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

[pdhenry]

Your profile says you are not certified. Your comments seem to back that up.

OK, so help me understand my error. One advantage I may have is that I've read the PADI OW manual and several computer manuals within the past week.

The context of this thread is the rec diver, whom I assume is using a rec computer, and the point I was replying to was whether the diver on a computer had the same expected actions as a diver using a table. The RDP has the diver follow one of two decomp profiles depending on whether the NDL was exceeded by less than or more than 5 minutes. That's all it's designed to do. Since it's one size fits all (two, actually) the decomp from the RDP will be conservative. When the computer notes that an NDL has been breached it doesn't have to require the diver to follow Decomp A or Decomp B - it can adjust the decomp time and profile more finely than that and still provide a safe decomp. The ones I've reviewed will tell the diver that decompression is required, and will show the depth and duration of the first (or next) decompression stop. It's not as cookie-cutter as the table's dictates.

Training with Tables: An 8 minute decompression stop at 15 feet is mandatory for breaches < 5 minutes with no diving for 6 hours; a 15 minute decmpression stop at 15 feet is urged (air permitting) for breaches > 5 minutes with no diving for 24 hours .

Training with computers: Do what the computer tells you to do, including stop depths and times.

 

[Storker]

OK, so help me understand my error.

Recreational computers are far from ideal platforms from which to complete decompression.

Case in point: Post #176

The Suunto RGBM algorithm will give you some credit for normal type deco stops, but it'll still scream bloody murder if you go into significant deco, and the 3m stop will be longer than for anything else I've seen. For my own amusement, I did a comparison of the Suunto RGBM, the VPM-B algorithm (free Android version of V-Planner, +2 setting), the Norwegian Navy table and the US Navy table for a 120 minute dive to 18m/60ft. The differences were... shall we say "interesting"?:

Depth, m   US Navy   VPM-B    No. Navy   Suunto RGBM    Suunto + No. Navy
 0             0        0           0          0              0       
18           120      120         120        120            120       
 9                                  5                         5       
 6                      6.8        25                        25       
 3            26       28          30        111             97       
--------------------------------------------------------------------------
Total time   149      157         183        234            250

 

[pdhenry]

Go back and read the post I quoted:

Does the PADI computer-based course teach emergency decompression or not?

The answer is yes, it does, but it says (paraphrasing) "Your dive computer will tell you what to do; different computers will give different guidance." PADI still uses the term "emergency decompression" when a diver's computer goes into decompression mode, but the RDP decomp procedure isn't strictly directed when a computer is used. The OW manual even differs in its guidance regarding whether you should dive following an emergency decompression depending on whether not you were using a computer. Using the RDP you "must" not dive for 6 or 24 hours; using a computer a repetitive dive is "not recommended" (Version 2.11, Page 219).

So yes, it's taught, but since the computer isn't limited to the square dive profile assumption which drives the RDP the actions directed by the computer can vary with the actual dive profile.

I'm not sure what a 120 minute dive to 18 meters has to do with a discussion of a rec diver noticing that he's strayed a little over the limit but there you go - the rec guidance probably isn't very good when you stop rec diving. I'd offer that the RDP really isn't much better in that instance.

 

[scubadada]

Up front, I am not certified for Deco. But if the people who you feel are qualified to comment don't appreciate you "flexible" view of dive planning and others that are not certified for deco are not qualified to comment on what you as an uncertified deco diver are doing, why are you posting?

If you are not going to accept criticism graciously, why are you asking for advise? Feel free to argue your point, but don't complain about others being contrary. The point of the back and forth in the forums is so that ideas get tested. If you are right, stick to your guns and articulate why you are right. Don't blame the culture of SB if you feel that people are piling on to you. Do you need to have a cert for deco? No law says so, but people around here have questions about your understanding of the risks involved in doing deco with out having a complete understanding of the risks involved in these dives. A ride in a deco chamber will put a big dent in your wallet and a complete recovery is not guaranteed and if you really screw the pooch you can die.

Do what you want on a dive, but if you don't like the responses on SB you have 3 choices. 1) you offer a clear, articulate explanation of your views that clarifies your views and persuades others, 2) You ignore the advise of others, rationalize your actions and continue doing what you feel is safe. 3) You look at the opinions of an array other divers and consider them and then re-evalutate your dive practices... Just don't complain about people who take the time to ask questions and offer opinions.

Dive Safe

One tiny correction here. I'm the OP, and that's very much not what I meant nor is this what this thread was meant to be about. I just wanted to clear up that that is NOT my position at all.

