The Atomic Bombings of Hiroshima and Nagasaki
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The Manhattan Engineer District >> The Atomic Bombings of Hiroshima and Nagasaki
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The best example of shielding by a hill was southeast of the center of
explosion in Nagasaki. The damage at 8,000 feet from X consisted of light
plaster damage and destruction of about half the windows. These buildings
were of European type and were on the reverse side of a steep hill. At the
same distance to the south-southeast the damage was considerably greater,
i.e., all windows and frames, doors, were damaged and heavy plaster damage
and cracks in the brick work also appeared. The contrast may be
illustrated also by the fact that at the Nagasaki Prefectural office at
10,800 feet the damage was bad enough for the building to be evacuated,
while at the Nagasaki Normal School to which the Prefectural office had
been moved, at the same distance, the damage was comparatively light.
Because of the height of the bursts no evidence was expected of the
shielding of one building by another, at least up to a considerable radius.
It was in fact difficult to find any evidence at any distance of such
shielding. There appeared to have been a little shielding of the building
behind the Administration Building of the Torpedo Works in Nagasaki, but
the benefits were very slight. There was also some evidence that the group
of buildings comprising the Medical School in Nagasaki did afford each
other mutual protection. On the whole, however, shielding of one building
by another was not noticeable.
There was one other peculiar type of shielding, best exhibited by the
workers' houses to the north of the torpedo plant in Nagasaki. These were
6,000 to 7,000 feet north of X. The damage to these houses was not nearly
as bad as those over a thousand feet farther away from the center of
explosion. It seemed as though the great destruction caused in the torpedo
plant had weakened the blast a little, and the full power was not restored
for another 1,000 feet or more.
FLASH BURN
As already stated, a characteristic feature of the atomic bomb, which is
quite foreign to ordinary explosives, is that a very appreciable fraction
of the energy liberated goes into radiant heat and light. For a
sufficiently large explosion, the flash burn produced by this radiated
energy will become the dominant cause of damage, since the area of burn
damage will increase in proportion to the energy released, whereas the area
of blast damage increases only with the two-thirds power of the energy.
Although such a reversal of the mechanism of damage was not achieved in the
Hiroshima and Nagasaki bombs, the effects of the flash were, however, very
evident, and many casualties resulted from flash burns. A discussion of
the casualties caused by flash burns will be given later; in this section
will be described the other flash effects which were observed in the two
cities.
The duration of the heat radiation from the bomb is so short, just a few
thousandths of a second, that there is no time for the energy falling on a
surface to be dissipated by thermal defusion; the flash burn is typically a
surface effect. In other words the surface of either a person or an object
exposed to the flash is raised to a very high temperature while immediately
beneath the surface very little rise in temperature occurs.
The flash burning of the surface of objects, particularly wooden objects,
occurred in Hiroshima up to a radius of 9,500 feet from X; at Nagasaki
burns were visible up to 11,000 feet from X. The charring and blackening
of all telephone poles, trees and wooden posts in the areas not destroyed
by the general fire occurred only on the side facing the center of
explosion and did not go around the corners of buildings or hills. The
exact position of the explosion was in fact accurately determined by taking
a number of sights from various objects which had been flash burned on one
side only.
To illustrate the effects of the flash burn, the following describes a
number of examples found by an observer moving northward from the center of
explosion in Nagasaki. First occurred a row of fence posts at the north
edge of the prison hill, at 0.3 miles from X. The top and upper part of
these posts were heavily charred. The charring on the front of the posts
was sharply limited by the shadow of a wall. This wall had however been
completely demolished by the blast, which of course arrived some time after
the flash. At the north edge of the Torpedo works, 1.05 miles from X,
telephone poles were charred to a depth of about 0.5 millimeters. A light
piece of wood similar to the flat side of an orange crate, was found
leaning against one of the telephone poles. Its front surface was charred
the same way as the pole, but it was evident that it had actually been
ignited. The wood was blackened through a couple of cracks and nail holes,
and around the edges onto the back surface. It seemed likely that this
piece of wood had flamed up under the flash for a few seconds before the
flame was blown out by the wind of the blast. Farther out, between 1.05
and 1.5 miles from the explosion, were many trees and poles showing a
blackening. Some of the poles had platforms near the top. The shadows
cast by the platforms were clearly visible and showed that the bomb had
detonated at a considerable height. The row of poles turned north and
crossed the mountain ridge; the flash burn was plainly visible all the way
to the top of the ridge, the farthest burn observed being at 2.0 miles from
X.
