When a B52 broke up while in flight over NC back in 1961, it was carrying 2 nuclear bombs. As the plane broke up (the reason for that is still a mystery) both bombs fell, one just slammed into the ground and did nothing but make a big hole, the other acted like it was activated. Its parachute opened and fell like it was armed, but luckily a low voltage device prevented it from exploding!!
The bomb was a lot more powerful then what was dropped on Japan during the war, but everyone living in NC at the time, were very fortunate it didn't go off!!
Of course, the US Govt said at the time, no one was in danger from a nuclear accident here in the States.
http://news.msn.com/us/nuclear-bomb-...-in-1961-paper