Back in the 1950s when nuclear war was thought to be a real possibility, we were all taught in school to “duck and cover” at the first flash, to dive under our desks and cover our heads with our arms. If outside, we were to crouch against a building. We now scoff to think such a feeble reaction would protect us from an atomic blast, but a recent large meteor fall in Russia’s Ural mountains illustrates its wisdom.
An eyewitness to the meteor fall says, “I was in the office when suddenly I saw a really bright flash in the window in front of me. Then I smelt fumes. I looked out the window and saw a huge line of smoke, like you get from a plane but many times bigger. A few minutes later the window suddenly came open and there was a huge explosion, followed by lots of little explosions.”
Note that the explosion came a few minutes after the flash. Both occurred simultaneously, but the flash arrived almost instantaneously at the speed of light while the explosion arrived later at the much slower speed of sound. When the explosion is very large and distant, the time difference could be a few minutes (or at least seem that long).
Now imagine a school classroom in an atomic attack. In the middle of a class there is an immensely bright, silent flash. What does everyone do? Go to the window to see what it was, but there is no sign of anything, only eerie silence. A minute or so goes by, very long under those circumstances, and everyone assumes it must be over, whatever it was. Then the explosion arrives, shattering the window in everyone’s face and knocking them to the far wall. They would have been much safer huddled under their desks.
Also back in those days, newspapers would publish a map with a bullseye centered over, say, Philadelphia’s City Hall as ground zero of an atomic blast. The first ring, one mile out, would mark complete death and destruction. The next ring, 5 miles out, would be severe destruction with a few survivors. The last ring, 20 miles out, would mark extensive damage with many blast survivors subject to lingering death from radiation. (This is only an approximation from my own memory, but you get the idea.)
“Duck and cover” was not expected to help those in the inner ring or even the next, but it could be a life-saver for the many more further out. The only criticism is that I have no recollection of being told how long to stay down. Few of us have any experience with distant explosions, and I would probably have stood up again within a minute, just in time to get a face full of glass.
(An interesting website, http://www.carloslabs.com/node/20, generates similar bullseye maps for any location and for a variety of bombs.)