Recreational Scuba Deco Diving

[tursiops]

This seems like one of those e-mail conversations at work that start out rather innocently but just drift off without ever really making a key point or advancing the ball.

Five phrases come to mind:

1) Mission-oriented diving with primary, secondary and tertiary objectives

2) Right training

3) Right equipment

4) Right planning

5) Risk assessment

This toe-dipping, “light deco”, flirtatious approach to decompression seems like it amounts to a casual conversation starter on the boat for the SI (as opposed to a deliberate method to explore).

If I were Murphy, this is the dive I’d love to be on.

Call me a curmudgeon or snobbish but “no thanks”.

I have been rather in agreement with you, but I do think there is one slight wedge of value in this issue.
If you routinely run an algorithm on your computer that gives you much less NDL than other algorithms, then perhaps there is room for a "few minutes of deco" because you are probably still within the NDL limits of some other computer. So it looks like deco, but it might not be. In fact, it is just operating in that gray zone between "absolutely safe" and "absolutely requires deco nonmatter what computer you are using."

@scubadada posted this:

So if I set my computer on 35/75, have an NDL of 17 minutes, but stay at depth an additional 10 minutes......am I REALLY in deco? Not by DSAT standards. So I can see someone putting their deco toe in the water using this methodology. At least they get to see what their computer looks like when it says they are in deco and they can practice holding stops. But -- at least by DSAT standards -- they don 't have a real deco obligation, so their "soft ceiling" is just virtual.
In fact, some Deco Procedures instructors teach this way; you carry two computers, one set on Nitrox that is your "real" computer because you are using Nitrox, and one set on air. You dive watching the air computer. It goes into deco, you incur 5-10 minutes of deco (whatever you have worked out in advance with planners so on air you are in deco but you are still within NDL on Nitrox, which is what you are using for the dive. you do the dive, you get to see your computer go injto deco, you get to follow all the procedures for ascending, but you were never really in deco.
But this, of course, is not what the OP means. He wants you to incur an in-water ceiling without the tools, knowledge, or training to do that. Why would he do that?

 

[Edward3c]

In the bad old days, we only had Tables to plan diving with. If you were using Tables that didn't include mandatory deco information you would be very reluctant to exceed the no stop times. Such dives were planned with the required gas management. Cylinders were full at 160bar, until the new high pressure 207bar came out.

Today most computers will give you that get out of jail information if you wander into mandatory deco. This has enabled individuals who don’t do the gas calculations to cross the line between dives with no mandatory deco and those requiring such stops.

In most instances’ individuals get away with it, but the “normalization of deviance” sets in. Now its becoming an OK thing to do.

 

[rjack321]

In the bad old days, we only had Tables to plan diving with. If you were using Tables that didn't include mandatory deco information you would be very reluctant to exceed the no stop times. Such dives were planned with the required gas management. Cylinders were full at 160bar, until the new high pressure 207bar came out.

Today most computers will give you that get out of jail information if you wander into mandatory deco. This has enabled individuals who don’t do the gas calculations to cross the line between dives with no mandatory deco and those requiring such stops.

In most instances’ individuals get away with it, but the “normalization of deviance” sets in. Now its becoming an OK thing to do.

What tables didn't include a contingency deco stop? O maybe I should ask, what year was this?

At least as of the early 1990s, the PADI and NAUI tables had deco stop times if you go over by like 5 mins. I don't remember if they went for any stops longer than 5 or 10 mins maximum though.

 

[tursiops]

At least as of the early 1990s, the PADI and NAUI tables had deco stop times if you go over by like 5 mins. I don't remember if they went for any stops longer than 5 or 10 mins maximum though.

The PADI rules for "emergency decimpression" are still in force, and are printed on their tables. I think of them as the Rule of 3 and 5. Do at least a 3 minute safety stop if you within NDL. If you violate NDL by 5 mins or less, then ADD 3 and 5 and do at least an 8 minute SS. If you violate NDL by more than 5 minutes, then MULTIPLY 3 and 5 and do at least a 15 minute safety stop. Plus stay out of the water (in the first case) for 6h to offgas and monitor for DCS. In the second case, stay out for 24h to washout your N2 and really monitor for DCS.

 

[NothingClever]

...But this, of course, is not what the OP means. He wants you to incur an in-water ceiling without the tools, knowledge, or training to do that. Why would he do that?

With the quality of most training so diluted and the price tag for proper technical training often elevated, I get the temptation to flirt with decompression diving.

But to try to codify it with an abbreviation (RSDD) just seems dorky. I just don’t think we’re on the cusp of a new paradigm. Most folks either avoid incurring a virtual ceiling or get trained to safely deal with multiple ceilings.

