Abnormally dangerous

What does Abnormally dangerous mean in American Law?

The definition of Abnormally dangerous in the law of the United States, as defined by the lexicographer Arthur Leff in his legal dictionary is:

More dangerous than is usual with places, persons, or things of that general variety. The possibilities for legal significance are obvious, e.g., one may have no tort liability toward one who has knowingly continued to work in a place which is normally a dangerous place, but may if it is abnormally dangerous even for such a place. And statutes and often labor contracts give employees the right to cease work if their work place becomes “abnormally dangerous.”