Another striking effect of the flash burn was the autumnal appearance of
the bowl formed by the hills on three sides of the explosion point. The
ridges are about 1.5 miles from X. Throughout this bowl the foliage turned
yellow, although on the far side of the ridges the countryside was quite
green. This autumnal appearance of the trees extended to about 8,000 feet
from X.
However, shrubs and small plants quite near the center of explosion in
Hiroshima, although stripped of leaves, had obviously not been killed.
Many were throwing out new buds when observers visited the city.
There are two other remarkable effects of the heat radiated from the bomb
explosion. The first of these is the manner in which heat roughened the
surface of polished granite, which retained its polish only where it was
shielded from the radiated heat travelling in straight lines from the
explosion. This roughening by radiated heat caused by the unequal
expansion of the constituent crystals of the stone; for granite crystals
the melting temperature is about 600 deg centigrade. Therefore the depth
of roughening and ultimate flaking of the granite surface indicated the
depth to which this temperature occurred and helped to determine the
average ground temperatures in the instant following the explosion. This
effect was noted for distances about 1 1/2 times as great in Nagasaki as in
Hiroshima.
The second remarkable effect was the bubbling of roof tile. The size of
the bubbles and their extent was proportional to their nearness to the
center of explosion and also depended on how squarely the tile itself was
faced toward the explosion. The distance ratio of this effect between
Nagasaki and Hiroshima was about the same as for the flaking of polished
granite.
Various other effects of the radiated heat were noted, including the
lightening of asphalt road surfaces in spots which had not been protected
from the radiated heat by any object such as that of a person walking along
the road. Various other surfaces were discolored in different ways by the
radiated heat.
As has already been mentioned the fact that radiant heat traveled only in
straight lines from the center of explosion enabled observers to determine
the direction toward the center of explosion from a number of different
points, by observing the "shadows" which were cast by intervening objects
where they shielded the otherwise exposed surface of some object. Thus the
center of explosion was located with considerable accuracy. In a number of
cases these "shadows" also gave an indication of the height of burst of the
bomb and occasionally a distinct penumbra was found which enabled observers
to calculate the diameter of the ball of fire at the instant it was
exerting the maximum charring or burning effect.
One more interesting feature connected with heat radiation was the charring
of fabric to different degrees depending upon the color of the fabric. A
number of instances were recorded in which persons wearing clothing of
various colors received burns greatly varying in degree, the degree of burn
depending upon the color of the fabric over the skin in question. For
example a shirt of alternate light and dark gray stripes, each about 1/8 of
an inch wide, had the dark stripes completely burned out but the light
stripes were undamaged; and a piece of Japanese paper exposed nearly 1 1/2
miles from X had the characters which were written in black ink neatly
burned out.
CHARACTERISTICS OF THE INJURIES TO PERSONS
Injuries to persons resulting from the atomic explosions were of the
following types:
A. Burns, from
1. Flash radiation of heat
2. Fires started by the explosions.
B. Mechanical injuries from collapse of buildings, flying debris, etc.
C. Direct effects of the high blast pressure, i.e., straight
compression.
D. Radiation injuries, from the instantaneous emission of gamma rays and
neutrons.
It is impossible to assign exact percentages of casualties to each of the
types of injury, because so many victims were injured by more than one
effect of the explosions. However, it is certain that the greater part of
the casualties resulted from burns and mechanical injures. Col. Warren,
one of America's foremost radioligists, stated it is probable that 7 per
cent or less of the deaths resulted primarily from radiation disease.
