Planned deco on a recreational dive?

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Well I wasn't trying to "convince" anyone of anything... Only pointing out that there are so many variables involved in this study of decompression "theory", that nobody can say much of anything with certainty. For every "perfect" dive plan, someone will get an unearned hit. Similarly, someone will blow off some huge decompression "obligation" and walk away unscathed...

As a number of folks have pointed out in this tread, that a mere adjustment of the settings on a dive computer can make deco go away. I use a Petral... I adjust gradient factors a dozen different ways and completely change my deco requirements.... Or go on a bender the night before. Or not drink enough water. Or drink too much. Or get cold. Or overheat...

You get my point I'm sure.
I agreed with your point before you made it.....what I disagreed with was your saying it was only a "theory" hence was only speculation.
 
It just comes down to people not knowing what they don't know. And like you said, we don't know a lot about deco and it's all theory. So if anything we should be conservative as hell and not be advocating non trained people to be doing "only a couple minutes" of deco.

I won't take exception to anything you said, and I am certainly not advocating treating deco lightly...

I sometimes question the argument that tables are somehow "safer" than computers (apart from dead batteries and so on). Tables are just a bunch of numbers that were derived through calculations and experimentation. Computers are really only the electric version of those tables. Both are "somebody's" idea of how bubbles are going to behave in the face of a few hundred variable. Tables have the advantage of allowing us to "round up"... next deepest depth, next longest time... in order to allow a safety factor. Those of us that had tables beat into us would never think of "rounding down". On the other hand, I think many people opt for a less conservative option on their computer because they want a longer bottom time, and because deco is often kinda boring.

Anyway, we are wandering far away from the purpose of this thread...

Suffice it to say that I don't think we are in disagreement... Deco should not be undertaken casually and without knowledge of the potential consequences if/when things go sideways.
 
I agreed with your point before you made it.....what I disagreed with was your saying it was only a "theory" hence was only speculation.

Well it certainly isn't speculation, but I suspect that there's an awful lot that we don't know. Whenever I read a discussion about decompression, it's always referred to as a "theory"... never a "law" or anything like that. It's a "work in progress". I think back to when I started diving in '74... "silent bubbles"... what? Ascent speed was 75 fpm, then 60 fpm, now 30. Safety stops weren't a thing. We used to dive "close" to the limits prescribed in our USN tables, and surface without a thought. And lived to tell about it. To believe that we know everything there is to know about decompression is ludicrous. (Admittedly, we must be close since most divers will manage to muddle along and never get bent their entire lives... either through good planning, good luck or divine intervention.)

I presented at a conference last year and one of the other speakers was a researcher at DCIEM in Toronto. All of his work on decompression theory centred around the concept of the body treating those pesky bubbles in the same way it treats infections... who knows where that will lead.
 
The issue was your comparison of going into deco and going into a cave. You said there was no such thing as "lite" Deco, just as there is no such thing as lite cave diving. Going a minute or two into deco is not a very serious problem. If you do get decompression sickness, it is a minor issue issue. Go an hour into deco, and there is a huge difference. In contrast, Go two minutes (100 feet) into a cave, turn around, and can't find the exit, you will die.

Except there are people that have blown off "minutes" of deco and had a very serious problem. DCS is never a "minor" issue. Some people with type 1 dcs just need some O2. Some people get serious symptoms and need a chamber. Everyone with type 2 needs a chamber and some people get better and some people have permanent residual symptoms for life. I would say the financial and health implications of DCS make it never a "minor" problem or "not a very serious" problem.

You can go 2 minutes in a cave and your chance for badness is greatly reduced when you compare it to a full cave dive out of the ambient light realm. I would argue that many many OW divers could go briefly into a cave or within ambient light turn around and come out without issue. This doesn't make it a safe thing or the right thing to do just because a lot of people could get away with it without getting hurt. Just like going 2 minutes into deco, most of the time would not cause issues. The issue is when it does cause an issue. When the non trained diver does just 2 minutes of a cave dive, and like you said gets lost and dies. Or the non trained deco diver blows off 2 minutes of deco, gets type 2 dcs or severe DCS possible from a PFO, and has paralysis for life. Just because a majority of the time people can get away with something doesn't make the risk at the population level acceptable.

If anything, I feel that this fits with my argument. As soon as we talk about cave diving people start to get fired up and say there is no lite cave diving. Going into a cave will kill you. But how can you say someone untrained doing deco is not going to get seriously injured?
 
I see lots of comments by folks with minimal diving experience and zero tech experience... some seem very cynical of the need for deco training before deco dives.

Seriously, just because someone did a few crappy specialty courses before, doesn't mean they should write-off the validity of further training for advanced dives.

