Exceeding the NDL during recreation diving

[chrisjur]

I have always interpreted that warning during the briefing as meaning "if you go into deco and don't clear it." In other words, if you surface with an omitted deco obligation. Which makes sense.

The recreational boats I dive are very clear about this: Don’t go into deco. If you do on your first dive, you will not be allowed to continue to your second (or third) dive.

The purpose of this is fairly straightforward: To stop people who are not properly trained in decompression procedures from getting hurt. Many rec divers wouldn’t even know what their computer is trying to tell them if it goes into deco, and others might not even have computers that support deco stops.

Never mind basic things like whether you’d have enough back gas to meet your deco obligation or whether you have proper redundancy if something went wrong during a required deco stop.

 

[Pbdiver84]

The recreational boats I dive are very clear about this: Don’t go into deco. If you do on your first dive, you will not be allowed to continue to your second (or third) dive.

The purpose of this is fairly straightforward: To stop people who are not properly trained in decompression procedures from getting hurt. Many rec divers wouldn’t even know what their computer is trying to tell them if it goes into deco, and others might not even have computers that support deco stops.

Never mind basic things like whether you’d have enough back gas to meet your deco obligation or whether you have proper redundancy if something went wrong during a required deco stop.

Then you get things like BSAC divers, who are trained and certified for limited deco on single cylinder back gas.

 

[crofrog]

Whether you allow yourself to go into DECO or avoid it, and thus shorten virtually every single dive you ever do is completely up to you and your level of risk tolerance

What were your identified risk factors and mitigations?

 

[lowwall]

I set my computer for the least conservative setting, and then simply stay away from the limit by getting shallower well before NDL hits 1, stretching time shallow, and making a very slow ascent from safety stop to surface.

I do this because I want to know the real limit in case something happens that would make me consider pushing it. For example to help another diver in trouble.

I think that's a lot safer than being in the same situation with a more conservative setting where I know that I'm reasonably safe going somewhat beyond the limit displayed, but being forced to guess where the real limit is.

 

[chrisjur]

Then you get things like BSAC divers, who are trained and certified for limited deco on single cylinder back gas.

Yeah that is kind of weird. But I don’t have any issues with that if people are trained and it’s planned.

Actually, a PADI Tec 40 cert allows for up to 15 mins of deco on single cylinder back gas, but does require a bailout. So yet another variation.

 

[Nick_Radov]

The conservatism settings on some dive computers such as Garmins are a bit confusing or mislabeled. Using a lower GF Low % isn't necessarily more conservative. If you exceed the NDL then it will increase the depth of your first deco stop relative to the nominal ZHL-16c algorithm. But more recent research indicates that maybe isn't safer from a DCS standpoint.

Gradient Factors in a Post-Deep Stops World

World-recognized decompression physiologist and cave explorer David Doolette explains the new evidence-based findings on “deep stops,” and shares how and why he sets his own gradient factors. His recommendations may give you pause to stop (shallower).

indepthmag.com

 

[happy-diver]

As I carry an auxilliary bottle due to divers asking crew how is it that guy dives alone when nobody else does

I fill it with 50% and do not go out of my way to go into deco but breathe from it when I choose deco or not

Yeah, if I build it and own it, then I'm going to pump with it boost through it and breathe underwater from it

without paying some dude to show me

How's my fifty year old brand new CCCP 3phase electric lubricated with glycerine O2 booster

 

[tursiops]

You said this; my comments beneath your post indicate my concerns.

I am not tech certified but I do carry a 19 or 30 cf pony bottle, many or even most of my dives are solo.

I often exceed NDL limits and incur anywhere from a 1 to 10 minute DECO obligation, most of which is offgassed before I even get to the required stop depth which is always 10' for a minute or two.

In fact when I dived Truk Lagoon last year, I found that it's commonplace for recreational divers to go into DECO on almost every dive, due to the large steel tanks and depth of the wrecks and the numerous dives per day. The practice is certainly not discouraged by the dive charter we used for a week long liveaboard trip.

