The Hiroshima bomb, which was a uranium gun bomb, was quite easy to set off accidentally. It was just a gun tube, with a propellant charge of powder in a silk bag, just like naval guns of the period, and fired by an ordinary detonator. The crew of the Enola Gay was under orders that if they had to return to base, they were to drop the bomb into deep water, rather than trying to land with it. It could easily have been set off in a crash or fire.

The plutonium bomb was an implosion bomb, and had to be set off with the simultaneous (< 1us difference) firing of all the explosive lenses to get a symmetrical compression. This was done by charging up a big capacitor bank and discharging it through a krytron switch (like a thyatron or SCR; there's a turn-on gate, but no turn-off) into resistance wires used as detonators. There were no intermediate explosive detonators; they weren't consistent enough on timing. Any inconsistency on timing would cause the explosion to blow out on one side rather than achieving full compression. That still might produce a "fizzle yield", tons rather than kilotons of TNT.

"Single point detonation safe" bombs came years later.

In reality, the early weapons were not "single-point safe". That means that should a single one of those shaped charges be fired via static electricity, etc., that there would be at the least severe contamination and quite likely somewhat of a yield.

The original nuclear bombs used hi voltage detonators, detonators which were incredibly highly sensitive - and they all had to be connected by hand just before the bomb was loaded. If you read the command&conquer book that was linked to above you will see that the risks that were being taken with early designs were just insane and it's incredible that we have not had an accidental detonation during the cold war.

You're right, there wasn't any immediate danger of fission. It's just that now we know how deadly and powerful these things were, it seems almost endearing to see them being handled this way.

Are they? These aren't the multi-megaton nuclear behemoths that people associate with nukes post-cold war. Those bombs are three orders of magnitude more powerful than the one shown in the picture. This bomb is probably comparable to a warehouse full of conventional weapons, which the shirtless youngster was probably manhandling in his everyday work.

And unlike a conventional weapon, it's pretty hard for a nuke of this design to accidentally explode.

They're still deadly, and as he said, it's simply endearing.

The Goldsboro incident went 5/6ths of the way: http://www.ecu.edu/cs-admin/news/brokenarrow.cfm