The greatest single factor influencing the occurrence of casualties was the
distance of the person concerned from the center of explosion.
Estimates based on the study of a selected group of 900 patients indicated
that total casualties occurred as far out as 14,000 feet at Nagasaki and
12,000 feet at Hiroshima.
Burns were suffered at a considerable greater distance from X than any
other type of injury, and mechanical injuries farther out than radiation
effects.
Medical findings show that no person was injured by radioactivity who was
not exposed to the actual explosion of the bombs. No injuries resulted
from persistent radioactivity of any sort.
BURNS
Two types of burns were observed. These are generally differentiated as
flame or fire burn and so-called flash burn.
The early appearance of the flame burn as reported by the Japanese, and the
later appearance as observed, was not unusual.
The flash burn presented several distinctive features. Marked redness of
the affected skin areas appeared almost immediately, according to the
Japanese, with progressive changes in the skin taking place over a period
of a few hours. When seen after 50 days, the most distinctive feature of
these burns was their sharp limitation to exposed skin areas facing the
center of the explosion. For instance, a patient who had been walking in a
direction at right angles to a line drawn between him and the explosion,
and whose arms were swinging, might have burns only on the outside of the
arm nearest the center and on the inside of the other arm.
Generally, any type of shielding protected the skin against flash burns,
although burns through one, and very occasionally more, layers of clothing
did occur in patients near the center. In such cases, it was not unusual
to find burns through black but not through white clothing, on the same
patient. Flash burns also tended to involve areas where the clothes were
tightly drawn over the skin, such as at the elbows and shoulders.
The Japanese report the incidence of burns in patients surviving more than
a few hours after the explosion, and seeking medical attention, as high as
95%. The total mortalities due to burns alone cannot be estimated with any
degree of accuracy. As mentioned already, it is believed that the majority
of all the deaths occurred immediately. Of these, the Japanese estimate
that 75%, and most of the reports estimate that over 50%, of the deaths
were due to burns.
In general, the incidence of burns was in direct proportion to the distance
from X. However, certain irregularities in this relationship result in the
medical studies because of variations in the amount of shielding from flash
burn, and because of the lack of complete data on persons killed outright
close to X.
The maximum distance from X at which flash burns were observed is of
paramount interest. It has been estimated that patients with burns at
Hiroshima were all less than 7,500 feet from the center of the explosion at
the time of the bombing. At Nagasaki, patients with burns were observed
out to the remarkable distance of 13,800 feet.
MECHANICAL INJURIES
The mechanical injuries included fractures, lacerations, contusions,
abrasions, and other effects to be expected from falling roofs, crumbling
walls, flying debris and glass, and other indirect blast effects. The
appearance of these various types of mechanical injuries was not remarkable
to the medical authorities who studied them.
It was estimated that patients with lacerations at Hiroshima were less than
10,600 feet from X, whereas at Nagasaki they extended as far as 12,200
feet.
The tremendous drag of wind, even as far as 1 mile from X, must have
resulted in many injuries and deaths. Some large pieces of a prison wall,
for example, were flung 80 feet, and many have gone 30 feet high before
falling. The same fate must have befallen many persons, and the chances of
a human being surviving such treatment are probably small.
BLAST INJURIES
No estimate of the number of deaths or early symptoms due to blast pressure
can be made. The pressures developed on the ground under the explosions
were not sufficient to kill more than those people very near the center of
damage (within a few hundred feet at most). Very few cases of ruptured ear
drums were noted, and it is the general feeling of the medical authorities
that the direct blast effects were not great. Many of the Japanese
reports, which are believed to be false, describe immediate effects such as
ruptured abdomens with protruding intestines and protruding eyes, but no
such results were actually traced to the effect of air pressure alone.
RADIATION INJURIES
As pointed out in another section of this report the radiations from the
nuclear explosions which caused injuries to persons were primarily those
experienced within the first second after the explosion; a few may have
occurred later, but all occurred in the first minute. The other two
general types of radiation, viz., radiation from scattered fission products
and induced radioactivity from objects near the center of explosion, were
definitely proved not to have caused any casualties.
