardless of what card they have in their pocket.

One saying goes "A little knowledge is dangerous", my contention is that OW training at minimum standards is that little knowledge.

It is a good thing that most newbees are in awe of authority and other than "trust me dive" issues they follow the party line. Once away from the party line however, they do not have the tools to expand their diving envelope safely, unless they do some serious reading and practice.


If You and the Ocean are on opposite sides of a chess game, you might be a Tech Diver
( appologies to Jeff Foxworthy )


Bob
-----------------------------------
I may be old, but I’m not dead yet.

Hey Bob,

I agree.

I am a former tug boat captain. I survived on the oceans because I had contingency plans to overcome problems that occur on the ocean. We had redundant machinery, gear, hausers, tow lines, and SOLAS gear. As a USCG licensed skipper, I was taught in the 70s that navigation required three location inputs in order for your charted position to become a "fix".

I approached my SCUBA diving avocation with the same mentality. During my OW cert classes, we discussed what happens when a diver overstays at depth and moves into a staged decompression regimen. And that was it. Dr. Thomas Sowell always teaches people to move beyond "stage one thinking."

As a professional mariner, I always asked myself and crew "What if...?" We had moved to "stage two thinking."

I asked everybody who knew anything about diving:

1) What if I get tangled in fish net and overstay a so-called "NDL"?
2) What if I get narced and dive beyond 130', come to my senses and then need to do staged decompression?

Everybody was fearful that I wanted more information on staged decompression because they rationalized-and-projected that if I were armed with staged decompression knowledge, that I would automatically go out and perform staged decompression diving. NOT SO!

I found the information myself. I now carry, when I dive, a laminated US Navy decompression chart that covers ascent time for decompression diving which includes what the rec industry calls "NDL."

I have never needed the information underwater, but what if my computer fails, or acts-up, and I want to "fix" my predicament with more information? Simple, I get my laminated card out of my BC and compare the information on my computer to what the card says. I am 2/3 the way to a "fix."

Side Bar: I find it interesting when I look at my US Navy decompression table. The matrix does not delineate between "NDL" and staged decompression. It is all covered under the same format: Decompression Diving. I'll trust the Navy on this one.

I enjoyed your opinion.

markm

 

[markmud]

Markmud, I agree that every dive is a decompression dive and even within the limits of a "REC" dive a dive may take a hit if they do ascend too rapidly, however, I will still stand by me definition and state that if I happened to be at 120 FSW for 5 minutes and had an issue I could head for the surface ( at an acceptable or maybe a bit faster pace) and live to dive again, however if I had spent 40 minutes at the same 120 FSW and ascended directly to the surface at the same acceptable rate, it would most likely result in a bit of hurt. However the rest of the industry defines, I will stick to the " soft or hard ceiling" as my defining point. Simply..whenever the surface is not an option.

Hey davetowz,

I realize I am splitting hairs and stuck on a this issue. Don't worry, I will move-on.

In Roseville Kalifornia, we have a "S____ ______." This sporting goods store is a chain and trains many divers.

I was begining to know the Dive Instructor at this store. She grew up on land, had not been diving for many years, but had completed all of the training that PADI requires to become a certified instructor. She did not seem to have the same "respect" for the ocean that I have. Having 350,000 nautical miles logged as captain in my USCG file (from logbooks), I have learned over and over again that one must respect the ocean. A human being is an insignificant little nothing while on the ocean. The ocean doesn't care about you, at all.

This instructor was teaching an AOW course. The students moved from class room theory to open water diving. They had to perform their deep dives.

One student freaked-out at about 100 fsw. He bolted for the surface. The instructor tried to hold him down. He was way to buoyant. He died--she did not. I don't recall what the COD was. (Disclaimer: This story is about 5 years old--he did die for sure, even if some of my details are a little off. As I recall, a heart issue was also a contributory factor--I don't remember)

I spoke with her after the incident. I did not talk about or ask questions regarding the incident because she was different. She had a glazed-over look about her. After that, I did not see her at the store anymore. The store removed the diving section a few months later.

I wonder if the student would have been mentally prepared for his "soft ceiling" if he had been taught, in-depth, about it (pun not intended). Did the mixed messages contained in PADI training manuals contribute to his death? Did double-speak play a part in his death?

