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For #4 I think there's a huge problem with full cave divers trying to encourage intro divers to break the limits of their training. I've had several former students tell me of people that tried to encourage them to dive to thirds almost immediately after they were done with intro. And while I'm not a fan of Kelly's idea of going back to the days of Single Tank Only, there's one benefit of being in a single tank -- you have a finite gas amount that will limit your penetration. Most of the gas is used just running the reel to the primary line anyway.
Instructors need to do a better job of reminding their students they have a responsibility to not take people beyond the limits of their training. We should all review the previous levels of training and explain in depth why taking people beyond their limits is a horrible idea.
#5 - that course exists, it's called Apprentice. Or Cave 1. Or "TekLite Cave Diver", depending on your agency.
#6 - It's difficult to have a significant statistical analysis of the safety of NAUI Cave 1 versus Intro because the numbers for Cave 1 are substantially lower. You can go out any day of the week and you're likely to run into an intro class, but rarely will you run into a NAUI Cave 1 course. BTW, NAUI Cave 1 requires 9 dives (2 cavern, 7 cave). Apprentice requires 10 (4 cavern, 6 cave). Probably not enough either way, and Cave 1 is really a "zero to hero" program so it is a lot for many people to digest at once.../
/....I think the difference isn't the standards on paper, but rather the quality of the instructors teaching the material. Twenty years ago, even the cave instructors that I thought were goof balls, were stellar cave divers and excellent at sharing how to cave dive safely. But now, not so much. We have "Cavern Instructors" that can't do a frog kick, and are taking students to the Keyhole in Ginnie while the instructor is in a single tank K-valve.
I think this drop in instructor quality goes back to the path taken to become a cave instructor. I mentored/co-taught under a dozen different cave instructors (in no particular order they were Bailey, Berman, Jablonski, Oestreich, Sorenson, Fowler, Cole, Murcar, Bernot, Wyatt, Sellers, Moon), and that used to be the norm. Not so anymore.