The proper designation of radiation injuries is somewhat difficult.
Probably the two most direct designations are radiation injury and gamma
ray injury. The former term is not entirely suitable in that it does not
define the type of radiation as ionizing and allows possible confusion with
other types of radiation (e.g., infra-red). The objection to the latter
term is that it limits the ionizing radiation to gamma rays, which were
undoubtedly the most important; but the possible contribution of neutron
and even beta rays to the biological effects cannot be entirely ignored.
Radiation injury has the advantage of custom, since it is generally
understood in medicine to refer to X-ray effect as distinguished from the
effects of actinic radiation. Accordingly, radiation injury is used in
this report to mean injury due only to ionizing radiation.
According to Japanese observations, the early symptons in patients
suffering from radiation injury closely resembled the symptons observed in
patients receiving intensive roentgen therapy, as well as those observed in
experimental animals receiving large doses of X-rays. The important
symptoms reported by the Japanese and observed by American authorities were
epilation (lose of hair), petechiae (bleeding into the skin), and other
hemorrhagic manifestations, oropharyngeal lesions (inflammation of the
mouth and throat), vomiting, diarrhea, and fever.
Epilation was one of the most spectacular and obvious findings. The
appearance of the epilated patient was typical. The crown was involved
more than the sides, and in many instances the resemblance to a monk's
tonsure was striking. In extreme cases the hair was totally lost. In some
cases, re-growth of hair had begun by the time patients were seen 50 days
after the bombing. Curiously, epilation of hair other than that of the
scalp was extremely unusual.
Petechiae and other hemorrhagic manifestations were striking findings.
Bleeding began usually from the gums and in the more seriously affected was
soon evident from every possible source. Petechiae appeared on the limbs
and on pressure points. Large ecchymoses (hemorrhages under the skin)
developed about needle punctures, and wounds partially healed broke down
and bled freely. Retinal hemorrhages occurred in many of the patients.
The bleeding time and the coagulation time were prolonged. The platelets
(coagulation of the blood) were characteristically reduced in numbers.
Nausea and vomiting appearing within a few hours after the explosion was
reported frequently by the Japanese. This usually had subsided by the
following morning, although occasionally it continued for two or three
days. Vomiting was not infrequently reported and observed during the
course of the later symptoms, although at these times it generally appeared
to be related to other manifestation of systemic reactions associated with
infection.
Diarrhea of varying degrees of severity was reported and observed. In the
more severe cases, it was frequently bloody. For reasons which are not yet
clear, the diarrhea in some cases was very persistent.
Lesions of the gums, and the oral mucous membrane, and the throat were
observed. The affected areas became deep red, then violacious in color;
and in many instances ulcerations and necrosis (breakdown of tissue)
followed. Blood counts done and recorded by the Japanese, as well as
counts done by the Manhattan Engineer District Group, on such patients
regularly showed leucopenia (low-white blood cell count). In extreme cases
the white blood cell count was below 1,000 (normal count is around 7,000).
In association with the leucopenia and the oropharyngeal lesions, a variety
of other infective processes were seen. Wounds and burns which were
healing adequately suppurated and serious necrosis occurred. At the same
time, similar ulcerations were observed in the larynx, bowels, and in
females, the gentalia. Fever usually accompanied these lesions.
Eye injuries produced by the atomic bombings in both cities were the
subject of special investigations. The usual types of mechanical injuries
were seen. In addition, lesions consisting of retinal hemorrhage and
exudation were observed and 75% of the patients showing them had other
signs of radiation injury.
The progress of radiation disease of various degrees of severity is shown
in the following table:
Summary of Radiation Injury
Clinical Symptoms and Findings
Day
after
Explo-
sion Most Severe Moderately Severe Mild
1. 1. Nausea and vomiting 1. Nausea and vomiting
2. after 1-2 hours. after 1-2 hours.
