Deco on Dives in Coz? Educate Me

[DandyDon]

Seriously? Or, are you just being facetious?

Oh it's $3/day if I have my own pc here. NOW she tells me.

If you'd like to, fine. I was just trying to discuss the minor risks of overdrawing NDL on a recreational Dive Computer for a small number of minutes - a low risk for those who understand and watch their computers well - my dive bud being an example of one who doesn't. I have a standing promised to his elderly mom to keep us both safe, but it gets challenging at times - we're both klutzes.

Everybody should also be aware that the algorithms in recreational computers are NOT designed to create a valid profile for staged decompression diving. Most recreational computers are not running that kind of decompression software (the X1 being an exception). They have simple fallbacks for exceeding NDLs, and the manual for the computer will warn you that the computer is NOT to be used to execute staged decompression diving.

Yep.

 

[FishOutUvH2O]

Oh it's $3/day if I have my own pc here. NOW she tells me.

If you'd like to, fine. I was just trying to discuss the minor risks of overdrawing NDL on a recreational Dive Computer for a small number of minutes - a low risk for those who understand and watch their computers well - my dive bud being an example of one who doesn't. I have a standing promised to his elderly mom to keep us both safe, but it gets challenging at times - we're both klutzes.

Actually, I meant do I seriously need to post definitions for no-decompression and decompression dives?

As for whether or not someone should push or exceed NDL's. . . While I'm willing and enjoy discussing and debating facts and theories, and the conclusions based on those facts or theories, I'm not willing to debate someone's personal choice. I'm a big believer in personal freedom and think that if a person chooses to push the limits, seems to know what they're doing, and it doesn't directly endanger me, then it's not my place to butt into their business.

 

[TSandM]

I don't think there is a definition for a no-decompression or a decompression dive, unless you define a no-decompression dive as any dive that YOUR computer never counts down to 0 minutes NDL time. All dives involve nitrogen absorption and elimination. Different decompression algorithms will give you different NDL times -- if my computer thinks I'm fine and yours thinks you're three minutes into deco, what kind of dive is it?

The fact is that, as dives get deeper and/or longer, the amount of time required to eliminate enough nitrogen to surface safely increases. But defining a "no-deco" dive requires that you define the algorithm AND its assumptions; if I am at 100 feet on a Suunto and it's giving me 2 minutes of no deco time remaining, that does NOT mean I can safely bolt for the surface. A certain ascent velocity is assumed, and exceeding that may well exceed the allowable gradients for that dive. If you do a stepped ascent with stops, your "no deco" time will be longer -- but is that a "no-deco" dive, if you are assuming stops? Is it a "no-deco" dive if it's assuming an ascent rate, or a "mandatory safety stop"? I think the definitions are much muddier than you are implying they are, and there is no bright line that separates "no-deco" from staged decompression diving.

Which, of course, is why I think people who are doing deep diving ought to get more training, and put more thought into what they are doing

 

[FishOutUvH2O]

I don't think there is a definition for a no-decompression or a decompression dive, unless you define a no-decompression dive as any dive that YOUR computer never counts down to 0 minutes NDL time. All dives involve nitrogen absorption and elimination. Different decompression algorithms will give you different NDL times -- if my computer thinks I'm fine and yours thinks you're three minutes into deco, what kind of dive is it?

The fact is that, as dives get deeper and/or longer, the amount of time required to eliminate enough nitrogen to surface safely increases. But defining a "no-deco" dive requires that you define the algorithm AND its assumptions; if I am at 100 feet on a Suunto and it's giving me 2 minutes of no deco time remaining, that does NOT mean I can safely bolt for the surface. A certain ascent velocity is assumed, and exceeding that may well exceed the allowable gradients for that dive. If you do a stepped ascent with stops, your "no deco" time will be longer -- but is that a "no-deco" dive, if you are assuming stops? Is it a "no-deco" dive if it's assuming an ascent rate, or a "mandatory safety stop"? I think the definitions are much muddier than you are implying they are, and there is no bright line that separates "no-deco" from staged decompression diving.

