UNDERWATER A-BOMBS PRODUCE SERIOUS LINGERING RADIATION. In underwater explosions, large portions of the bomb's radioactive wastes will be "trapped" by the water and then spread over the immediate area. Under these conditions, serious ground pollution is to be expected.
After a water or underground burst a cloud of very radioactive mist or dust might form and spread, particularly downwind, injuring people who weren't well sheltered.
STAY UNDER COVER FOR AT LEAST AN HOUR AFTER GROUND OR UNDERWATER BURSTS. If the explosion has been underground, at ground level, or in the water, stay in your shelter. If caught in the open, get indoors right away. Then stay indoors for at least an hour or until you get instructions. It may be necessary to stay inside for three or four hours. The reason for this is that most lingering radioactivity loses its power very fast. So staying undercover for a while will greatly reduce the danger.
AVOID GETTING WET AFTER UNDERWATER BURSTS. Any rain or mist that comes right after an atomic explosion should be considered dangerous, even though it may not always be radioactive. Keep from getting wet if you possibly can.
And remember that an air burst will leave no lingering radioactivity of importance, so after a few minutes it will be safe to get out and help fight fires or to help people who may need it.
HOW IS RADIOACTIVITY DETECTED?
While we cannot see, hear, feel, smell, or taste radioactivity, its presence readily can be detected