Is it unexpected when it is briefed? I don't do unexpected failures that aren't briefed, in fact i brief my students that any truly unexpected failure that wasn't briefed as "possible" means it is real.
Reading back on the first page of this thread I came across the above, which I had seemingly overlooked previously.
So, illustrative case in point; back in the day, on a planet far far away, another student and I were doing the last dive in a strenuous cave course with a friend who also was a very
very very well know instructor, a legend even today with those that know their 'technical' and even 'pre-techical' diving history.
Be that as it may, deep (as in a long way) inside the Peacock Cave system (IIRC now) in Florida, just as were about to make a jump to head back out, the instructor had a free flow reg 'anomaly' that he could not kill. He then went to turn off the isolator knob on his doubles. Low and behold it was stuck fast and he couldn't get it to turn. (Now remember, this is a guy who had helped write the book on deep cave exploration and deep ocean diving, and by
deep I mean
deep, even back in the day when gas - helium - was not available, and had been there, done that in spades.)
So he was now pointing somehwat 'excitedly' for one of us students to crack it (start the turn of the isolator knob). Well both of us green-horns thought he was 'pulling our leg / taking the piss' (as the Brits would say), as this free flow incident had not been discussed pre-dive (as was his usual practice for drills, that is
tell which / what drill may take place,
but not when), and now this had just happen to have happened in the far reaches of the system, and as I said above, just as we were about to make a 'jump', so we took some time to react because we both thought it was at best an unannounced out-of-character drill, not a real emergency, so took our time swimming up to him as it were (
yes, I said we were green-horns!).
Anyway, if looks could kill we (us two students) would be dead now, but that look made us act quick smart, and long story short, all turned out well, although we did exit the cave a little quicker than planed, and received a good dressing down / bollocking for our lax behavior, as was rightly his due. (And what a thing to have had on his tomb; "
Killed by two students who did not react fast enough in a real emergency ". Why, he certainly would not have lived it down (
obviously), and neither would ever have we !)
So, lesson learnt, almost the hard way. And one that I carried over when I became a 'technical' instructor. That is I would announce what drill/s we would do / what 'emergency'
may take place pre-dive,
but not when.
So to answer the 'question' posed -
Is it unexpected when it is briefed? - yes it can be if the drill is made
aware of pre-dive, but not
when it may / will take place during the dive. That way then keeps em' on their toes the
whole dive.
(And so yes, back to the topic at hand, I still think turning off someones o2 unannounced, especially to a student on a re-breather,
is asinine!)
NEXT DAY EDIT; Moved one sentence above so the "turning off o2 is asinine'' sentence can be read as a stand alone, NOT as an integral part of my example / comment on doing unbriefed drills,
which was the intent of my commentary here; as it seems some people have misread my post (i. e. cannot see the separation of the two distinct incidents I bring up here) because, possibly, I did not have that bracketed sentence as the last stand alone sentence in my post. Hopefully the movement of that sentence makes it somewhat, and possibly only somewhat to some, clearer now.