Why is 18m set for OW?

[Diver-Drex]

There was no recreational limit other than the table’s limit of 130fsw during my OW class in ‘84. There was also no CESA taught, it was a free ascent.
My understanding is the 60fsw limit was established because during a ‘typical’ dive with an AL80 you were gas limited and not NDL limitted. At any point during the dive up to and including completely exhausting your breathing gas you could safely make a direct ascent at 60ft/min. Deeper than 60fsw you can exceed your NDL while still having gas available. The NAUI table NDLs and an RMV of .6 pretty much bear this out.

 

[xrcjdx]

Ascent rate ascent rate ascent rate. The navy (and padi) rate was pegged at 60' (18m)/minute. (Now reduced to 30' (9m).) Faster ascent rates permitted when ascending to 18m from deeper depths. That, and money.

 

[Bob DBF]

Remember that J-valves were the norm at the time, so you "always" had a gas reserve, but we still don't have a "NDL reserve."

Depends on the time. In '62, when I started to dive, the tanks where I dove were maybe half j-valve with the majority being post valves. The new/newer ones had the j-valves. There were some regs that mitigated the issue by offering a j-valve built into the reg. This was so a diver didn't have to replace all their valves.


At the time, the emphasis was on watermanship skills in diving. Ditching your rig and swimming up was an emergency procedure. The ability to go one minute, 60' @ 60 fpm to the surface, without needing to take a breath was a common skill at the time.


Bob

 

[tursiops]

Depends on the time. In '62, when I started to dive, the tanks where I dove were maybe half j-valve with the majority being post valves. The new/newer ones had the j-valves. There were some regs that mitigated the issue by offering a j-valve built into the reg. This was so a diver didn't have to replace all their valves.


At the time, the emphasis was on watermanship skills in diving. Ditching your rig and swimming up was an emergency procedure. The ability to go one minute, 60' @ 60 fpm to the surface, without needing to take a breath was a common skill at the time.


Bob

Ha. The first thing we did when we got to the bottom in New England with our J-valves was to remove the pull rods and use them as tickle-sticks for bugs, then reinstall them before surfacing just in case the rangers were watching.

 

[wildbill9]

Scrane hit it on the nose imho. When I got my cert there was never any mention of a 60 ft limit. I was floored once I found scuba board and found out I had been breaking the law for the past 40 years. I started looking over my shoulders for the scuba police, I tried to by a depth jammer in case someone saw me exceeding 60 ft, I would often go to (gasp) 61 ft just to see if anyone arrest me when I exited. It made diving exciting again, sharks....blah....juvenile trunk fish....snooze time....herds of pygmy seahorses ride on frog fish....yawn. It was all about exceeding 60 feet and not dying or getting arrested. I am still waiting to get busted........

 

[RainPilot]

Oh, Bill. Why are you so wild?

 

[TMHeimer]

like many things that are standard in SCUBA, I suspect it was a number picked by a bunch of old white dudes sitting around the PADI conference table and pulled it out of their a$$. Nothing wrong with it mind you, just that there are a lot of things that you may try to find a scientific backing for and there just isn't one.

Now, to be somewhat rational about it, IIRC they say that 60ft is the deepest effective depth for a CESA, so that's a convenient reason to choose 60ft over 50ft or 70ft, and I also believe there was a study done about nitrogen narcosis and that 3ata was a major tipping point in cognitive function and since we live in the imperial world, it was rounded to "Safety" which is 60ft not 70ft. Had that decision been made by an agency based on Europe or if the USA was on the metric system, then it would probably have been 20m and whatever archaic swine left on the imperial system would have had to deal with a non-round number

I just returned from a trip and read all the posts--like this one best, though I do agree with boulderjohn in that I don't see any real connection between CESA and freediving. The whole question of how deep can one do a truly "safe" CESA has been debated as well.
I have come to the conclusion that no one truly knows the answer to the OP's question.

 

[DerekR]

I was beyond shocked when my wife was recently taking an OW course and she informed me that there was a 60' "limit" for OW divers. In my 46 years of diving I have never seen a sign at any depth that read, "No OW divers beyond this point!". My training taught me to adhere to the Navy dive tables, which go WAY beyond 60 feet! With that being said, I have to admit that the difference in the training that my wife received, versus what I was taught is so diverse that they each seemingly came from different a universe! I was taught to be self-supportive. She was taught to rely on someone or something else (like a computer).
I also see the gap in training in the supposedly "qualified" divers on boat dives, many of whom I deem as hazards to both themselves and the environment. From what I can tell, the 60' limit is there as an indicator of the lowest common denominator of today's certification. It's a "pay me for another class and you can go deeper" attitude that is having a very obvious effect on the quality of divers that the industry is currently certifying - and it isn't pretty!

 

[tursiops]

I was beyond shocked when my wife was recently taking an OW course and she informed me that there was a 60' "limit" for OW divers. In my 46 years of diving I have never seen a sign at any depth that read, "No OW divers beyond this point!". My training taught me to adhere to the Navy dive tables, which go WAY beyond 60 feet! With that being said, I have to admit that the difference in the training that my wife received, versus what I was taught is so diverse that they each seemingly came from different a universe! I was taught to be self-supportive. She was taught to rely on someone or something else (like a computer).
I also see the gap in training in the supposedly "qualified" divers on boat dives, many of whom I deem as hazards to both themselves and the environment. From what I can tell, the 60' limit is there as an indicator of the lowest common denominator of today's certification. It's a "pay me for another class and you can go deeper" attitude that is having a very obvious effect on the quality of divers that the industry is currently certifying - and it isn't pretty!

Nostalgia is just not what it used to be.

 

[boulderjohn]

Nostalgia is just not what it used to be.

Many years ago, I was one of a couple journalism teachers at a school. Back in those days, writing a headline was a laborious task. You wanted it to fit in a specific space, and with each font size taking up a different amount of space and each letter being a different width, you had to use a complex counting system from the Associated Press (AP) to make the headline fit the allotted space. Then you sent it to a typesetter and hoped the results you got back matched your count. Then came computers, and you could see your results in front of your very eyes, and when it looked right, you pressed the letter P and printed it. Suddenly the whole counting system and typesetters were a thing of the past. It was cheaper to buy a room full of computers than pay a single typesetter.

I moved on to a different school and different teaching assignments. One day I visited the old school and stopped in to visit with the other journalism teacher who was still there. Her students were taking a test on the AP counting system for headlines. "Why on earth are you still teaching that?" I asked. She told me with gritty determination that the AP headline counting system has always been a part of a journalism course, and she was not going to lower her standards and stop teaching it just because nobody anywhere used it any more.

This sort of belief that everything we did in the past is so important that it must be continued forever can be found in almost all walks of life.