The Making of the Atomic Bomb: 25th Anniversary Edition

by Richard Rhodes

Yale Medical School pathologist working with a joint American-Japanese study commission a few months after the war, Averill A. Liebow, observes: Accompanying the flash of light was an instantaneous flash of heat . . . Its duration was probably less than one tenth of a second and its intensity was sufficient to cause nearby flammable objects . . . to burst into flame and to char poles as far as 4,000 yards away from the hypocenter [i.e., the point on the ground directly below the fireball]. . . . At 600–700 yards it was sufficient to chip and roughen granite. . . . The heat also produced bubbling of tile to about 1,300 yards. It has been found by experiment that to produce this effect a temperature of [3,000° F] acting for four seconds is necessary, but under these conditions the effect is deeper, which indicates that the temperature was higher and the duration less during the Hiroshima explosion.