3: Summary of Damages and Injuries
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Both the Hiroshima and the Nagasaki atomic bombs exhibited similar effects.
The damages to man-made structures and other inanimate objects was the
result in both cities of the following effects of the explosions:
A. Blast, or pressure wave, similar to that of normal explosions.
B. Primary fires, i.e., those fires started instantaneously by the heat
radiated from the atomic explosion.
C. Secondary fires, i.e., those fires resulting from the collapse of
buildings, damage to electrical systems, overturning of stoves, and other
primary effects of the blast.
D. Spread of the original fires (B and C) to other structures.
The casualties sustained by the inhabitants of both cities were due to:
A. "Flash" burns, caused directly by the almost instantaneous radiation of
heat and light at the moment of the explosion.
B. Burns resulting from the fires caused by the explosion.
C. Mechanical injuries caused by collapse of buildings, flying debris,
and forceable hurling - about of persons struck by the blast pressure
D. Radiation injuries caused by the instantaneous penetrating radiation
(in many respects similar to excessive X-ray exposure) from the nuclear
explosion; all of these effective radiations occurred during the first
minute after initiation of the explosion, and nearly all occurred during
the first second of the explosion.
No casualties were suffered as a result of any persistent radioactivity of
fission products of the bomb, or any induced radioactivity of objects near
the explosion. The gamma radiations emitted by the nuclear explosion did
not, of course, inflict any damage on structures.
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
distance damage, although comparatively light, extended for several more
miles. Glass was broken up to 12 miles.
In Nagasaki, a smaller area of the city was actually destroyed than in
Hiroshima, because the hills which enclosed the target area restricted the
spread of the great blast; but careful examination of the effects of the
explosion gave evidence of even greater blast effects than in Hiroshima.
Total destruction spread over an area of about 3 square miles. Over a
third of the 50,000 buildings in the target area of Nagasaki were destroyed
or seriously damaged. The complete destruction of the huge steel works and
the torpedo plant was especially impressive. The steel frames of all
buildings within a mile of the explosion were pushed away, as by a giant
hand, from the point of detonation. The badly burned area extended for 3
miles in length. The hillsides up to a radius of 8,000 feet were scorched,
giving them an autumnal appearance.
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