However, this begs the question of what caused the flames and
smoke? If the fuse was intact, it's unlikely. If it was an AC power
line fault of some sort (lightning hit, lost neutral, hi-v distribution
line falls on power line drop), it would have destroyed other pieces
of test equipment in the lab. Pardon my suspicious nature, but
methinks you should run it with the covers off and keep an eye
on this scope for a while.

Though Jeff is almost certainly correct, it's possible that the original
"blast" was caused by a screwed-up ground.

I haven't used my scope in a long time because I'm paranoid (probably
without reason) about connecting it to a DUT that is also connected to the
power line. (Go ahead, start throwing garbage at me for my
ignorance/stupidity.)