Let's stick to the facts. I have never stated this nor do I believe it. This is YOUR invention that the tables were created around doing these yo-yo dives. I don't think you've presented any evidence other than your "feelings" that they were intended to cover such a diving anomaly.
Post 129 includes how various tables consider repetitive ascents/descents conducted within a single dive. Moreover, I've communicated that decompression table development has taken such scenarios into consideration and this has been reflected in the rules that have been established by the authorities. Perhaps you might re-address this by opening a diving textbook and reading the rules outlined. In-particular, what constitutes one dive and how multiple ascents/decents are to be treated. You will find the evidence that you have up until now overlooked.
Please comment on whether you agree with each of these premises and present "solid scientific evidence" either way. I believe this will serve to clarify what you actually believe.
1. Instructors should not worry about setting a great example. 2. Students can not or will not imitate their instructor's behaviors during class.
Instructors should encourage students to dive within their ability and diving safety envelope. They should also be made aware that what is safe practice is based upon their training and experience. Some divers are capable of doing dives that exceed the level of training of other divers. Students should follow the policies and protocols of their training program.
3. Kneeling during class does not result in divers kneeling after class. 4. Scuba can not be taught adequately without kneeling. 5. Neutral buoyancy and great trim are not achievable during an average Scuba class.
The foundation of this question is based upon a personal choice of yours, which is that it's improper for a diver to kneel on the bottom. Any Instructor who teaches in this way is setting a "bad example." This may be your choice, but that doesn't make it a "bad example." I would rather put it into context for the student. Standing/kneeling on the bottom may create poor visibility caused by silt and debris. This isn't something that enhances the diving experience. Kneeling on coral damages the environment.
I personally don't want the students using the bottom for a crutch. My aim is for them to develop good 'buoyancy skills.' Because of this I want them to select the depth and establish neutral buoyancy from the beginning. The bottom is used during some exercises, such as station breathing and doff and don (after they have demonstrated a satisfactory level of buoyancy control). My approach is that Students have the capacity to think for themselves. I try to explain why I say or do something in a particular way.
6. Yo-yo dives are fun and an acceptable way for the average Joe to dive. 7. The tables were specifically designed to accommodate multiple yo-yo dives. Please cite the study(ies) on this.
I want my students to be able to create a decompression solution regardless if the batteries in their PDC function or not. I teach the tables to the letter. My student understand the rules that have been created by the table authorities and they apply them as intended. If during a dive something is dropped and collected, I teach how to deal with the scenario. No one has committed any grievous error, nor do they expect to necessarily leave it on a shallow bottom or have to die in the recovery. They go down and get it
if they have the gas to do the decent together and that no breach of the decompression tables will occur. They know the rules and they're taught not to break them. I don't tell them "person rules" that can't be substantiated.
As to the Tables:
The evolution of how the U.S. Navy Decompression Tables is available on-line at:
STANDARD AIR DECOMPRESSION TABLE.. You can see for yourself how the decompressions solutions were calculation (including the definitions of bottom time and repetitive dive).
The DCIEM Tables (Air) were based upon the Kid-Stubbs model (which was created in 1962) and applied to the USN table considering multi-level and repetitive dives. The approach was to dive the model and when symptoms of DCS occurred, to change the parameters of the model making it more conservative. They went through several variations of the model, improving the safety after each iteration. The revelation at that time was that the human body was better represented by a series arrangement of tissues.
By 1967, over 5,000 experimental dives had been conducted to validate the K-S model. In 1971, the K-S decompression model was approved in Canada as a safer alternative to the U.S. Navy tables. Subsequent to my involvement at DCIEM in 1972, we initiated a critical re-evaluation of the K-S model using digital computers to control various scenarios (including yo-yo dives) and utilizing specially-designed Doppler ultrasonic bubble detectors to evaluate the severity of the dive profiles. Thousands of verification diving and improvements of the theory were performed and the dive table for air diving was released in 1992. The current theory is based upon this dive table. The project plan is still restricted, so this documentation isn't available to the general public.
8. Doing CESAs vertically are far more important than developing the skills to avoid having to do them altogether.
Of course not; but one doesn't exclude the other. CESA is a last resort that can make the difference in a diver safely making the surface or not.
9. Studies have shown that during class, vertical CESAs are better than horizontal CESAs. Please cite the study(ies) on this.
This is subject to the opinion of the Instructor teaching the skill and the recommended practice of the certification agency that must be followed. "A BAD EXAMPLE" would constitute teaching in a manner that is not supported by the certification agency, or would be otherwise contrary to the best interests and safety of the student.
Personally I teach CESA vertically because I believe that it's in the best interests of the student if it's taught properly. In a recent DAN report (Alert Diver) "an analysis of 964 diving fatalities found that emergency ascents were involved in 30 percent of cases — 288 to be exact. In 189 of these emergency ascents involved a rapid ascent (faster than 60 FPM)."
How can an Instructor test a student's ability to ascend at a safe rate during a CESA if this is being undertaken horizontally??? Seems like the Instructor isn't confident in the student's ability to begin with. I'd question if the student requires more training before going to open water. And to think that some Instructors believe that this diver has demonstrated 'mastery' and is ready to be certified....
10. Instructors have never ever been harmed doing multiple vertical CESAs.
None that I'm aware of, but I welcome your scientific evidence (should you presume that this is not the case).
My premise is that we should be setting a great example for our students at all times in order to avoid confusion or to send conflicting messages. In that respect, since I don't want my students kneeling on the bottom or doing yo-yo dives, I refrain from doing them. Yes, I think it's a bad example for an instructor to set and that their students will follow their example, often when they are away from their instructor.
You claim this to be a bad example. Perhaps you
can substantiate your opinion. What proof do you have that this is an unsafe practice? Perhaps you can cite one case where "bubble pumping" has been attributed as the cause of
any injury in 60 FSW or less! Is it common practice for you to formulate an opinion based on nothing, or is it permissible for you to criticize others as showing a "bad example" based solely on your mood or feeling??? Now that I've answered your little quiz, perhaps you will substantiate the science that your opinion is based. This should be good....
