NDL

[Charlie99]

biscuit7 once bubbled...
P.S. My built in level of conservatism means I get all wobbly if I see my NDL time approaching 10 minutes. [/B]

This IS a thread on NDL's, so I'll comment on your p.s.:

If you want to maintain a constant level of conservatism, then you shouldn't be aiming just for 10 minutes minimum NDL. 10 minute NDL at 120' means you have just gotten there, are lightly loaded, and upon ascent (at a reasonable rate!) you will "regain" a lot of NDL time. On the other hand, 30 minutes of NDL at 40' would be very heavy loading, and if using the PADI RDP that would even invoke the special rules mandating minimum SI times.

A crude method to set personal limits might be to set an NDL limit that is a constant fraction of allowable clean diver NDL for that depth, or perhaps to just to go roughly the same fraction down each depth column on the PADI RDP. I.E., 7 min NDL at 100', 12 minutes at 80', 30 minutes at 50', and 60 minutes at 40' are all roughly the same level of conservatism (around 85% of M-value in the medium speed tissues)
Perhaps this is a bit obtuse, but the most basic message is that allowing no less than 10 minutes NDL is conservative while deep, but it is not at all conservative while shallow.


Charlie

 

[wreckchick]

Charlie99 once bubbled...
This IS a thread on NDL's, so I'll comment on your p.s.:

If you want to maintain a constant level of conservatism, then you shouldn't be aiming just for 10 minutes minimum NDL. 10 minute NDL at 120' means you have just gotten there, are lightly loaded, and upon ascent (at a reasonable rate!) you will "regain" a lot of NDL time.

Correct, but I'm also not going to diving to 120' on air because the safety margin is so thin and there is no room for error at that depth and I'm risking pretty noticeable narcosis at that depth.

On the other hand, 30 minutes of NDL at 40' would be very heavy loading, and if using the PADI RDP that would even invoke the special rules mandating minimum SI times.

The tables have that dive ending in pressure group W and there are minimum surface intervals if there are 3 or more dives planned that day. I do see your point on this one, but it would also mean that my air supply lasted for a 110 minutes which is unlikely in my case.

A crude method to set personal limits might be to set an NDL limit that is a constant fraction of allowable clean diver NDL for that depth, or perhaps to just to go roughly the same fraction down each depth column on the PADI RDP. I.E., 7 min NDL at 100', 12 minutes at 80', 30 minutes at 50', and 60 minutes at 40' are all roughly the same level of conservatism (around 85% of M-value in the medium speed tissues)
Perhaps this is a bit obtuse, but the most basic message is that allowing no less than 10 minutes NDL is conservative while deep, but it is not at all conservative while shallow.


Charlie

You make a good point and I will take that idea into account when I'm planning repetative dives and work the same kind of calculations into my plan for the day. I hadn't really thought about it in those terms before.

My point about the 10 minutes was that this thread discusses riding the fine line between a dive that is within NDL and one that exceeds them. If I see 10 minutes on my computer (and I don't really unless I'm rather deep), I know that I need to get up and out of there because for me that's not giving me the time I need to feel like I can appropriately react to a delay in ascent.

One of the points that's been made in this thread is that appropriate air supply should play a larger role in a dive plan that NDL alone. If I ride my computer to the edge of the NDL at 40', I'm out of air, on a first dive. On repetative dives with or without appropriate SI time, that balance shifts to make the NDL the controlling factor on a dive.

Rachel

 

[MikeFerrara]

biscuit7 once bubbled...


I think both of you are wrong. Not only is a mistake to take a diver to a deep(ish) wreck with a single AL80 and a computer, but it's also a mistake to tell a newer diver that getting the deco training and learning to dive with doubles makes them safe for extended periods of time at depth. That diver is just as at risk if they have a problem at 100' within the NDL and make a direct ascent or has to do emergency deco as the new tech diver with doubles and a plan they blow off because they freaked out when something unforeseen happened.

[/B]

You're missing my whole point. I'm not tell any one to go into deco. All I'm saying is that they should have enough gas to do a dive (including contingency gas) and they should understand all the issues, including decompression. When I say that a diver should understand decompression I'm not saying they should intentionally incure a decompression obligation or enter any kind of overhead at all. I am not saying that they should seek technical training. I'm saying that they should understand the decompression issues as they pertain to the dive they are doing or want to do.

Just so I'm plain enough...When I say decompression, in the context of this thread, I'm not refering to multi-gas staged decompression diving. I am refering to the decompression we all do anytime we ascend from any dive

 

[Diver0001]

MikeFerrara once bubbled...


<snip>
I got the impression that some of you objected to the subject in general or the idea that the average diver should be encouraged to learn something about decompression. Maybe I misunderstood but that was the impression I got from roturners first post and yours that followed. <snip>

I was afraid that's what you made of it.

