I recall a news piece from some years back regarding this very thing. Kings Island in Cincinnati used to have this coaster where you had to kind of stand up. There was a bicycle seat type thing that you sort of sat on, like when the thing went upside down. King Cobra, maybe? IDK. Anyway, this fat woman got on and the harness couldn't lock properly. She was flung from the ride and killed.  Needless to say, hubby sued and the ride got shut down. I don't have any details and it could be an urban legend, but that story has stuck in my mind for years.  Imagine all the children that were permanently traumatized by that.