3. NO DEFINITE SYMPTOMS
4.
5. 2. Diarrhea
6. 3. Vomiting NO DEFINITE SYMPTOMS
7. 4. Inflammation of the
mouth and throat
8. 5. Fever
9. 6. Rapid emaciation
10. Death NO DEFINITE SYMPTOMS
11. (Mortality probably 2. Beginning epilation.
12. 100%)
13.
14.
15.
16.
17.
18. 3. Loss of appetite
19. and general malaise. 1. Epilation
20. 4. Fever. 2. Loss of appetite
21. 5. Severe inflammation and malaise.
22. of the mouth and throat 3. Sore throat.
23. 4. Pallor.
24. 5. Petechiae
25. 6. Diarrhea
26. 7. Moderate emacia-
27. 6. Pallor. tion.
28. 7. Petechiae, diarrhea
29. and nose bleeds (Recovery unless com-
30. plicated by previous
31. 8. Rapid emaciation poor health or
Death super-imposed in-
(Mortality probably 50%) juries or infec-
tion).
It was concluded that persons exposed to the bombs at the time of
detonation did show effects from ionizing radiation and that some of these
patients, otherwise uninjured, died. Deaths from radiation began about a
week after exposure and reached a peak in 3 to 4 weeks. They practically
ceased to occur after 7 to 8 weeks.
Treatment of the burns and other physical injuries was carried out by the
Japanese by orthodox methods. Treatment of radiation effects by them
included general supportative measures such as rest and high vitamin and
caloric diets. Liver and calcium preparations were administered by
injection and blood transfusions were used to combat hemorrhage. Special
vitamin preparations and other special drugs used in the treatment of
similar medical conditions were used by American Army Medical Corps
officers after their arrival. Although the general measures instituted
were of some benefit no definite effect of any of the specific measures on
the course of the disease could be demonstrated. The use of sulfonamide
drugs by the Japanese and particularly of penicillin by the American
physicians after their arrival undoubtedly helped control the infections
and they appear to be the single important type of treatment which may have
effectively altered the earlier course of these patients.
One of the most important tasks assigned to the mission which investigated
the effects of the bombing was that of determining if the radiation effects
were all due to the instantaneous discharges at the time of the explosion,
or if people were being harmed in addition from persistent radioactivity.
This question was investigated from two points of view. Direct
measurements of persistent radioactivity were made at the time of the
investigation. From these measurements, calculations were made of the
graded radiation dosages, i.e., the total amount of radiation which could
have been absorbed by any person. These calculations showed that the
highest dosage which would have been received from persistent radioactivity
at Hiroshima was between 6 and 25 roentgens of gamma radiation; the highest
in the Nagasaki Area was between 30 and 110 roentgens of gamma radiation.
The latter figure does not refer to the city itself, but to a localized
area in the Nishiyama District. In interpreting these findings it must be
understood that to get these dosages, one would have had to remain at the
point of highest radioactivity for 6 weeks continuously, from the first
hour after the bombing. It is apparent therefore that insofar as could be
determined at Hiroshima and Nagasaki, the residual radiation alone could
not have been detrimental to the health of persons entering and living in
the bombed areas after the explosion.
The second approach to this question was to determine if any persons not in
the city at the time of the explosion, but coming in immediately afterwards
exhibited any symptoms or findings which might have been due to persistence
induced radioactivity. By the time of the arrival of the Manhattan
Engineer District group, several Japanese studies had been done on such
persons. None of the persons examined in any of these studies showed any
symptoms which could be attributed to radiation, and their actual blood
cell counts were consistently within the normal range. Throughout the
period of the Manhattan Engineer District investigation, Japanese doctors
and patients were repeatedly requested to bring to them any patients who
they thought might be examples of persons harmed from persistent
radioactivity. No such subjects were found.
It was concluded therefore as a result of these findings and lack of
findings, that although a measurable quantity of induced radioactivity was
found, it had not been sufficient to cause any harm to persons living in
the two cities after the bombings.
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