The truly apathetic puddlestomping public isn't represented here so I sometimes throw these things into the discussion to shake things up and make people realise that most divers (ie the majority of people getting training) aren't like the ones reading this forum. That you thought I was objecting to the subject in general is understandable but it wasn't the effect I was going for. I was counting on you knowing me better by now..... oh well.... I'm obviously not leaving the impression I thought I was....(either that or I play the devil's advocate better than I thought).

As it is, I believe, as does biscuit7, I think--otherwise she wouldn't be here--that you're much better off knowing it. The reality is, however that insisting that everyone should be interested isn't realistic. You know this. I know you do. Training divers in today's world is searching for a balance between principle and pragmatism. It's easy to say how the world should be when one is behind a keyboard but it's a very different matter when it comes down to practical in-water training sessions on very short timelines. You have a very short time to make the really important stuff stick. Remembering the NDL and forgetting the rest is one symptom of this.

Getting to the point. If there is something I object to then it must be " judging " the puddlestompers for being what they are. They are what they were trained to be, on the one hand, and they are what they want to be on the other. The most you can do is make them aware of what they don't know and try to get them warm for learning it. If they don't want it I believe it is on everyone else to be more accepting of that fact. What I see a lot is an arrogance towards puddlestomping and I find it, well, shameful and hypocritical to consciously train people to be puddlestompers and then moan about the fact that this is what they become. I don't mean you personally but it's a theme I see over and over on the forums.

As for pushing people to think " technically ", as it were: Aside from those who don't care and those who don't want it there is also a big group of those who think technical diving is cool but don't have the discipline to do it right. Doing it 1/2 (realising that the NDL is not a hard boundary but then going into the mist the way Seajay did) is worse, in my opinion than not starting on it, or even being somewhat afraid of it. I personally can't quite get past the thought that if someone as skillful, knowledgeable and experienced as Steve Bermen can make it go snafu then it's just too risky for most people to be experimenting with. I believe that they're better off instead riding their computers and " sharpening the saw " they were given--if you follow. If everyone just really learned what they were given in OW then the world would be a safer place. They don't need to become tekkies for that.

And--to go off on a completely new tangent--that's not to mention some of the tech-wannabe fads like....well....er.....never mind. " Tech " thinking has never been more popular and the potential for mishaps so great as it has been since people can take a tech-wannabe class, learn deco-for-dummies, strap on their if-I-just-wear-this-then-I-can-never-die twin-set, spew arrogant nonsense in the direction of puddlestompers and trot off proudly to jump tall buildings in a single bound. It's an absolute tribute to--in particular--some of the rapidly growing agencies that they've managed to keep the body count down (or quiet) as long as they have. The BSAC hasn't been so lucky. DCI accounts for 30-odd% of all their incidents and blown deco is growing rapidly among their members. On the surface it almost looks as though they're teaching deco procedures instead of water skills. And talking about failing to teach water skills, PADI is set to get seriously in the tek-wannabe game now too.....which gives me the heebiejeebies given the quality control problems in the rec-programme..... All this is to say that I'm not at all convinced that a progression towards " tek " diving is going to land well in the mainstream or that it somehow represents a panacea for safety. I have serious reservations about this assertion even *If* we were to accept that it was all going to be taught right and everyone was going to learn it and apply it.

R..

 

[MikeFerrara]

Diver0001,

You are of course right about many things. There isn't anything in your last post that I can disagree with. I just have a few comments.

I think that just as most drivers shouldn't be race car drivers I also think that most divers shouldn't get in to technical diving. I don't say that because I'm great and they're not. I say that because when there is a cieling you can't pass the game changes totally.

In my beginning I was ignorant to think I could "change things" just by offering something different. Later I realized that it wouldn't be that easy but isnisted on trying to the end. Now that the financial end is near I realize that most divers are getting exactly what they want. I'm no longer sure of my willingness to sacrifice my own financial well being to save those who don't wish to be saved. Every one in the industry is happy except me. LOL. The agencies, resorts and equipment manufacturers are giving the masses exactly what they want, a fast painless way to engage in underwater tourism.

Lastly, I don't believe that the situation is compatable with the recent boom in tech diving. There may be some real learning taking place. Just as I have seen divers used to diving under supervision get hurt when they venture out alone I think we may see new wave tech divers get an education the first time they dive without their tech diving DM. The divers that the current system puts out are not prepared for technical diving, IMO. It isn't a natural progression.

 

[SeaJay]

...But since the flames over at the *other thread* appear to be completely extinguished, leaving nothing to talk about (since the tech conversation came over here), I'll break my promise to mysef and open my pie-hole.