Which, of course, is why I think people who are doing deep diving ought to get more training, and put more thought into what they are doing

This is what I meant by over complicating something when it doesn't have to be. You obviously knew the standard definitions for these terms, you stated them. But, logically, if every dive is a decompression dive and there is no distinction between a "no-decompression dive" and a "decompression dive" we would not have "no-decompression limits". So, by extension, using whatever computer or tables you choose to calculate NDL's, and planning the dive to stay within, and staying within, those NDL's is a "no-decompression dive". More practically, and where the definition becomes standardized in the dive community, is that the U.S. Navy, NOAA, PADI, NAUI, and just about every training agency and dive institution all use the terms, and make a distinction between, "no-decompression dive" and "decompression dive". And they all use them in pretty much the same way to mean the same thing. . .

The basic difference between the two-

no-decompression dive = No required stops. A direct ascent to the surface can be made with minimal risk of DCS.

decompression dive = Stops are required. Failure to plan for and execute the required stops significantly increases the risk of DCS.

I can appreciate your desire to further educate people, but how do you even begin to get to the main point of your discussion if even the most basic definitions can't be agreed on?! These terms are prominent throughout the dive community. And from my understanding they have been since the inception of NDL's. But, it seems that as people progress in their knowledge of diving and the complexity of their diving, they lose track of the fact that many of these terms have basic meanings and are taught in basic OW. Are these terms oversimplified? Maybe. But, when you say them to even the least experienced certified diver, they should have a basic understanding of the concept you're talking about. It's from that starting point that you build on to expand their knowledge.

 

[ggunn]

This is what I meant by over complicating something when it doesn't have to be. You obviously knew the standard definitions for these terms, you stated them. But, logically, if every dive is a decompression dive and there is no distinction between a "no-decompression dive" and a "decompression dive" we would not have "no-decompression limits". So, by extension, using whatever computer or tables you choose to calculate NDL's, and planning the dive to stay within, and staying within, those NDL's is a "no-decompression dive". More practically, and where the definition becomes standardized in the dive community, is that the U.S. Navy, NOAA, PADI, NAUI, and just about every training agency and dive institution all use the terms, and make a distinction between, "no-decompression dive" and "decompression dive". And they all use them in pretty much the same way to mean the same thing. . .

The basic difference between the two-

no-decompression dive = No required stops. A direct ascent to the surface can be made with minimal risk of DCS.

decompression dive = Stops are required. Failure to plan for and execute the required stops significantly increases the risk of DCS.

I can appreciate your desire to further educate people, but how do you even begin to get to the main point of your discussion if even the most basic definitions can't be agreed on?! These terms are prominent throughout the dive community. And from my understanding they have been since the inception of NDL's. But, it seems that as people progress in their knowledge of diving and the complexity of their diving, they lose track of the fact that many of these terms have basic meanings and are taught in basic OW. Are these terms oversimplified? Maybe. But, when you say them to even the least experienced certified diver, they should have a basic understanding of the concept you're talking about. It's from that starting point that you build on to expand their knowledge.

In my OW training, my instructor said, more than once, "every dive is a decompression dive". That's because there is compression and decompression that takes place on every dive, and you can quite easily suffer a hit of decompression sickness even if you never come close to NDL if you don't follow procedure on your ascent. That said, I don't think anyone is going to confuse that with what we refer to as "going into deco" on our computers, which, by the way, is a different point for different computers.

 

[blue steal]

Great thread. I'm absorbing information like nitrogen on a deep dive, hope it stays with me, (the information that is).

 

[TSandM]

You can certainly accuse me of overcomplicating something . . . or I can respond that the dive industry oversimplifies it.

Saying that a "no decompression" dive is a dive where a direct ascent to the surface (remember, it's got to be at a prescribed ascent rate, and may require stops) begs the question of what kind of dive it is when you have three teammates and no two computers agree on what the no-deco limits are.

Example: A couple of years ago, Peter and I met our friends Ken and Claudette and Jaye at Casino Point in Southern California. We did three dives that day. The first one, we were pretty much all together for the whole dive, and nobody went into decompression, according to their computer. On the second dive, Ken and Peter dipped a few feet deeper than Claudette and I did, to look at a ray. At the end of that dive, which we finished together, Ken and Claudette showed no decompression obligation on their Aeris computers. Jaye had none on her Suunto. I had none other than minimum deco according to the way I run decompression. Peter had 20 minutes of deco on his Suunto! So, was that a no-decompression dive, or a staged decompression dive, or what was it?

