Arch. Myriam B. Mahiques Curriculum Vitae

Thursday, April 22, 2010

Report on the destructions of two cities: Hiroshima and Nagasaki

Among many considerations, the target of Hiroshima and Nagasaki, was selected because of the expectation to produce the greatest amount of damage by primary blast effect, and next greatest by fires. So, the targets would contain a large percentage of closely-built frame buildings and other construction that would be most susceptible to damage by blast and fire.
The maximum blast effect of the bombs was calculated to extend over an area of approximately 1 mile in radius. Therefore, the targets should contain a densely built-up area of at least this size. (Manhattan Engineer District, 1946, adapted)
From The Atomic Bombings of Hiroshima and Nagasaki. By The Manhattan Engineer District. June 29, 1946: 
Ruins of the Hiroshima Promotion Hall. From

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 ½ 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. 

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