The number of casualties which resulted from the pure blast effect alone
(i.e., because of simple pressure) was probably negligible in comparison to
that caused by other effects.

The central portions of the cities underneath the explosions suffered
almost complete destruction. The only surviving objects were the frames of
a small number of strong reinforced concrete buildings which were not
collapsed by the blast; most of these buildings suffered extensive damage
from interior fires, had their windows, doors, and partitions knocked out,
and all other fixtures which were not integral parts of the reinforced
concrete frames burned or blown away; the casualties in such buildings near
the center of explosion were almost 100%. In Hiroshima fires sprang up
simultaneously all over the wide flat central area of the city; these fires
soon combined in an immense "fire storm" (high winds blowing inwards toward
the center of a large conflagration) similar to those caused by ordinary
mass incendiary raids; the resulting terrific conflagration burned out
almost everything which had not already been destroyed by the blast in a
roughly circular area of 4.4 square miles around the point directly under
the explosion (this point will hereafter in this report be referred to as
X). Similar fires broke out in Nagasaki, but no devastating fire storm
resulted as in Hiroshima because of the irregular shape of the city.

In both cities the blast totally destroyed everything within a radius of 1
mile from the center of explosion, except for certain reinforced concrete
frames as noted above. The atomic explosion almost completely destroyed
Hiroshima's identity as a city. Over a fourth of the population was killed
in one stroke and an additional fourth seriously injured, so that even if
there had been no damage to structures and installations the normal city
life would still have been completely shattered. Nearly everything was
heavily damaged up to a radius of 3 miles from the blast, and beyond this