When I got certified ages ago, I used to go on a boat called Peace. It was well known for its hot tub. It was from Oxnard to Channel Islands.
During one trip, I was seasick and spent many hours sleeping in a bunk.
I do remember safety instruction given, but it has been very long time to remember the details.
I may have remembered any hatch and fire escape instructions. They were mostly about life jackets and life boat locations.
I do remember on a 2-day fishing trip from SD, the captain gave the safety lecture. What stuck in my mind was that----if you need to "feed the fish" at night, be sure to do it in a trash can and not from the railing. The reason was that, if angler bent over falls in the water, no one will know for a long time.
My guess would be:
a) fuel leaking over a hot generator. Engines would be off at night. b) nitrox tanks leaking, but they are outside. c) an electrical short, but it was too fast.
It is indeed a tragedy.