What the Fire Service Should Know About the Atomic Bomb
In the preparation of this article, the editors have drawn very heavily upon a series of two articles which appeared in the Bulletin of the U. S. Army Medical Department (Vol. VIII, No. 5 and Vol. VIII, No. 7, 1948). These two articles, from which the excerpts have been made, present in a very concise, yet comprehensive manner, data which are understandable to the men who have had little or no chemical engineering training.
They also provide convincing argument that a great deal remains to be done in the preparation of our American fire departments for handling this new and awesome agent of destruction, and possible future agent of peacetime power production. Though other nations than England, America and Canada may not now possess the secret of the atomic bomb, nor the facilities for manufacturing it, it is generally conceded that this condition will have changed within the next few years. And should the present tense situation existing between nations flare up into open warfare, it is quite certain that American fire fighters will have to face the task of combatting fires brought about by atomic warfare. THE EDITOR
THE atomic bomb is primarily a strategic weapon, and the choice of target and method of employment require the evaluation of a number of factors. Thus far, five atomic bombs have been detonated, three of them under test conditions. The one factor that makes an atomic bomb detonation different from the detonation of any other type of weapon is the nuclear radiation produced. All high-explosive weapons produce high temperature and high blast pressure, and the only difference in these respects between atomic and conventional weapons is the increased magnitude of the blast and thermal effect produced by the atomic bomb. However, no other weapon devised to date is capable of releasing nuclear radiation.
The first bomb was set off under experimental conditions from a tower near Alamogordo, New Mexico, on July 16, 1945. The second bomb was dropped August 6, 1945, on the city of Hiroshima from a B-29 bomber. Over four square miles of the city were instantly and completely devastated; 66,000 people were dead or missing and 69,000 were injured. On August 9 another B-29 dropped an atomic bomb on Nagasaki, totally destroying 1.5 square miles of the city. The number of persons dead and missing in Nagasaki was 39,000, and 25,000 more were injured. The fourth atomic bomb was dropped by a B-29 on target vessels assembled in Bikini lagoon on July 1, 1946, and the fifth was detonated under water on July 25, 1946. Test animals placed on various locations on the target vessels yielded important data on the bomb effects. This work was under the supervision of the Naval Medical Research Center.
The detonation of the atomic bomb generates a crushing wave of high pressure. The bomb also liberates an enormous quantity of electromagnetic radiations and neutrons. The electromagnetic radiations included infra-red, visible light, ultraviolet, x-ray, and gamma radiation. Thereafter, the fission products formed emit gamma rays and beta particles. The unfissioned bomb residue emits alpha particles. Substances bombarded by neutrons released at detonation, which become radioactive by induced radioactivity, may also emit nuclear particles and gamma rays. A large fraction of the gamma rays is emitted in the first few microseconds (millionth parts of second.—Ed.) of the atomic explosion. Neutrons also accompany this reaction. The range of neutrons is negligible at 1,000 yds. because of their absorption in the air. In an underwater burst, greater absorption occurs, resulting in induced radioactivity of the sea water.
At detonation, practically all of the lethal gamma radiation is released, and the remaining small fraction of the total dose is given off by the resultant fission products that rise rapidly in the bomb cloud. The column of radiating fission products and combustion material rapidly rises into the air and begins to mushroom out when the temperature of the column is equal to the temperature of the surrounding atmosphere. The climatic and meteorologic conditions will govern the diffusion, dispersion, and radiation activity of the cloud. The fissioned and unfissioned material in an airburst will be distributed in the atmosphere; while in a sub-surface waterburst, the adjacent water, ships, and facilities in proximity to the detonation will be seriously contaminated. Fission products in the cloud may be dispersed as fine particles of varying size, and depending on many factors, a shower of the radioactive material will fall on nearby areas. The fission products. _____fore, present a continuing health _____rd for a considerable time as an _____math of the explosion. In general, re_____rdless of the technique of bomb detonation, radioactive materials emitting alpha and beta particles and gamma rays will be be encountered. The radioactivity of these substances will range from a few seconds to years.
In the underwater detonation of the bomb, thousands of tons of water rise in a column, a few thousand feet in the air, followed immediately by a rapidly moving mass of water, constituting the base surge. The turbulent waters contain a high percentage of the fission products and unfissioned residue. Immediately at detonation and for a short period thereafter an enormous amount of radiation is emitted. The falling column of water and mist, depending on wind conditions and depth of detonation, contains a high percentage of the fission products and unfissioned residue that can contaminate an area of several square miles for a considerable period.
