UNCLASSIFIED

” Seeunity tnformation

RADIOLOGICAL
DEFENSE

wo UNCCASSTFIED __
avrn 80, 105.0). 1953
pat EP 24.1954

SECURITY GFFIQZER

Vol. Il

The Principles of

Military Defense against Atomic Weapons

Armed Forces Special Weapons Project

November 1951

UNCLASSIFIED

THE ATOMIC BOMB IN WARFARE
e Hiroshima Bomb

1.01. The first use of the atomic bomb in warfare
OK curred on 6 August 1945, at Hiroshima, in Japan.
is port city, which at the time had an estimated

: inited States aircraft appeared over the city,
but little attention was paid to them. Half an hour
be efore, the “‘all clear” had been sounded from an ear-
lier warning and, consequently, all but a few persons
had left the air-raid shelters and were on their way to
york. It is estimated that some three-quarters of the
population were then in the congested 4-square-mile
enter of the city, many of them still in the streets.

1.02. The bomb was dropped over the center of
Hiroshima and exploded at a height of about 2,000
eet above the ground. This altitude was chosen
erately, as will be seen later, in order to pro-
lu e the maximum amount of damage to structures
in the city. The explosion was accompanied by a
brilliant flash of light and an intense wave of heat,
that was felt nearly 4 miles away. Immediately
hereafter came a violent blast of air the force of

Buildings damaged by the blast were particularly
Inerable to the spread of fire, and within 20

RESTRICTED
Security Information

Chapter 1
HISTORICAL EXPERIENCE

flames. However, little or nothing could have been
done to restrict the conflagration. It is true that
the fire-fighting services and equipment in Hiroshima
were poor by American standards, but it is very
doubtful if much could have been achieved, in the
circumstances, by more efficient fire departments.
Nearly 70 percent of the city’s fire-fighting equip-
ment was destroyed and about 80 percent of the
firemen on duty were immediate casualties. Even
if the men and machines had survived the blast,
many places were inaccessible because of the streets.
being blocked with debris. Further, the damage to
water pipes made the water pressure so low that it
would have been of little use for controlling fires.

1.04. The atomie explosion over Hiroshima re-
sulted in the death of about 70,000 persons and the
injury of an almost equal number. Thus, nearly
half of the city’s population became immediate
casualties. Many people betame sick in subsequent
weeks due to overexposure to the nuclear radiation
that is a characteristic of the atomic bomb. The high
casualty rate in Hiroshima was undoubtedly due to
the fact, mentioned above, that at» the time of the
explosion a considerable proportion of the population
was concentrated near the center of the city, with
an unusually large number in the streets.

1.05. The three planes, which appeared over the
city so soon after an “‘all clear’? had been given, were
not taken seriously. It was thought that they were
observation planes, and even if they had been
bombers, their bomb load was evidently not con-
sidered sufficient to merit a further disruption of
the city’s daily routine. From the standpoint of
defense against the atomic bomb, the important
lesson is that no enemy plane, whether it comes singly
or in a group, can be disregarded. Had the inhabit-
ants of Hiroshima remained in their shelters, the
number of casualties would have been greatly de-
creased. The material destruction would presumably
have been the same, but care of the injured and

RESTRICTED
Security Information

2 CHAPTER 1

Figure 1.02a. The Hiroshima Prefecture (approximately 1,000 yards from ground zero) before the atomic explosion.

rehabilitation and repair of the city after the ex-
plosion would have been greatly facilitated.

The Nagasaki Bomb

1.06. Three days after the attack on Hiroshima,
at 1102 on 9 August 1945, an atomic bomb was ex-
ploded over the industrial seaport of Nagasaki, with
a population of 230,000.
plain which extends up two relatively narrow valleys,
between hills rising some 1,000 feet above sea level.

The city lies on a small

The heavily industrialized part was located in the
larger of the two valleys, and it was approximately
2,000 feet above this area that the bomb was ex-
ploded (fig. 1.06). As a result, the huge Mitsubishi
Ordnance Plants, which were in the Arakami valley,
were destroyed, but the harbor and commercial areas,
and much of the residential area, escaped serious
damage. One of the factors responsible was the hilly
nature of the terrain. Many houses, built in ravines,
were sheltered by the hills, and thus protected from
the blast.

1.07. The fires which followed the blast spread
more slowly and covered a smaller area (about 1.8

square miles) than at Hiroshima. There were two

reasons for this. First, the factory area at Nagasaki,
over which the bomb was dropped, contained less
combustible material than the business and resi-
And second, the wind,
which developed some time after the conflagration

dential parts of Hiroshima.

had become well established, tended to carry the fire
up the valley in a direction where there was nothing
to burn. Had the wind been in the opposite direction,
toward the shore instead of away from it, the con-
sequences might have been quite different.

1.08. Because of the tremendous psychological
shock and the disruption of communications follow-
ing the bombing of Hiroshima, reliable news was not
available in other parts of Japan. Consequently,
Nagasaki was little better prepared for the atomie
attack, with the result that about 36,000 people were
killed and 40,000 injured. The city had been on a
warning alert for more than 2 hours before the bomb
fell, but no raid alarm had been given and only a few
hundred persons were in shelters. However, because
of the time of day, and the different circumstances,
the proportion of the population in the streets in
Nagasaki was not so large as at Hiroshima. This may
account, in part, for the smaller number of casualties,

HISTORICAL EXPERIENCE 3

Figure 1.02b. The Hiroshima Prefecture after the atomic explosion.

1.09. Since a large number of the inhabitants as
well as considerable residential areas of the city sur-
vived the explosion, rescue efforts at Nagasaki were
soon organized. The water supply was partially re-

stored by the second day after the dropping of the
bomb, and some electric power was available at the
end of the same day. On the following day a few
streetcars and railway trains were running again.

Studies of Damage and Casualties
1.10. The damage and casualties due to the atomic
bombs at Hiroshima and Nagasaki are summarized
in table 1.10. For purposes of comparison the cor-
responding figures are given for the destructive air
raid on Tokyo on 10 March 1945, made largely with
incendiary bombs, and the average of 93 air attacks
on Japanese cities with similar weapons. The out-
- standing feature of the atomic bomb is seen to be the
high casualty rate per square mile destroyed. Thus,
atomic bombs have a greater “saturation” character
than bombs of the more conventional type.

1.11. Soon after the cessation of World War II,
teams of observers from the United States and from
Great Britain went to Japan to make detailed studies

of the effects of the atomie bombings on both struc-
tures and personnel. The main purpose of the studies
was to obtain information useful in the development
of defense measures. Comprehensive reports have
been issued both by the United States Strategic
Bombing Survey and the British Mission to Japan.

Table 1.10. Comparison of Casualties from Atomic and

Conventional Bombs!

Average of
Hirosh im a oe ki 1 Naa 7 as make
Homb | “Bomb | Incendiary | Incendiary
per attack
Population per
square mile 35,000 | 65,000 | 130,000 _
Square miles de-
stroyed: .. <)> « 4.7 1.8 15.8 1.8
Killed and missing 70,000 | 36,000 83,000 1,850
Injured 70,000 40,000 | 102,000 1,830
Mortality per square |
mile destroyed 15,000 20,000 5,200 1,000
Casualties per square |
mile destroyed 30,000 42,000 11,800 2,000

“The Effects of Atomic Weapons,” U.S. Government Printing Office,
Washington, D.C. .

4 CHAPTER 1

t ok,

i \ ft ; A

a. i 22 Sie

Figure 1,06, Aerial photographs taken over Nagasaki before and after the atomic bomb explosion; circles of 1,000 and 2,000 feet radius
are shown,

In addition, the Atomic Bomb Casualty Commission
‘of the United States National Research Council,
sponsored by the Atomic Energy Commission, is
still (1951) in Japan investigating the possible de-
_ layed effects of the bomb on humans.

TEST ATOMIC EXPLOSIONS

The Alamogordo Test

1.12. The first atomic bomb actually to be ex-
ploded was that in the historic test held in the early
hours of the morning of 16 July 1945, in a remote
section of the Alamogordo Air Base in New Mexico.
As seen above, the bomb proved to be a weapon of
tremendous destructive power.

1.13. In the test at Alamogordo, the bomb was
mounted on a steel tower, about 100 ft. above the
ground. The great heat produced turned the steel
into vapor, and the powerful force of the explosion
aused a wide, shallow crater to form. The dirt and
other debris disturbed by the blast was sucked up
‘by a tremendous updraft, thus forming, with the
psidual bomb materials, a dense column of smoke.
This rose rapidly to a height of nearly 5 miles before
spreading out into the mushroom-shaped cloud
tharacteristic of many atomic explosions.

_ 1.14. Even before the explosion, most of the ef-
fects of the atomic bomb had been anticipated. Due
precautions were accordingly taken to avoid injury
to the personnel responsible for making observations
both during and after the explosion. As a result, the
bomb caused no casualties.

Operation CROSSROADS

1.15. The three atomic explosions described above
took place over land areas. In order to be in a posi-
tion to protect the fleet in the event of an atomic
war, the Navy, in particular, wished to know some-
thing of the effects of an atomic explosion at sea.
Consequently, plans were set in motion for what was
known as Operation CROSSROADS, a technical
ration on a large scale, designed to supply data
for naval and military defense against the atomic
bomb. It was to be a joint effort of all the armed
forces, and when actually carried out at Bikini in
July 1946, it involved a total of 42,000 men, 242
‘ships, and 156 aircraft. Two bombs were exploded
one in the air (Test Able) and one under water
(Test Baker). Among the 70 ships of various types

‘ HISTORICAL EXPERIENCE 5

forming the target array, there were 5 battleships,
2 aircraft carriers, 4 cruisers, 12 destroyers, 8 sub-
marines, and many landing craft and merchant-type
vessels.

