Ad absurdum per aspera wrote:
100HPx746Wx3600s = 3 billion joules. How much is that in dynamite? :-),

About 1530 pounds, ie 1.5 kilotons

Erm, it would doubtless be "killa" if you were standing nearby at the
time of an uncontained failure but it isn't "kilo" (1.5 kT = 3 million
pounds, said of the blast aspect of nuclear weapons in broad comparison
to TNT).

I also think the amount of time needed to spin it up is irrelevant to
a calculation of how much rotational kinetic energy it has when done
(though perhaps highly relevant to how much energy will drain out of
you when you get the electric bill!); and that's the key fact for
safety.

BTW, I think the energy use is 268 MJ, not 3 GJ, if you run a 100 hp
(input) motor for an hour. Check my logic... A horsepower is 745 W.
A watt is a joule per second, so if you do that for 3600 seconds you
get 268,200,000 joules.

Assuming you lose nothing to friction during that hour of the giant
heavy drum spinning.

- Logan