The emission of infrared, visible and ultraviolet light occurs a few milliseconds after the explosion. The ball of fire in the airburst grows rapidly in size. As it grows, its temperature and brightness decrease. Several milliseconds after the initiation of the explosion, the brightness of the ball of fire is several times the brightness of the sun. Most of the infrared and ultraviolet radiation is given off after the point of maximum intensity. The ball of fire rapidly expands from the size of the bomb to a radius of several hundred feet at one second after the explosion. Thus, the infrared and ultraviolet radiation comes in two bursts—-an extremely intense one lasting a fraction of a millisecond and a less intense one of much longer duration lasting several seconds.
The heat from the flash in an airburst occurs in a short time, and since there is no time for any cooling to take place, the temperature of a person’s skin can be raised 50 degrees C. (90 deg. F.) by the flash of infrared and ultraviolet rays in the first millisecond at a distance of over 4,000 yards. People may be injured by flash burns at even greater distances. Gamma radiation danger does not extend nearly so far, and the neutron danger zone is still more limited. High skin temperatures result from the first flash of high intensity infrared and ultraviolet and are probably as significant for injuries as the total doses that come mainly from the second, more sustained, ball of fire.
Effectiveness Against Personnel
For personnel in the open, within onehalf mile of zeropoint of the airburst detonation, death would occur almost instantaneously or within a few hours from the blast, heat and radiation effects. Within a radius of ore-half mile and one mile from zeropoint, some persons would die instantly, while a majority would receive varying degrees of injury. Ordinary houses and structures would suffer complete destruction or extensive damage and fires would be widespread. Outside a radius of one mile and within a radius of two miles from zeropoint, personnel would suffer injuries from flash burns and indirect blast effects. Outside a radius of two miles and within a radius of four miles, personnel would be injured by flying fragments and suffer superficial wounds. Structures would be half or partially destroyed within this radius. In an airburst explosion 70 per cent of those exposed would suffer from trauma (injury or wound.—ed.), 65 per cent from burns and over 35 per cent from radiation.
The Radiologic Hazard
In general, any radioactivity that remains in the area as fission products or induced radioisotopes will constitute a hazard. Fission products from the airburst bomb may be dispersed in the ground or spread out over wide and diffuse areas, depending on the technique employed in the detonation. Consequently, the degree and extent of residual radioactivity would depend on the height of detonation, climatic and meteorologic conditions conducive to the showering of the products on a specific area, and the nature and composition of the terrain. For example, because of the height of the detonation, certain prescribed areas of the bomb crater might remain hazardous. Also, because of the composition of the ground, dust particles intermixed with fission products might rise in the cloud. Many of these “dust particles” might also become radioactive as a result of neutron bombardment released at detonation and thus contribute to the hazard.
When the bomb is detonated over a modern city that contains countless thousands of items composed of iron, zinc, copper, and other “neutron capture materials,” it is possible that many of the elements within the effective neutron range may become radioactive for a considerable period. In an underwater burst the main hazard, following detonation, will be the result of the deposition of a large percent of the fission products in the water and on nearby objects.
The radiologic hazard can be divided into two phases. The first phase includes the immediate or prompt release of any ionizing particles or radiations caused by the explosion during the period of visible flash of the bomb. These prompt ionizing radiations include beta particles, neutrons, x-rays, gamma and alpha particles from unfissioned bomb residue, and the ionizing radiations from fission products. After the flash of the bomb has subsided, a matter of a few seconds, the delayed phase of the radiologic hazard is of importance. The hazard here is from fissioned and unfissioned material and from radioactive elements induced by neutrons from the explosion. The nature and persisteney of the second phase depends on the technique of detonation. In addition to the phase of the radiologic hazard, the protection problem depends on whether the radiation concerned is external or internal to the body. Alpha particles, for example, present no external hazard; but if they are inhaled and become fixed in the bone, depending on the amount, the results may be lethal. Although very little can be done to protect personnel in the open within the lethal range at the instant of detonation, a few points in connection with the second phase may be useful.
The relative protection against gamma radiation by shielding, in order of effectiveness, is given by iead, iron, concrete, earth, water, and air. Using the gamma radiation from radium as an illustration, a 5-inch thickness of concrete gives about the same protection as a 1-inch layer of lead. Where no shielding is available, “distance” is the best means of protection. It should be noted that neutrons pass through lead with extreme ease, but are readily absorbed by hydrogenous materials and boron.
