I worked in a Naval plant that repaired and aligned the guidence systems for ICBMs on our subs.
It was a given that we’d see no flash, as our nervous system doesn’t work that fast.
Telling them not to look at the flash was not sillier than telling them to get under their desks! But apparently they had drills; just like today students have fire drills and tornado drills, they had nuclear bomb drills. LOL He confesses he was terrified at the idea of strangers coming and taking the teacher away. Would his mom still be allowed to pick him up? It makes me wonder what the purpose of that was... maybe trying to bring up a generation scared of the Soviets?