Test Able

1.16. In Test Able, the central target vessel was
the battleship NEVADA, and around it, within a
radius of about 1,000 yards, were about 20 other
ships. Outside this primary target area were spaced
the remaining target ships along radial lines, some-
what like the spokes of a wheel (fig. 1.16). The ships
were located much closer to each other than is usual
under operating conditions because it was desired
to obtain information as accurate as possible con-
cerning the dependence on distance from the ex-
plosion of the whole range of damage, from complete
loss, at one extreme, to complete immunity, at the
other extreme.

1.17. On the decks of the target ships were ex-
posed a wide variety of military equipment for test
purposes: these included airplanes, ammunition,
battle equipment, clothing, and packaged food. In
addition, about 400 goats and pigs, and 5,000 rats
were distributed throughout the target fleet so that
the effects of the bomb on animals could be studied.
To record the physical characteristics of the ex-
plosion, nearly 5,000 pressure gauges, 25,000 radia-
tion-measuring instruments, 750 cameras and 4 tele-
vision transmitters had been placed at strategic
points on and around the target array.

1.18. The Test Able bomb, dropped from a B-29
flying at about 30,000 ft., burst a few hundred feet
above the level of Bikini lagoon soon after 0900 on
1 July 1946. Immediately after the explosion, pilot-
less aircraft were flown over the target area. These
planes, controlled by radio, were guided through the
mushroom cloud to collect air samples for analysis.
Then, planes with observers circled the lagoon, re-
cording the damage visually and by means of
cameras. A merchant-type vessel, the GILLIAM,
the only target ship within 300 yards from surface
zero, Was seen to have sunk in less than a minute of
the explosion. A destroyer, the ANDERSON, at
less than 750 yards, was ablaze and sank in 8 min-
utes, Another merchant-type vessel, located about
1,000 yards from surface zero, sank some 40 minutes
after the burst.

6 CHAPTER 1

DD DESTROYER LST LANDING SHIP TANK LCM LANDING CRAFT MECHANIZED
SS SUBMARINE LC! LANDING CRAFT INFANTRY ARDG FLOATING DRYDOCK
APA ATTACK TRANSPORT LCT LANDING CRAFT TANK B BARGE

Figure 1.16. Drawing of the Bikini Test Able target array as the bombardier might have seen it. In order to give accurate instrumenta-
tion of graded damage the concentration of ships was much higher than would normally be found in a tactical situation.

1.19. A second destroyer, the LAMSON, had
capsized, and the Japanese cruiser SAKAWA was
low in the water (fig.1.19a). Both vessels sank
slowly, the destroyer in 8 hours, and ie cruiser on

light aircraft carrier INDEPENDENCE, less than
1,000 yards from surface zero, suffered severely
(fig. 1.19b). The flight deck was bulged up and

broken and the four stacks were demolished (fig.
6.97). Fire broke out on the hangar deck, adding to
the general destruction.

1,20. Nearly all vessels within 1,000 yards of sur-

face zero at the Bikini Test Able were either sunk
or so badly damaged as to seriously impair their
‘military efficiency. Moderate damage extended
ut to about 1,500 yards, and minor damage was
experienced within a radius of 2,000 yards. Although
the conditions of the explosion were not quite the
same as those in the air bursts over Japan, it would
seem that the area over which warships would suffer
damage due to an atomic bomb is considerably less
‘than for structures on land. This is to be expected,
since warships are built to withstand a reasonable
amount of blast. Military vehicles, such as tanks,
which were exposed on the decks of some of the tar-
get ships, also proved to be resistant to damage.
However, aircraft, similarly exposed, were found,
by comparison, to be very vulnerable.

1.21. Thenumber of fires aboard the ships was small.
This was partly due to the relative absence of combus-
tible matter on the decks. Such fires as did occur
were mainly in packaged goods exposed for the test.

1.22. Patrols entered the lagoon about 2 hours
after the detonation to determine whether it had been
appreciably contaminated by the residue from the
_air-burst atomic bomb. Only a few areas were found
to present any hazard, and in midafternoon the entire
region was declared safe. The observing fleet then
entered the lagoon. By sundown, 18 target vessels had
been boarded and the recovery of scientific instru-
_ ments and test animals was in progress. During the
following week, inspection teams made a detailed
examination of the damage suffered by the target
‘ships and their contents.

- Test Baker

1.23. The four preceding atomic explosions had all
taken place in the air, and so Test Baker at Bikini

HISTORICAL EXPERIENCE 7

presented a new feature, namely, an underwater
burst. The bomb, in a watertight caisson, was sus-
pended by a steel cable below a small landing vessel,
the LSM-60. Around this was a new target array,
again consisting of 70 ships of various types; 40 of
these were within a mile of the LSM-60, while the
others lay farther out. Each target vessel was fitted
with gauges to determine strains in the hull, and with
devices for measuring radiations that might arise
from the exploding bomb. Instruments for determin-

ing underwater shock pressures and wave heights

were placed in suitable positions.

1.24. At 0835 on 25 July 1946, the atomic bomb
under the surface of Bikini lagoon was exploded by
means of a radio signal. Instantaneously, a luminos-
ity appeared in the water, rapidly followed by the
formation of a dome-shaped bulge in the surface
above the point of burst. A fraction of a second later
a great hollow column or pillar of water began to rise
at a great speed. This column, attaining a diameter
of more than 600 yards, rose to a height of over a
mile. The hollow stem, with walls believed to be some
100 yards thick, was capped by a huge cloud, giving
the over-all appearance of a gigantic cauliflower
(fig. 1.24). The total weight of water carried upward
in the column was estimated to be well over a million
tons.

1.25. Within a few seconds of the explosion, water
from the column began to fall back into the lagoon
and there developed at the surface, around the base
of the hollow pillar, a great wave or cloud of mist,
similar to clouds of spray formed at the bottom of
Niagara Falls or other large waterfalls. This dense
mist, which can be seen above the surface of the la-
goon in figure 1.25, represents the initial stage of
what has become known as the base surge.

1.26. In a very short time, the base surge cloud was
roughly 1,000 feet high and moving rapidly outward,
maintaining an ever-expanding, doughnut-shaped
form. In about 3 minutes it reached its greatest ex-
pansion with an over-all diameter of some 3 miles.
Then it drifted downwind, appearing gradually to
lift from the surface of the water and merging with
the cauliflower-shaped cloud (fig. 1.26). Some 15
minutes later the base surge cloud was entirely clear
of the target array and was being lost among the
natural clouds of the sky.

p>
—
—

CHAPTER 1

Figure 1.19a. The Japanese cruiser SAKAWA after Test Able at Bikini.

Figure 1.19b. The light aircraft carrier INDEPENDENCE after Test Able at Bikini.

Saas se eee an ld

2 mrtarenetires animes em a> 5

HISTORICAL EXPERIENCE

Figure 1.24. The water column and “cauliflower” cloud formed by the underwater atomic explosion (Test Baker) at Bikini.

1.27. An intermittent, moderate rainfall, moving
with the wind and lasting for nearly an hour after the
In its

large

explosion, developed from the cloud system.
early stages, the rain was augmented by
amounts of water falling from the cauliflower cloud,
and carrying with them considerable quantities of
radioactive material.

1.28. When the base surge lifted, it was seen that
the 34-year old battleship ARKANSAS, which had
been near the LSM-60, had sunk, as also had a con-
crete oil barge and a landing craft in the vicinity, as
well as the LSM-60 itself. Later, it was found that
three submerged submarines had also been sunk.
The aircraft carrier SARATOGA was low in the

10 CHAPTER 1

+ nilbenat ince bitay Ay Pe oe

Figure 1.25. Initial stage of the base surge

water and listing slightly to starboard (fig. 1.28).
Many other ships showed obvious signs of severe un-
derwater damage. In addition, measurements indi-
cated that part of the energy produced by the ex-
plosion under water had been transmitted to the air.
Because the water absorbed most of the heat from
the bomb, there were no fires.

: at the base of the water column in Test Baker.

1.29. At first it was thought that the SARATOGA
might be beached for examination, and salvage tugs
entered the lagoon for the purpose. But it soon be-
same apparent that the radioactive contamination of
the carrier and the surrounding water was such that
it might involve a hazard exceeding the rigorous
tolerance limits imposed for the test operation. The

HISTORICAL EXPERIENCE 11

Figure 1.26. The base surge merging with the natural clouds of the sky.

tugs were therefore ordered to withdraw while the
crippled SARATOGA slowly sank, disappearing
completely under the surface of the lagoon by late
afternoon.

1.30. In connection with contamination after the
burst, Test Baker had an unexpected result from

which important defensive lessons have been learned.
The amount of water thrown into the air by the ex-
plosion had been predicted quite accurately, but some
of the consequences of its return to the lagoon, par-
ticularly the base surge, had not been anticipated.
The drops of water constituting the base surge cloud
were highly contaminated with the residue from the

12 CHAPTER 1

Figure 1.28. The aircraft carrier SARATOGA, several hours after Test Baker at Bikini. The damage to the stacks was not produced
by air blast, but by mass movement of water.

atomic bomb, and these droplets, passing over and
falling on ships,-left them in a condition hazardous
to human life.

1.31. Before the target vessels could be boarded, it
was necessary to remove or decrease the radioactive
contamination. This contamination cannot be neu-
tralized nor destroyed, but it may be diminished in
two ways. First, it may be washed, scrubbed, or
blasted off, in one manner or another, from the sur-
face to which it is attached, and thus diluted and
transferred elsewhere, for example, into the sea. And
second, advantage may be taken of the fact that all
radioactive material undergoes a spontaneous de-
crease of activity with time, usually referred to as
radioactive decay.

1.32. In general, both methods were used at Bikini
following Test Baker. After the lapse of a few days,
the contamination had decayed sufficiently to permit
personnel to approach all ships without exceeding the
tolerance limits which had been established for this
peacetime operation. Then various emergency meas-
ures were adopted for preliminary decontamination

to remove some of the radioactive material, so that
the ships could be returned to the United States for
examination.