The Flash Burn
At detonation, the flash burns from infrared and ultrared caused a higher percent of casualties than the radiologic effect, because of the increased range of the flash. Light shades of loosely fitting clothing, antiflash cream, and protection of the entire body surface will reduce the percent of casualties. Protection by these means will not reduce the effects of burns produced by secondary fires in buildings or facilities. The problem here is to minimize the amount of inflammable material as far as practicable. Flash burn is not a serious factor in an underwater detonation.
To sum up, airburst atomic bombs will produce lethal effects over an area of two square miles and measurable effect over an area of seven square miles as a result of the prompt gamma radiation emitted at the time of detonation. The residual, radioactivity is of little importance except in the area close to the center of a low-altitude explosion. In an underwater detonation, radioactive fission products and unfissioned material will be spread by the cloud and base surge over a large area. The gamma radiation from these materials will be lethal to exposed personnel more than two miles downwind, and serious contamination will result at much greater distances. This contamination will provide a serious hazard for an indefinite period. Prompt evasive action at the time of the detonation will permit the reduction of casualties, and orderly evacuation and re-entry procedures will undoubtedly pay great dividends in minimizing the effects.
Protection Against Atomic Bombs
The important effects of the atomic bomb against which protection must be developed are: (1) the blast or shock wave; (2) visible light, ultraviolet, and infrared radiations; (3) nuclear radiation; and (4) psychological effects.
Blast: The effects of the atomic bomb rapidly decrease in intensity as one moves away from the point of detonation; thus, distance is always the best protection. Primary shock, or blast damage is defined as the compressive and tearing action of the shock wave on the human body. When one interposes between the blast and the body an object of strength similar to that of an ordinary wall, this form of damage is effectively reduced. Primary shock is thus of importance only when a person is in the open, in which case he is exposed simultaneously to lethal amounts of other effects of the atomic bomb. Living things are remarkably resistant to blast damage and are much stronger in this respect than normal buildings. Underground shelters and normal reinforced concrete buildings protect against this effect very close to the point of detonation. Hemorrhages of the lung occur from blast damage in its mildest forms. In its severest forms major abdominal hemorrhages appear.
Secondary shock, or blast damage, is caused by flying objects hitting and and lacerating the body. A shock wave is very much like a wind of several hundred miles per hour, arising instantaneously, and lasting for about a second. This wind is strong enough to throw the body several feet. It also breaks windows, knocks down plaster, and throws other objects around with great violence. When these objects strike a person, secondary shock damage results. There are many things a person can do for himself to reduce his chances of this type of injury if he has some advance warning of the detonation. He should keep away from windows and lie fl_____ the floor or ground. He should standing under overhanging coni_____ chimneys, and other heavy objects at are easily knocked down. Underground installations or shelters greatly reduce this effect, because very little of the air shock is transmitted through the ground and thence into shelters or basements. In Japan, this form of injury combined with burns accounted for most of the casualties. The rapid follow-up of the fire on the blast damage caused many deaths among the injured. Injuries of this type require evacuation and hospitalization. In the case of primary shock damage there is an amazingly small boundary zone. One is either killed immediately or is all right after a few minutes, so far as this effect is concerned. There is much that can be done in the design of vital installations to reduce damage from these secondary shock effects.
Flash burns are injuries created by direct exposure to the visible and nearvisible radiation emanating from the point of detonation. The thinnest type of nontransparent material will shield effectively from this effect. Light-colored clothing is particularly good as it reflects almost all this radiation. Dark clothing will not transmit this radiation but will catch fire and produce flame burns on the skin beneath the clothing. This form of damage is important only when a person is in the open and in direct line of sight with the point of detonation. Because of the nature of the atomic bomb, this form of damage occurs at greater distances than those caused by any other effect.
Flame burns are produced by fires started in inflammable materials or buildings. These were prevalent in Japan, but they would occur to a lesser degree in an American city. This possibility of fire and subsequent injury can be greatly reduced by making structures less inflammable. The development of large quantities of adequate fire fighting equipment and trained personnel can furnish great protection. To reduce this form of damage it will be necessary to have fire fighting equipment and personnel so located that a major proportion will not be wiped out by the detonation. Accounts from Hiroshima and Nagasaki point out the inadequacy of Japanese fire fighting equipment and procedures. In both cities, about 90 per cent of the equipment and personnel for these duties were wiped out immediately. Major efforts should be directed to reducing the possibility of flame burns, not only because they produce a large number of casualties, but also because these casualties need so many trained persons and so much equipment for treatment and hospitalization.
