I had about 900 dives when I became an instructor ... and had spent nearly a year and a half as a DM working with multiple instructors prior to that. I also had, by then, taken AN/DP ... so that would also qualify me as a "tech diver". And although I had all that background, I almost failed my IE ... because one of my evaluators felt I was not positioning myself properly during the demonstrations to be in control of my students. She then demonstrated that point by simulating a panic and getting away from me quicker than I thought was possible.
Nothing in a "tech diver's" training will teach them how to position themself to intervene in this situation.
So the tech diver ... even the well-trained, very experienced one ... takes a complete newb on a 30-foot tour at an easy dive site. Simplicity itself, right? But somewhere along the way, the diver accidentally floods his mask ... or aspirates a bit of water ... or suddenly gets that familiar "I can't get enough air" that comes from exertion and CO2 buildup ... and succumbs to an overpowering urge to head for the safety of the surface ... leaving his very experienced dive buddy suddenly looking up and well past the point of being physically able to do anything to prevent it.
They talked about "never hold your breath" prior to the dive ... but in a moment of near panic, said newb doesn't remember that part ... does what instinct tells him to do ... and blows his lungs out on the way to the surface.
If you think this doesn't happen, you haven't spent enough time reading the Incidents and Accidents forum. It happens ... even to instructors, if they're not careful.
We don't train for when dives go right ... we train for when they go wrong. And if your training doesn't include student management, you're trusting that nothing will ...
... Bob (Grateful Diver)
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... I haven't yet met one of those that I would trust training someone I loved ...
... Bob (Grateful Diver)