General thoughts on the dive physics questions

[boulderjohn]

I started my DM class in 2004 and got my instructor certification a couple years later. Seeing these questions reminds me of the time I studied the Encyclopedia of Recreational Diving so I could answer them. In some cases, I can remember them easily because the concepts reappeared in the OW course materials I taught so many times over the years. In other cases, I have not seen the questions or answers since I last studied them so many years ago. I would have to look them up again.

That fact makes me wonder how many things we teach in these courses that a diver really doesn't need to know. At the same time, how many things that a diver really should know are we either skimming over or not teaching at all? I think it is all because of a phenomenon common in all instruction teaching evolving content needs.

I had my first realization of this more than a half century ago when I was studying for my state high school exam (NY Regents) in chemistry. My father handed me the review book from his high school chemistry regents exam. I received an award as the top chemistry student in my school, and I did great on my exam, but I would not have passed his exam. It was not because his exam was harder--mine was much harder by far. The difference was that chemistry content had changed so much in those years; for example, we learned that you could spit the atom. His course focused on the memorization of silly trivia that was barely mentioned in our course. And it continues; the subjects in today's chemistry classes blow mine away.

Another example occurred when I was selected to be on a team of teachers working on revisions to a then-popular standardized test, the Iowa Test of Basic Skills. I was on a team focusing on one section of the test, and our team staged a massive rebellion--or at least tried to. A major portion of the 12th grade test, we protested, was something we don't teach any more. It was something that was part of the curriculum in 1948, but it had not been in a 12th grade curriculum for decades. As content, it was easy as pie, but modern students would never get any of those questions right because they never learned it. They were busy learning stuff that was not on the exam at all.

The reaction of the ITBS people showed the problem. They refused to change it. They saw it as a lowering of standards. If people were learning this in 1948, then, by golly, they should be learning it now. (That is honestly very nearly a direct quote.)

I think I see a lot of the same thing in scuba. It is really hard to make an honest appraisal of what should be taught in scuba classes because of the same sort of psychological block against removing something of lesser value to replace it with that which may be better suited for the modern world.

 

[Storker]

That fact makes me wonder how many things we teach in these courses that a diver really doesn't need to know. At the same time, how many things that a diver really should know are we either skimming over or not teaching at all? I think it is all because of a phenomenon common in all instruction teaching evolving content needs.

I truly believe that most diving issues can be solved by the application of common sense and basic physics. Unless there are medical issues intervening.

Problem is, common sense usually is neither common nor particularly sensible.

 

[TMHeimer]

I started my DM class in 2004 and got my instructor certification a couple years later. Seeing these questions reminds me of the time I studied the Encyclopedia of Recreational Diving so I could answer them. In some cases, I can remember them easily because the concepts reappeared in the OW course materials I taught so many times over the years. In other cases, I have not seen the questions or answers since I last studied them so many years ago. I would have to look them up again.

That fact makes me wonder how many things we teach in these courses that a diver really doesn't need to know. At the same time, how many things that a diver really should know are we either skimming over or not teaching at all? I think it is all because of a phenomenon common in all instruction teaching evolving content needs.

I had my first realization of this more than a half century ago when I was studying for my state high school exam (NY Regents) in chemistry. My father handed me the review book from his high school chemistry regents exam. I received an award as the top chemistry student in my school, and I did great on my exam, but I would not have passed his exam. It was not because his exam was harder--mine was much harder by far. The difference was that chemistry content had changed so much in those years; for example, we learned that you could spit the atom. His course focused on the memorization of silly trivia that was barely mentioned in our course. And it continues; the subjects in today's chemistry classes blow mine away.

Another example occurred when I was selected to be on a team of teachers working on revisions to a then-popular standardized test, the Iowa Test of Basic Skills. I was on a team focusing on one section of the test, and our team staged a massive rebellion--or at least tried to. A major portion of the 12th grade test, we protested, was something we don't teach any more. It was something that was part of the curriculum in 1948, but it had not been in a 12th grade curriculum for decades. As content, it was easy as pie, but modern students would never get any of those questions right because they never learned it. They were busy learning stuff that was not on the exam at all.

The reaction of the ITBS people showed the problem. They refused to change it. They saw it as a lowering of standards. If people were learning this in 1948, then, by golly, they should be learning it now. (That is honestly very nearly a direct quote.)

I think I see a lot of the same thing in scuba. It is really hard to make an honest appraisal of what should be taught in scuba classes because of the same sort of psychological block against removing something of lesser value to replace it with that which may be better suited for the modern world.

I didn't know you were from NY originally. I took those dreaded Regents exams in 1971-- all the teachers grilled us by going over past Regents exams, so I did OK.
I agree with you on the points about scuba instruction. I've said before I think PADI did a good thing to eliminate some of the theory in the DM course that really wasn't absolutely necessary for a working DM to know in favour of the more practical Deep & S&R aspects. Also my usual comparison to my music degrees in that I may have used 20-30% of that knowledge in my teaching.
Oh, my younger brother lucked out in 1974 (?) when someone broke into Albany and stole most of the Regents exams (think he only had to take one). He then became an Annapolis grad. and retired USN Captain. Guess the Regents weren't very important for his future.