The use of nuclear radiation in warfare presents new problems for both the military and the civil population. These effects are not only important but complex, as they may be caused by external and internal radiations and may be immediate or delayed. For all nuclear radiation effects, distance is by far the best protection. Immediate radiation effects are produced in a matter of a few thousandths of a second after detonation. With the atomic bomb, about 99 per cent of the nuclear radiation produced comes out in the first fraction of a second after the detonation. It consists of penetrating radiations that come from outside the body and therefore constitute an external hazard.
Large quantities of gamma rays are produced almost immediately by the detonation and radiate in all directions. These rays travel in a straight line as does light. They are highly penetrating, and it takes a large amount of material to absorb and stop them. It is important to realize the directional and shadow producing characteristics of this radiation. One does not need shielding on all sides but merely on the side of the detonation. In shielding against gamma radiation the important thing is the weight of the material that is between the body and the source. The chemical characteristics of the shield are of no importance. Lead is often used in laboratories where gamma radiation or x-radiation occurs. This is a suitable substance because it occupies a very small volume in comparison to its weight. The effectiveness of a shield is most often described by means of thickness of the material that is necessary to reduce the intensity to half the initial amount. This is called the half-thickness of that material. The approximate halfthickness of common construction materials are 1 inch for steel, 3 inches for concrete and 4 inches for wood or earth.
Neutrons also constitute an external hazard at the time of the detonation. They are not as effective at great distances as the gamma rays, but they require consideration because, being uncharged particles, they are difficult to stop and shield against. Shielding is not as simple as in the case of gamma radiation, because the weight of the shielding material is not the important factor. Instead, the important characteristic is the ability of the particular element or compound to slow down and then capture neutrons. The neutrons that occur in the detonation of an atomic bomb are essentially fast neutrons. Substances such as cadmium and boron capture slow neutrons to an amazing degree; but, since these neutrons are not slow, these substances arc of little value in defense against the atomic bomb. The best substances are those with low atomic weights. Hydrogen, the lightest of all substances, is the best; hence, in shielding against neutrons, the best substances for their weight arc those containing large amounts of hydrogen, such as water or paraffin. The approximate half-thicknesses of common materials are between 3 inches and 12 inches for steel and about 6 inches for concrete, earth, wood, and water. Since neutrons, like gamma rays, travel in a straight line from the point of detonation, radiating in all directions, the shielding need be only between the person and the source.
About 1 per cent of the nuclear radiation produced by an atomic bomb is not produced immediately, but comes from the decay of the fission products. In an air burst, where the fireball and mushroom cloud containing the fission products go up in the air to be dispersed by the wind, this delayed radiation is negligible. In an underwater burst, or possibly a surface land burst, a base surge will probably occur. This cloud, moving close to the ground, contains a large proportion of the fission products. As this cloud sweeps out over ships or cities, it surrounds buildings, people, and equipment. The radiating material is then extremely close to a person. The relatively small amount of radiation that is left after the detonation is greatly enhanced because of its proximity. This base surge, in comparison to the mushroom cloud after the air burst, produces radiation intensities on the ground that are higher by many thousandfold. This is due solely to the fact that the base surge can surround individuals on the ground. When it is realized that at Bikini this base surge moved over an area of about 5 sq. mi., this is seen to be a very real hazard. It takes time for this cloud to move, and, as the radiation from it is only of importance when it surrounds the point in consideration, there is available a varying amount of time in which to get out of the way or to dodge the cloud. This base surge moves with varying speeds. Initially it spreads out at about 50 m.p.h. Its speed constantly decreases until it is dispelled. For this cloud to spread over its maximum area requires several minutes. If one is in a city, great protection will be afforded if one gets down into a basement or sub-basement, or into an air raid shelter. It is of importance also to note that this radiation from the base surge is nondirectional, as it comes from all points in the cloud. Hence, any shield that is devised must be on all sides, including the top, of the location considered.
