CHARACTERISTICS OF THE DAMAGE CAUSED BY THE ATOMIC BOMBS


The damage to man-made structures caused by the bombs was due to two
distinct causes: first the blast, or pressure wave, emanating from the
center of the explosion, and, second, the fires which were caused either by
the heat of the explosion itself or by the collapse of buildings containing
stoves, electrical fixtures, or any other equipment which might produce
what is known as a secondary fire, and subsequent spread of these fires.

The blast produced by the atomic bomb has already been stated to be
approximately equivalent to that of 20,000 tons of T.N.T. Given this
figure, one may calculate the expected peak pressures in the air, at
various distances from the center of the explosion, which occurred
following detonation of the bomb. The peak pressures which were calculated
before the bombs were dropped agreed very closely with those which were
actually experienced in the cities during the attack as computed by Allied
experts in a number of ingenious ways after the occupation of Japan.

The blast of pressure from the atomic bombs differed from that of ordinary
high explosive bombs in three main ways:

A. Downward thrust. Because the explosions were well up in the air, much
of the damage resulted from a downward pressure. This pressure of course
most largely effected flat roofs. Some telegraph and other poles
immediately below the explosion remained upright while those at greater
distances from the center of damage, being more largely exposed to a