1.33. A study of the damage provided valuable
data to be used in the design of ships which might
be subject to atomic attack. In addition, systematic
efforts were made to develop simple and effective de-
contamination procedures. It is of interest to men-
tion that two contaminated submarines were cleaned
and returned to service free from risk to operating
personnel. On the other hand, because of its bat-
tered condition no attempt was made to decontami-
nate the small aircraft carrier INDEPENDENCE.
Yet, long before the vessel was disposed of, the nat-
ural decay had so decreased the radioactive con-
tamination that the vessel could be occupied with
complete safety.

Further Tests

1.34. In April and May, 1948, three atomie weap-
ons of new design were tested at the United States
Atomie Energy Commission Proving Ground on

_Eniwetok Atoll, in the Marshall Islands. The major
emphasis was on the scientific and technical aspects
of weapons development. But, at the same time, im-
_ portant information, particularly in connection with
the various radiations emitted by the bomb, was ob-
tained that could be used for defensive purposes.

1.35. During 1951, further studies of the effects of
atomic explosions have been made, both in the con-
finental United States, at the Nevada Proving
Ground, and at Eniwetok. The data obtained have
served to improve our knowledge and understanding
of atomic weapons. Much of the material contained
in this manual is based on measurements and obser-
vations made at the various tests.

Atomic Explosions in Russia

- 1.36. The place of atomic defense in the nation’s
plans was given increased emphasis on 23 September
1949. On that day the President of the United States,
in a brief announcement, told the world that this
country was no longer the sole possessor of the
atomic bomb.

*“We have evidence that within recent weeks an
ttomic explosion occurred in the U.S.8. R.,” the
President said. ‘“‘Ever since atomic energy was first
released by man, the eventual development of this
new force by other nations was to be expected * * *.”
Two additional Russian atomic explosions were an-
nounced by the President in October 1951.

HISTORICAL EXPERIENCE 13

CONCLUSION

1.37. The fact that a single bomb, which can be
carried by a single plane, can cause essentially the
same damage as TNT bombs requiring a thousand
planes, has opened up a new era in offensive warfare.
But, throughout history, the introduction of a new
weapon has always been followed by the development
of protective measures which have lessened its effec-
tiveness. And in this respect the atomic bomb is no
exception. F

1.38. Since the atomic bomb is a relatively new
weapon, it is evident that the history of atomic de-
fense is short. Nevertheless, organizations in each
branch of the armed forces have been making inten-
sive studies of the problems of defense in atomic war-
fare. Every item of information, accumulated at
Alamogordo, Hiroshima, Nagasaki, Bikini, Eniwetok
and Nevada, as well as experience gained from other
types of warfare, has contributed to the store of de-
fensive knowledge. From this knowledge, new
methods of coping with atomic attack are being
devised.

1.39. The atomic weapon is known to be in the
hands of at least one other power, and might conse-
quently be used against this country’s troops, ships,
installations, and cities. Thus, an understanding of
the characteristics of the atomic bomb and of the de-
fensive measures which can be used to decrease its
effectiveness is vital to all members of the Armed
Services.

14

CHAPTER 1

SUMMARY

| The history of atomic defense began with the explosion of the bomb over Hiro-
shima, Japan, on 6 August 1945. This was the first time an atomic weapon had been
used in warfare. Because of a lack of preparation and the fact that much of the
population was in the streets at the time of the explosion, the proportion of casual-
ties was high. Three days after the attack on Hiroshima, an atomic bomb was
dropped on Nagasaki, Japan. Due to the nature of the terrain and the direction
of the wind, and the fact that fewer people were in the open, the proportion of
casualties at Nagasaki was smaller.

After the war, trained observers went to Japan to make detailed studies of the
effects of the atomic bombings on structures and personnel. In this way, much
information vital to the planning and organization of atomic defense has been
obtained.

Operation CROSSROADS, carried out at Bikini in July 1946, was a large-scale
technical operation, designed to supply data for naval and military defense against
the atomic bomb, Two bombs were exploded: one in the air (Test Able) on 1 July
1946 and the other under water (Test Baker) on 25 July 1946. Subsequently, a
number of other tests have been carried out and these have greatly improved our
understanding of the effects of atomic explosions.

The information gathered at Hiroshima and Nagasaki, as well as that obtained
from various test explosions, is being used as a basis for devising new methods of
coping with the effects of the atomic bomb. Since the weapon is known to be in
the hands of at least one other power, it is necessary that all members of the Armed
Services should become familiar with its characteristics, and with the defensive
measures which can be taken to decrease its effectiveness.

CHARACTERISTICS OF AN AIR BURST

0 1000 ; ~ 3000

Figure 3.14a, Chronological development of an atomic air burst: 0.5 second after detonation.

Almost at the instant of detonation of an atomic bomb in the air, an intensely hot and luminous ball of fire forms.
Due to its very high temperature, it emits thermal radiation capable of causing burns of exposed skin at a distance
of 2 miles on a clear day. The explosion process and the radioactive decay of the resulting fission products are ac-
companied by nuclear radiations which are also emitted from the ball of fire. These radiations can cause injury to
unprotected persons up to a mile or so away.

Very soon after the explosion a destructive shock or blast wave develops in the air and moves away from the ball
of fire. At 0.5 second after the explosion of a “nominal’’ (20-kiloton TNT equivalent) atomic bomb in the air, the ball
of fire has nearly attained its maximum size of 300 yards across, The shock wave has progressed roughly 250 yards

ahead of the ball of fire, as indicated in the figure. The overpressure in the shock front, that is, the pressure in excess
of the normal atmospheric pressure of 14.7 psi, is about 30 psi. For an air burst at a height of 2,000 feet, this shock

wave will not have reached the ground by the end of 0.5 second,

27

28 CHAPTER 3

COMME

° 1000 2000 3000

Figure 3.14b. Chronological development of an atomic air burst: 1.5 seconds after detonation.

The shock wave touches the earth’s surface at about 0.7 second after the explosion and continues to move outward
at a rate of roughly one-third of a mile per second (20 miles per minute). When this primary shock wave strikes the
ground, another shock wave is produced by reflection. At a certain point, which depends upon the height of burst
and the energy of the bomb, the primary and reflected shock waves fuse near the ground to form a reinforced wave,
called the Mach wave. For the explosion of a nominal atomic bomb at an altitude of 2,000 feet, the fusion commences
at about 1.5 seconds after the detonation. The shock front is then about 1,050 yards from the center of the explosion,
or 750 yards from ground zero, as seen in the figure. The overpressure at the front of the primary shock wave in the
air is 8 psi, but that of the reinforced Mach wave at the ground level is 24 psi. The fusion of the primary and re-
flected shock waves has thus resulted in a three-fold increase in the pressure of the air blast on the ground. Hence
the Mach effect considerably enhances the destructive effect of the explosion,

CHARACTERISTICS OF AN AIR BURST 29

YARDS ° 1000 2000 3000 4000
i 20! is! gl 5! 3I 2

ACCUMULATED THERMAL DOSAGE (CAL/CM®)

Figure 3.14c, Chronological development of an atomic air burst: 3 seconds after detonation.

As time progresses, the Mach wave front increases in height and moves outward, so that by the end of 3 seconds
after the explosion it is more than 1,600 yards from ground zero. The overpressure on the ground at the front of the
Mach wave is about 8 psi, compared with 4 psi of the primary shock wave in the air. The wind velocity on the ground
is 100 to 150 miles per hour, and the air blast has considerable destructive potential.

The interior of the ball of fire is still very hot at 3 seconds after the explosion, but the surface has cooled to such
an extent that the thermal radiation is no longer significant. Nuclear radiation, however, from the ball of fire continues
to reach the ground.

The total accumulated doses of thermal radiation, expressed in calories per sq. cm., received at various distances

from ground zero on a moderately clear day, are shown on the scale below the figure.

30

YARDS

CHAPTER 3

FORMING AND RISING

Cae WIND :

° 1000

29 17 10 5 3 2
PEAK OVERPRESSURE (PSI)

Figure 8.14d. Chronological development of an atomic air burst: 10 seconds after detonation.

After 10 seconds, the shock wave has progressed nearly 24 miles from ground zero. Although the wind velocity
near the ground is about 40 miles per hour, the overpressure at the front of the Mach wave is only about 1 psi.
Consequently, apart from plaster damage and window breakage, the destructive effect of the shock wave is essentially
over.

The ball of fire is now no longer luminous. However, it is still very hot, so that the gaseous residue from the bomb
behaves like a hot-air balloon, rising at the rate of about 220 feet per second (150 miles per hour). As it rises, it
causes air to be drawn inward and upward, somewhat similar to the updraft of a chimney. This produces a ground
wind which raises dirt and debris from the earth’s surface to form the stem of what will eventually be the charac-
teristic mushroom cloud.

The seale at the bottom of the figure shows the maximum or peak values of the overpressure on the ground
attained in the shock wave during its outward motion.

48

CHAPTER 4

| esa
CONDENSATION (WILSON) CLouD

AIR SHOCK WAVE
WATER LEVEL

0 1000 2000 3000
CRATER BOTTOM

Figure 4.10a. Chronological development of a shallow underwater burst: 2.0 seconds after detonation,

When an atomic bomb is exploded under the surface of the water, essentially all of the instantaneous nuclear
radiations and the thermal radiation are absorbed by the water. If the detonation occurs at a moderate depth, the
bubble of hot gases will burst through the surface. As a result, a hollow chimney or “plume” of water and spray is
shot upward, reaching a height of nearly 5,000 feet in 2 seconds. The gaseous bomb residue is then vented through the
hollow central portion of the plume.

