Unavoidable accident is an accident which human prudence or foresight could not prevent, or an event or casualty happening against the will and without the negligence or default of a party.
"The occurrence of an unavoidable accident is not foreseeable or anticipated and could not have been prevented by the exercise of ordinary care under the attendant circumstances. In order to constitute an unavoidable accident, an event must have occurred without negligence on the parties' part." [Fry v. Carter, 375 Md. 341 (Md. 2003)]