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

[DiveNav]

To OP. Nice post!

.... "figure out what your computer looks like when it goes into deco.....

In each of our online classes for model-specific dive computers we have a specific video that shows how a model-specific dive computer behaves during deco and explains what the diver should do.

Additionally, all our simulators include deco screens and alarms for all the model-specific dive computers we support (~50).

1 picture is better than 1,000 words. 1 video is better than 1,000 pictures. 1 trained diver is better than 1,000 videos.

Alberto (aka eDiver)

 

[Lorenzoid]

You know, when I joined the board, there was a frequent poster named Mike Ferrara. Mike said something once that has stuck with me. He said that, if he wanted to do a dive that would push recreational limits, he'd much rather plan it as an honest technical dive and take the gases and equipment to do it easily and safely, rather than plan it as an "edge of the envelope" recreational dive. It made a huge amount of sense to me. I got my technical training so I could do exactly that sort of dive . . . the one you COULD pull off with recreational gear and gases, but you'd be pushing it, have short bottom times, and see your NDLs count down into single digits. I do them on a light helium mix with a deco gas, and know I'm at the conservative end of what I can do with that setup, rather than being at the extreme liberal end of typical recreational diving.

If you want to push limits, go get some more training, and do it safely. Otherwise, plan your profiles so you aren't on the ragged edge.

This is something I have been thinking about. However, it's very common for dive ops to take a boat full of supposedly experienced rec divers to sites that could easily "push recreational limits," with the implicit understanding that although it's a challenging dive you are expected to stay within rec limits, not let your computer go into deco, etc. It would be great if I were to get tec training so that when I dive those wrecks in FL and NC I'm not "on the ragged edge," but I fear if I were to do so I would be severely limiting my choice of dive op to go with, since the majority of trips out to the wrecks I have in mind explicitly limit divers to traditional recreational profiles. I can imagine some dive ops would think it silly, wasteful, etc., if people wanted to do a 30 minute dive on the Spiegel Grove in doubles with trimix and no more than a few minutes of deco. Am I wrong? And what about elsewhere in the world? I've read reports of Truk liveaboards seriously pushing the envelope of "rec"; are there some that accommodate tec divers who want to dive pretty much the same profile as everyone else but just do it with the added safety provided by tec equipment and training?

That said, I have seen it done. There are ops in Key Largo that will mix rec and tec divers on a boat, with the rec divers doing a double-dip on the wreck while the tec divers do a single deco dive. I suppose such dive ops would be fine with a tec-equipped/trained diver's explanation that instead of a single long deco dive he plans to do two much more conservative dives. From what I've seen, I just don't think it's common to mix tec and rec divers on a boat, or to have a boat go out on which everyone is a tec-equipped/trained diver who plans to dive a more or less recreational profile. Or is it more common than I realize?

 

[tracydr]

I had never noticed that, but sure as shootin' there's one in there. 8min mandatory stop at 15ft for <5min over NDL. 15min mandatory stop at 15ft for>5min over NDL. It's pretty basic, and not NEARLY exact enough....but it's a good starting point, and absolutely better than running straight to the surface.

Edited to add: Minimum SI for <5min NDL breach is 6 hours, minimum SI for >5min breach is 24 hours....both as recommended by PADI's RDP. Check the RDP on the "reverse" side (repetetive dive side) for PADI's official wording.

There is a surprising amount of good-to-know information in the fine print of an RDP table. Or, on the eRDP.

---------- Post added January 22nd, 2014 at 11:13 AM ----------

A few weeks ago I took my 15 yr old on a dive with a 135 ft max depth. He stayed up around 120 or so I think. We were using computers (and nitrox) and we went a little into deco. We each had a pony bottle. We had not really planned to put him into deco and for some reason his computer showed more deco than me... maybe 6 minutes. He had an aluminum 80 tank.

It was no big deal really, but it did show me a problem with my somewhat causal attitude about teaching him this stuff (he was issued a PADI Jr. Diver card several years ago). Normally, I am pretty casual about safety stops and I generally lead and he follows and he often will stay 5-8 feet below me on ascent and on the hang. He can control his level easily (if he cares), but I've been pretty casual about it, I guess.

So we get up to the stop at 20 ft (a slow ascent has not reduced our deco time)and I have a reel and a float, so I have it easy, I just dump air from the BC, get heavy and hang down from the float with no need to pay attention to depth, since I am effectively tethered at the desired depth. Well the kid keeps sinking down and hanging like 5 ft below me. I signal to ascend a little and he does, but then 30 seconds later he is 5 ft below me. I quickly loose patience with him on this and my signals get more frantic and intense, and he still doesn't seem to "get it" that I want him hanging RIGHT with me at the desired depth. In retrospect, I should have handed him the float and that would have fixed his deco stop depth.