The explosion under water causes a shock wave to move outward, just as in the case of an air burst. The shock
wave in water, however, travels more rapidly than in air, so that the front is more than 2 miles from surface zero at
the end of 2 seconds. The expulsion of the hot gas bubble also produces a shock wave in the air as shown in the figure.
The energy of the air blast is about one-fourth that due to the detonation of a nominal atomie bomb in the air.

After the air shock wave has passed, a dome-shaped cloud of condensed water droplets, called the Wilson cloud,
is formed for a few seconds. While this phenomenon is of scientific interest, it has no significance as far as atomic
attack or defense is concerned,

CHARACTERISTICS OF SUBSURFACE AND SURFACE BURSTS

"CAULIFLOWER"
CLOUD

FIRST WATER WAVE - HEIGHT 94 FT

Figure 4.10b. Chronological development of a shallow underwater burst: 12 seconds after detonation.

At 12 seconds after the explosion, the diameter of the plume is about 2,100 feet, and its walls of water and spray
are some 300 feet thick. The bomb residue venting through the central hollow portion spreads out to form the cauli-
flower-shaped atomic cloud, partly obscuring the top of the plume. The cloud is highly radioactive, due to the
presence of fission products, and hence it emits nuclear radiations. But the distance from the surface is too great
for these to be a significant hazard to personnel on ships surviving the explosion.

At 10 to 12 seconds after the underwater burst at Bikini, the water falling back from the plume reached the surface
of the lagoon and produced around the base of the column a ring of highly radioactive mist, called the base surge.
This ring-shaped cloud moved outward at the rate of about 120 feet per second (70 knots), parallel to the water surface.

The disturbance due to the underwater explosion caused large water waves to form. After 12 seconds, the first
of these was 300 to 400 yards from surface zero, and its height, from crest to trough, was 94 feet.

49

50

YARDS

CHAPTER 4

o 1000 2000 3000
WATER WAVE — HEIGHT 56 FT

Figure 4.10c. Chronological development of a shallow underwater burst: 20 seconds after detonation.
q i 4 t

As the water and spray forming the plume at Bikini continued to descend, the base surge cloud developed. The
highly radioactive ring of mist billowed upward and moved outward across the surface of the water. At 20 seconds
after the explosion the height of the base surge was about 800 feet, and the front was some 700 yards from surface
zero. It was then progressing outward at the rapid rate of approximately 90 feet per second (50 knots).

At about this time large quantities of water and spray, sometimes called the massive water fall-out, began to
descend from the cauliflower cloud. Its initial rate of fall was about 50 feet per second. Because of the loss of water
from the plume, in one way and another, its diameter had now decreased to 1,800 feet.

By the end of 20 seconds, the first water wave had reached 500 to 600 yards from surface zero, and its height,

from crest to trough, was roughly 56 feet.

4000

CHARACTERISTICS OF SUBSURFACE AND SURFACE BURSTS

1000 2000!
4 3 2 — | ——————- SURFACE WAVES

Figure 4.10d. Chronological development of a shallow underwater burst: 60 seconds after detonation.

At 60 seconds after the underwater burst at Bikini, the water falling from the cauliflower cloud just reached the
surface of the lagoon, as indicated by the region of primary cloud fall-out in the figure. There was thus an essentially
continuous ring of water and spray between the cloud and the surface.

At this time, the base surge cloud had become detached from the plume, so that its ring-like character was ap-
parent, as shown in cross section in the figure. The height of the base surge was about 1,000 feet and its front, moving
forward with a velocity of some 47 feet per second (30 knots), was approximately 1,600 yards from surface zero.
Its intense radioactivity is indicated by the radiation dose rate of 50,000 roentgens per hour at 60 seconds after the
detonation.

Several water waves have now developed, the first, with a height of 19 feet from crest to trough, being 1,600 to
1,700 yards from surface zero.

51

52

CHAPTER 4

2-1/2 MIN

ee. oe tid 7
MIST ~~

OR CLOUD

°
SURFACE WAVES 6 3

Figure 4.10e. Chronological development of a shallow underwater burst: 24 minutes after detonation.

By 23 minutes after the underwater explosion at Bikini, the front of the base surge was about 2,700 yards from
surface zero and had almost attained its maximum thickness of roughly 1,800 feet. The greatest effective spread of
the base surge, reached in roughly 4 minutes, was approximately 3,000 yards from surface zero, or nearly 34 miles
across. Owing to natural decay of the fission products, to condensation of the water, and thinning out of the mist
by air, the nuclear radiation dose rate at 24 minutes has decreased to 2,500 roentgens per hour. While this is much
less than in figure 4.10d, it is still very considerable. At about this time, the base surge cloud appeared to be rising
from the surface of the water. This effect was probably due to several factors, such as actual increase in altitude,
thinning out of the cloud by engulfing air, and raining out of the larger drops of water.

The descent of water and spray from the plume and from condensation in the cauliflower cloud resulted in a con-
tinuous mass of mist or cloud down to the water surface. Ultimately, this merged with the base surge, which had
spread and thinned out, and also with the natural clouds of the sky (fig. 1.26), to be finally dispersed by the wind.

CHARACTERISTICS OF SUBSURFACE AND SURFACE BURSTS

NT conducted at Dugway Proving Ground, Utah, in May of 1951. The base
The similarity of the appearance of this explosion with the underwater

Figure 4.48. Underground explosion of 160 tons of T

surge can be clearly seen during the early stages of formation.
atomic explosion shown in fig. 1.25 should be noted,

82

CHAPTER 6

Overpres- MILES} YARDS
sure

(psi)
5 2.25
2.0
2.0
1.75
3.0 1.6
4.0
1.25
5.0
6.0
i
8.0
07
ue
17
0.5
25
0.25
36

Table 6.59. Blast damage to various types of structures and matériel due to an air burst of a nominal atomic bomb at 2,000 feet altit

(LIGHT DAMAGE — OUT TO 8 MILES)

6,000 ~— HOMES — Plaster damage and window breakage.

3,500—«- STRUCTURES — Limit of partial damage,

“+ WOODEN FRAME BUILDINGS — Light damage.

3,00
STRUCTURES — Limit of moderate damage.
RADIO, RADAR, VEHICLES, REINFORCED CONCRETE AND
STEEL-FRAME BUILDINGS — Light damage.
2.500 WOODEN FRAME BUILDINGS — Moderate damage.
.)

ARTILLERY —Light damage.
2,000 RADIO AND RADAR, LIGHT STEEL-FRAME BUILDINGS—
Moderate damage.

— STRUCTURES —Limit of severe damage.

1,500

BUILDINGS, LIGHT VEHICLES — Moderate damage.
RADIO, RADAR, LIGHT STEEL~FRAME BUILDINGS—Severe damage.

re sult CONCRETE AND HEAVY STEEL-FRAME

—* LIGHT ARTILLERY, HEAVY VEHICLES —Moderate damage.
1,000

—® HEAVY STEEL- FRAME BUILDINGS—Severe damage.
—* LIGHT VEHICLES—Severe damage.

—* LIGHT ARTILLERY, REINFORCED CONCRETE BUILDINGS—
Severe damage.

500
HEAVY ARTILLERY, TANKS —Moderate damage.
HEAVY VEHICLES —Severe damage.

—t HEAVY ARTILLERY—Severe damage.
~*- TANKS —Severe damage.

GROUND ZERO

84 CHAPTER 6

Reinforced Concrete and Heavy Steel-Frame Buildings

6.71. While all types of structures can be damaged
by sufficiently high blast pressures, some are less
vulnerable than others. Reinforced concrete build-
ings and those with heavy steel frames are the most

When

partial failure occurs, for example, buckling or col-

resistant types of construction (fig. 6.71).

lapse of roof and floors, or fracture of columns, the
undamaged members can often still carry the whole
weight of the structure. In these circumstances,
complete collapse will not occur, and the damaged
portions of the building are more likely to distort

than to break.

6.72. Reinforced concrete buildings are also the
most fire resistant, for the concrete protects the steel

structural members from the heat. However, if the
contents of the building are combustible and continue
to burn intensely for some hours, the concrete can
crumble and thus expose the reinforeing steel. This
may then be weakened by the heat and the building

may collapse.

6.73. Because the strength of the steel members
decreases markedly at moderately high temperatures,
steel-frame buildings of all types are susceptible to
serious structural damage by fire. As in the case of
reinforced concrete buildings, the nature of the con-
tents and interior construction is important in de-
termining the extent of damage. If the structure has
wooden walls and floors or contains combustible
stores, the heat from the fire will cause steel members

Figure 6,71, Reinforced concrete building, 240 yards from ground zero in Japan, The walls are intact although the interior was de-
stroyed by fire.

EFFECTS OF ATOMIC EXPLOSIONS ON STRUCTURES AND MATERIEL 85

to weaken or to fail. Complete collapse of the build-
ing is then probable.

Light Steel-Frame Buildings

6.74. Many industrial buildings, repair shops, etc.,
have relatively light steel frames. In such buildings,
fracture of supporting members and joint connections
is not common, but the lightness of the frame makes
mass distortion probable (fig. 6.74). Sheathing of
corrugated iron or asbestos sheet is likely to be blown
off, leaving only the frame standing. If such sheathing
offers little resistance to the blast, the frame will suffer
little or no structural damage. However, the contents
of the building may be rendered useless by debris.
The remarks made above with respect to the effect
of fire on steel-frame buildings apply equally here.

To

—

—_

- 2B

_
‘

,
-R
.
=

+

= ——— i >” <
peas

Masonry and Brick Buildings

6.75. Heavily constructed masonry buildings may
stand up well to blast because of their great size and
weight. But, when the pressure is large enough to
cause such a structure to distort slightly, or to fail
locally, e.g., by breakage of mortar connections, the
whole building may collapse. When such a masonry
building does fail, the heavy structural material will
cause severe damage to equipment and supplies in the
interior. Light masonry and brick structures have
little resistance to blast. The debris will bury equip-
ment in the building, and will provide missiles which
will injure persons in the vicinity.

