Terminology: "Required Safety Stop"

[daniel1948]

I hope this is the correct forum for this post.

In another thread, a question was raised as to why the PADI RDP states that the safety stop is "required" if a dive comes within 3 pressure groups of the no-decompression limit. The question is, If the safety stop is required, then is it not a decompression stop? And in that case, why is the dive called a "no-decompression-stop" dive? Doesn't the requirement to stop change the category of the stop from a "safety" stop to a "decompression" stop?

As a PADI-certified OW diver, I do not know if other agencies have the same ambiguity in their tables.

 

[rstofer]

Please note that I was corrected in the other thread. The 1989 version of the NAUI table does specify an ascent rate of 30 fpm. The 1987 version, to which I referred, specified a maximum 60 fpm. PADI still uses 60 fpm for the table and in their training manuals..

I would hope we can nail down the 'safety stop' as recommended versus required. It certainly isn't clear to me. The PADI table definitely says the safety stops within 3 pressure groups of the NDL are required.

Richard

 

[Captain CaveMan]

I'm not a instructor for Padi but will try to answer this the best I can.
Padi want to use the Safety stop as a way of making sure you keep your accent slow and steady. A nother reason is at 3ata your body is on gassing rapidly and a slow accent directly to the surface could make you bent. So a 3min safety stop was added in Safety to help off gas.
If you read the Padi non deco tables it say what to do if you pass your NFL time. If I remember correctly ( have not used padi tables in some time) it says to do a 8min stop at 15ft and stay out of the water for some time.

 

[drbill]

What is "required?" Keep in mind that what is actually "required" is a function of YOUR body and YOUR dive. Even the stops (deco or not) listed as "required" by tables or by your computer are based upon our best understanding and are not tailored to your specific requirements (since these cannot be easily assessed).

I am not a PADI instructor, but PADI's "requirement" for the 3-min non-deco "safety stop" is based on what is felt to be a safe practice for the majority of divers. As an agency they can "require" whatever level of safety margin they wish, both as a safety measure for divers certified under their program AND to limit potential legal liability should someone not follow that "requirement."

As an old fart with many decades of diving under my weightbelt, I personally "require" even more of a safety margin and always extend my stops whether they are recommended or "mandatory." Those are my standards.

 

[Walter]

IThe question is, If the safety stop is required, then is it not a decompression stop?

It is.

And in that case, why is the dive called a "no-decompression-stop" dive?

I don't call it that. As for PADI, everything is about marketing.

Doesn't the requirement to stop change the category of the stop from a "safety" stop to a "decompression" stop?

Yes.

As a PADI-certified OW diver, I do not know if other agencies have the same ambiguity in their tables.

They don't. You'll also find many agencies have more conservative tables than the RDP, especially when it come to repetitive diving.

 

[daniel1948]

All of this makes sense. But it does not address the question: Why don't they call it a "decompression" dive when they "require" a stop? Once the stop becomes required, it moves from being a safety stop to a decompression stop. No?

Obviously, they cannot actually require anything, because they have no legal authority. They create a set of protocols, and those protocols have recommendations and requirements. If you violate a requirement you have stepped outside the protocol, whereas you can skip a recommended safety stop without violating the protocol.

So the question is one of terminology: An NDL dive is one where you can safely ascend to the surface without a stop. A safety stop is recommended because it increases the margin of safety, but by definition you don't have to make a stop from an NDL dive.

So suddenly, three pressure groups from the "ND limit" a "safety stop" is required. But if it's required, they are saying you cannot safely ascend without a stop, and now, by definition, it is no longer a no-stop dive.

My question is not about safety. I'm going to stay well within all the recommendations. I'm always going to do my safety stops, and after all I've read here on Scoba Board I am going to extend them a bit. My question is about PADI's terminology. Why not call those required safety stops "decompression stops" and mark the no-decompression limit at the place where the safety stop becomes a requirement under the protocol?

Edit: I cross-posted with Walter. He posted while I was composing this post.

 

[Walter]

All of this makes sense. But it does not address the question: Why don't they call it a "decompression" dive when they "require" a stop?