The shielding requirements are similar to those in the previous situation, in that the same haif-thicknesses are applicable. There are no delayed neutrons of significance; hence, special shielding is of no importance in this problem. In the delayed situation we also have important beta radiation. Immediate beta radiation occurs but does not travel a very great distance from the source, because of the efficient shielding furnished by air. Where the base surge is surrounding the location in question, beta radiation is important, because the half-thickness of air is about 4 yd. Normal clothing furnishes sufficient shielding to beta radiation. Similarly, thin walls and the glass in windows are adequate. It is, of course, nondirectional and comes from all sides. The extent of the external hazard furnished by beta radiation is not well understood. It is believed comparable to that of gamma radiation when a base surge has been created. Alpha radiation occurs from the nonfissioned plutonium and uranium. This radiation constitutes no external hazard, as the skin furnishes adequate shielding. All the alpha rays are absorbed in the epidermis with no resulting damage to living tissues.
Internal radiation gets into the body through inhalation, ingestion, or injection. This is a delayed hazard and is possible only where one is in the base surge, the mushroom cloud, or an area over which the base surge has previously passed. The internal hazard generally occurs only where there is also an external hazard. If one is exposed to the base surge or is in the mushroom cloud, the external radiation is often lethal without any consideration of an internal hazard. Particularly if one is working in a highly contaminated area after the detonation, there is a significant, but not necessarily lethal, degree of internal hazard. This is created by disturbing the dust and usually enters the body through inhalation. An additional hazard exists from eating with contaminated hands and thus getting the active material into the body through the mouth.
In the case of an atomic explosion, a small amount of this radioactive material is in the form of a true gas or vapor. Almost all of it exists on particles of dust or droplets of water. The filter in a modern gas mask is believed to give adequate protection. This filter is extremely efficient. It is quite possible that new masks will be devised that will protect against atomic, biologic, and chemical warfare. Such a development is highly desirable. Protective clothing would be required for workers entering contaminated areas. It would probably be permeable clothing. Its main requirement is that it should be disposable. Its functions would be to keep contaminated material from the skin and possible later entry into the body. Disposability is desirable, as these materials cannot be rendered harmless by any physical or chemical means.
Collective protectors with filters or inclosed air-conditioning systems are probably indicated for vital installations and underground shelters in anticipation of atomic warfare. Such items would prevent the highly contaminated air of the base surge from entering installations that otherwise would furnish adequate protection against the effects of the atomic bomb. The development of decontamination techniques and facilities is indicated to reduce the long-term possibility of personnel becoming contaminated and later having active material enter the body through the respiratory and digestive tracts. Such techniques will probably consist of washing away, carrying away, or burying the active material.
In an attack on a modern city it is believed that about 50,000 deaths would result from a single bomb. It is felt that, if the individual civilian and soldier in such a city were adequately trained as to what he could do for himself after the detonation occurs, perhaps 10,000 lives could be saved. The development of atomic defense for the individual will be the subject of much work in the future. The education of large numbers of persons, both civilian and military, for special jobs in atomic warfare is important and will probably be given to such people as radiologic safety personnel, medical officers, civilian doctors, and civil defense technicians. The method by which the individual indoctrination and the specialized traini_____ given will determine to a large ex_____ the psychological preparation that be attained in a population. It is hi_____ desirable that we impart the proper degree of knowledge to all so that each individual has a respect for the special hazards of atomic warfare, thereby avoiding the undesirable extremes of excessive fear or ignorance. This will be a difficult job and the Nation is far from attaining this goal at present.
A large amount of detailed defense planning will be required for the protection of the Nation. It will include large-scale training of such specialists as fire fighters, evacuation control personnel, first aid personnel, and decontamination groups. Large stock piles of food supplies, medical supplies, and disaster equipment will be required in relatively invulnerable locations. Preparations will be required for mutual aid between cities and major installations. All civil and military groups must be equipped and trained in the detection and isolation of contaminated areas. This new hazard created by nuclear radiation is the one hazard that may not be detected by any of the physical senses. It requires special instruments and special consideration. With sufficient indoctrination and a few minutes warning of an attack, it is quite possible that a 50 per cent saving in casualties can be effected. This establishes the fact that development of advance detection techniques and warning signals is of the greatest importance to insure the continuation of our present existence.