@rx7diver - I’d probably love to have you as my neighbor, loan you my tools, loan you a car if your battery’s flat, close the lid to your rubbish bin and pull it up your drive...all those sorts of things.

But follow along with your half-pregnant approach?

Nah.

My available backgas scopes the dive or my dive objectives scope the required backgas....that’s just the way it is for me.

 

[rx7diver]

I’d probably love to have you as my neighbor, loan you my tools, loan you a car if your battery’s flat, close the lid to your rubbish bin and pull it up your drive...all those sorts of things.

But follow along with your half-pregnant approach?

Nah.

@NothingClever,

LOL. To be accurate, though, I am not attempting to promote or codify anything. I am simply attempting to learn something about what people actually might be doing. My OP is an enquiry.

As mentioned, I suspect many people are doing this. After all, diving this way is not new. And my own, current circumstances, not rare or unique by any stretch, suggest to me that many people are doing this: I live in a locale where obtaining EANx and oxygen is difficult. However, if I wanted to do a local air dive with air deco, I would plan it and do it. Simple. As mentioned, I would use independent doubles (because this is a solution that works best for me for the solo diving I likely would be doing).

I ''get" that some people would not consider doing this. And I "get", now, that some people would not admit here to currently doing this. And then, as always, you have the usual zealots ...

rx7diver

 

[Storker]

To the OP:

1. No planned deco. My tanks don't allow for the gas reserves needed for going into deco. I'm almost always gas limited rather than saturation limited.
2. Shore diving and boat diving in roughly equal amounts
3. Salt water
4. Buddy diving. Always.
5. Single tank, BP/W, long hose
6. Max 30-ish m, up to one hour
7. Typical activities: Sightseeing, photography and/or harvesting.

 

[Brett Hatch]

I have been rather in agreement with you, but I do think there is one slight wedge of value in this issue.
If you routinely run an algorithm on your computer that gives you much less NDL than other algorithms, then perhaps there is room for a "few minutes of deco" because you are probably still within the NDL limits of some other computer. So it looks like deco, but it might not be. In fact, it is just operating in that gray zone between "absolutely safe" and "absolutely requires deco nonmatter what computer you are using."

@scubadada posted this:
View attachment 632342

So if I set my computer on 35/75, have an NDL of 17 minutes, but stay at depth an additional 10 minutes......am I REALLY in deco? Not by DSAT standards. So I can see someone putting their deco toe in the water using this methodology. At least they get to see what their computer looks like when it says they are in deco and they can practice holding stops. But -- at least by DSAT standards -- they don 't have a real deco obligation, so their "soft ceiling" is just virtual.

I do not find this argument compelling. In the PADI rec courses I took, the instructions for how to use one's computer were simple: do what it says. When you put your GFs to 35/75, you're making an agreement to yourself to follow it. If you are willing to accept a higher risk of DCS, the right way to do it is to set your computer to a more progressive mode. From your chart, GF Lo of 45 yields similar bottom time to DSAT, so that's the obvious choice here. Or use a different computer.

Diving with a conservative computer and then arbitrarily adding bottom time and ignoring the deco ceilings "because you know better" is like trying to use a wrench as a hammer. Divers who don't have the training shouldn't do it because they aren't prepared to, and divers with the training shouldn't do it because it just doesn't make sense.

And look, I know you've been in the diving world for years, and already know this, and have taught it, and have fancy titles, so I'm not trying to give you a lecture here. But this seems like an important point to flag, misusing one's tools is a mistake.

 

[KenGordon]

I think you are finding that very often the first time people learn deco it is on a course that teaches accelerated deco (advanced nitrox) and that is how they think it must be done and anything else is madness. On the other hand there are people that learn deco as a progression from simple dives and who see deco and redundancy as slightly orthogonal issues.

Personally, I am much more scared of a free flow at 30m within NDL than running out of gas at 5m with 5 minutes of air deco owing.

edit tbc this is a reply to the OP two posts back.

 

[boulderjohn]

From your chart, GF Lo of 45 yields similar bottom time to DSAT, so that's the obvious choice here. Or use a different computer.

In making the chart, Tursiops just repeated the settings. He also understands enough to know that the setting of 45 for GF lo is meaningless on a recreational dive. So it is not an obvious choice at all, since it doesn't matter.

Diving with a conservative computer and then arbitrarily adding bottom time and ignoring the deco ceilings "because you know better" is like trying to use a wrench as a hammer.

Except that the computer gives you options, and you can use those options as you see fit, depending upon your understanding of the theory behind it. It is not like using a wrench as a hammer; it is like using a tool to its full capacity, which the novice is unable to do.

The computer section of the PADI course you took is very generic because it has no way of knowing what computers the divers will use. Not only could it not tell what features might be available in the computer you would use at the time the course was written, it had no way of knowing what features would be available in newer computers years later.