Having said that, Scubadada has taken a more predominant role in this thread than I have as others with more experience than me have taken my side of that conversation. Andy, you definitely captured what HIS argument is as clear as day. Scubadada can dive how he wants, it's no bother to me....however I don't get his perspective as anything even approaching safe. He's attacked me as well as others for our online profiles not showing as many dives or as many certs as he believes necessary to have an opinion worth noting. My wife (just got AOW, no tech aspirations, <40 dives) truly believes that ANY deco is beyond what any rec diver should be incurring. I asked her what SHE would do if her computer went in to deco, and she responded with "I'd calmly ascend to like, 20ft or whatever the computer tells me. Then I'd go up SUPER slow from there, and be done for the day....because I'm NOT dumb enough to let that happen on accident, and if I let it happen on purpose it's because something went really wrong."

My point is that too many divers don't know what they don't know. A clear line *should* be drawn in the proverbial sand between Rec and Tec. Without the training AND equipment to do a dive safely, no amount of experience, hubris, or bravado will get you to the surface safely. Scubadada, the position you've taken is one of being bulletproof. "It can't happen to me. I'm better than that. I've done LOTS of dives." is simply NOT the attitude one should take as a Tech diver. I can tell you now I would've failed all of my Tech courses if I showed my instructor HALF of that attitude. I'm sure most/all Tech-certified divers can agree with me on this, but my Tech courses have shown me that no matter how good I am compared to the Rec crowd....I've got a LONG way to go before I become a "good diver" amongst the Tech crowd. That realization has kept me cautious, attentive, and always wanting to learn more and do better. It was a BIG TIME eye-opener, and I'm glad I had it.

Thanks so very much for your constructive criticism. I execute my extensively planned, occasional, light deco dives with great care. I fully accept the responsibility and risk of such dives. This is a personal decision that all of us must make. I'm certain that there are many other divers out there with similar behavior.

Good diving, Craig

 

[Ricky B]

I have a specific example of going over the NDL that seems to be within the scope of this thread. And it doesn’t fit neatly into the hypothetical facts that seem to be assumed in discussing the issue.

I was at Club Med in the Bahamas. Rather than have an insta-buddy, I chose to join a group with a divemaster guide (for an extra fee). There were five of us guest divers in the group plus the divemaster. It was on my second dive of the morning when my Suunto Zoop went into deco mode. I showed the divemaster the Zoop, and he understood that I was in deco mode. His computer (not a Suunto) was not in deco mode. My practice is to stay about five to ten feet above the divemaster for most of the dive so my computer going into deco mode was not because I was diving deeper than the group.

The maximum depth of the dive that went into deco mode (as far as the computer is concerned) was 92 feet and average depth was 45 feet. The duration of the dive was 53 minutes, including the mandatory 8-minute safety stop and the subsequent ascent. (The prior dive that day was to a maximum depth of 102 feet with an average depth of 52 feet and a duration of 49 minutes.) The water temp was 79 degrees, and I was wearing an exposure suit. It was a clear, sunny day, and the sea was calm

This was a boat dive, and there was a hang bar at 15 feet plus lines to hold onto. There were at least two regulators on long hoses up to the boat to provide additional air should one run out.

The club has about two dozen dive sites it takes guests to. I imagine that the club probably goes these sites hundreds of times each year and it has been doing so for many years. The club has its own hyperbaric chamber.

I have an AOW cert, have been a dive tourist for about 30 years (started diving in the days of J valves and no SPG), and do not mind switching regs underwater. I typically come up with more air than the other guests.

When my computer went into deco mode, what should I have done?

First, what actually happened. The divemaster indicated we should continue the dive, which we did. When it came time for the safety stop, I had an 8-minute mandatory safety stop at 15’ per the Zoop. I then surfaced slowly. The subsequent surface interval was 20 hours.

Here are the options. If you see others, let me know.

Option 1. I could leave the group by myself and go to the safety stop until the computer cleared me, perhaps extend it till my air was down to 500 psi, and then ascend to the surface. This seems unwise to me because then I am solo diving. Furthermore, while the viz was good, I don’t know that I could have found my way back to the boat and the hang bar by myself because I was depending on the divemaster for navigation. Once we were about a minute’s travel time away from the boat, it was not visible.

Option 2. The divemaster and I could leave the group, the divemaster could accompany me back to the boat, see that I get on the hang bar, and return to the group. This leaves the rest of the group unattended by the divemaster (for which they have paid), and maybe some will wander off. This also requires the divemaster to assume that I know how to use my computer, an assumption that the divemaster had no basis for making since he didn’t know me and we hadn’t discussed what knowledge, if any, I had of my computer.

Option 3. The divemaster calls the dive and the entire group returns to the boat. While this would clearly be the most conservative approach, I would be pissed if the tables were turned and my computer (and the divemaster’s) showed plenty of no deco time and I had plenty of air.