I've read this thread with a great deal of interest... And I haven't had to say anything at all because it all seems to be covered nicely. As soon as I think of a response, someone else posts it, saving me from getting flamed.

<crispy>

Alright, then... I have a question for y'all.

I've literally grown up on the water. I was born in a hospital room overlooking the same sound that my home butts up to now. Don't think, though, that I've been here all my life. I lived in New Jersey for a long time, and then Arizona... But I always came back home to South Carolina, and I know these waters like the back of my hand. I've fished and swam and played and skied and fished and swam again my whole life.

When I was seven I learned to water ski. That same summer I learned to sail and boat, and my mother - the consistent winner of a local regatta when she was a child - taught me to sail. I was a natural. At nine I won my own first regatta... Solo.

When I was eleven I got really serious about water skiing, and by fourteen I was competitive.

I first dove, uncertified, in 1986. I was 16 years old, and said "yes" to an offer from a certified buddy to go diving. He told me to "stick with him no matter what," and I did just that. It was an amazing experience.

Over the next decade or so I dove a few more times, but never really got serious with it. I had an interest, but you know... You just get carried away with your life.

A year ago I ran into someone who certified me... I took one of those two week PADI courses to become OW certified, and I excelled easily. Before my open water certification was in my mailbox, I was hooked.

AOW came a few months later, and I became a volunteer diver at the SC Aquarium. I dove whenever I could, and when I couldn't, I was studying information on shipwrecks and all off the 'net and in libraries. The summation of my work is on display on my website.

From AOW came Rescue, which involved First Aid and CPR certifications as well. My interest piqued about DIR, based on what I heard on this board, and I took the DIR-f course in February. It was a real eye-opener in a variety of ways, but it boiled down to this: I wanted to dive like my instructors dove. I've never seen anything like it, and for the first time in my scuba career, I wasn't able to do something that I saw them do. It was truly shocking at the time.

...So I got even more serious. I bought some gear and began to practice. I quit smoking. I changed my diet. I've got 200+ career dives now. In fact, I believe I'm somewhere up around 240, if you count the dives that I did before I was actually certified.

...So what's in the future? Well, I'm working on getting going on Divemaster right now. Nitrox is something that I'd really like, but with it's unavailability here, I don't know that it'd do me much good. However, as we discussed before, I understand that deco theory is taught in Advanced Nitrox, and so I might go in that direction.

Frankly, I had a long discussion with y'all about this just a few weeks ago... Where to go from here.

Now...

Me and my actions on this particular dive (I question whether or not I should have shared at this point) have been torn to shreds by the sharks on this board. I actually had my buddy from my local dive shop call me and ask me to remove any reference of him or his shop from my posts... So that he wouldn't be affiliated with me. How's that for a nice "screw you?" Thanks, bud. Apparently he felt that it wasn't in his best interest to be affiliated with me any more. Sad. Just sad.

Anyway, I've been really chastized for "diving beyond my training." PADI said many dives ago that I was ready for a dive to 100'... And yet y'all have totally chewed me for overdiving my training.

...So my question for y'all is this... When, exactly, do you think I would have been prepared for this dive? Divemaster? Tech III? Trimix?

Let's also make something clear here... I completely agree that there is a sort of arrogance on the board from those people who CLAIM to be ultra-certified and ultra-capable. However, I don't believe that anyone's pushed me to learn more, or pushed me towards lots and lots of certifications. It's been my own personal excitement level that has driven me, and I am somewhat miffed by people who think that I am just a follower listening to other people. Believe me, it's been my own deal to go out and seek more information. I've put in countless hours, lots of dollars, and tons of effort.

...So if I've got a hunger for information... And I don't have a problem retaining the information that I've got... And I'm diving my a** off and have a couple hundred dives in the past ten or twelve months...

Why all of the accusations of being such a newbie? Why does everyone here think that I'm some sort of dumbass, uneducated greenie who's got no business in the water?

Making a mistake in my last dive cost me an extra twelve minutes at a safety stop. That's really all that happened. I thought I might overstay, evidence of the thread a few weeks ago... But I was prepared to handle that if it happened. I fell back on my training.

I keep getting messages saying, "Glad you made it out alive." Well, I'm very flattered... Thanks. I'm glad I made it out alive, too... But I didn't have an OOA. I did not come close to death. I did not fizz or bend, and I did not have an airlift. I never had any of those things... Some of these messages are coming across like I had a near-death experience.

I overstayed my NDL. That's all. It was relatively anti-climatic. I even stayed the "optional" three extra minutes for a little extra margin of safety. I'm not trying to downplay my mistake... I'm trying to add a dose of reality here: Let's not lose perspective of this mistake.