6.76. Brick and masonry buildings with load-
bearing walls if close enough to ground zero may be
destroyed by the blast. If they are, the question of
structural damage by fire is not important. However,

Figure 6.74. Light steel frame industrial bu ilding, 600 yards from ground zero in Japan. The roof and wall sheathing was stripped by
the blast, and the combustible contents destroyed by fire.

86 CHAPTER 6

fire can contribute to the damage independently by
weakening the remaining supports, thus encouraging
collapse of the building, and can add to the over-all
destruction by consuming the contents.

Wooden Buildings

6.77. Owing to their light construction, wooden
buildings have little rigidity and are easily deformed
by air blast pressure. The nailed joints are relatively
weak and can withstand little strain. Consequently,
wooden buildings will quickly collapse as the result
of an air burst. Even when they are beyond the
range of severe destruction, they may suffer damage
to roof, wall panels, and interior partitions. Stores
and equipment inside the buildings are less likely to
be damaged by the light debris, but, on account of

the inflammability of the wooden structural material,
they are more susceptible to destruction by fire.

Bridges, Highways, and Railroads

6.78. By virtue of their design, bridges are, on the
whole, remarkably resistant to air blast. It was
found after the atomie bombings of Japan that steel-
girder bridges with reinforced concrete decks suffered
relatively little (fig. 6.78). Even when there was
some damage, such as destruction of road surface or
shifting of the decks, they generally remained usable.
In a few instances only was a span blown off its piers
or abutment. However, an underground or surface
burst would probably have proved more destructive.
Long-span suspension bridges will stand a good
chance of surviving an air burst because of their

Figure 6.78. Steel plate girder railway bridge, about 280 yards from ground zero in Japan, The plate girders were moved about 3 feet
by the blast, but the bridge was essentially intact,

flexibility. Steel military bridges may be expected to
esist blast almost as well as the permanent type.
imergency bridges of makeshift construction will
probably not stand up well to an atomic explosion.

679. Highways, railway roadbeds, and rails are,
on the whole, relatively invulnerable to damage by
ir blast. They may be covered by rubble and debris,
but this can be removed. Even after a nearby surface
underground burst highways and railroads can be
restored to operation without difficulty, if necessary
by bypassing the severely damaged area. Railway
stock has the same vulnerability as other
ructures of a similar type.

vee
no
nN =

Airfield Runways

2. Runways of airfields are built to withstand

considerable pressure, and will probably not be seri-
ously damaged by blast in an air burst. However,
they may be expected to suffer severely from a sur-
face or underground burst in the vicinity.

Tanks

6.81. Medium and heavy tanks and armored cars
aire very resistant to blast, shock, and thermal radi-
ation. However, exposed equipment such as an-
tennas, sighting mechanisms, lights, and machine-
min mounts are vulnerable. Tanks that are not
roperly buttoned up will suffer severe interior dam-
due to the entrance of the blast wave through
ports and hatches. Near to the point of burst, such
damage may oceur even when the tank is buttoned
up. The blast wave can then break through motor
yentilation openings and the inspection plates be-
tween the motor and fighting compartments. The
ressure build-up may blow hatch covers open.
Furthermore, the blast wave may throw the tank
some distance or overturn it. However, in spite of
the possibility of damage, a medium or heavy tank
will, in general, provide much protection against the
‘effects of an atomic air burst.

Ordnance and Ammunition

6.82. While heavy weapons are somewhat more
sily affected than heavy tanks, they are still very
resistant to damage. Nevertheless, as with tanks,
exposed parts, such as fire control equipment, will
suffer. Ammunition is not as vulnerable to heat as
1 night be expected. While exposed powder, such as

EFFECTS OF ATOMIC EXPLOSIONS ON STRUCTURES AND MATERIEL 87

artillery and mortar powder increments, can be
ignited by thermal radiation, enclosed or encased
ammunition is fairly resistant. Neither artillery
shells nor small-arms ammunition will be affected by
thermal radiation except, of course, near ground zero.

Vehicles

6.83. Essentially all types of vehicles, including
jeeps, trucks, ete., and other mobile equipment will
be subject to considerable damage due to direct ac-
tion of the blast and shock or as a result of destrue-
tion of surrounding buildings. Overturning of ve-
hicles or bumping of one against another will be
contributory factors. Light damage will include
breakage of windows, electrical equipment, and wir-
ing, and infiltration of dirt or grit into the working
parts of engines. Nearer to ground zero, wheels, ex-
posed parts of the motor such as spark plugs and
carburetors, tires and the body, may suffer in addi-
tion. In zones of heavy damage, there may also be
warping of frames, collapse of roofs, and rupture of
fuel tanks. In the latter event, ignition of the gasoline
may result, and then there will be much fire damage.
Thermal radiation may cause superficial damage to
tires, paint, ete., but it will not ignite gasoline unless
the tank is ruptured.

Electrical and Electronic Equipment and Machinery

6.84. Lightly constructed sensitive equipment, like
switchboards, radar and radio sets, telephones, and
radiation detection instruments, are highly vulner-
able. Even if they are not directly affected by blast
or shock, they can be ruined by debris or fire. Heavier
equipment, for example, machine tools, motors, and
generators can also be damaged by debris and by fire.
Valuable industrial equipment, even if undamaged by
blast, debris, or fire, can be rendered useless by rust
due to exposure to the elements (fig. 6.84). Conse-
quently, machinery of all kinds will suffer less in
reinforced concrete or heavy steel-frame buildings
than in light metal or wooden construction.

Public Utility Lines
6.85. Poles carrying overhead power and telephone
lines are vulnerable to blast, shock, and fire and may
be seriously damaged. The lines themselves may be
blown down by the blast beyond the distance where
the poles are more or less intact. Water and gas dis-
tribution lines running above the surface may suffer

88 CHAPTER 6

-

Figure 6.84. Machinery lightly damaged by debris and by fire, but exposed to the elements after the atomic attack on Japan.

breakage, either due to the air blast or to the destruc-
tion of the buildings through which they pass.

6.86. In the case of an air burst, underground dis-
tribution lines usually will be undamaged, except
directly below the burst, where ground shock may be
responsible for damage to sewer pipes and drains at
shallow depths. Damage to buried pipes and fittings
may result from the weight of the debris on the
ground above them.

6.87. All underground utilities will suffer greatly
from the displacement of the ground and the shock
pressure due to a subsurface explosion. Sewer, gas
and water mains will be particularly susceptible. It
is possible that electric mains will suffer much less
because of their ductility. However, above-ground
lines may be broken as a result of tower and pole
distortion, caused by the earth shock.

Supply Dumps
6.88. Supply dumps have little exterior protection
and are therefore subject to considerable damage and
destruction by blast, shock and fire unless dug in as
12.30. and oil

dumps will be particularly vulnerable, because rup-

described in paragraph Gasoline
ture of containers may well be followed by serious
fires.
whole, probably suffer less severely unless fire breaks
out.

Ration and ammunition dumps will, on the

Rations and Water

6.89. In the event of an air burst, rations which
survive the blast and fire should generally be usable.
But after a surface or subsurface burst special pre=
cautions will have to be taken against the possibility

Unpackaged food

of radioactive contamination.

EFFECTS OF ATOMIC EXPLOSIONS ON STRUCTURES AND MATERIEL 89

which has been in direct contact with the base surge

or with the fall-out will be unfit for consumption.
However, if there was no actual contact with the food
itself, it will be unaffected. The radiations as such
ean do no harm to food. It is only when the radioac-
tive particles are on the food, and can thus enter the
body, that there is real danger. Canned and pack-
aged goods are not affected in any way. Provided
contamination, if present, can be washed off the ex-
terior without risk, and the hands are clean, the
contents may be safely consumed.

6.90. Potable water supplies, if exposed, may be-
come contaminated, but not necessarily to a danger-
ous level. However, if stored in closed tanks the
water will be safe for consumption. Due care must,
of course, be taken to prevent the water from becom-
ing contaminated by subsequent handling.

EFFECTS AT SEA
/ Damage Ranges for Shock and Blast

6.91, All the information concerning the effects of
_atomic explosions on ships was obtained from the
tests at Bikini, where many of the vessels were of
obsolete types, and were, in any case, riding at an-
chor. From these observations certain conclusions
_have been drawn concerning what might be expected
from modern vessels. While these are often only in-
telligent guesses, they are worthy of consideration.
In the discussion which follows, thermal radiation is
not mentioned. The Bikini tests indicated that it
would not be an appreciable factor in producing dam-
age at sea, since the exposed portions of naval ves-
sels are practically fireproof. However, this does not
exclude the possibility of secondary fires involving
such combustibles as gasoline or explosives where
there has been extensive blast damage.

6.92. The approximate limiting distances from sur-
face zero at which various degrees of damage may
occur to ships and their equipment, from an air burst
and a moderately shallow underwater burst, are
given in table 6.92. This refers to a nominal atomic
bomb. For purposes of comparison with effects of an
air burst on land, the distance scale in table 6.92 is in
intervals of 500 yards, the same as in table 6.59. A
comparison of blast damage at sea and on land, for
an air burst, is also given in figure 6.92, Severe dam-
age implies that the ship will be sunk or damaged to

such an extent as to completely lose its military
effectiveness; moderate damage means immobiliza-
tion and probable flooding of at least one primary
compartment; light damage refers to damage to
electronic and other light equipment. It is of interest
to note that beyond about 1,500 yards from surface
zero only damage of a minor character should be
experienced at sea.

6.93. In sealing for the effects of bombs of different
energies, the cube-root rule may be used to calculate
the damage ranges for an air burst. The various dis-
tances in table 6.92 should thus be multiplied by the
factor (W /20)'/3. For an underwater burst, where the
damage is largely due to shock, rather than to blast,
this factor would probably underestimate the damage
range. If scaling is necessary it would be advisable
to use the factor (W/20)!/*. The range of appreciable
contamination on ships due to the base surge and
fall-out following an underwater burst, will be the
same as given in paragraph 6.67, that is, about 2
miles crosswind from the center of the explosion and
still farther in the downwind direction.

