In 1958 the U.S. Air Force accidentally dropped an un-armed Mark 6 nuclear bomb from 15,000 feet in the unincorporated community of Florence County, South Carolina. Because the nuclear core was stored separately on the plane, no nuclear detonation occurred. However, the conventional high-explosive trigger containing about 2,000 lbs of TNT detonated upon impact. This left a crater roughly 70 feet wide and 30 feet deep, completely leveling the home of railroad conductor Walter "Bill" Gregg, damaging neighboring buildings, and injuring six family members. Miraculously, no one was killed.
Here is one of the largest pieces of shrapnel found after the detonation.