How Bomb Effects Are Produced
Lieutenant-Colonel David B. Parker, of the Manhattan Project, War and Navy Departments Armed Forces Special Weapons Project, pointed out in an address before the International Association of Fire Chiefs, in New York in August of last year that the atomic bomb causes damage to buildings in three ways. First, the ordinary high pressure blast wave, which knocks the building down and blows windows, shatters foundations, pillars and columns, blows roofs in and flattens the whole building:
Secondly, primary fires. The heated radiations are so intense that readily ignitable material is ignited at the instant of explosion;
Third, probably the greatest cause of damage are the secondary fires which are caused when buildings collapse, wire circuits are shorted, roofs fall in and heating equipment gets out of control.
In discussion the atomic bomb attacks on Japan, Colonel Parker said: “In the case of the Japanese attacks, we purposely exploded the bombs high in the air in order to minimize radiation effects, for humane or any other reason you may like to choose. One of the reasons we burst them so high in the air was to avoid delayed radioactivity. Of course I’d better add also the altitude we selected worked out very well from the physicist’s angle to cause the maximum blast damage. If we had set bombs off on the ground, put contact fuses on them, so that they did not explode until they hit the ground, these dangerous fission products would have been exploded around the scene of the explosion in a very efficient manner and the radio activity would have become the major factor in injuring people though it would not have done any more damage to the buildings.
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“Finally, the bomb caused in Japan, land can cause again, injury or death by direct compression. Doctors tell us it takes 250 pounds per square inch of pressure — remember, ordinary atmosphere is just under 15 — it takes 250 additional to kill a man by compressing his lungs or injuring some other internal organ, and a pressure of only 1 or 2 pounds per square inch will knock a building over, since the governing factor is force, or pressure times area, and in the case of a building, we have many, many square feet of areas; and if you have a building with few windows and doors, it is likely to accumulate enough force to knock it down, although the compression would not be sufficient to kill a person, unless he is burned, radiated, or has the building fall on him.
“Another interesting feature of the Japanese attack was the downward thrust which results from the high-altitude burst we mentioned. Many of the roofs w’ere blown downward and some of the buildings right under the bottom were straightened out, straight down almost. That is a phenomenon we have never seen before with ordinary explosions and we wouldn’t have it if we hurst the bomb on the ground.
“The points about atomic explosions which will concern men who have to deal with fires, are these: First, you will have a tremendously large devastated area, larger than any you ever had to deal with before. That means it will be difficult to get your fire fighting apparatus around if there is any left to move around, and if there are any of vou left to handle it.
“Someone suggested that perhaps if we are going to seriously build ourselves against future atomic attacks, we had better design fire fighting vehicles that can go over devastated areas before cleared lanes have been made.
“Next is your water supply, which may very well dwindle into nothing; some means must be employed to be sure that you will have water to use if you do get your equipment to the scene.
“The high air burst in Japan did not destroy the water mains under the ground because the pressure so many hundred feet from the center of the explosion was not great enough. However, every time a building with pipes falls down, you have hundreds of broken water connections, and your water dissipates very rapidly and your pressure goes down to almost nothing.
“Another problem which I believe is almost insolvable—and I don’t think the fire departments can handle it—is how to get your equipment around safely through an area not only devastated, but covered with fission products or other radiating material.
“The problem of the fire fighting man .would then be how to protect himself from these radiations, or how to pick his way through the dangerous areas. Now, that is something which I believe our civic organizations in all our large cities are going to have to face very soon. They must have the instruments which arc commonly known by the name of Geiger counters, so they can measure radioactivity, so they can map out safe lines through which people can evacuate themselves and through which you may pass if you have to fight the fires.
“Just to emphasize what your problem will be—the problem of all of us if we do have atomic bombs burst over our city—I would like to quote from the British report, which is highly recommended by all who know about it, when they made their own investigation of Hiroshima and Nagasaki. They translated it in terms of their own City of London, which is interesting, because our cities resemble London more than they do the Japanese. They said, ‘If a bomb burst over London, it would have caused complete collapse of all buildings up to 3,000 feet from the center of the explosion; it would have badly damaged everything up to a mile away from it. It would have caused a need for extensive repair to all dwellings up to one and one-half miles; it would have necessitated first aid repairs out to tw’o or two and one-half miles. The net result is that 30,000 homes would have been wrecked, 35,000 would have been badly damaged, and 50,000 to 100,000 would have been seriously damaged.’ Thus, they estimate 400,000 people would have been rendered homeless by one airburst atomic bomb. Fortunately, or unfortunately, not all 400,000 would have to seek other homes, because 50,000 would be dead or die within eight weeks.”