 

[JamesBon92007]

I

I had my first realization of this more than a half century ago when I was studying for my state high school exam (NY Regents) in chemistry. My father handed me the review book from his high school chemistry regents exam. I received an award as the top chemistry student in my school, and I did great on my exam, but I would not have passed his exam. It was not because his exam was harder--mine was much harder by far. The difference was that chemistry content had changed so much in those years; for example, we learned that you could spit the atom. His course focused on the memorization of silly trivia that was barely mentioned in our course. And it continues; the subjects in today's chemistry classes blow mine away.
.

I have a chemistry book from the early 50s which states that there is no known commercial use for silicone.

As for the dive physics, I was mildly surprised yesterday when my girlfriend told me that they didn't teach her in her OW class that one reason to ascend at the proper rate is because if you ascend too slowly your body will still be absorbing nitrogen instead of expelling it. Personally, I do much better if I understand the reasons than just blindly following the "rules" with little or no explanation given. I have found myself thinking about this last year during an emergency situation and I suspect that the situation could have become an incident or possibly a tragedy had I not known what I consider to be the basic stuff. Sure, if you read your computer manual it will probably tell you that kind of stuff but it doesn't seem like it would take up much of the classroom time to go over the nitrogen absorbtion details a bit more thoroughly.

 

[boulderjohn]

I have a chemistry book from the early 50s which states that there is no known commercial use for silicone.

I just saw a presentation of the history and future of helium, which is now considered to be vital for deep diving. For many years following its discovery, it was said to have no practical use.

As for the dive physics, I was mildly surprised yesterday when my girlfriend told me that they didn't teach her in her OW class that one reason to ascend at the proper rate is because if you ascend too slowly your body will still be absorbing nitrogen instead of expelling it.

While that is true in decompression diving, the effects of ascending slower than the standard ascent rate for NDL diving have not been adequately studied. According to someone in the know about the research leading to the PADI tables, they used 60 FPM for the standard ascent rate because that is what everybody did in those days, but the research did not indicate a problem with going slower. That is why they say to ascend "no faster than 60 FPM" but do not specify a rate that is too slow. If you read the DAN articles on ascent rates, you will see the same thing--they will not mention a rate that is too slow because they don't know if any rate is too slow, assuming you do not go so slow as to violate NDLs.

There is thus a good reason it was not mentioned.

 

[dmaziuk]

This goes back to teaching "common sense": you'd think by common sense slower is safer. IRL there has to be a delta-pressure in order to off-gas (or on-gas), and obviously, with ascent rate (and dP) of 0 you're not off-gassing at all. I.e. there has to be an ascent rate that is "too slow" to be "safer".

Similarly, a good dive computer does not promise you won't get bent, it only promises you a consistent 1 in X chance of getting bent, dive in, dive out. Common sense says more conservative is safer, but IRL that X is low enough already and if you get an "undeserved" hit, it's probably because of something the computer never tracked in the first place. So in fact "more conservative" by the computer is not "safer".

How many people are comfortable looking at things that way, and trying to teach it to others, is also a question.

 

[divinh]

Things that aren't common sense...

- Not holding your breath when immersed in water
- Not exercising to warm up
- Letting air expand out of your lungs in CESA

Once you're taught the physics of it, it does make sense.

 

[boulderjohn]

About 6-7 years ago I certified 2 friends to dive. We did the academics and pool work in my home town, and then we traveled together for a vacation in Akumal, MX. There a local dive shop allowed me to complete their certification, renting equipment from them and diving from their boats. On the first day of diving, we worked on setting up the gear we were renting from them, using bungee cords to put trim weights on the BCD cam bands. Their instructors gathered around, asking why we were putting weights on the cam bands when we could be putting all the weight on the weight belt, as everyone else did.

I explained about trim, and why distributing weight like that was valuable. I also told them that the new PADI standards, which they would be required to use in the coming months, required them to teach about trim. They knew nothing about it.

Last fall my family returned to that area for a vacation, which is a major snorkeling destination. Snorkeling with my grandchildren, we went over an OW class kneeling on the ocean floor. They had no trim weights.

I would consider that to be an example of something new that has trouble working its way into an old curriculum.

 

[MargaritaMike]

Problem is, common sense usually is neither common nor particularly sensible

Common sense is uncommon!

Cheers - M²

 

[wstorms]

The subject relevance also greatly depends on the context. For example, for an OWD it will suffice to know to
- ascent slowly (think about the expanding balloon)
- stay away from NDL (think about opening a bottle of coke)
This will keep them safe, which is the main objective.

Now for a DM the objective changes. Not only should a DM practice safe behavior, he/she is also expected to be able to explain stuff to new divers (as an extra to the instructor). the same subject is more complicated in this context. It is fair to expect a DM to understand ongassing, having a sense of compartments, and therefor really think about the student's question and be able to answer it backed with science.