'Negligent' means one or more specific actions or failings of yours was the cause of the problem.
IMO, they are absolutely NOT interchangeable, although our laughable tendency to whitewash and Clintonize reality means it gets called "accidental" or "unintended" nearly every time it's referenced by the media or the legal system. We'd get much further by calling a spade a spade. It's negligence when your avoidable actions cause a problem to occur, unintended though it might be. Basically, it comes down to how one was raised, whether truth meant just that, or whether it was allowed to mean something else.