I realize that simply because no one else’s computer went into deco mode doesn’t mean that I was not incurring a deco obligation. The divemasters take turns diving so mine probably hadn’t dived the previous day. Maybe the others in the group hadn’t dived as often as I had (two morning dives each of the three preceding days) and even if they had, maybe their dive profiles were not the same as mine.

On the other hand, the Suunto is conservative, and the divemasters take these routes hundreds of times a year. Based on experience, they know that the standard dive is not going to present a problem. Furthermore, in years past, I would dive without a computer and simply rely on the divemaster to take us on a no-deco dive.

Option 1 was a non-starter for me. I am not about to leave the group by myself and try to find the boat. Option 2 was not under my control. Option 3 was technically not under my control, but by frantically giving the thumb up sign and seeming to freak out about going into deco mode, I suppose I could have induce the divemaster to call the dive.

So, should I have done what I did or something different?

 

[RDRINK25]

A dive to 64' 37 min on air. SI of 30 min then down to 40' for 60min my computer put me in deco. I didnt recognize it and stayed at 15 for an extra 5 min.

 

[DevonDiver]

RickyB:

If you're gonna ignore your planning/management method, I'd advise getting a second-hand RDP, or downloading the Navy tables... it's a lot cheaper and would provide precisely the same benefit.

DM is not god. Any incllnation to ignore your signal to surface merely indicates their professionalism and lack of experience. Don't do 'trust me' dives. DMs love for you to think they know it all. It's an ego thing. The biggest egos are often the least experienced, or worst DMs. NEVER abdicate responsibility to a DM.

Dive the way you were taught to do in training. Accidents happen when short-cuts are made. You are not currently diving like you were taught to. It's that simple.

Conservative is good. Let that be your mantra. You seem to make bad decisions or, at least, allow others to make decisions for you. You're better off with a more forgiving algorithm under those circumstances.

Another mantra... one used by higher-echelon divers... "Any diver can abort any dive, at any time, for any reason'. It is your right to preserve your safety. To do so outranks any other factor on a fat, dumb and happy tourist dive. This isn't a crucial Navy SEAL mission. You aren't saving the world from Armageddon. Enjoy seeing the fish, blow some bubbles, come up when you know it is safe and prudent to do so.

If you don't see that following your computer explicitly is safe and prudent, ditch the computer. Neither you... your DM.... nor your dive group are qualified or educated to second-guess the dive computer.

Don't allow yourself to start believing that short-cuts, compromises and complacency are the 'mark' of experienced diving. It's dumb diving. It's a fast-track to becoming a statistic.

In practical terms:

1. Decide your own time margin from deco - be prudent with that. The same way you keep a reserve of air, keep a reserve of no-deco time.
2. Signal the DM sufficient warning before you go into deco. That allows them to plan ahead accordingly (if you cannot do that, realize how ill-prepared you actually are)
3. Going into deco without the appropriate knowledge, training and equipment is an emergency. Treat it as one.
4. If you go into deco, signal that fact - with urgency - to your dive leader. If necessary, physically show them your computer and gas supply.
5. In deco, calculate your gas supply time versus your deco time. If you don't know how to do that, then assume the worst (and realize how ill-prepared you actually are)
6. If the dive leader doesn't react to that communication, then take steps to preserve yourself... ascend.
7. Do not assume that the dive leader knows better. Assume the worst of your divemaster and plan to look after yourself.
8. Try to ascend with a buddy, at least, rather than alone. But ascend alone if necessary (if that concerns you, realize how ill-prepared you actually are)
9. Do not ignore your computer. *An exception exists for those with Phd mathematics and photographic memory who can re-calculate mentally in real time.

 

[Basking Ridge Diver]

"I have an AOW cert, have been a dive tourist for about 30 years (started diving in the days of J valves and no SPG), and do not mind switching regs underwater. I typically come up with more air than the other guests.

When my computer went into deco mode, what should I have done?

First, what actually happened. The divemaster indicated we should continue the dive, which we did. When it came time for the safety stop, I had an 8-minute mandatory safety stop at 15&#8217; per the Zoop. I then surfaced slowly. The subsequent surface interval was 20 hours.

Here are the options. If you see others, let me know.

Option 1. I could leave the group by myself and go to the safety stop until the computer cleared me, perhaps extend it till my air was down to 500 psi, and then ascend to the surface. This seems unwise to me because then I am solo diving. Furthermore, while the viz was good, I don&#8217;t know that I could have found my way back to the boat and the hang bar by myself because I was depending on the divemaster for navigation. Once we were about a minute&#8217;s travel time away from the boat, it was not visible."

I have a similar background in diving J valves and no spg.

