Report of the British Mission to Japan
Conclusions
89. Consider a British urban area with an overall housing density of about 15 per acre (including open spaces), and a population density of about 45 per acre: and apply to it the radii of damage listed in paragraph 38. The explosion of a single atomic bomb of the power and at the height of those in Hiroshima and Nagasaki would demolished or damage beyond repair approximately 30,000 houses. The number of houses requiring extensive repair would be approximately 35,000; the number temporarily uninhabitable and requiring first-aid repairs would be between 50,000 and 100,000. Thus a total of roughly 400,000 people might be rendered temporarily homeless, of whom about one-half could return to their houses after lesser repairs. Not all the remaining 200,000 would constitute a rehousing problem: because about 50,000 of them would be dead or would die within eight weeks, and a comparable number would require extended hospital treatment. Therefore the number of non-casualties to be rehoused, either permanently or for the months required to carry out major repairs, would be approximately 100,000.
90. This picture somewhat over-estimates the average effect; for example, in the nature of things, cities of less than 400,000 inhabitants could hardly have so many homeless. In fact, few British urban areas are as dense as this through-out a circle of 4 to 5 miles diameter, such as the application of paragraph 38 presupposes. Nevertheless, the figures make vivid the scale of the disaster; and will be appropriate to an incident in the larger British and other western cities.
91. As paragraphs 29-35 show, the distances at which factory buildings would be affected are roughly comparable, and the scale of the immediate industrial loss would therefore be of the same order. The final industrial loss, however, would be considerably lower if fire precautions were adequate and if machines were not left to weather.
92. It has long been known from the experience of raiding on Great Britain that reinforced concrete and steel framed buildings are much more resistant to blast than are buildings of the normal British and Continental design, having load-bearing wails. The observations at Hiroshima and Nagasaki reported in paragraphs 24-28 fully confirm this. Casualties in framed buildings are usually the result of structural collapse, falling ceilings and partitions, and flying debris and glass. These risks remain, and to them are added the risk from flashburn, from fire (see paragraph 68), and from gamma rays. Framed buildings in which these risks have been minimized should be advocated for all public and semipublic buildings.
93. The conditions of the explosions in Hiroshima and Nagasaki could be changed in a number of ways. One way is, that the height of burst could be lowered. This would probably reduce the area of damage, but damage to massive buildings and to bridges near the centre would become more severe, and from sufficiently low bursts would extend to underground services. The increase in casualties near the centre, particularly from gamma rays, would be expected to be offset by the decrease in more distant casualties. A serious effect, however, would be created by the greater density of fission products on the ground which would result from a lower explosion, for these would make the area dangerously radio-active for a period of days.
94. The overall picture, then, is sombre. Even ignoring changes in attack and in the development of the bomb, the damage figures given, say, in paragraph 89, are very serious. And these figures are a measure only of the blast effect of the bomb. With them must be kept in mind the grave problem of fire, direct and indirect, which the bomb has created, which has been discussed in paragraphs 62-68. Both are overshadowed by the scale of casualties produced by the bomb, which make the mere disposal of the dead a major problem. The figures given in Chapter VII speak for themselves.
89. Consider a British urban area with an overall housing density of about 15 per acre (including open spaces), and a population density of about 45 per acre: and apply to it the radii of damage listed in paragraph 38. The explosion of a single atomic bomb of the power and at the height of those in Hiroshima and Nagasaki would demolished or damage beyond repair approximately 30,000 houses. The number of houses requiring extensive repair would be approximately 35,000; the number temporarily uninhabitable and requiring first-aid repairs would be between 50,000 and 100,000. Thus a total of roughly 400,000 people might be rendered temporarily homeless, of whom about one-half could return to their houses after lesser repairs. Not all the remaining 200,000 would constitute a rehousing problem: because about 50,000 of them would be dead or would die within eight weeks, and a comparable number would require extended hospital treatment. Therefore the number of non-casualties to be rehoused, either permanently or for the months required to carry out major repairs, would be approximately 100,000.
90. This picture somewhat over-estimates the average effect; for example, in the nature of things, cities of less than 400,000 inhabitants could hardly have so many homeless. In fact, few British urban areas are as dense as this through-out a circle of 4 to 5 miles diameter, such as the application of paragraph 38 presupposes. Nevertheless, the figures make vivid the scale of the disaster; and will be appropriate to an incident in the larger British and other western cities.
91. As paragraphs 29-35 show, the distances at which factory buildings would be affected are roughly comparable, and the scale of the immediate industrial loss would therefore be of the same order. The final industrial loss, however, would be considerably lower if fire precautions were adequate and if machines were not left to weather.
92. It has long been known from the experience of raiding on Great Britain that reinforced concrete and steel framed buildings are much more resistant to blast than are buildings of the normal British and Continental design, having load-bearing wails. The observations at Hiroshima and Nagasaki reported in paragraphs 24-28 fully confirm this. Casualties in framed buildings are usually the result of structural collapse, falling ceilings and partitions, and flying debris and glass. These risks remain, and to them are added the risk from flashburn, from fire (see paragraph 68), and from gamma rays. Framed buildings in which these risks have been minimized should be advocated for all public and semipublic buildings.
93. The conditions of the explosions in Hiroshima and Nagasaki could be changed in a number of ways. One way is, that the height of burst could be lowered. This would probably reduce the area of damage, but damage to massive buildings and to bridges near the centre would become more severe, and from sufficiently low bursts would extend to underground services. The increase in casualties near the centre, particularly from gamma rays, would be expected to be offset by the decrease in more distant casualties. A serious effect, however, would be created by the greater density of fission products on the ground which would result from a lower explosion, for these would make the area dangerously radio-active for a period of days.
94. The overall picture, then, is sombre. Even ignoring changes in attack and in the development of the bomb, the damage figures given, say, in paragraph 89, are very serious. And these figures are a measure only of the blast effect of the bomb. With them must be kept in mind the grave problem of fire, direct and indirect, which the bomb has created, which has been discussed in paragraphs 62-68. Both are overshadowed by the scale of casualties produced by the bomb, which make the mere disposal of the dead a major problem. The figures given in Chapter VII speak for themselves.