As a rec diver, what to do if I breach my computer's NDL???

[TSandM]

Boulderjohn, I totally agree with you, and in that, I think the CMAS system is better than ours.

When I did OW, I know I came away with the idea that deco was an extremely bad thing that I could only hope never to have anything to do with.

Deco does raise the risk of the dive by a certain (but often unknowable) amount. But the only real major issue of a deco obligation is that you have to do it -- you have to have the skills to hold the stop or stops, and YOU HAVE TO HAVE THE GAS TO DO THE TIME. Many recreational divers flunk the skills test (I know I did for almost a year after getting certified). MOST don't have the information to know how much gas is needed to satisfy a deco obligation. Often, they are not carrying enough gas, or have not maintained adequate reserves. (If you respect rock bottom calculations, as long as your buddy doesn't run out of gas, you're likely to have enough to satisfy any deco obligation you "inadvertently" ran up -- this may not apply if you're just being obstinate or overconfident and STAYING where you shouldn't be.)

People do deco all the time and go have a beer afterwards. Knowing a little bit about that is a safety thing; to that degree, I think classes like Fundamentals and Peter's Techreational Diver class, classes that introduce technical level skills and technical attitudes toward gas planning and reserves, are a highly desirable education for people whose SAC rate, tank size, and diving environment make coming nose to nose with a deco obligation a foreseeable possibility.

 

[victorzamora]

It made us discount any later warnings about drugs as meaningless scare tactics.

I don't think it should have to be a scare tactic. Make it a recommendation. Instead of, "A REPETITIVE DIVE WILL KILL YOU!!!!" I'm thinking it'd be more like:

"Look, since you're not well versed in deco theory, just follow your computer on up....you'll be fine. However, because you're not sure what's going on in terms of deco...take the day off. Drink some water, you'll be fine. Start over tomorrow, and be more cautious with your times."

PADI's RDP already recommends a 6 or 24 hour SI after deco. I think that giving the students (most of whom just want to see pretty fishies and couldn't give a crap about deco theory) an easy guide or rule that is aggressively on the safe side is much safer than just saying, "Dive your computer until you run out of gas." I think you'll also get a lot less people passing out if it were a simple guide instead of in-depth deco. My wife couldn't care less about deco theory, she'd be one of those students. However, she'd totally follow the rule of thumb I'm talking about.

---------- Post added January 7th, 2014 at 02:56 PM ----------

classes that introduce technical level skills and technical attitudes toward gas planning and reserves, are a highly desirable education for people whose SAC rate, tank size, and diving environment make coming nose to nose with a deco obligation a foreseeable possibility.

But do you really think these classes are acceptable/realistic for the majority of OW divers in an OW class? It would add to the cost and complexity of getting certified, and scuba isn't really the growingest of hobbies. It's also more than most rec divers need (or have much/any use for).

 

[boulderjohn]

I don't think it should have to be a scare tactic. Make it a recommendation. Instead of, "A REPETITIVE DIVE WILL KILL YOU!!!!" I'm thinking it'd be more like:

"Look, since you're not well versed in deco theory, just follow your computer on up....you'll be fine. However, because you're not sure what's going on in terms of deco...take the day off. Drink some water, you'll be fine. Start over tomorrow, and be more cautious with your times."

PADI's RDP already recommends a 6 or 24 hour SI after deco. I think that giving the students (most of whom just want to see pretty fishies and couldn't give a crap about deco theory) an easy guide or rule that is aggressively on the safe side is much safer than just saying, "Dive your computer until you run out of gas." I think you'll also get a lot less people passing out if it were a simple guide instead of in-depth deco.

As I said earlier, PADI's requirement for 6 or 24 hours of surface interval when using the RDP is simply because they do not have any calculations for decompression in the table. they have to make sure you are completely clear again before you can do another dive using the table. For most people those long intervals will not be needed, but there is no way to tell who needs it and who doesn't. There is no way to plan the next dive if you exceeded the limits. They are worst case scenarios. The computer does have that ability, so they don't have to resort to worst case scenarios.

