OPERATION CROSSROADS. EFFECT OF AIR BLAST ON SUPERSTRUCTURE

The properties of the air blast engendered by the detonation of an atomic bomb from the physicist's point of view are described in detail in other Crossroads reports. For purposes of evaluating the effects of air blast on ship structure, and, more especially, superstructures, a brief description and analysis of the characteristics of air blast from the engineer's point of view is of value. Measurements of air blast during Tests A and B indicate that the air blast caused by the atomic detonation has the same essential characteristics as air blast caused by TNT and similar molecular detonations. The air blast results in Test A show that the atomic detonation was roughly equivalent in its blast effects to 20,000 tons of TNT exploded at the same point at which the bomb burst. The air blast results over the range of distance 500 yards to 1300 yards in Test B agree well with the air blast which would be produced by 4,000 tons of TNT exploded at ground level over smooth ground. The air blast is in the form of a spherical pressure wave. This wave moves outward from the center of detonation very rapidly. The speed of advance of the wave is a function of the peak or maximum pressure in the wave at any point. About 300 yards from the center of detonation, the maximum or peak pressure is about 150 pounds per square inch and the speed of advance of the wave is about three times the speed of sound at atmospheric pressure. At 50 pounds per square inch peak pressure, the speed of the wave is about one and three-quarters times the speed of sound at atmospheric pressure, the speed of advance of the wave is approximately sonic speed.