Nitrox course. What's the point?

[boulderjohn]

I have certainly done my 'shallow' second dive on a rich / optimum mix to flush Nitrogen so that the following morning I can maximise my dive time. [A typical behaviour in Scapa.] Yes, if I avoided the second dive altogether, I would have had more time available than if I did the second dive on an optimum Nitrox mix.

Maybe.

On a long technical dive while doing the final stop on oxygen, if you look at the tissue loading graph on a computer that has one during the last minutes of your final stop, you will see that when you finally go to the surface, during your surface interval, you medium and slow tissues with be off-gassing, as is true for any diving, but your faster tissues will be on-gassing while breathing surface air.

Astronauts and high altitude military pilots breathe pure oxygen for several hours before taking off, hopefully eliminating all oxygen do they can do that fast ascent without getting bent.

 

[Storker]

I was taking the two extremes for simplicity.

While I think I understand your basis, that's quite another can of worms. A lot of folks seem to think it's either/or, and the gray area inbetween be damned.

So, you can either:

• dive Nitrox as if it where air and get a safety benefit

OR

• dive Nitrox as Nitrox and gain extra in water time. And get no safety benefit

OR

• dive Nitrox and gain some extra water time and get a safety benefit

 

[Gareth J]

Maybe.

On a long technical dive while doing the final stop on oxygen, if you look at the tissue loading graph on a computer that has one during the last minutes of your final stop, you will see that when you finally go to the surface, during your surface interval, you medium and slow tissues with be off-gassing, as is true for any diving, but your faster tissues will be on-gassing while breathing surface air.

Astronauts and high altitude military pilots breathe pure oxygen for several hours before taking off, hopefully eliminating all oxygen do they can do that fast ascent without getting bent.

Shouldn't have used the term 'flush', should have said 'reduce' the Nitrogen uptake.

My Bad

 

[boulderjohn]

While I think I understand your basis, that's quite another can of worms. A lot of folks seem to think it's either/or, and the gray area inbetween be damned.

So, you can either:

• dive Nitrox as if it where air and get a safety benefit

OR

• dive Nitrox as Nitrox and gain extra in water time. And get no safety benefit

OR

• dive Nitrox and gain some extra water time and get a safety benefit

Here is something I wrote in this thread quite a few posts ago.

I have many times seen people write as if there were only two choices while diving nitrox--either dive to air tables or dive all the way to nitrox NDLs. I have seen articles in major dive magazine (like Dive Training) that have said precisely that--you can either dive nitrox to air limits for safety, or you can dive to the nitrox limits for extended bottom time. You cannot, the writers insist, have both added safety and extended bottom time.

What such writers seem to be saying is that if you are using 36% nitrox and diving to 80 feet (using PADI tables), you must either end the dive at 30 minutes (air tables) or end the dive at 55 minutes (36% tables). You are absolutely forbidden to dive for 40 minutes to get both safety and extended bottom time! I don't know who is policing you down there, but, dammit, if you go past 30 minutes, you'd better make sure you have enough nitrox in your tank to get all the way to 55, because stopping short of that is not allowed.​

 

[doctormike]

• There is a gray area between NDL dives and decompression dives, a fuzzy region where you as an individual might be better off doing a brief decompression stop. The people trying to explain that were apparently stymied in finding a concise way to to say "OK, you are getting close to a required decompression stop here, so in view of individual physiological differences, we really think it would be a good idea to do one in the range of dives." They settled on the phrase "required safety stop."

Right, and that's a failure of communication on the part of the training agency. Poor communication of technical or scientific issues to a lay audience can be deadly, as we have seen again and again in the context of COVID-19.

I'm sure that you know far more about the history of these decisions than I do, but in this case, they had a pre-existing term which had a widely accepted - safety stop - meaning an extra stop which increases safety (for a variety of reasons), but which could be skipped if necessary for other reasons.

So when new decompression science and expert consensus determines that in this particular case, the agency should recommend a non-optional stop, it would have been better to use a different term than the internally contradictory "required safety stop".

Was there a problem with "required stop"? I mean, these aren't legal definitions. "Required" - even in technical diving - means that skipping it is associated with a significantly increased decompression stress and risk of DCS. I don't think that was the case for safety stops.

 

[DiveClimbRide]

Personally I think diving nitrox on anything other than the correct table/computer setting is stupid. If you want extra safety just don't dive to ndl. Simple and now your computer is also tracking the correct tissue loading and mod.

 

[Storker]

that's a failure of communication on the part of the training agency.

Is it, really?

Remember that an OW class caters to the lowest common denominator. "What if", "it depends", "find your personal limits" work fine with advanced divers who have a serious interest in diving. With those wanting a dip or four while on a vacation down south and don't want to be bothered, not so much. Those ***** need simple rules which they can memorize and (hopefully) follow.

As an educator, I think PADI has done a lot of things right. They make their money from certifying everyone, and they have an obligation to ensure that only an acceptable fraction of their students are hurt. So they follow the KISS principle. I'd do that as well if I had a comparable body of students.

 

[doctormike]

Is it, really?.

Clearly. It's confusing enough so that it's endlessly brought up here.

Remember that an OW class caters to the lowest common denominator. "What if", "it depends", "find your personal limits" work fine with advanced divers who have a serious interest in diving. With those wanting a dip or four while on a vacation down south and don't want to be bothered, not so much. Those ***** need simple rules which they can memorize and (hopefully) follow.

Right, glad you agree. A simple rule would be to use the term "required stop" in situations where PADI was recommending a stop that was not "optional", like a safety stop.

As an educator, I think PADI has done a lot of things right. They make their money from certifying everyone, and they have an obligation to ensure that only an acceptable fraction of their students are hurt. So they follow the KISS principle. I'd do that as well if I had a comparable body of students.

I'm not PADI bashing, and the fact that I have a problem with the oxymoron "required safety stop" isn't an indictment of the agency's educational efforts in general.

Again, the KISS principle would be that if you are requiring your students to do a stop in any given circumstance, you should use the term "required stop". How does saying "required safety stop" make it LESS confusing?

 

[boulderjohn]

Is it, really?

Remember that an OW class caters to the lowest common denominator. "What if", "it depends", "find your personal limits" work fine with advanced divers who have a serious interest in diving. With those wanting a dip or four while on a vacation down south and don't want to be bothered, not so much. Those ***** need simple rules which they can memorize and (hopefully) follow.

As an educator, I think PADI has done a lot of things right. They make their money from certifying everyone, and they have an obligation to ensure that only an acceptable fraction of their students are hurt. So they follow the KISS principle. I'd do that as well if I had a comparable body of students.

Google any of the explanations of interference theory, and you will see that too much information is the enemy of memory. In a well-planned curriculum design, the first step is dividing potential information into groups:

1. Essential learning--your curriculum needs to focus on this to make certain all students learn it well.
2. Good to know--this will be a secondary focus.
3. Nice to know--De-emphasize this and consider omitting it. Time spent learning it interferes with the ability to learn and remember parts 1 and 2.
4. Don't need to know--Omit it. Time spent learning it interferes with the ability to learn and remember parts 1 and 2.

Here is an example. It is essential for the new diver to know the relationship between depth and volume and how that relates to on-gassing and off-gassing. It is not necessary to know that this is known as Boyle's Law, and it is not at all essential to know the details of Dalton's Law and Henry's Law.

 

[Storker]

It's confusing enough so that it's endlessly brought up here.

My thoughts on that matter would probably violate the ToS or at least the Special Rules for the forum we're in. I'll limit myself to saying that I don't necessarily believe that that confusion is PADI's fault.