The current computer version of the PADI OW course explains all of this. I have taught it a number of times. I will teach it this weekend. It isn't that hard.

Think about this in terms of danger for the recreational diver. The incidence of DCS on recreational dives is something like 0.02%. It's pretty darn rare. On the other hand, studies of diver fatalities have shown that the number one cause of fatalities (other than cardiac events) is an embolism following a rapid ascent to the surface. I wonder how many were making those rapid ascents because they were as terrified as my dive buddy of going into deco?

---------- Post added January 7th, 2014 at 01:13 PM ----------

PADI's RDP already recommends a 6 or 24 hour SI after deco. I think that giving the students (most of whom just want to see pretty fishies and couldn't give a crap about deco theory) an easy guide or rule that is aggressively on the safe side is much safer than just saying, "Dive your computer until you run out of gas."

Who says this?

 

[victorzamora]

Plenty of people have made that claim in this thread alone. Instead of worrying, just watch what your computer says until it clears you or run out of gas.

As for the computer version teaching all of that, could you explain what "all of this" is? Does it explain what to do if you accidentally breach NDLs, or does it actually teach light deco theory? Also, is this the "newest" version (focusing on midwater skills)? I've watched over a dozen classes be taught and never heard a thing about deco or deco theory....but that was last year and using the "older" OW course outline.

As for the embolisms, I don't know why my little blurb would cause a panic.

 

[boulderjohn]

Plenty of people have made that claim in this thread alone. Instead of worrying, just watch what your computer says until it clears you or run out of gas.

As for the computer version teaching all of that, could you explain what "all of this" is? Does it explain what to do if you accidentally breach NDLs, or does it actually teach light deco theory? Also, is this the "newest" version (focusing on midwater skills)? I've watched over a dozen classes be taught and never heard a thing about deco or deco theory....but that was last year and using the "older" OW course outline.

Let me sum up what I feel people are saying, which is what the PADI course has taught for several years now:

1. Don't plan to go into decompression.
2. If you do go into compression, understand how the computer is telling you to make a safe ascent.
3. Follow those instructions.
4. To plan for the next dive, use the computer's dive planning function to tell when you have had sufficient surface interval to do the next dive to the depth and time you intend.

If you have watched over a dozen courses and never heard a thing about deco mentioned, then you need to report that instructor for violating standards. How are students doing on the questions on the final exam? Are they told to ignore them?

 

[halocline]

I think that was the thinking behind the movie Reefer Madness that we were forced to watch in high school to scare us away from the absolute terror of marijuana usage. Of course, when we learned the truth, it made us discount any later warnings about drugs as meaningless scare tactics.

So what you're saying is, if you find yourself on a recreational dive accidentally in deco, smoke a joint at the safety stop and everything will be okay.

An example of how some SB conversations go.....


On a more serious note, this is a good thread. I am sometimes amazed at the differences in the way suunto and oceanic computers calculate off gassing credit. They can't both be right. On some dives I've been with a buddy that has a suunto, he's slipped into deco while my aeris is happy as a clam. It's enough of a difference so that computer choice is a relevant factor in the topic of this thread. Meaning, I'd be more willing to violate a suunto by a few minutes than I would a more liberal computer.

I also think that a basic understanding-basic- of compartment models is very useful to recreational divers. An extended stop at 10-15 ft can be very effective for clearing out the faster compartments which are often controlling on recreational dives. Not always, but often.

 

[Tigerman]

So what you're saying is, if you find yourself on a recreational dive accidentally in deco, smoke a joint at the safety stop and everything will be okay.

An example of how some SB conversations go.....
...

Problem is I never get that damn thing lit up - any ideas how I can rectify that?

 

[victorzamora]

Let me sum up what I feel people are saying, which is what the PADI course has taught for several years now:

1. Don't plan to go into decompression.
2. If you do go into compression, understand how the computer is telling you to make a safe ascent.
3. Follow those instructions.
4. To plan for the next dive, use the computer's dive planning function to tell when you have had sufficient surface interval to do the next dive to the depth and time you intend.

