I'm really not sure why we're still alive.
Anthropic principle / many-worlds interpretation? All the outcomes in which these accidents lead to nuclear war are no longer observable ;-)
Hardly. For starters, I don't agree that the risk of nuclear explosion was high, given the electronic precision required to detonate a hydrogen bomb's explosive lenses correctly. And had the W53 warhead exploded at its full nine-megaton potential, Nukemap predicts 3rd-degree burns would not have extended even as far as Conway, and 11000 casualties of which 2500 were fatal (probably much less with a 1980 population).
The state would have faced a greater threat from fallout, but considering the advance warning of a detonation, lack of damage to infrastructure outside the immediate blast zone, and general cold war readiness for the effects of a nuclear explosion, casualties from fallout would have been far below the worst-case scenario. Two days' shelter while fallout radiation fell to 1% of its initial level would be easily achievable.
Please do explain that. As far as I understand, the explosives and the radioactive materials are all there in the warhead, the "precision" only affects the "quality" of the explosion (i.e. the number of "megadeaths" https://en.wikipedia.org/wiki/Megadeath )
Only the first few atom bombs had the missing part of the radioactive matter outside the of the bomb when the bomb was fully unarmed, technically making the explosion impossible, as there isn't enough mass for an explosion without the missing part.
But since the early fifties, all the material needed for the nuclear explosion is always in the warhead.
Note that in the event here discussed (it was an explosion of the fully equipped H-warhead missile in Damascus, Arkansas, US)
really nothing "special" happened: one of the technicians just accidentally dropped one metal socket during his maintenance work, that was all:
And that was enough to cause the explosion of the rocket. Would any "expert" before that event claim it was all that was needed?
"The W53 warhead landed about 100 feet (30 m) from the launch complex's entry gate; its safety features operated correctly and prevented any loss of radioactive material."
(I am not a nuclear engineer)
If you have a ball of fissile material, there are two sizes that are interesting to you. There's the point at which the material goes critical: on average, every neutron emitted causes the emission of more than one neutron. However, there are two types of neutron emission: prompt neutrons (released immediately when an incoming neutron breaks apart an atom), and delayed neutrons, released eventually by the decay of fission products. If you're producing one prompt neutron on average, then you're at prompt criticality.
Nuclear reactors prompt-subcritical but delayed-critical. Because the exponential growth of neutrons in a delayed-critical material is relatively slow, it can be managed by futzing with control rods.
If undisturbed, a supercritcal fissile mass will explode. The question is, how energetically? If it's delayed-critical, not very. The time scale characterizing the exponential growth is large compared to the time required for the explosion to propagate through the mass, so the mass will explode with not much more than the minimal amount of energy required to render it subcritical again. This is messy, but not what you think of when you imagine a nuclear explosion.
If the mass is prompt-critical, then the exponential growth is much faster. Even once the mass has released enough energy to explode, it still takes time for the mass to expand enough to be rendered subcritical. In that time, a prompt-supercritical mass will undergo many more generations, resulting in an actual nuclear explosion.
To get an actual nuclear detonation, then, you need to get your fissile material from subcritical to prompt-supercritical as fast as possible, so it doesn't predetonate unimpressively. This is a tricky task, requiring carefully shaped explosives, and pretty unlikely to happen by chance.
It's not "by chance," the warhead is carefully designed to make it and everything needed is already there, there are no missing parts. The "software" maybe doesn't activate the parts optimally or at all if there's luck but nothing is missing inside.
In the given case, "only" the rocket body exploded (with the fully functional warhead on it) even if it's not designed to do so, and only because of one single fallen small piece of metal (a single socket).
In that sense, we would've lost Arkansas, turning it into a place with hardly any residents
On the another bomb, from which point of view the dropping sequence was less "normal" (the breakup of the plane made less clear-cut case from the perspective of that one, so some internal components didn't activate) the same switch was discovered in the "on" position.
So it was really, really close call.
(A "small" curiosity: These bombs are two-stage bombs, one weaker nuclear explosion forces the next, one stronger. The "weaker one" part of one of the bombs, with its radioactive content that has enough material for a nuclear explosion is still there(!) deep in the ground.)