Earlier quoted context omitted.
There are not a lot of controls that work really well. And a lot of the controls that do exist were fought for tooth and nail. That is the entire point of the book. :) For example, the locks in place at each Titan II facility all had exactly the same code (1111). And they were left unlocked. Regarding the accidents, here are a few examples: Thule Airbase crash: https://en.wikipedia.org/wiki/1968_Thule_Air_Base_B-52_c…
The other way to interpret these facts is that it takes a lot of work to actually detonate a nuclear weapon, so they are pretty safe by default and can handle abuse.
As an example, an implosion type bomb needs to be detonated at several places around the bomb simultaneously. It's designed such that if you don't have detonation of the explosives all at the exact same time then the pit won't make a nuclear blast.
They're very safe in terms of accidental nuclear detonation, but still, if the explosives are detonated it's going to make quite a mess to say the least.