General Effects of Blast and Shock on Ships

6.94. Ships as a whole are remarkably resistant to
blast damage. This follows from a consideration of
the requirements which must necessarily be built into
a seagoing vessel. For example, a considerable por-
tion of the topside area of a combatant ship is built
to withstand blast from the firing of its own guns.
The hull proper is required to withstand impact of
waves, as also are portions of the superstructure.
Furthermore, many important stations are protected
by armor or splinter shields, which are strongly built.

6.95. The design and materials of construction per-
mit deflection and yielding without rupture. In ad-
dition, the ship is floating in water and can yield as
a whole (by rolling or heaving) without sustaining
any damage due to this motion, whereas a structure
of comparable size on land would be damaged by the
very act of moving the entire assembly relative to
its foundations.

6.96. Orientation and shape of structure will have
a considerable influence on damage. Surfaces nearly
parallel to the direction of burst will be damaged less
than those more nearly perpendicular to it: In some
locations not exposed to the direct blast, damage will
result from the combined effect of deflection and re-

90 CHAPTER 6

AIR BURST

UNDERWATER BURST

+ LIGHTLY-BUILT TOPSIDE STRUCTURES —Limit of damage.

+ AIRCRAFT CARRIERS, BATTLESHIPS, CRUISERS,

2,000 TRANSPORTS —Light damage.

BOILERS —Light damage.

1,500—~- LIMIT OF IMPORTANT DAMAGE TO SHIPS.

+ BOILERS — Moderate damage.

ANTENNAS, DIRECTORS, LIGHT EQUIPMENT,
BOILERS —Severe damage.

—+ DESTROYERS— Moderate damage.

— AIRCRAFT CARRIERS, CRUISERS, TRANSPORTS —
Moderate damage.

BATTLESHIPS—Moderate damage,
DESTROYERS—Severe damage.
= ORDNANCE —Severe damage.

1,000

AIRCRAFT CARRIERS, BATTLESHIPS,
CRUISERS, DESTROYERS—Light damage.

AIRCRAFT CARRIERS, BATTLESHIPS,
CRUISERS, DESTROYERS— Moderate damage,
AIRCRAFT CARRIERS, BATTLESHIPS,
CRUISERS, DESTROYERS— Severe damage.

—- SUBMERGED SUBMARINE — Sunk.

AIRCRAFT CARRIERS, LIGHT CRUISERS, TRANSPORTS—

Severe damage

HEAVY CRUISERS— Severe damage.
* BATTLESHIPS— Severe damage.

SURFACE ZERO

Table 6.92. Comparison of damage ranges to ships, due to air burst at 2,000 feet altitude and shallow underwater burst of a nominal
atomic bomb.

flection of the blast wave from exposed surfaces into
pockets or dead ends under overhanging structures,
sun _sponsons, ete.

6.97. On ships having large exposed deck areas,
such as the well decks of older type cruisers, quarter-
decks of battleships, cargo-handling decks of mer-
chant-type vessels, the decks may be deformed as a
result of blast pressure. The main strength water-
tight hull will not be affected materially at ranges
greater than 600 yards from the explosion of a nom-
inal atomic bomb. This approximate limit applies
to both air bursts and underwater bursts. For an
underwater burst at ranges up to about 600 yards the

underwater shock is sufficient to cause direct rupture
of the hulls of most vessels, due to the effects pre-
viously discussed in paragraph 6.17. For an air
burst, at distances closer than 600 yards the strength
hull may be distorted above the water-line sufficiently
to initiate cracks which will progress to below the
water-line and permit extensive flooding. On light
aircraft carriers, warping and buckling of flight decks
probably will occur to about 700 yards (fig. 6.97).
It is possible that the airplane elevators will be dis-
lodged from their position, and it is still more likely
that the distortion of the deck and resulting mis-
alignment will render operation of the elevators
impossible.

91

EFFECTS OF ATOMIC EXPLOSIONS ON STRUCTURES AND MATERIEL

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EFFECTS OF ATOMIC EXPLOSIONS ON PERSONNEL

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134

CHAPTER 9

Figure 9.30a. Map of a typical military base in a forward area, Shown in red are contours of equal radia-
tion intensity as they might be plotted at control center, from monitoring data corrected to one hour after det-
onalion. An underground burst, with 10 m.p.h. surface wind, was assumed,

MEASUREMENT AND EVALUATION OF RADIOLOGICAL HAZARDS 135

Figure 9.30b. Map of a typical municipal and harbor area. Dose-rate contours show mon itoring data cor-
rected to one hour after detonation as in figure 9.30a, except that an underwater burst with 5 m.p.h. wind was
assumed,

PROTECTION OF PERSONNEL

10.28. Tunnels, storm drains, and subways would
provide effective shelter, unless there were a nearby
underground explosion. The thickness of the earth
will, in general, be sufficient to reduce the gamma
radiation to harmless proportions. In addition, the
structure of the tunnel, etc., will usually be strong
enough to withstand blast and fire, although it may
be somewhat vulnerable to underground shock.

10.29. In case of a subsurface explosion, persons
taking shelter in existing buildings or structures
may become exposed to residual radioactivity from
contamination. Closing doors, windows, and other
openings will provide some degree of safety. But,
if the blast should break the doors and windows,
and let in the radioactive mist or dust, this precau-
tion will be of little value. In these circumstances,
if no gas masks are available, breathing through a
folded handkerchief will help to reduce the hazard.

10.30. In military installations, there often are
not many buildings which are strong enough to
provide effective shelter from an atomic burst. Cul-
verts, drains, and ditches could be used in the event
of an emergency, but they would offer only partial
protection. Consideration should, therefore, be
given to the desirability of making proper provision
for sheltering personnel, in some such manner as is
described below.

Shelter Afloat

10.31. Larger ships, and especially those having
protective armor, can furnish excellent shelter from
blast, thermal radiation, and immediate nuclear
radiation effects at one-half mile or more from sur-
face zero in the air burst of a nominal atomic bomb.
Such shelter would, of course, be available only to
members of the ship’s company whose duties will
permit them to be stationed behind shielding.

10.32. In general, the further below the main
deck, the better will be the protection from nuclear
radiation. Shielding is provided by armored decks,
the shell plating and side armor, and by the wing
water and fuel-oil tanks which form part of the
antitorpedo protection. Furthermore, in the case of
personnel located well below the water line, the ex-
ternal sea water itself offers valuable shielding
against the immediate nuclear radiation. This

arises because for even a fairly high air burst oc-

=

147

curring one-half mile away, or more, the radiation
will strike the ship at such an angle that it must
pass through an appreciable thickness of water
before entering the ship below the water line.

10.33. In the event of an underwater burst there
will be no immediate radiation, but steps should be
taken to prevent entry of the base surge. Conse-
quently, all openings should be secured upon warning
of an impending attack.

10.34. Unless special shielding is available, topside
personnel will be exposed to both thermal and nu-
clear radiation, as well as to the effects of blast. In
case of an air burst, self-preservation measures, to be
described later, should be taken. After an under-
water explosion, at not too close quarters, there may
be time to obtain shelter from the base surge and
water fall-out in those cases where it is not possible
for the entire ship to avoid this contamination by
means of maneuvering.

Specially Constructed Shelters

10.35. For personnel and services of essential im-
portance to the functioning of a military establish-
ment or installation, it may be considered desirable
to construct special shelters. These should be built
underground of reinforced concrete, perhaps 2 feet
thick, and with a considerable earth cover. A struc-
ture of this kind would provide satisfactory protec-
tion, even at ground zero, from an air burst of a
nominal atomic bomb at 2,000 feet. If sufficiently
massive and built to withstand ‘lateral shock, the
structure could also provide protection from the ef-
fects of a nearby underground explosion.

10.36. Two aspects of specially constructed shelters
require attention—these are access and air supply.
Each shelter should have at least two exits, in case
one caves in or is blocked by debris. The entrance
passages (or ramps) should be at right angles to the
shelter proper, so as to avoid direct exposure to blast,
and thermal and nuclear radiations. To prevent the
entry of contamination, the shelter should be air-
tight, except for provision made for supplying air by
fans or blowers. An efficient filter should be placed
in the inlet duct to remove contaminated dust par-
ticles. The Army Chemical Corps No. 6 Filter is
suitable for this purpose. Because there may be a
power failure in the event of an atomic attack, an

148 CHAPTER 10

emergency supply of electricity should be available
to provide lighting and to operate the ventilation
system.

10.37. Where shelters are required mainly for pro-
tective purposes and not to house vital operational
or control activities, much simpler methods can be
used. Tunnels cut in a hillside, with entries at right
angles to the main tunnel, form very effective shel-
ters. In Nagasaki, such shelters protected persons
from blast and from thermal and nuclear radiations
very close to ground zero (fig. 10.37).

10.38. If the terrain is flat, several other cheap
forms of shelter, which use earth as a protective
medium, are possible. In the “cut-and-cover” type,
a deep pit or trench is dug, and the sides are shored
up with planks and wooden columns. Stout beams
are placed across the excavation and upon them are
laid sheets of corrugated iron. These are finally coy-
ered with a layer of earth at least 3 feet thick. The

approach to the shelter is by a right-angled ramp
entrance, there being two such entrances to each
shelter (figs. 10.38a and b). Digging tools should be
available as a further precaution against entrapment
by cave-in. A shelter of this kind will provide good
protection against all the effects of an air-burst nom-
inal atomic bomb beyond one-half mile or so from
ground zero.