He now understands that when we do a "real deco" dive, he needs to be a little more precise in his drift diving deco stop depth precision. On the boat, I explained that the scubaboard Nazi's worry about holding stop depths to less than a foot and they seem to make it into some sort of competition.

So the precision of the stop depth is something that may be a little different for a recreational versus technical diver.

Please, take this advice with a grain of salt, its JMHO, as a physician with some extra knowledge of disco science. I'm by no means a trained dive doctor and am just beginning my tech career.
I'd be curious to see in 10-20 years if the agressive diving your son has done from an early age effects his bone development. I would be very reluctant to dive this aggressively with a growing adolescent, with soft growth plates. I'm sure he is a "Guinea pig" in a science project, since there can't be that many children with this type of diving experience. Not something I would want my grandchildren to experiment with. Most likely he'll be fine but there's a slight chance that he won't, especially if he has any genetic predisposition to blood clots, which significantly increases the risk of dysbaric osteonecrosis.
At the very least, it would probably be beneficial to review the literature on diving in children, to see if anything has been published on it. Check the Rubicon Foundation for literature. Or, check with a good dive doctor, who should be familiar with the literature.
The other thing is that teenagers don't usually have the mental maturity to focus on things like decompression stops, which your son has clearly demonstrated in a couple of posts. Plus, he obviously hasn't had proper training on holding accurate stops, which should be practiced on shallower dives without a deco obligation, until accurate. Plus, most young people, particularly boys, have a complete lack of sense when it comes to mortality. I know that I was "immortal" until I was 25-30 years of age and I'm female. Males tend to develop this sense later than girls.
I guess, what I'm saying is that if he were my son, I'd wait to do these types of dives until his bones are fully developed and he's shown some serious maturity, ability to pay attention to details and skill in holding stops.

---------- Post added January 22nd, 2014 at 12:26 PM ----------

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

Brownies or pot butter?

 

[Tigerman]

Mmmmm *droool* brownies

 

[tracydr]

This is a great thread. Too bad it's in the advanced folder, this is a good thread to be read by newbies too.

I ran into this exact situation on my second (or third??) dive trip. I was diving on a rented computer, and was diving very aggressively...and didn't understand that my computer was telling me to get the h%ck up into shallower water. So as a reward, I had a 6 hour ride in GC's lovely gas tank. I am ridiculously conservative now, own two computers, but have always worried what a deco stop (on my Sunnto) looks like in real time. You can read the manual all you want, but at least for me, it doesn't stick until I see it live (trust me, this foilable isn't just in diving, either).

The 'double computer fake deco' is an excellent idea. It's on my list for my next trip. Also, an excellent reason why a computer should be one of your first purchases!

Too bad we can't move this to the newbie section...it would be a great one for a lot of us 'pretty fish' divers to read.

Try the free online classes for your computer. They're really good. I think there is a post mentioning the classes right before this post.

 

[boulderjohn]

This is something I have been thinking about. However, it's very common for dive ops to take a boat full of supposedly experienced rec divers to sites that could easily "push recreational limits," with the implicit understanding that although it's a challenging dive you are expected to stay within rec limits, not let your computer go into deco, etc. It would be great if I were to get tec training so that when I dive those wrecks in FL and NC I'm not "on the ragged edge," but I fear if I were to do so I would be severely limiting my choice of dive op to go with, since the majority of trips out to the wrecks I have in mind explicitly limit divers to traditional recreational profiles. I can imagine some dive ops would think it silly, wasteful, etc., if people wanted to do a 30 minute dive on the Spiegel Grove in doubles with trimix and no more than a few minutes of deco. Am I wrong? And what about elsewhere in the world? I've read reports of Truk liveaboards seriously pushing the envelope of "rec"; are there some that accommodate tec divers who want to dive pretty much the same profile as everyone else but just do it with the added safety provided by tec equipment and training?

That said, I have seen it done. There are ops in Key Largo that will mix rec and tec divers on a boat, with the rec divers doing a double-dip on the wreck while the tec divers do a single deco dive. I suppose such dive ops would be fine with a tec-equipped/trained diver's explanation that instead of a single long deco dive he plans to do two much more conservative dives. From what I've seen, I just don't think it's common to mix tec and rec divers on a boat, or to have a boat go out on which everyone is a tec-equipped/trained diver who plans to dive a more or less recreational profile. Or is it more common than I realize?

I understand your problem. If you want to do some light deco diving and are certified to do it, you can have a very hard time finding the opportunity. Many trips seem to be all basic rec or all serious tech, and it's hard to find that in between slot. But it can be done. A lot depends upon the operator and how you prepare ahead of time. Here are some examples.

