GENERAL DESCRIPTION OF DAMAGE CAUSED BY THE ATOMIC EXPLOSIONS
Posted by amad on August 13 2007 17:24:00
In considering the devastation in the two cities, it should be remembered
that the cities' differences in shape and topography resulted in great
differences in the damages. Hiroshima was all on low, flat ground, and was
roughly circular in shape; Nagasaki was much cut up by hills and mountain
spurs, with no regularity to its shape.
In Hiroshima almost everything up to about one mile from X was completely
destroyed, except for a small number (about 50) of heavily reinforced
concrete buildings, most of which were specially designed to withstand
earthquake shock, which were not collapsed by the blast; most of these
buildings had their interiors completely gutted, and all windows, doors,
sashes, and frames ripped out. In Nagasaki, nearly everything within 1/2
mile of the explosion was destroyed, including heavy structures. All
Japanese homes were destroyed within 1 1/2 miles from X.
Underground air raid shelters with earth cover roofs immediately below the
explosion had their roofs caved in; but beyond 1/2 mile from X they
suffered no damage.
In Nagasaki, 1500 feet from X high quality steel frame buildings were not
completely collapsed, but the entire buildings suffered mass distortion and
all panels and roofs were blown in.
In Nagasaki, 2,000 feet from X, reinforced concrete buildings with 10"
walls and 6" floors were collapsed; reinforced concrete buildings with 4"
walls and roofs were standing but were badly damaged. At 2,000 feet some
9" concrete walls were completely destroyed.
In Nagasaki, 3,500 feet from X, church buildings with 18" brick walls were
completely destroyed. 12" brick walls were severely cracked as far as
5,000 feet.
In Hiroshima, 4,400 feet from X, multi-story brick buildings were
completely demolished. In Nagasaki, similar buildings were destroyed to
5,300 feet.
In Hiroshima, roof tiles were bubbled (melted) by the flash heat out to
4,000 feet from X; in Nagasaki, the same effect was observed to 6,500 feet.
In Hiroshima, steel frame buildings were destroyed 4,200 feet from X, and
to 4,800 feet in Nagasaki.
In both cities, the mass distortion of large steel buildings was observed
out to 4,500 feet from X.
In Nagasaki, reinforced concrete smoke stacks with 8" walls, specially
designed to withstand earthquake shocks, were overturned up to 4,000 feet
from X.
In Hiroshima, steel frame buildings suffered severe structural damage up to
5,700 feet from X, and in Nagasaki the same damage was sustained as far as
6,000 feet.
In Nagasaki, 9" brick walls were heavily cracked to 5,000 feet, were
moderately cracked to 6,000 feet, and slightly cracked to 8,000 feet. In
both cities, light concrete buildings collapsed out to 4,700 feet.
In Hiroshima, multi-story brick buildings suffered structural damage up to
6,600 feet, and in Nagasaki up to 6,500 feet from X.
In both cities overhead electric installations were destroyed up to 5,500
feet; and trolley cars were destroyed up to 5,500 feet, and damaged to
10,500 feet.
Flash ignition of dry, combustible material was observed as far as 6,400
feet from X in Hiroshima, and in Nagasaki as far as 10,000 feet from X.
Severe damage to gas holders occured out to 6,500 feet in both cities.
All Japanese homes were seriously damaged up to 6,500 feet in Hiroshima,
and to 8,000 feet in Nagasaki. Most Japanese homes were damaged up to
8,000 feet in Hiroshima and 10,500 feet in Nagasaki.
The hillsides in Nagasaki were scorched by the flash radiation of heat as
far as 8,000 feet from X; this scorching gave the hillsides the appearance
of premature autumn.
In Nagasaki, very heavy plaster damage was observed in many buildings up to
9,000 feet; moderate damage was sustained as far as 12,000 feet, and light
damage up to 15,000 feet.
The flash charring of wooden telegraph poles was observed up to 9,500 feet
from X in Hiroshima, and to 11,000 feet in Nagasaki; some reports indicate
flash burns as far as 13,000 feet from X in both places.
Severe displacement of roof tiles was observed up to 8,000 feet in
Hiroshima, and to 10,000 feet in Nagasaki.
In Nagasaki, very heavy damage to window frames and doors was observed up
to 8,000 feet, and light damage up to 12,000 feet.
Roofs and wall coverings on steel frame buildings were destroyed out to
11,000 feet.
Although the sources of many fires were difficult to trace accurately, it
is believed that fires were started by primary heat radiation as far as
15,000 feet from X.
