The Atomic Bombings of Hiroshima and Nagasaki | Page 5

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
waves.
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.

MAIN CONCLUSIONS
The following are the main conclusions which were reached after
thorough examination of the effects of the bombs dropped on
Hiroshima and Nagasaki:
1. No harmful amounts of persistent radioactivity were present after the
explosions as determined by:
A. Measurements of the intensity of radioactivity at the time of the
investigation; and
B. Failure to find any clinical evidence of persons harmed by persistent
radioactivity.
The effects of the atomic bombs on human beings were of three main
types:
A. Burns, remarkable for (1) the great ground area over which they
were inflicted