10.39. A half-buried shelter, which is partly above
and partly under ground, is similar to, but not quite
so good as, the type just described. These are very
simple to construct. Wood may be used for roofing
in place of the corrugated sheets, but it is, of course,
less permanent. A baffle of earth and boards at the
entrance is desirable, to prevent direct access of
blast and radiation. In Japan, half-buried shelters
were made of a framework of poles, over which was
placed tarpaulins; the whole was then covered with
a thick layer of soil (fig. 10.39).

Figure 10.37, Tunnel shelters in hillside, very close to ground zero in Nagasaki, protected the occu pants from blast, thermal radiation,
and immediate nuclear radiation.

PROTECTION OF PERSONNEL 149

DIRT FILL. CORRUGATED SHEET METAL

PROTECTIVE EAVE,

~

DRAINAGE 90° RAMP ENTRANCE

S wes a Hh er.

Figure 10.38a & b. Simple earth shelter suitable for a military establishment.

Figure 10.39. Simple pole and earth shelter, one mile from ground zero, undamaged by fire and blast although surrounding buildings
were destroyed in the atomic bombing of Japan. (Debris was cleared from the roadways before the photograph was taken.)

150 CHAPTER 10

10.40. In a more elaborate, and more expensive,

. form of the cut-and-cover shelter, a quonset hut can

be placed in an excavated area and covered with
earth (fig. 10.40a). Two ramp entrances, dug at right
angles, would lead to the doors. A somewhat sim-
ilar shelter could be made from steel culvert sections
of large diameter, which are obtainable commercially.
Several sections could be joined together, placed in
an excavation, and an appropriate earth cover added
(fig. 10.40b).

Figure 10.40a & b. Alternate types of simple earth shelters suit-
able for a military establishment.

10.41. For men at regular sentry duty in guard
posts, small shelters can be provided at little cost.
These may consist of a steel culvert section of about
3 feet diameter, or even of two open-ended oil drums
joined together. The cylinders are then buried, or
semiburied, with an earth cover of at least 3 feet.
A ramp entrance must be provided for the completely
buried shelter. One or two men lying down inside
will be well protected beyond about one-half mile
from ground zero in the event of an air burst.

10.42. Slit trenches and foxholes (see fig. 7.40)
provide the simplest of all shelters which can be
made available at military installations. Where the
number of personnel is large, then more elaborate
shelters are not practicable. The chief drawback
trenches and foxholes is, of course, their lack of pro
tection from above. A high air burst at not
great a distance would send blast, heat, and nuclear
radiations directly into the trench or foxhole (fig
10.42a). The deeper the trench is dug, the greate

AIR BURST

Figure 10.42a. A high air burst sends radiations (thermal and
nuclear) into a small foxhole.

the protection it offers. A soldier lying, sitting,
crouching at the bottom of a deep trench can escape
most of the air burst bomb’s effects, even quite close
to ground zero (fig. 10.42b). Trenches and foxholes
would, however, be damaged by shock from nearby
surface and subsurface bursts.

AIR BURST

Figure 10.42b. A soldier crouching on the bottom of a moderately

deep trench or foxhole is largely protected from the effects of

radiation, even fairly close to ground zero. Some scattered nuclear

radiation (dotted lines) may be received, but the amount will be
comparatively very small.

10.43. A warning should be given in connection
vith the use of sandbags in the construction of earth
helters. If sufficiently close to the explosion, the
lap or other materials are likely to be scorched by

thermal radiation. The bag may then collapse
and its contents will be spilled.

10.44. All the simple types of earth shelter suffer
from the fact that they cannot be made airtight. It
would thus be impossible to keep out radioactive
contamination due to a subsurface burst. The only
satisfactory way to overcome the immediate effect
this hazard would be to supply each individual
vith a filter mask or respirator. If this is not pos-
sible, then dust may be largely kept out by breathing
through a handkerchief or a piece of cloth.

_ 10.45, It may be possible in the field to take ad-
vantage of the terrain. A hill between an individual
and the exploding bomb will almost completely cut
off the thermal radiation. Although it may not en-
irely eliminate the effects of blast and the imme-
diate nuclear radiation, it may well reduce them to
such an extent that they are harmless.

Dispersion

10.46. An important way in which casualties in
the field might be reduced is by dispersion of person-
nel over a large area. The figures in table 10.46
show the estimated percentages of personnel injured
and killed in the open as a result of the air burst of
a nominal atomic bomb, assuming them to be con-
centrated in circular areas of various radii about
ground zero. Dispersal of troops over a large area
will thus appreciably decrease the number of casual-
ties. The data in table 10.46 are based on the as-

Table 1048, Estimated Effects of Dispersion of Personnel

in the Open

Circular area of radius Percent casualties
) Killed Injured Total
1,500 90 10 100
j 2,000 | 51 29 80
2,500 33 36 69
; 3,000 23 40 63
\ 4,000 14 | 8 42

NT

4It should be noted that the casualty ranges given in table 10.46 are

based primarily on thermal rather than nuclear radiation effects, since the

limiting distance for radiation casualties would be about 1500 yards. On

ord other hand, if personnel are in foxholes or trenches and thereby shielded

thermal radiation, nuclear radiation becomes more significant in de-

_ termining the amount of dispersion required to avoid excessive casualties
Gee figs. 7.24 and 7.40).

PROTECTION OF PERSONNEL 151

sumption that the troops are in the open at the time
of the explosion.’

10.47. Commanders should consequently give care-
ful consideration to the possibility of distributing
personnel, and especially key personnel, as widely as
possible (see par. 12.09). All operating procedures
should be examined closely to determine whether
unnecessarily large numbers of personnel are being
concentrated in small areas during these operations.
For example, dispersal of aircraft at an air base
might reduce casualties to maintenance crews as well
as to the planes.

10.48. Dispersal of ships, both at sea and in port,
will decrease the total amount of damage and hence
the casualties in an atomic explosion. Consideration
should consequently be given to the matter of in-
creasing the operating distance between ships when
an attack is expected. Because of the great range
of destruction resulting from an atomic burst, some-
what different defense tactics are required than in
the case of HE bombs and depth charges.

Smoke Screen

10.49. If large numbers of personnel have to re-
main in the open and cannot take shelter, for ex-
ample, in an amphibious landing, it might be desir-
able to employ a smoke screen as a protective device.
As stated in paragraph 3.41, this would very greatly
reduce the range of thermal radiation and conse-
quently decrease the number of flash-burn injuries.
On the other hand, protection from thermal radia-
tion is so relatively simple that it is questionable
whether a smoke screen would be justifiable, except
in special circumstances, as indicated above. The
effective use of a smoke screen is only possible if
there is adequate warning of an attack. In any case,
it must not be permitted to distract attention from
the necessity for obtaining protection from blast and
nuclear radiation effects.

INDIVIDUAL PROTECTION
Self-preservation

10.50. If there is a sufficient, warning in advance of
an atomic attack, the obvious step is to make for the
best shelter that is available, as quickly as possible.
In the ease of members of the armed forces on duty,
their behavior must be determined by the cireum-

a

152

stances existing at the time. In general, this will be
the same as those prescribed for an attack by ordi-
nary HE bombs.

10.51. In the event of a surprise atomic explosion,
certain actions can be taken by individuals which
might mean escape from death or serious injury.
The same applies to men on duty who cannot leave
their posts. In an air burst the actions are determined
by the following facts mentioned earlier in this man-
ual. First, the thermal radiation may continue to be
emitted for a second or so after the burst; second,
about 50 percent of the immediate nuclear radiation
is given off in the first second, and about 80 percent
within 10 seconds; and third, the blast wave takes
about 8 seconds to reach a distance of 2 miles, which
is the approximate range of serious to moderate me-
chanical injury.

10.52. The first indication of an unexpected atomic
air burst may be a brilliant flash of light. No matter
whether in the open or inside a building, the immedi-
ate reaction should be for the person to drop to the
ground, face down, at the same time trying to cover
exposed portions of the skin, such as the face, neck,
and hands. If this can be done within a second of
seeing the bright light, some of the heat radiation
may be avoided. Ducking under a table, if indoors,
or into a trench or ditch, if possible, outdoors, with
the face away from the light, will provide added
protection.

10,53. If shelter of some kind can be reached within
a second, it might be possible to miss about half of the
immediate nuclear radiation. But, as stated earlier,
shielding from nuclear radiation requires a consider-
able thickness of material, and this may not be avail-
able in the open. By dropping to the ground, some
advantage may be secured from the shielding pro-
vided by terrain and surrounding structures. How-
ever, since the radiations continue to reach the earth
from the atomic cloud as it rises, the protection will
be only partial.

10.54. The prone position taken immediately upon
seeing the light from the bomb should be held for at
least 10 seconds, or longer if heavy objects are still
falling. This will allow time for the blast wave to
pass and thus decrease the danger from flying mis-
siles. At a distance of 2 miles from the point of burst,
8 seconds will elapse before the sound of the explo-

CHAPTER 10

sion is heard. By this time the immediate effects w
be over.

burst will probably be the sensation of an earthquake
like concussion of the ground, together with t
appearance of the column of water or earth. For
tunately, the thermal and nuclear radiations emitte
at the time of the explosion will be absorbed by th
water or the earth, respectively. However, there m
still be the radiation hazard from the base surge ar
the fall-out.

10.56. Although the effects of blast and shock m
be felt before it is fully realized that a subsurface
plosion has occurred, there may still be time to obtai
some shelter from the base surge and fall-out. ]
should be remembered that the base surge is like
fog and envelopes everything over which it passe
Adequate shelter can thus be obtained only in
closed space which the radioactive fog cannot pene
trate. The fall-out, on the other hand, descends ver
tically (or almost so) and protection is much easier to
obtain. If it is impossible to find shelter from bot
base surge and fall-out in a short time, then protec
tion from the fall-out, at least, should be sought.
a filter mask is not available, a handkerchief should
be held over the mouth and nose while the base surge
is passing.