But for me - the one issue that I thought was most concerning about was "I don't know that I could have found my way back". This I would think with an AOW cert should be a given or the number of dives I am assuming you have since you started. For me, Deco obligation or not - I need to know how to get back to my starting point. If I feel like I am getting beyond that point I use a reel or I go back to familiar territory. If it is a reef or a wall you should not get lost but checking your bearing under water should be like checking your spg and computer.

Everyone is different but when it hits the fan - I want to know which way is out and I am gone.

 

[Lorenzoid]

RickyB, great post, thanks for sharing your actual experience. I have been diving Suuntos for a number of years, and as you have discovered, they are conservative. The options you laid out show you have really given it some thought. I don't know which option would be best.

What I do know is how to prevent that sort of thing from happening--that is, going into deco on an otherwise easy recreational dive. First of all, I rarely dive with an insta-buddy. On the rare occasion that my regular buddy has not been with me, I discuss in advance with my insta-buddy what we are going to do if I run out of no-deco time. I explain I'm diving a conservative Suunto, etc., and that it's not uncommon for me to have to ascend a bit when the no-deco time ticks down to single digits. If my insta-buddy refuses to agree to ascend with me when I signal to him, I tell the DM I can't dive with that person and why. (Actually, that has never happened. I have been lucky with insta-buddies.) Second (or maybe this is the same issue) I watch my computer so that I can monitor how fast it is reducing my no-deco time. As I said, if I see it going into the single digits, I signal my buddy that we have to ascend a little. Third, I recognize the idiosyncracies of the Suunto RGBM algorithm. Apparently, things that trigger the Suunto to add conservatism include multi-day diving, sawtooth profiles and reverse profiles. Knowing that, I do what I can to maximize the no-deco time the computer computes for me. For example, if I've been doing four dives a day for the past three days (or some such intense schedule), I take a day off in the middle of my vacation. The Suunto seems to love that. Avoiding reverse profiles is easy, as it's a common practice (though some have said the alleged benefits are unproven). Sawtooths are theorized to promote microbubble growth (okay, I'm getting over my head here, but it's my understanding that sawtooth profiles somehow trigger the Suunto RGBM algorithm to add conservatism).

In summary, by maintaining good buddy practices, monitoring my computer's NDL display vigilantly, and understanding my computer's deco algorithm, I have been able to avoid the kind of situation you found yourself in. Admittedly, I had a similar situation once, when my computer was new to me. That was my wake-up call.

 

[scubadada]

RickyB, great post, thanks for sharing your actual experience. I have been diving Suuntos for a number of years, and as you have discovered, they are conservative. The options you laid out show you have really given it some thought. I don't know which option would be best.

What I do know is how to prevent that sort of thing from happening--that is, going into deco on an otherwise easy recreational dive. First of all, I rarely dive with an insta-buddy. On the rare occasion that my regular buddy has not been with me, I discuss in advance with my insta-buddy what we are going to do if I run out of no-deco time. I explain I'm diving a conservative Suunto, etc., and that it's not uncommon for me to have to ascend a bit when the no-deco time ticks down to single digits. If my insta-buddy refuses to agree to ascend with me when I signal to him, I tell the DM I can't dive with that person and why. (Actually, that has never happened. I have been lucky with insta-buddies.) Second (or maybe this is the same issue) I watch my computer so that I can monitor how fast it is reducing my no-deco time. As I said, if I see it going into the single digits, I signal my buddy that we have to ascend a little. Third, I recognize the idiosyncracies of the Suunto RGBM algorithm. Apparently, things that trigger the Suunto to add conservatism include multi-day diving, sawtooth profiles and reverse profiles. Knowing that, I do what I can to maximize the no-deco time the computer computes for me. For example, if I've been doing four dives a day for the past three days (or some such intense schedule), I take a day off in the middle of my vacation. The Suunto seems to love that. Avoiding reverse profiles is easy, as it's a common practice (though some have said the alleged benefits are unproven). Sawtooths are theorized to promote microbubble growth (okay, I'm getting over my head here, but it's my understanding that sawtooth profiles somehow trigger the Suunto RGBM algorithm to add conservatism).

In summary, by maintaining good buddy practices, monitoring my computer's NDL display vigilantly, and understanding my computer's deco algorithm, I have been able to avoid the kind of situation you found yourself in. Admittedly, I had a similar situation once, when my computer was new to me. That was my wake-up call.

The relative merits of the available decompression algorithms are frequently discussed on SB. Most would agree all are safe, when followed, and there is not data to differentiate them. One way to avoid the situration described is to dive a more liberal decompression algorithm, of course, this is a personal decision, and not one that everyone is comfortable with. Lorenzoid's strategy is fine for him but not for me.

I never have the shortest NDLs diving my Oceanic computers rurnning the DSAT algorithm, but don't always have the longest either. I had longer NDLs before I switched from my Cochran computers to Oceanic.

Good diving, Craig