Whether you allow yourself to go into DECO or avoid it, and thus shorten virtually every single dive you ever do is completely up to you and your level of risk tolerance. Of course you need to have good gas management. You don't want to be in a situation where you've got a 5 minute DECO obligation but only 500 psi in your only tank.

Sure, dive charters will say "if you go into DECO you're done for the day" but as long as you clear your computer before you surface, they aren't going to know. Unless you're diving with an over zealous intrusive dive guide in which case you might have to dive more conservatively.

There's no PADI police down there.

• You are not tech certified; I assume that also means not tech-trained. You have presumably learned your deco procedures on your own, from reading. Do you know what you don't know?
• You refer to your 19 or 30 pony as a redundant air supply. Yes, for NDL diving, as taught in all solo courses which do NOT teach deco as a solo procedure.
• Good divemasters will usually know if you;ve gone into deco and cleared it before you surface, and will almost certainly know if you did an actual deco stop.
• You refer to an over-zealous dive guide.....so you are ignoring their responsibility for you during a dive.

This post also referred to the above post

Textbook example of normalization of deviance.

And received multiple Bullseyes and Likes.

You responding by saying this, which was actually a useful thing to say, but it ignores the fact that your knowledge and experience gained was on-your-own so possibly if not likely incomplete

Textbook example of gaining knowledge and experience and applying it to enhance the experience.

So I gave you a caveat rather than allowing you to say you had complete knowledge and experience.

Partial knowledge and inadequate experience.

Your response:

Do I know you? Do you know me and my level of knowledge and experience?

Didn't think so

Your posts say volumes about your knowledge and experience. You appear to be an untrained tech diver that assumes you know it all. Steinbil was right:

Textbook example of normalization of deviance.

 

[crofrog]

Not understanding the question.

As I said I carry a redundant gas supply and I have plenty of gas remaining to satisfy my DECO obligations.

When discussing risk tolerance, it's essential to first identify all possible threats that contribute to those risks. Risk tolerance isn't just about deciding what level of risk you’re willing to accept; it’s about systematically recognizing every potential hazard and developing clear mitigation plans. This process helps you fully grasp the scope of what you're dealing with, ensuring that you have accounted for every variable that could impact your safety.

Without a thorough risk assessment, simply having a redundant gas supply might not adequately address all potential scenarios. Identifying risks is the first critical step in understanding and managing your overall risk exposure.

1. Have you identified all potential failures that could occur during a decompression dive with a single cylinder and a small pony bottle? For example, how would you handle a situation where both your primary and pony regulator systems experience issues?
2. In your current setup, how many simultaneous failures can you realistically manage?
3. What’s your plan if you experience a high-stress situation that significantly increases your gas consumption during decompression? How does your current gas supply account for unplanned delays or increased workload?
4. What’s your plan if you’re delayed leaving the bottom dealing with a failure?

 

[tursiops]

Yes I have learned my deco procedures on my own, from reading and from experience. Is there something wrong with that? Does everything have to be taught be a real live person in order for it to be valid?

The question is of course, rhetorical.

What you've learned may be completely valid, depending on the source. There is a lot of quite incorrect info out there that should be ignored. . It is what you have NOT learned, or is incorrect, that may kill you.

You are saying that divers don't do DECO as solo divers? Wow who knew.

No, I did not say that. I said that Solo courses only teach NDL diving.

Good divemasters won't know if a diver has done a DECO stop if the diver is not under their supervision, which would be the case if they're diving solo. You really need this spelled out?

I referred to an overzealous dive guide, who happened to be below me on the line, I did not dive with this DM and was not under his supervision- as clearly explained in my post that you apparently missed.

I guess I do not understand. You are on the same deco line...but not under that DM's supervision? Was he a private DM for someone and not the DM for the group?