10.57. After a contaminating burst or an RW at
tack every action should be taken with the thought
of minimizing the spread of the contaminati¢
Within the contaminated area, eating, drinking,
smoking, chewing gum, or any action which requi
putting the hand to the mouth, must be strictly f
bidden. This will help prevent entry of radioactive
particles into the body. Personnel should be warned
against stirring up dust and stepping into puddle

buildings and objects in the contaminated area must
be avoided. These instructions should be stressed to
counteract the temptation to pick up souvenirs.

10.58. The internal radiation hazard due to inha-
lation of radioactive particles is even greater
that due to ingestion. Realistie evaluation of
dust hazard by laboratory analyses should be ms
as soon as feasible. If found serious, shelter from d

clouds raised by the wind, by aircraft propellers, by
moving vehicles, ete., should be taken, if possible.
Otherwise a gas mask, or handkerchief, should be
used, as described above, for protection. In the case
of aircraft in flight, if there is reason to believe that
he plane may be in the vicinity of an atomic cloud,
protection for the crew can be obtained by shutting
off the ventilation or pressurization system. Further
individual protection can be obtained by the use of

_ 10.59. As soon as the initial effects of the explosion
are over, every survivor should look around to see if
he can render first aid or emergency help of any kind
to individuals nearby (see ch. 7). It is important to
emphasize that after an air burst the administration
of such help involves no special problems. The situ-
‘ation from this standpoint will be no different from
that following an HE or incendiary attack. As indi-
eated in paragraph 7.39, there is no danger involved
in approaching or touching a person who may have
received a dose of immediate nuclear radiation from
an air burst.

10.60. Persons with wounds, which might permit
radioactive material to enter the body, should be
taken to the nearest medical station for treatment.
Regardless of the indicated extent of the contami-
‘nation, amputation is entirely unnecessary, in spite
of statements which occasionally have been made to

Ordinary Clothing

10. 61. Military uniforms and civilian clothing pro-
vide good protection against thermal radiation
emitted at the time of an air burst.. The protection
s, however, supplementary rather than primary, in
nature. If a person is beyond the zone of serious
age from blast and nuclear radiation, he may
be vulnerable to thermal radiation, since this has
e greatest damage range. In these circumstances
arts of the body that are covered by clothing will be
fairly well protected from flash burns. As far as radi-

value of clothing is that it keeps radioactive contami-
Nation from actual contact with the skin.

=. ia of Vas ¥ =" +t - + |... * = 7 FF

PROTECTION OF PERSONNEL 153

Special Clothing and Equipment

10.62. Personnel whose duties, as members of
emergency and damage control teams, as decontami-
nation crews, or as monitors, require them to enter
contaminated areas or to come into contact with
contaminated objects, should wear special clothing
when available (fig. 10.62). Such clothing normally
would be issued from a control point or change sta-
tion. It should be washable or expendable, and
should be tightly woven or nonporous. It should
cover the body completely, and should have tight
connections with gloves at the wrists, and with shoes
at the ankles. An overlapping connection should also
exist between the clothing at the neck and a respira-
tor or filter mask. Equipment of this kind will pre-
vent contamination of the skin.

10.63. After each use, the clothing should be moni-
tored.® Most contaminated clothing can be laun-
dered and used again (par. 10.82). An alternative to
laundering or disposal is to store the clothing to per-
mit the radioactivity to decay. The soiled clothing
is set apart in special containers and allowed to stand
until its contamination has decayed sufficiently for it
to be worn again.

10.64. The special clothing which should be used,
if available, by personnel entering contaminated
areas, can be itemized as follows:

Any type of head covering, preferably tight-
fitting.

Goggles.

Suitable washable and/or disposable outer gar-
ments.

Bootees.

Gloves, canvas type for manual labor.

Filter masks.

10.65. Because of the possible confusion following
an atomic attack, the special clothing may not be im-
mediately available; satisfactory substitutes may be
improvised as follows:

Standard military clothing or combat fatigues.

Clothing tightly buttoned at neck and tied at
wrists and ankles with string, or stuffed into
top of combat boots.

‘This is sometimes referred to as “protective” clothing, although it

offers virtually no protection from gamma radiation. The term “protec-
tive’’ may consequently be misleading in this respect.

‘Further discussion of the monitoring of clothing will be found in the
Department of Defense “Handbook of Atomic Weapons for Medical Officers.”

an De Aa

—— —

a
Appendix | .

SCALING LAWS FOR ESTIMATING BLAST, THERMAL, AND IMMEDIATE NUCLEAR RADIATION
EFFECTS FOR ATOMIC BOMBS OF DIFFERENT ENERGIES

A.1. A number of figures are appended here which the ground due to an air burst (fig. A.la), the ther
will permit fairly accurate scaling estimates to be mal energy received (fig. A.lb), and_ the immediate
made rapidly. They a the peak overpressure on _— nuclear (gamma) radiation dose (fig. A.le), respec=

30

25

20

PEAK SHOCK OVERPRESSURE (psi )

5 hy
ae NSS ;
4
4
:
;
i

4
SS
j
;
l b
1,000 2,000 3,000 4,000 5,000 6,000

DISTANCE FROM GROUND ZERO (yards) /
Figure A.1a. Scaling for blast from atomic air bursts, Variation of peak overpressure on ground with distance from ground zero.

218

a

SCALING LAWS FOR ESTIMATING BLAST, THERMAL, AND IMMEDIATE NUCLEAR RADIATION EFFECTS 219
tively, at various distances from ground zero, for sure; (ii) the thermal energy on an average clear
: bombs of different energies. It should be noted that day; and (iii) the immediate nuclear radiation dos-
in figure A.lb, the ordinates are thermal energies, sage, at a point 2,000 yards from ground zero, due
in calories per sq. cm., divided by the kiloton TNT to the air burst of a 60-kiloton TNT equivalent
energy equivalent of the bomb, i.e., the thermal atomic bomb?
energy per kiloton TNT of bomb energy. To obtain (i) From figure A.la, using the curve marked “60
the results for a bomb of energy equivalent to W kilotons TNT,” the peak overpressure at 2,000:
_kilotons TNT, the ordinates are multiplied by W. yards is seen to be about 9.5 psi.

(ii) The thermal energies received on an average
Example: What would be (i) the peak overpres- clear day may be regarded as being roughly mid-

0.50

= thermal energy in cal./sq. cm. per kiloton TNT

0.20

0.10

SES ols
Ree en

THERMAL ENERGY IN CAL./SQ. CM
ENERGY OF BOMB IN KILOTONS TNT

0.02
° 1,000 2,900 3,000 4,000 5,000 6,000 7,000
DISTANCE FROM GROUND ZERO (yards)

Figure A.1b. Scaling for thermal radiation from atom ic air bursts. Variation of thermal energy received with distance from ground zero
for different states of the almosphere,

220

IMMEDIATE (gamma) RADIATION DOSAGE (roentgens)

way between those for the curves marked “mod-
erately clear’ and “exceptionally clear.” The
ordinate of figure A.1b corresponding to a distance
of 2,000 yards, is thus found to be about 0.5 cal./
sq.cem. Upon multiplying by 60, which is the
kiloton TNT equivalent of the bomb, the result is

30 cal./sq. cm. as the energy received.

Gii) From figure A.le, using the curve marked

$00

200

100

uw
°o

n
°o

ro)

APPENDIX |

“60 kilotons TNT,” the immediate nuclear radia-
tion dose at 2,000 yards is seen to be 66 roentgens.

Kxample: What is the limiting distance from
ground zero at which moderate skin burns would be
experienced on an average clear day as the result of
the air burst of a 30-kiloton TNT equivalent
bomb?

20 KILOTONS TNT

40 KILOTONS TNT
60 KILOTONS TNT

100 KILOTONS TNT

() 5,00 1,000 1,500 2,000 2,500 3,000

DISTANCE FROM GROUND ZERO (yards)

Figure A.te, Sealing for immediate nuclear radiation from atomic air burst. Variation of total radiation dosage with distance fron
ground zero,

ee "ieee ‘energy required to produce mod-
_ erate skin burns is 3 eal./sq. em., and this divided
by 30, the kiloton TNT equivalent of the bomb,
is 0.1. The ordinate 0.1 in figure A.1b for an aver-
age clear day, i.e., between ‘‘moderately clear”
and “exceptionally clear,” corresponds to a dis-
tance of 3,750 yards from ground zero. This is the
required limiting distance.

A.2. Some of the scaling data have been plotted
m a simpler manner in figure A.2. While this is less
: ymplete than the figures given above, it is simpler
use. It should be noted that the thermal radiation
surves refer to an average clear day.

Example: At what distance from ground zero

“tn ee) Pe we se aie Aa ta tance}
e-

LING LAWS FOR. ESTIMATING BLAST, THERMAL, / AND IMMEDIATE NUCLEAR RADIATION EFFECTS 221

~ would the air burst of a 100-kiloton TNT equiva-
lent bomb produce (i) a peak overpressure of 5 psi
on the ground; (ii) 3 cal./sq. em. of thermal radia-
tion on a clear day; (iii) 450 roentgens of imme-
diate nuclear radiation?

(i) The estimated distance for 5 psi, obtained by
interpolation between the curves ‘3 psi’ and
“10 psi,’ is about 3,500 yards, for a 100-kiloton
TNT bomb.

(ii) From the curve for “3 cal./sq. em.” of ther-
mal radiation, the distance is found to be about
6,000 yards.

(iii) The curve ‘450 roentgens” indicates that
the distance would be approximately 1,650 yards.

222 APPENDIX |

a
EU Se
Pe
Pi os
Of RR

ENERGY OF BOMB (kilotons TNT equivalent )

60

A ea
SU | 7
A/V ee
LU A AAA
VA
a a

° 1,000 2,000 3,000 5,000 7,000

40

20

DISTANCE FROM GROUND ZERO (yards)
Figure A.2. Distances from ground zero at which various effects are produced by the air burst of atomic bombs of different energies,