Mystery - Strong Fuel Smell

I was just relating to a fellow tech about an extreme case of this. Decades ago our private shop serviced the vehicles for a sports equip reconditioning company, one of the
E350 fleet was dropped off overnite for service the next day. We pulled it in for the nite as it was single digits outside, who wants to work on a 5deg vehicle right? Unfortunately
the hired help filled the tank on the way over, at a station that just got a fresh load of fuel, oh and he topped her off good,lol! The shop heater was a hung gas unit that was
pointed right at the van,.... the next morning there was a puddle almost the size of the van under it, & the entire building was so heavy w/fumes.........I still can't believe that
place didn't blow up!! The fuel swelled up and forced its way out the canister vent all over..............