You can write a definition, but applying it to any given dive is going to show up these inconsistencies. Better to consider all dives decompression dives, and know what the deco you need to do for any given dive actually is.

 

[craracer]

An algorithm is just that...an algorithm. It's not a guarantee that deleterious outcomes will not occur. So, why push the limits?

Technical divers exceed NDLs as a matter of routine -- but they do a tremendous amount of planning for adequate gas supply to do so, and for coping strategies for contingencies that might interfere with doing the required time.

I'm taking an Advanced Nitrox/Deco class, and had my first dives last weekend. I, and my team spent more time planning the three dives than we actually spent doing them.

After participating in the didactic portion, and doing the dives, it greatly concerns me that people appear to have a somewhat cavalier attitude regarding deco obligations.

As long as you understand the potential risks, and are willing to accept them (I would also check with your family/loved ones/friends for consent), have at it. Just know that you are, IMHO poking a sleeping bear with a pretty short stick.

I don't mean to sound preachy, but a lack of knowledge in this area is something that can definitely hurt you, if not worse.

"Deco for Divers" is an excellent book. I'm about 1/2 way through it, and can't wait to reread it. Take a class and you'll be one-up on simply reading about it.

 

[FishOutUvH2O]

You can certainly accuse me of overcomplicating something . . . or I can respond that the dive industry oversimplifies it.

Saying that a "no decompression" dive is a dive where a direct ascent to the surface (remember, it's got to be at a prescribed ascent rate, and may require stops) begs the question of what kind of dive it is when you have three teammates and no two computers agree on what the no-deco limits are.
According to the definition, if it requires a stop it's a decompression dive. Ascending, regardless of speed is still continuous upward movement, therefore, not a stop.

Example: A couple of years ago, Peter and I met our friends Ken and Claudette and Jaye at Casino Point in Southern California. We did three dives that day. The first one, we were pretty much all together for the whole dive, and nobody went into decompression, according to their computer. On the second dive, Ken and Peter dipped a few feet deeper than Claudette and I did, to look at a ray. At the end of that dive, which we finished together, Ken and Claudette showed no decompression obligation on their Aeris computers. Jaye had none on her Suunto. I had none other than minimum deco according to the way I run decompression. Peter had 20 minutes of deco on his Suunto! So, was that a no-decompression dive, or a staged decompression dive, or what was it?
Decompression is an individual event since each person can be effected differently, and is responsible for determining and/or agreeing to a particular dive plan. And each person buys and uses their own computer, tables, planned stops, etc. If that person's computer says that they've exceeded NDL's and now requires a stop(s), then that person is doing a decompression dive, regardless of what other computers in their group say. They bought that particular computer for a reason, if they're going to use it as a computer than they're stuck with what it comes up with. You know better than most that there are several different decompression models out there. Which one to use is up to the individual, either by direct choice through knowledge, or by default in buying a particular computer. As a team member you may have been stuck doing the deco-stop with him, but according to your computer you were not doing a decompression dive.

You can write a definition, but applying it to any given dive is going to show up these inconsistencies. Better to consider all dives decompression dives, and know what the deco you need to do for any given dive actually is.
If the dive plan you're diving has no decompression obligations/requirements, then you could accurately say that it is a no-decompression dive. Hence, the origin of the term. I don't need to consider every dive a decompression dive as a hard rule. Whether or not the dive is or isn't going to require deco-stops will be determined when the dive plan is made. Plan the dive, dive the plan, so to speak.

While I don't expect these definitions to fit every possible scenario, most definitions don't, they seem to do a pretty good job. And again, they're already well established terms.

 

[ggunn]

While I don't expect these definitions to fit every possible scenario, most definitions don't, they seem to do a pretty good job. And again, they're already well established terms.

Nobody is arguing that or trying to redefine anything. In the English language it is quite common for a word to have several different definitions depending on context. For example, I also often use the word "decompression" to mean relaxing with a beer after a long hard day at work. I don't think that anyone will assume that I am drinking and diving from hearing me say that.

In this case, by saying "every dive is a decompression dive", my instructor meant that on every dive literal decompression is involved and careful attention to ascent rates and bottom time is called for. No one in the class was confused by his use of the term in that way or thought he was redefining the word.