Had a former neighbor learn this the hard way.
Boat blew up and burned right down to the waterline. The explosion killed his wife and his dog. He was hospitalized for almost three years recovering from burns on more than 90% of his body.
I’ve owned a total of 5 boats in my lifetime. The first 3 were outboards so it wasn’t an issue. The last two were I/O with big V-8 engines. I’d go so far as to open the engine compartment for a while, then close it, and then run the blower.
Gasoline fumes are more easily detonated than dynamite and just as powerful.
L