Now, I'm not going to tell y'all that what I did was right. What I did was a mistake. As I called it before, I liken it to overshooting a turn in a car. Before I even got in the driver's seat, though, I knew it could happen, and so I made sure I was prepared. Of course I did not to mean to surface with 200 psi... But I did ensure that I surfaced with SOME psi...

...So let me ask y'all this... If PADI says that a couple hundred dives ago I was ready for a 100', non-penetration wreck dive, what authority do you have to say that I am not ready for that?

Especially since none of you have ever dived with me...

The "I can just tell" or the "well, I don't agree with your thought process" posts are the epitome of arrogance.

And that's the most disturbing attitude on this board.

Let me ask y'all this... Do you think you have enough guts to post your mistakes?

...And don't tell me that you have never made them. We know better.

 

[MikeS]

My impression from the limited information I have is that you didn’t understand the data from your computer and hence made bad decisions that resulted in going into deco mode. This is offered totally without animosity. In my admittedly limited experience, in over a hundred open water dives, I’ve yet to put my Cobra into deco mode; hope it works if I need it.

SeaJay once bubbled...
.. I overstayed my NDL. That's all. It was relatively anti-climatic.

No, it’s not that simple. You can’t go to confession, admit your sins and be forgiven. You crossed the line! Crossing the line meant that you no longer could simply pass Go and collect $200. You incurred a decompression obligation! The line is the point where a decompression injury was statistically insignificant if you went straight to the surface. You did this without forethought and appropriate training.

You faced the demon and won, this time!

That’s my opinion for whatever it’s worth. I’m glad you’ve shared since I’ve learned from your experience.

Mike

 

[Se7en]

SeaJay

If you have that sort of confidence and experience, then you probably are ready to start planning some longer dives.

Start off with some dives to the limit of your NDLs, but put together a deco plan for 10 minutes longer bottom time, including whatever level of deep stops and conservitiveness you are happy with.
Pick a SAC which is reasonable for you for that dive, and make sure you have redundancy. (ie make sure you have enough gas to surface and do deco, even if you loose your primary gas at the end of your bottom time). Plan your gas usage.
Find a buddy who is at least as capable as you are, and get them to develop their own plan for deco and gas usage. Make sure that either off you has enough gas to get the other back to the surface with all deco.

Dive your plan, using whatever tools you want

Analyse your dive. Did you hit your stops and runtimes exactly? Did you deploy a DSMB at the appropriate point. Did you hold your stops within a couple of feet?

If you did everything OK, then do it again. Once you go from able to get it right, to unable to get it wrong, then you are there.

If you can't plan a dive to say 130 feet for 20minutes bottom time, with bailouts and lost gas contingencies, then I'd suggest some training. Something like IANTD deep includes some minimal deco, and is a good way to start thinking about the important stuff.

Divemaster is not about learning to dive. It's about learning to help teach.

Mike

 

[Se7en]

To perhaps make you feel better SeaJay

Yes - I've put my computer into deco, with or without planning, on a single tank (no redundancy). I did it before I had a good idea of what my gas requirements were to meet my personal deco schedule, and I've done it since when I've known how much gas I needed. (I always use 20 litres per minute ~ 3/4 of a cuft as my SAC for these calcs. Lots of reserve).

Never been OOA. Never blown off any deco.

Some of the early experiments were like yours - a bit dumb. I'd like to think it was now a calculated decision.

And, FWIW, I dive twins most of the time now, and make sure I have heaps of gas, and the redundancy. I highly recommend it.

MIke

 

[wreckchick]

I said I wasn't going to post to this thread anymore either. I'm tired of being flogged by Mike Ferrara. But here I am anyway.

What I have to say is very simple: SeaJay, you did not make a mistake, you overstepped your training. Why was this not a mistake? Because you knew it could happen and when you had acquired enough information to believe it wouldn't kill you you went ahead and did it. You looked at your plan, you looked at your computer and you made a conscious choice to violate both. Why? My guess is because you thought in your head that you had enough information to live through the experience, and you did.

In the other thread you mentioned that the dissection of this dive and the flaming you took was denial of the other posters that it could happen to them. Anything can happen to anyone of us on any dive. That's a reality. Making good decisions all the way from our houses to the site into the water all the way through the dive back to the surface and back home again is what gives any one of us a more than substantial chance of diving again another day.

Your bad decisions started the day you decided to work up a contingeny plan "in case" you broke your NDL. Planning to accidently exceed it and then exceeding it does not constitute a mistake. It constitutes forethought and a plan to violate your training.

You could have done any number of things to keep within your limits. You could have decided that one dive that day was enough. You could have stayed on the surface for another hour. You could have understood your equipment better. You could have dove your plan. You did none of that and insist on calling it mistake. I respectfully disagree.

R