Roof damage extended as far as 16,000 feet from X in Hiroshima and in
Nagasaki.
The actual collapse of buildings was observed at the extreme range of
23,000 feet from X in Nagasaki.
Although complete window damage was observed only up to 12,000 feet from X,
some window damage occurred in Nagasaki up to 40,000 feet, and actual
breakage of glass occured up to 60,000 feet.
Heavy fire damage was sustained in a circular area in Hiroshima with a mean
radius of about 6,000 feet and a maximum radius of about 11,000 feet;
similar heavy damage occured in Nagasaki south of X up to 10,000 feet,
where it was stopped on a river course.
In Hiroshima over 60,000 of 90,000 buildings were destroyed or severely
damaged by the atomic bomb; this figure represents over 67% of the city's
structures.
In Nagasaki 14,000 or 27% of 52,000 residences were completely destroyed
and 5,40O, or 10% were half destroyed. Only 12% remained undamaged. This
destruction was limited by the layout of the city. The following is a
summary of the damage to buildings in Nagasaki as determined from a ground
survey made by the Japanese:
Destruction of Buildings and Houses Number Percentage
(Compiled by Nagasaki Municipality)
Total in Nagasaki (before atomic explosion) 50,000 100.0
Blasted (not burned) 2,652 5.3
Blasted and burned 11,494 23.0
Blasted and/or burned 14,146 28.3
Partially burned or blasted 5,441 10.9
Total buildings and houses destroyed 19,587 39.2
Undamaged 30,413 60.8
In Hiroshima, all utilities and transportation services were disrupted for
varying lengths of time. In general however services were restored about
as rapidly as they could be used by the depleted population. Through
railroad service was in order in Hiroshima on 8 August, and electric power
was available in most of the surviving parts on 7 August, the day after the
bombing. The reservoir of the city was not damaged, being nearly 2 miles
from X. However, 70,000 breaks in water pipes in buildings and dwellings
were caused by the blast and fire effects. Rolling transportation suffered
extensive damage. The damage to railroad tracks, and roads was
comparatively small, however. The electric power transmission and
distribution systems were badly wrecked. The telephone system was
approximately 80% damaged, and no service was restored until 15 August.
Despite the customary Japanese lack of attention to sanitation measures, no
major epidemic broke out in the bombed cities. Although the conditions
following the bombings makes this fact seem surprising, the experience of
other bombed cities in both Germany and Japan show Hiroshima and Nagasaki
not to be isolated cases.
The atomic explosion over Nagasaki affected an over-all area of
approximately 42.9 square miles of which about 8.5 square miles were water
and only about 9.8 square miles were built up, the remainder being
partially settled. Approximately 36% of the built up areas were seriously
damaged. The area most severely damaged had an average radius of about 1
mile, and covered about 2.9 square miles of which 2.4 were built up.
In Nagasaki, buildings with structural steel frames, principally the
Mitsubishi Plant as far as 6,000 feet from X were severely damaged; these
buildings were typical of wartime mill construction in America and Great
Britain, except that some of the frames were somewhat less substantial.
The damage consisted of windows broken out (100%), steel sashes ripped out
or bent, corrugated metal or corrugated asbestos roofs and sidings ripped
off, roofs bent or destroyed, roof trusses collapsed, columns bent and
cracked and concrete foundations for columns rotated. Damage to buildings
with structural steel frames was more severe where the buildings received
the effect of the blast on their sides than where the blast hit the ends of
buildings, because the buildings had more stiffness (resistance to negative
moment at the top of columns) in a longitudinal direction. Many of the
lightly constructed steel frame buildings collapsed completely while some
of the heavily constructed (to carry the weight of heavy cranes and loads)
were stripped of roof and siding, but the frames were only partially
injured.
The next most seriously damaged area in Nagasaki lies outside the 2.9
square miles just described, and embraces approximately 4.2 square miles of
which 29% was built up. The damage from blast and fire was moderate here,
but in some sections (portions of main business districts) many secondary
fires started and spread rapidly, resulting in about as much over-all
destruction as in areas much closer to X.
An area of partial damage by blast and fire lies just outside the one just
described and comprises approximately 35.8 square miles. Of this area,
roughly 1/6th was built up and 1/4th was water. The extent of damage
varied from serious (severe damage to roofs and windows in the main
business section of Nagasaki, 2.5 miles from X), to minor (broken or
occasionally broken windows at a distance of 7 miles southeast of X).
