This is a little off topic but having read a few books about the bombings and the damage I have always been a supporter of duck and cover, my impression is that if they knew what it was and had been conditioned to protect themselves from the burns and flying debris the casualties would have been far fewer, including the blindness.
Well Okay... Of course at that time, even we did not really know what the total effects would be. I think warning them to leave was more than enough - of course, if we have given them much more information, they would have sent their complete Air Force to stop it.... One bomber did not scare them...