1. I have done mixed tech and rec trips in Cozumel. I sought out an operator who does this sort of thing regularly (Deep Exposure), made contact well ahead of time to explain my purpose, and worked out a plan. In this case, it so happened that this was my first trip after recovering from pretty bad injuries, so I wanted to ease my way back. I therefore experienced it all. I did some pure recreational diving, then I did some diving with tech gear and some light deco, and then I went full tech. No problem.

2. I have gone on trips in south Florida that were pure recreational other than me and my teammates. The boat crews knew our credentials, knew what we were doing, and were fine with it. We just had to be aware of their dive schedule and not interfere--no 90 minute run times.

3. Yes, some operators will set up a mixed trip, where the tech people do one really long dive while others are doing two dives. I haven't seen that often, but I have seen it.

4. I stay in South Florida for at least a month every winter. The dive operator nearest my condo will do pretty much anything you want provided you make the arrangements ahead of time and have a minimum number of people (not that many) committed to it. They will put your plan on the schedule and see if anyone wants to join. I am sure some other boats will do something similar.

5. In some areas you can get on a mailing list or Meetup group of like minded people who can put together enough people to get an entire boat at no great cost.

6. Yes, In Truk Lagoon you can do deco dives.

7. I put this one last because it is controversial. There was a recent death on a wreck in which two divers had penetrated well into the wreck, using a reel and line for guidance, which is technical wreck diving. The one bringing out the reel didn't make it. The dive briefing before the dive had made it clear that there would be no penetration, and the thread about the death started off with the idea that they had violated the rules. It turned out that the dive operator knew they were going to do that, figured they were good enough to do it, and had let them know that the "no penetration" rule did not apply to them. The problem was that they were neither properly trained nor equipped for that. The story is a good example of why a little learning about tech is a dangerous thing. Either get the full training or stay away. On the other hand, if they had been properly trained and equipped, they probably would have been just fine.

I think the overall lesson is to scout ahead, make some phone calls, and find out what options you have.

 

[tracydr]

An "algorithm" sounds very scientific, but don't confuse precision with accuracy. They are all compiled by reverse engineering incidence of DCS into mathematical formulae.

But as everyone knows there are huge random elements you cannot account for. Anecdotally people tend to get "skin bends" before they get "joint bends". But there are any number of incidents where people have had joint bends without any skin presentation. Similarly "the chokes" is pretty rare, but again, has been known to occur without other symptoms presenting. If the rate at which tissue absorbed and off-gassed was linear, that should never happen - symptoms would always present in order. But they don't. There is simply a randomness to incidents of DCS that we can't fully account for. Hence algorithms which are designed to be a "best guess".

Actually, skin bends is sometimes felt to be a light type 2 hit. ( bad). It's also been correlated with PFO, especially if it occurs as an "undeserved" hit.with PFO the diver is more likely to get type 2 hits. Also with PFO, hits are more likely with exertion after diving. Since 10-25% of the population has PFO it makes sense to limit exertion aftermore aggressive dives. There are two, maybe three types of skin bends. Some more serious than others.
Here's a good article on skin bends by Natalie Gibbs:
http://scuba.about.com/od/divemedic...-Form-Of-Decompression-Sickness-In-Divers.htm

 

[Lorenzoid]

I understand your problem. If you want to do some light deco diving and are certified to do it, you can have a very hard time finding the opportunity. Many trips seem to be all basic rec or all serious tech, and it's hard to find that in between slot. But it can be done.

Thanks. I don't have immediate plans to seek this route, but it did occur to me, and it also occurred to me that there is some irony to it. That is, we are so often cautioned to maintain a margin of safety by not pushing NDLs, yet it's apparently not easy to find a dive op that advocates using tec equipment and methods to err on the side of safety on dives that are (barely) within recreational limits. You have to make some effort. I'm encouraged to hear it is not THAT difficult to arrange.

6. Yes, In Truk Lagoon you can do deco dives.

What I meant was that I suspect the most frequented dive ops will tell you they are rec-only, and that I suspect it would take just as much (or nearly as much) effort to arrange to dive in tec gear (doubles, trimix, etc.) with them on a rec-oriented trip as it would anywhere else. I mean, I'd be happy to dive essentially the same profiles that I see in rec divers' trip reports on Truk, but I think it would be a great idea to do it on helium so that I actually remember what I saw at 130 feet. I'm sure there are dive ops and liveaboards that are geared toward tec divers, but that's not what I'm referring to.

 

[Tigerman]

In the red sea I do see "rec boats" bringing tec divers.
They usually go in a bit before the rec divers and comes up after us or just before us, depending on their profile, making their tec dives about 1,5-2 hours..

 

[scubadada]

Many of us do to light deco (<10 minutes?) quite frequently. Personally, I have a redundant air supply to cover the obligation. I'm disappointed that so many SB posters are so inflexible in their thinking.