FWIW, according to Daniel Ellsberg†, the switch in question was the pilot's arm/safe switch. I would think that switch would be more like the lawnmower switch and less like the other three switches, which were presumably operated by sensors and circuitry.
E.g., an automatic system senses the bomb is dropping, so it deploys the chute and charges up the firing capacitors. Then another system detects the bomb has reached firing altitude and tries to detonate, but nothing happens because the arm/safe switch is on safe.
E.g., an automatic system senses the bomb is dropping, so it deploys the chute and charges up the firing capacitors. Then another system detects the bomb has reached firing altitude and tries to detonate, but nothing happens because the arm/safe switch is on safe.
†http://en.wikipedia.org/wiki/1961_Goldsboro_B-52_crash