....and that all makes sense. I was just saying that by putting a penalty on breaching NDLs (and therefore training limits), it might motivate divers to be more vigilant. By making it self-imposed, you keep it from being a huge deal. By making it just "time to offgas" you allow the more experienced divers to make their own decisions.

If you have watched over a dozen courses and never heard a thing about deco mentioned, then you need to report that instructor for violating standards. How are students doing on the questions on the final exam? Are they told to ignore them?

Mostly guessing and then being quickly corrected. However, I was only there for a few tests.

 

[waterpirate]

JImminy Christmas!

What happened to make a safe and controlled ascent.

For this extra special person you are portraying, I read safe as doing what the puter tells you. If you do not do what the puter says, you are clearly unsafe and sloppy. I also will point out that the list for rec divers I provided is not a chinese menu. If you accept one premise you must accept them all. That brings to bear the redundancy of your mandated buddy's brain. If you dismiss any one thing on my list it prompts immediate further training as you have allready made the decision to go beyond accepted safe practices for a rec diver.

Training now is wildly different than it used to be. We can not and should not go back there. My OW class test included working out a repetitive dive gone deco on the navy tables. That was pre safety stop. Now it is modular with speed bumps and clear lines that should not be blured as the corna copia of training is widely available. I would add one more item that is you should do the majority of your diving below your highest cert level. When that is no longer possible it is an indicator that more training is needed.
Eric

 

[Dirty-Dog]

On a more serious note, this is a good thread. I am sometimes amazed at the differences in the way suunto and oceanic computers calculate off gassing credit. They can't both be right. On some dives I've been with a buddy that has a suunto, he's slipped into deco while my aeris is happy as a clam. It's enough of a difference so that computer choice is a relevant factor in the topic of this thread. Meaning, I'd be more willing to violate a suunto by a few minutes than I would a more liberal computer.

I also think that a basic understanding-basic- of compartment models is very useful to recreational divers. An extended stop at 10-15 ft can be very effective for clearing out the faster compartments which are often controlling on recreational dives. Not always, but often.

This is an excellent point.
We were on Cozumel and the port had been closed by an El Norte. Around noon on the second day, they opened it. The good folks at Aldora called to see if we wanted to head out (duh!). So off we went.
We had a great first dive. During the SI, it was obvious that daylight was going to become an issue, since we'd started diving late and were doing longish dives. Twilight wasn't a real problem, since everybody had a light, but the group didn't really want to do a night dive (I'm kind of a fanatic about lighting, and always carry at least two on a night dive).
Profiles:
1st Dive: Santa Rosa Wall, 1:02 run time, max depth 84FSW
SI: 60 min exactly.
2nd Dive: Tunich, 57:20 run time, max depth 74FSW
We had been diving the day before, but in cenotes with a max depth of less than 30 feet.
I can provide the details of the profiles if needed.
The point is that on these dives, I was wearing a Suunto Stinger as my primary computer, with an Aeris XR1NX as backup. And 36 minutes into the second dive, at 59FSW, the Suunto had me in deco while the Aeris was happy as a clam. I knew the Suunto was ultra conservative, and I knew this was likely to happen. I had about 2200PSI left. I have no deco certifications, but I am also not an idiot. I could have just chosen to dive the Aeris. I let the DM know I was in deco, spent the next 3 minutes ascending to 40 feet (which did not clear the deco), stayed at 40 feet for 5 minutes, then ascended to 15 feet, where I shot a DSMB and hung around for the 10 minutes of deco the Suunto said I stilled owed, plus couple minutes more.
Again, the Aeris was happy as a clam throughout. But it's a console, and I prefer a wrist mount, so I didn't want to lockout the Suunto.
I've since replaced the Suunto with an Aeris Manta.

Those who reflexively decry anybody without formal deco training incurring even a light deco obligation will no doubt be bothered by my doing so. On the other hand, they wouldn't be at all upset if I'd simply ignored the Suunto and dove the Aeris.