That's called one-point safety. One detonation point, that is. It relies on the fact that, to achieve nuclear yield, the plutonium core must be compressed symme

That's called one-point safety. One detonation point, that is. It relies on the fact that, to achieve nuclear yield, the plutonium core must be compressed symmetrically. That requires that all the shaped charges placed around the core are set off nearly simultaneously. If they are not (e.g., if the bomb is in a fire, and the first charge cooks off), then the core is destroyed without being compressed in the manner necessary to initiate a chain reaction. See http://en.wikipedia.org/wiki/Nuclear_weapon_design#Warhead_design_safety http://en.wikipedia.org/wiki/Nuclear_weapon_design#Warhead_d...