I believe I did answer the question.

 

[nereas]

... with many decades of diving under my weightbelt, I personally "require" even more of a safety margin and always extend my stops whether they are recommended or "mandatory"...

As anyone thinks about offgassing gradients, this conclusion of Bill's is the only reasonable one that anyone can come to.

Young inexperienced divers are impatient and "want to get out of the water as soon as possible" and so they fret about what is optional or what is "required."

Experienced seasoned divers instead focus on what makes the most sense, and the most sense is not ending up in a recompression chambre. The best way to avoid this is to stop at 1/2 of your MOD for a 1 min deep stop, and then egress from there in 10 ft increments of 1 min each, until you reach the surface, for any "NDL" dive.

 

[TSandM]

Daniel1948, it's poor use of terminology, indeed.

What you are learning is that there is no hard and fast line between "no decompression" and "decompression" diving. ALL diving involves decompression; we all absorb nitrogen, and we all have to get rid of it safely. The deeper you go, and the longer you stay there, the more nitrogen you absorb, and the more important it becomes to execute an ascent strategy that minimizes the risk of decompression symptoms.

What you're taught in class can leave you with the impression that, if you spend 10 minutes at 120 feet, you can go straight to the surface with impunity, but if you spend 11 minutes, you can't. That really isn't true. There is a gradation of risk, as you go deeper or stay longer. At 30 feet for 40 minutes, you can probably take 30 seconds to get to the surface and never have any problems. At 150 feet for 40 minutes, using a 60 fpm ascent rate directly to the surface is going to get you bent. Somewhere between those two dives, there's a gray area where some people will get bent, some won't, some will on one day and not on another.

The purpose of tables and stops is to lower the risk of symptomatic DCS to an acceptable level (which varies with the model you are using). PADI introduces a "required" safety stop as a kind of acknowledgment that dives which push recreational limits on depth and time are safer if they are executed as a kind of "techreational" dive, with greater control of ascent and offgassing time.

The terminology "required safety stop" is bad, but so is "no decompression dive".

 

[daniel1948]

Daniel1948, it's poor use of terminology, indeed.

What you are learning is that there is no hard and fast line between "no decompression" and "decompression" diving. ALL diving involves decompression; we all absorb nitrogen, and we all have to get rid of it safely. The deeper you go, and the longer you stay there, the more nitrogen you absorb, and the more important it becomes to execute an ascent strategy that minimizes the risk of decompression symptoms.

What you're taught in class can leave you with the impression that, if you spend 10 minutes at 120 feet, you can go straight to the surface with impunity, but if you spend 11 minutes, you can't. That really isn't true. There is a gradation of risk, as you go deeper or stay longer. At 30 feet for 40 minutes, you can probably take 30 seconds to get to the surface and never have any problems. At 150 feet for 40 minutes, using a 60 fpm ascent rate directly to the surface is going to get you bent. Somewhere between those two dives, there's a gray area where some people will get bent, some won't, some will on one day and not on another.

The purpose of tables and stops is to lower the risk of symptomatic DCS to an acceptable level (which varies with the model you are using). PADI introduces a "required" safety stop as a kind of acknowledgment that dives which push recreational limits on depth and time are safer if they are executed as a kind of "techreational" dive, with greater control of ascent and offgassing time.

The terminology "required safety stop" is bad, but so is "no decompression dive".

Actually, I remember reading that rather than speak of "no-decompression" dives, we should speak of "no-stop" dives... except that with the recommended safetry stop, every dive deeper than 20 feet is a "stop" dive.

I also understood, early on in my study, that we take on nitrogen any time we go down, and the principal difference between so-called "no-stop" dives, and so-called "decompression dives" is the somewhat arbitrary (but relatively small) level of risk of surfacing without a stop that distinguishes the two types of dives.

I just think that once they "require" a stop, they should no longer call it a no-stop or a no-decompression dive. And unless someone from PADI comes along with a justification for the terminology they use, I am going to conclude that their terminology is misleading.

One of the local dive shops is SSI. I am going to ask if they have an SSI equivalent of the RDP, and compare the numbers.