Decompression and the recreational diver

[nolatom]

Many boats have "boat rules". One of them may be that if you surface with an uncleared deco obligation on your computer, you're going to sit out the next X dives, or Y hours. And if you do it a second time, you're relegated to bubble-watcher status.

So "light deco" for these operators is equivalent to "poor gas management" if you ran low and had to surface before you quieted your computer, or alternatively "lack of computer/deco ceiling understanding" if you had enough gas and yet climbed on board with your computer still "nuclear".

Either way, you're not endearing yourself with either the captain or the DM, who will then believe you to be either a not-very-good or a not-cautious-enough diver, or both. On an offshore liveaboard, these are the divers whose problems if left unchecked may cause an interruption of everyone's diving, and scrutiny from the relevant authorities. This will make you unpopular with a whole lot of folks whose unhappiness you've caused.

So if you're going to intentionally plan on "light deco", make sure you know how to not end up in "dive jail" back on the boat.

Or, just don't plan on it in the first case. Be the safety stop diver who donates an octo, rather than needs someone else's

 

[ajduplessis]

This course is considered a recreational course and is one of the prerequisites for moving on to technical diver or normoxic trimix diver training.

No it's not a prerequisite to move to either.

 

[Jaydubya]

I guess it depends on the definition of prerequiste. While not a requirement, ART can be used to satisfy the prerequisites for the technical courses I mentioned.

 

[Akimbo]

Mike, that isn't entirely true.

You can't do the decompression stop without the gas. Agreed

And you won't have the gas unless you planned for it. Not necessarily. Anybody can carry lots of extra gas, leave bottom with a large reserve, and/or get a sense of how much gas they need from experience. Unfortunately more people probably do that instead of calculating anything.

And you won't have the knowledge without the training. That depends on how you define training. There are lots of people around the world that can’t calculate gas requirements, including in the US and Europe. There are also a lot of people who never had any formal training on how to use a decompression table and figured it out by reading it. Even more just use their computer.

And you won't get the training in a recreational course. Sure you can. The simple fact that decompression dives are successfully performed hundreds, if not thousands, of times a day by recreationally trained divers makes this statement false. There are lots of courses that provide the essential knowledge that are not classified as technical. Performing those dives may not be blessed by that certifying agency, but they teach the essential information.

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I’m not recommending these shortcut methods, but there are lots of divers that use them every day. None of this is magic and pretending that they are solely of even correctly the realm of technical diver training is a disservice to the community.

Developing a method of calculating gas consumption entirely on their own is well within the capability of anybody halfway through a high school physics class. I would hope that even the most basic and shoddy open water course at least makes students aware that decompression limits exist. They all teach how to make a safety stop today. It isn’t much of a stretch to figure out decompression stops from there… let’s see, the red lights mean stop and green means go.

The reality is the training industry seems to think that they can avoid teaching the most basic aspects of physics and physiology and people will buy more courses because they tell them they are too stupid to make decompression dives if they don’t. That is great until they get on a boat in the tropics and see what everyone around them is doing, follow the leader, and figure they are good to go. Either that or they make a few dives, scare the crap out of themselves because they appreciate their incompetence, and spend their money on something more fun.

 

[DevonDiver]

Again... I'll point out that there is a fundamental difference between 'being able to do a deco stop/dive' and being able to 'safely carry out decompression dives'.

One situation supposes the ability to; carry enough gas, control your buoyancy and follow what your computer tells you to do.

The other situation supposes the ability to; do the above, but deal with any contingencies, providing a virtually guaranteed certainty of survival on every occasion, on a repeated basis, indefinitely.

Training isn't needed to do decompression dives? Ok.. but training is needed to do decompression dives safely, without reasonable risk of accident.

 

[Hank49]

When I worked as a dm and instructor on Boracay there was one site where almost all the divers went into deco. It was a 110 foot, blue water descent to a wall with a strong current. The basic rule was let the dm know when you reached half tank and everyone would ascend after watching the sharks, dog tooth tuna, giant trevally, turtles etc etc. Most experienced divers were 4-6 minutes into deco by then. Out of 21 shops there, only one tried to avoid any deco obligations.
As far as I know, no one got bent there. The worst thing was people dropping way to deep as they drifted into the wall.

 

[Akimbo]

Again... I'll point out that there is a fundamental difference between 'being able to do a deco stop/dive' and being able to 'safely carry out decompression dives'.

One situation supposes the ability to; carry enough gas, control your buoyancy and follow what your computer tells you to do.

The other situation supposes the ability to; do the above, but deal with any contingencies, providing a virtually guaranteed certainty of survival on every occasion, on a repeated basis, indefinitely.