As intended, the bomb was exploded at an almost ideal location over
Nagasaki to do the maximum damage to industry, including the Mitsubishi
Steel and Arms Works, the Mitsubishi-Urakami Ordnance Works (Torpedo
Works), and numerous factories, factory training schools, and other
industrial establishments, with a minimum destruction of dwellings and
consequently, a minimum amount of casualties. Had the bomb been dropped
farther south, the Mitsubishi-Urakami Ordnance Works would not have been so
severely damaged, but the main business and residential districts of
Nagasaki would have sustained much greater damage casualties.
Calculations show that the structural steel and reinforced concrete frames
which survived the blast fairly close to X could not have withstood the
estimated peak pressures developed against the total areas presented by the
sides and roof of the buildings. The survival of these frames is explained
by the fact that they were not actually required to withstand the peak
pressure because the windows were quickly knocked out and roof and siding
stripped off thereby reducing total area and relieving the pressure. While
this saved the building frame, it permitted severe damage to building
interior and contents, and injuries to the building occupants. Buildings
without large panel openings through which the pressure could dissipate
were completely crushed, even when their frames were as strong as those
which survived.
The damage sustained by reinforced concrete buildings depended both on the
proximity to X and the type and strength of the reinforced concrete
construction. Some of the buildings with reinforced concrete frames also
had reinforced concrete walls, ceilings, and partitions, while others had
brick or concrete tile walls covered either with plaster or ornamental
stone, with partitions of metal, glass, and plaster. With the exception of
the Nagasaki Medical School and Hospital group, which was designed to
withstand earthquakes and was therefore of heavier construction than most
American structures, most of the reinforced concrete structures could be
classified only as fair, with concrete of low strength and density, with
many of the columns, beams, and slabs underdesigned and improperly
reinforced. These facts account for some of the structural failures which
occured.
In general, the atomic bomb explosion damaged all windows and ripped out,
bent, or twisted most of the steel window or door sashes, ripped doors from
hinges, damaged all suspended wood, metal, and plaster ceilings. The blast
concussion also caused great damage to equipment by tumbling and battering.
Fires generally of secondary origin consumed practically all combustible
material, caused plaster to crack off, burned all wooden trim, stair
covering, wooden frames of wooden suspended ceilings, beds, mattresses, and
mats, and fused glass, ruined all equipment not already destroyed by the
blast, ruined all electrical wiring, plumbing, and caused spalling of
concrete columns and beams in many of the rooms.
Almost without exception masonry buildings of either brick or stone within
the effective limits of the blast were severely damaged so that most of
them were flattened or reduced to rubble. The wreckage of a church,
approximately 1,800 feet east of X in Nagasaki, was one of the few masonry
buildings still recognizable and only portions of the walls of this
structure were left standing. These walls were extremely thick (about 2
feet). The two domes of the church had reinforced concrete frames and
although they were toppled, they held together as units.
Practically every wooden building or building with timber frame within 2.0
miles of X was either completely destroyed or very seriously damaged, and
significant damage in Nagasaki resulted as far as 3 miles from X. Nearly
all such buildings collapsed and a very large number were consumed by fire.
A reference to the various photographs depicting damage shows that although
most of the buildings within the effective limits of the blast were totally
destroyed or severely damaged, a large number of chimneys even close to X
were left standing, apparently uninjured by the concussion. One
explanation is that concrete chimneys are approximately cylindrical in
shape and consequently offer much less wind resistance than flat surfaces
such as buildings. Another explanation is that since the cities were
subject to typhoons the more modern chimneys were probably designed to
withstand winds of high velocity. It is also probable that most of the
recently constructed chimneys as well as the more modern buildings were
constructed to withstand the acceleration of rather severe earthquakes.
Since the bombs were exploded high in the air, chimneys relatively close to
X were subjected to more of a downward than a lateral pressure, and
consequently the overturning moment was much less than might have been
anticipated.
Although the blast damaged many bridges to some extent, bridge damage was
on the whole slight in comparison to that suffered by buildings. The
damage varied from only damaged railings to complete destruction of the
superstructure. Some of the bridges were wrecked and the spans were shoved
off their piers and into the river bed below by the force of the blast.
Others, particularly steel plate girder bridges, were badly buckled by the
blast pressure. None of the failures observed could be attributed to
inadequate design or structural weaknesses.