I don't know.

markm

 

[boulderjohn]

Side Bar: I find it interesting when I look at my US Navy decompression table. The matrix does not delineate between "NDL" and staged decompression. It is all covered under the same format: Decompression Diving. I'll trust the Navy on this one.

There is a very important difference between the U.S. Navy tables and tables like the PADI Recreational Dive Planner that explains this. Not many people know this. I will try to explain it briefly, but I will warn you that the full details are pretty technical.

Tables are based on the well established theory that different tissues absorb and release nitrogen at different rates. These rates are called halftimes because the rate is not constant. As the tissues get closer and closer to equilibrium, the rate slows down. We approximate that through the concept of half times. A 5 minute tissue will be half way to equilibrium in 5 minutes, and then half way from that level in the next 5 minutes, and then half way from that level in 5 more minutes. A tissue is considered to be at equilibrium in 6 halftimes, so a 5 minute tissue is at equilibrium in 30 minutes.

When a basic table is constructed, it has to use a theoretical tissue that it believes is most critical for planning. This is called the controlling tissue. When the U.S. Navy tables were constructed, its numbers were based on the 120 minute theoretical tissue, because it was believed that this tissue was most appropriate to that kind of diving. That is why the Navy tables "wash out" in 12 hours (6 X 120 minutes).

When PADI did its extensive research leading to the RDP, it reasoned that recreational divers did not dive the kinds of dives that Navy divers do. Recreational divers are frequently more shallow, and they do shorter dives. It tested divers on those kinds of dives. Their research showed that when diving within the limits you see on the the RDP, the 40 minute tissue actually controlled the dive (and subsequent surface interval). To be more conservative, they selected the 60 minute theoretical tissue for the RDP. That is why the PADI tables "wash out" in 6 hours (6 X 60 minutes).

The Navy tables use the 120 minute compartment for the entire tables. PADI did not test below the limits of the RDP and cannot confirm that the 60 minute compartment is a valid choice beyond those limits. In fact, it knows that it is not valid beyond certain limits. That is why the WX and YZ rules demand longer surface intervals for repetitive dives approaching NDLs.

 

[Ste Wart]

It's all just diving.

It's getting as bad as the music industry, so many genres. Rock, Hard Rock, Classic Rock, Blues Rock, Metal, Nu-Metal, Speed Metal, Death Metal, Thrash metal.. etc etc etc etc

Music

Diving

Lets just go and play and leave the worrying to the people who haven't discovered diving.

 

[markmud]

There is a very important difference between the U.S. Navy tables and tables like the PADI Recreational Dive Planner that explains this. Not many people know this. I will try to explain it briefly, but I will warn you that the full details are pretty technical...

Hey boulderjohn,

I have read this information before. I can't get enough of it. Very interesting.

However, my point was not to bash the PADI methodology, just to point out that no overt distinction is made by the US Navy table regarding NDL and deco. Ascent time was the criterion for the creaton of this table and the so-called "NDL" is treated the same as a staged deco dive. Ascent time whether you are making deco stops or not.

The Navy table I have has, for the most part, the same "NDL" limits that the PADI tables have. It is the format that I was comparing.

Sorry I did not make my point well. I usually don't!

markm

 

[Thalassamania]

The major difference lies in the handling of the Repetitive Group Designators.

 

[markmud]

It's all just diving.

It's getting as bad as the music industry, so many genres. Rock, Hard Rock, Classic Rock, Blues Rock, Metal, Nu-Metal, Speed Metal, Death Metal, Thrash metal.. etc etc etc etc

Music

Diving

Lets just go and play and leave the worrying to the people who haven't discovered diving.

Hey Wart,

Maybe you just forced me to swerve into what I am having a problem with! In my simple mind, I may have boiled MY SCUBA diving down to one simple axiom: Decompress apropriately for the dive underway. Forget all of the BS.

Did my last sentence make sense?

markm

 

[markmud]

The major difference lies in the handling of the Repetitive Group Designators.

Thanks,

I have not compared repetitive dive groups!

thanks,

markm

 

[Thalassamania]

Do not expect the letters to cross compare in any meaningful way, the represent partial saturation of completely different compartments.