Training isn't needed to do decompression dives? Ok.. but training is needed to do decompression dives safely, without reasonable risk of accident.

The facts do not support your assertion. A vast number of complex decompression dives have been successfully completed by people with no more training than a good recreational Scuba course, reading a book or manual, talking to friends, gradually developing skills, and reflecting on their experience. After all, this is how the skills you teach were developed.

I have been fortunate enough to receive far more formal training than the vast majority divers. Yet have seen people with far less training who outperform me and most classmates. A basic knowledge is required for sure but intellect, watermanship, analytical thinking, experience and emotional control trumps a lot.

Again; I am not recommending this as the easiest or fastest method, but formal training is not the only method or necessarily the best. The slower approach is appropriate if it coincides with your desire and developing the confidence and skill to make these dives. Both can be equally safe. Formal training is certainly the fast-track towards the same end, providing you don’t acquire C-cards faster than the judgment to back them up.

Regardless of how you get there, the people with their brains engaged will ensure they are properly prepared. No amount of classes can give someone the sense and actual skills to prevent doing something stupid when the world doesn’t match their curriculum.

 

[captain]

I have a library of diving instruction books and several issues of Navy diving manuals from 1955 to the present. Those and a YMCA scuba course in 1970 are all the whole of my instruction. I was doing what are now called tech dives long before the term came into use.

 

[Hatul]

I consider light deco within the scope of recreational diving. A short deco stop can be considered a slow ascent. If diving by a conservative set computer, the deco stop can be one required by the conservatism of the algorithm, so the distinction between deco and non deco diving is blurred.

Technical diving requires the dive to be pre-planned with regards to deco stops and gas supply, but recreational diving is less restrictive. I find an AI computer useful for gas management on the fly for recreational diving. I set my tank reserve to 650 psi, allowing 150 psi with a regular size tank for a 3 minute safety stop. As long as my depth in feet/30 is less than the Remaining Air Time, I know I can come up at the required rate, make the safety stop and still surface with 500psi, and have some reserve (because the Remaining Air Time is based on staying at depth). If I need to do a short deco stop I add that to the required Remaining Air Time.

 

[Thalassamania]

... But what's the motivation in shouting about it, or pushing for it to be a recognised diving discipline?

For the life of me, I can't figure that one out.

You can't do the decompression stop without the gas,
And you won't have the gas unless you planned for it,
And you can't plan for it without the knowledge,
And you won't have the knowledge without the training,
And you won't get the training in a recreational course.

Cute, succinct, deceptively straightforward, with just enough truth to hide the realities: plenty of folks dive huge or doubles because they can't do math; you don't need to take a class to gain knowledge about something; there are recreational courses that cover decompression, at least as a contingency and most all courses do a three at ten, but call it a "safety stop," it is really a just-in-case decompression stop.

To me - the issue revolves around the necessity to maintain the deco stop. It's a virtual ceiling, but nonetheless it is very real.

It does not surprise me that you see divers who can't hold a stop, but should they all not have demonstrated the ability to adequately hold a three minute stop at a specified depth between twenty and ten feet? Or are you trying to turn that into another PADI separately priced product like PPB?

Technical diving isn't just about the use of exotic gasses - it's about having a very high standard of core skills, extensive planning/preparation and covering all reasonable contingencies so that the deco obligation can be achieved. Nothing in the recreational diving syllabus comes close to providing that level of training, that focus or that mindset.

Perhaps nothing in YOUR comes close to providing that level of training, that focus or that mindset, but you have no business speaking for everyone else.

Any argument that divers can take a 'recreational' approach to decompression diving has to be based on a limited scope of decompression. It has to be 'light' decompression. What I see in those arguments is a mindset to deco that links 'light' with 'safe if broken'. "It's only 6 minutes, so if I screw up, then I'll be ok". In essence, it is reducing 'light deco' to the status of a glorified safety stop. It's a dangerous and irresponsible mindset to encourage/allow.

"Safe when broken" is a "safety stop" not a decompression stop. I don't know the exact difference between "light" deco and deco, but I do know that if there's just a ten foot stop I'd tend to call it light and if there is a required 30 foot stop I would not. Between those two there are lots or rather meaningless lines that everyone could scribble.

How many 6 minute light deco/glorified safety stops does the diver have to complete, before they feel confident and justified to extend to 10 minute stops? to 15 minutes? to 20 minutes?

It's less a question of how many and more a question of" "how well did they do the last one?" A diver who hits the stop with perfect buoyancy, never has to touch the line and does not vary depth more than a foot either way is ready for longer stops ... right? What does it matter how many times they've done it before?