The roads, and railroad and street railway trackage sustained practically
no primary damage as a result of the explosion. Most of the damage to
railroads occurred from secondary causes, such as fires and damage to
bridges or other structures. Rolling stock, as well as automobiles,
trolleys, and buses were destroyed and burned up to a considerable distance
from X. Streets were impassable for awhile because of the debris, but they
were not damaged. The height of the bomb explosion probably explains the
absence of direct damage to railroads and roads.
A large part of the electric supply was interrupted by the bomb blast
chiefly through damage to electric substations and overhead transmission
systems. Both gas works in Nagasaki were severely damaged by the bomb.
These works would have required 6-7 months to get into operation. In
addition to the damage sustained by the electrical and gas systems, severe
damage to the water supply system was reported by the Japanese government;
the chief damage was a number of breaks in the large water mains and in
almost all of the distributing pipes in the areas which were affected by
the blast. Nagasaki was still suffering from a water shortage inside the
city six weeks after the atomic attack.
The Nagasaki Prefectural report describes vividly the effects of the bomb
on the city and its inhabitants:
"Within a radius of 1 kilometer from X, men and animals died almost
instantaneously and outside a radius of 1 kilometer and within a radius of
2 kilometers from X, some men and animals died instantly from the great
blast and heat but the great majority were seriously or superficially
injured. Houses and other structures were completely destroyed while fires
broke out everywhere. Trees were uprooted and withered by the heat.
"Outside a radius of 2 kilometers and within a radius of 4 kilometers from
X, men and animals suffered various degrees of injury from window glass and
other fragments scattered about by the blast and many were burned by the
intense heat. Dwellings and other structures were half damaged by blast.
"Outside a radius of 4 kilometers and within a radius of 8 kilometers
living creatures were injured by materials blown about by the blast; the
majority were only superficially wounded. Houses were only half or
partially damaged."
The British Mission to Japan interpreted their observations of the
destruction of buildings to apply to similar construction of their own as
follows:
A similar bomb exploding in a similar fashion would produce the following
effects on normal British houses:
Up to 1,000 yards from X it would cause complete collapse.
Up to 1 mile from X it would damage the houses beyond repair.
Up to 1.5 miles from X it would render them uninhabitable without extensive
repair, particularly to roof timbers.
Up to 2.5 miles from X it would render them uninhabitable until first-aid
repairs had been carried out.
The fire damage in both cities was tremendous, but was more complete in
Hiroshima than in Nagasaki. The effect of the fires was to change
profoundly the appearance of the city and to leave the central part bare,
except for some reinforced concrete and steel frames and objects such as
safes, chimney stacks, and pieces of twisted sheet metal. The fire damage
resulted more from the properties of the cities themselves than from those
of the bombs.
The conflagration in Hiroshima caused high winds to spring up as air was
drawn in toward the center of the burning area, creating a "fire storm".
The wind velocity in the city had been less than 5 miles per hour before
the bombing, but the fire-wind attained a velocity of 30-40 miles per hour.
These great winds restricted the perimeter of the fire but greatly added to
the damage of the conflagration within the perimeter and caused the deaths
of many persons who might otherwise have escaped. In Nagasaki, very severe
damage was caused by fires, but no extensive "fire storm" engulfed the
city. In both cities, some of the fires close to X were no doubt started
by the ignition of highly combustible material such as paper, straw, and
dry cloth, upon the instantaneous radiation of heat from the nuclear
explosion. The presence of large amounts of unburnt combustible materials
near X, however, indicated that even though the heat of the blast was very
intense, its duration was insufficient to raise the temperature of many
materials to the kindling point except in cases where conditions were
ideal. The majority of the fires were of secondary origin starting from
the usual electrical short-circuits, broken gas lines, overturned stoves,
open fires, charcoal braziers, lamps, etc., following collapse or serious
damage from the direct blast.
Fire fighting and rescue units were stripped of men and equipment. Almost
30 hours elapsed before any rescue parties were observable. In Hiroshima
only a handful of fire engines were available for fighting the ensuing
fires, and none of these were of first class type. In any case, however,
it is not likely that any fire fighting equipment or personnel or
organization could have effected any significant reduction in the amount of
damage caused by the tremendous conflagration.
A study of numerous aerial photographs made prior to the atomic bombings
indicates that between 10 June and 9 August 1945 the Japanese constructed
fire breaks in certain areas of the cities in order to control large scale
fires. In general these fire breaks were not effective because fires were
started at so many locations simultaneously. They appear, however, to have
helped prevent fires from spreading farther east into the main business and
residential section of Nagasaki.