Doing a dive like the OP describes just ONCE probably has a low risk of catastrophe. It's a horrid 'trust me' dive, but if nothing goes wrong, then it's eminently survivable.

The real danger stems from doing such a dive and allowing oneself to become convinced that it proves some sort of competency... and, thus, validates doing further dives beyond one's training.

I've seen this a lot with marginally experienced divers... especially those skeptical of training... who firmly succumb to "normalisation of deviance" and fall foul of a typical delusion that uneventful dives somehow prove a capacity to assuredly survive dives that are patently beyond their ability and training.

The need for specialist training for deeper and/or decompression dives isn't based on nothing going wrong... it's based on providing a reassurance that you'd survive compound factors occurring that'd otherwise kill or injure you.

You can trust to luck for your safety with recreational dives... as they're ultimately very forgiving. The parameters are deliberately kept forgiving... thus preserving safety even with minimal, or ineffective training.

Technical dives aren't forgiving. Increases in depth and bottom time drastically increase the severity of consequences for any situation you're unable to deal with.

You might 'get away with it' once. Or twice. Or 50 times. But eventually you'll be faced with a scenario that you can't handle using recreational level equipment and protocols. When that certainty occurs.... you'll have zero options available to preserve yourself.

Is it really worth the risk, just to save a few $$$ on training and equipment? Or because you don't have the moral fortitude to resist temptation or slight peer pressure?
 
The issue was your comparison of going into deco and going into a cave. You said there was no such thing as "lite" Deco, just as there is no such thing as lite cave diving. Going a minute or two into deco is not a very serious problem. If you do get decompression sickness, it is a minor issue issue. Go an hour into deco, and there is a huge difference. In contrast, Go two minutes (100 feet) into a cave, turn around, and can't find the exit, you will die.

Decompression Sickness is a "minor Issue
" ? How is that determined? I have seen people paralyzed from decompression sickness, even though they did not incur required decompression or do anything to violate their computer.
 
Decompression Sickness is a "minor Issue" ? How is that determined? I have seen people paralyzed from decompression sickness, even though they did not incur required decompression or do anything to violate their computer.

Those would not have been saved even if they had skipped 2 minutes of deco then.


As we've been trying to explain for a while, 2 minutes of deco is nothing. I can take many algorithms that will make those two minutes from my computer to be well within NDL (as John already proved). So what should we do, blame anyone that doesn't dive [insert most conservative algorithm ever here] for doing dives that call for deco stops?
The difference in gas load between 0 and 2 minutes of deco is hardly existent...
 
Decompression Sickness is a "minor Issue" ? How is that determined? I have seen people paralyzed from decompression sickness, even though they did not incur required decompression or do anything to violate their computer.
@Patoux01 Ignore dumpsterDiver. He is both trying to be obtuse and trying to troll BoulderJohn.
 
He is both trying to be obtuse and trying to troll BoulderJohn.
Plus, he's been banned.
 
My cousin learned scuba about then. I recently asked him about is instructional path. He said 100% of his instruction was provided by the salesman at the sporting goods store that sold him his gear. The instruction was done on the sales floor as the sale was being consummated.

My dad taught me, with a half dozen dives more than me. The good news is that I had to read and was tested on The New Science of Skin and SCUBA Diving, which was the SCUBA training manual of the day for YMCA and the basis for the training manuals of the SCUBA agencies. Since there was no need for certification in order to dive the quality of instruction was, shall we say, all over the board. My dad got the equipment from Sears mail order, and it contained a little instruction pamphlet to teach the recipient how to dive, he picked up the "New Science..", book to learn from so I was lucky to get better training than many.

2. Spend 20 minutes at 100 feet on air, and you are within NDLs on the PADI tables (3 minute safety stop required), but if you spend 25 minutes (as allowed by the old Navy tables), you are in serious emergency decompression procedures.

You should decide what algorithm you are using just as you would a computer as one may put another into deco on the same dive. In addition, the Navy has had a few revisions to their tables since then as well, so the comparison may be a lot closer.

As for diving, I used the old Navy tables until I got a computer in 2000 something, the one issue I did have was on me and not the tables. I never did get a hit when deco diving on the tables, but I was much younger then.

If the equipment and training for deco diving was as good then as it is now, I probably would have continued on tech diving.

Ascent speed was 75 fpm, then 60 fpm, now 30.

In the US it was 60 fpm from before I certified in '62, until it changed ti 30 fpm. The USN wanted a standard ascent rate for SCUBA and hardhat so 60 fpm was the compromise. Other countries may vary.



Bob
 
https://www.shearwater.com/products/perdix-ai/

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