How many times do they accidentally or deliberately break their virtual overhead, before they start to believe that "deco is all hype" and begin rationalising that the implications for skipped 'light' deco obligation are inconsequential? How long will it be before they start scoffing at "You're gonna die" comments when they gain the confidence to start admitting that they've blown their 'light' deco through lack of preparation, planning and/or dive ability.

Therein is encapsulated your skill as a teacher. If you have a problem with that you need to closely examine what you do and how you do it.

There really is no need to justify decompression without training. Training is now commonly available and easily accessible to the dive community. It's no longer a mysterious 'dark-side'.

It never was, all the information needed, and more, is right there, in the 1955 USN Manual, in the Science of Skin and Scuba of the same era, hell I think it was even in Bill Barada's, "Let's Go Diving." Hardly the "dark side."

This weekend I am teaching a PADI Tec40 course. My student has 50 dives experience, certified as an AOW & nitrox diver. The cost of his course is the same as I charge for an Open Water course. It'll take 4 days. The first day is 'recreational' deep open-water dives - 'check-outs' where I can assess and remediate his core skills. Then we have 3 days of 'tech'. The theory work is intense - detailed dive planning techniques, equipment configurations and 'technical mindset'. We also have 4 training dives. The first 3 dives are shallow-water and skills intensive. He'll learn to safely operate doubles and a single stage of nitrox (-/=50%). He will learn how to gas switch and hold a deco stop with precision. The course will finish with a single, planned decompression dive to a maximum depth of 40m/130ft with no more than 10 minutes of deco.

On qualification, he'll be certified to conduct decompression dives, to a maximum of 10 minutes deco, down to 40m/130ft, using nitrox up to 50%.

Isn't that the sort of 'light' deco we are talking about?

Does that course sound unreasonable in terms of scope, time, cost or commitment?
Does the course sound excessive for the benefits gained?
Is there any mystique or 'black magic' involved?

It sounds like a lot of makeup work that the student should have mastered previously, but didn't, so you had to provide it. Good thing you could and were willing to, but you really should be complaining about this student's previous teacher(s) rather than bragging on what a hard program you present.

My problem with the tech 40 as you describe is that it is light deco with training wheels. Max ten minutes deco? Most tech instructors I run into have very high standards for accepting anyone into a adv ntx/deco proc class. Either you are ready for 30 at 30 with 30 accumulated or you are not.

The major problem that most students I have trained have with longish stops is dealing with boredom not with skill performance.

I think that easing into the pool with light deco, no matter what we are calling it is a crutch. I would draw the line at an intro to tech class and then either go straight to you accept the risks involved with 30/30/30 or not. While education at an early stage is good, I do not agree with teaching so light a deco. The argument could be made that cause there is nothing to 30/130/10 then deco to deeper depths for longer is just as easy.

First you simulate, then you practice in simulation then you do it for real. Frankly I see no need to actually make a deep diver or expose anyone to the potential dangers of decompression in a decompression course, conducting a deep dive and decompressing on the way out are two different things and can be handle in an integrate or a separate fashion.

Again... I'll point out that there is a fundamental difference between 'being able to do a deco stop/dive' and being able to 'safely carry out decompression dives'.

Once again I must point out that safety means "without risk." There is no decompression diving that is without increased risk so the very idea of being able to 'safely carry out decompression dives' is claptrap. What one must do is learn to minimize risk whilst carrying out a decompression schedule. That is a very different mind set.

One situation supposes the ability to; carry enough gas, control your buoyancy and follow what your computer tells you to do.

The other situation supposes the ability to; do the above, but deal with any contingencies, providing a virtually guaranteed certainty of survival on every occasion, on a repeated basis, indefinitely.

Any properly trained open water diver should have the ability to; carry enough gas, control your buoyancy and follow what your computer tells you to do. Your other "situation" is quite impossible since there are no guarantees, not on any dive, especially not on one requiring decompression, which is a stochastic process, and thus never guaranteed.

Training isn't needed to do decompression dives? Ok.. but training is needed to do decompression dives safely, without reasonable risk of accident.

Training is not needed to do decompression dives, I did hundreds before I was mentored by someone who had done far fewer, but who had some good tricks. I guess it would be safe to say that I still have yet to be so "trained."

I have a library of diving instruction books and several issues of Navy diving manuals from 1955 to the present. Those and a YMCA scuba course in 1970 are all the whole of my instruction. I was doing what are now called tech dives long before the term came into use.

Say it isn't so Captain, please, say it isn't so!