Unfortunately, a "case-by-case basis" usually means figuring out what happened after it's happened, and useful as it might be in overall progress, it's cold comfort to the people it's already happened to. If indeed, such accidents are simply inevitable, I would suppose one way to prevent them would be to remove the implements of accidental injury from places where the inevitable will have the most undesirable cost-benefit ratio. Like classrooms, maybe?
Interestingly, this reserve police officer who was giving his students a lesson on gun safety wasn't even authorized to have a weapon in the school to begin with.
And when the gun went off it was because he was "making sure that it wasn't loaded".
So much for training, unless they are teaching that the way to check to make sure a gun (which wasn't supposed to be there to begin with) isn't loaded by pulling the trigger.*
At least he wasn't looking down the barrel to see if a bullet was in it when he did that.
I have to think that this goes well beyond the classification of occasional, unavoidable accidents, and clearly demonstrates that rules and training are not going to be the answer to the gun problems we are confronting.
* - My father gave me my first lesson in handling firearms when I was around ten years old. (Hey, it was the early Sixties. And it was West Virginia. By those standards I was something of a late bloomer.)
We went out to an open field with a hill at one end (Not hard to find in WV.) and he handed me the rifle, an old '42 Mossberg .22LR which I still have.
I was thrilled and excited. My very first time holding a real rifle.
He said,
"Don't be afraid, it isn't loaded yet. Just put it to your shoulder, and look down the barrel. Try to get the rear sight lined up with the front, and gently squeeze the trigger. Just to get the feel for it."
I did all that, and I can still remember the sound of that rifle going off to this day. It sounded louder than anything I had ever heard, and I swear it has never sounded that loud since then.
While I was still shaking from the shock and surprise, he then said;
"NEVER believe ANYONE when they tell you a gun isn't loaded. ALWAYS open it up, take it apart and check it YOURSELF."
And I always have.