as in Hiroshima and Nagasaki, and add to the difficulties of the situation. For the examples air bursts were used and no important local fallout would be anticipated from airbursts. For surface bursts the ranges at which the effects would appear are decreased somewhat, but actually not enough to greatly ease the situation. The surface burst is the source of the early fallout which is the principal delayed effect against which we must defend in nuclear war. FALLOUT The fission reaction in nuclear weapons results in the creation of intensely radioactive elements which are called fission products. The radioactive material from megaton weapons used in war may contaminate hundreds and thousands of square miles to the point where the radiation may become a hazard to life. The mechanism by which the radioactive fallout is produced and reaches the ground has been described in detail in reports, public booklets, films, the press, and other media. Because of the amount of time and space devoted to the subject, fallout in nuclear war should be the nuclear hazard best understood by officials and the public. In brief, a nuclear weapon, when detonated so that the fireball comes in contact with the surface, draws up a vast amount of earth. The earth is melted and mixed with the fission products in the process; and when the temperature drops, radioactive substances condense with the particles of earth. In a matter of minutes the particles will commence to fall toward the surface and be deposited in a rough circle around the point of detonation under the mushroom cloud and then downwind. EARLY FALLOUT In the discussion of fallout it is convenient to consider it in two parts: early fallout and delayed fallout. Early fallout is defined as that which reaches the ground during the first 24 hours following a nuclear explosion. It is the early fallout from surface, subsurface, and low air bursts that is capable of producing radioactive contamination over large areas with an intensity great enough to represent an immediate biological hazard. The early fallout may be influenced by fractionation, which is a change in composition of the fission product mixture. The occurrence of the phenomenon is shown by the fact that the larger particles deposited near the point of detonation have radiological, physical, and chemical properties different from those of the fine particles which leave the radioactive cloud later and are deposited farther downwind. DELAYED FALLOUT Delayed fallout, that arriving after the first 24 hours, consists of very fine, invisible particles that settle in low concentrations over a considerable portion of the earth's surface. The radiation from delayed fallout is greatly reduced in intensity as a result of radioactive decay during the relatively long time that the particles remain suspended in the atmosphere. Delayed fallout radiation generally poses no immediate danger to health, although there may be a long-term hazard. FALLOUT PATTERNS As an illustrative device we are accustomed to discussing fallout patterns as rather smooth elliptical figures. In the Pacific and in Nevada the actual fallout patterns have been_characteristically irregular and variable in radiation distribution. For planning purposes we can make use of predictions, but for local, operational purposes there is no satisfactory substitute for measurements. We should expect overlapping of fallout patterns from two or more detonations in a nuclear attack. There is every probability that an area contaminated by one explosion will receive more fallout from other explosions leading to a more serious situation. In preparing planning assumptions, conditions such as this must be treated; that is, conditions which occur because of the combination of effects from two or more weapons. INDUCED RADIOACTIVITY The second delayed effect is that of radiation from neutron-induced radioactivity. Some of the neutrons liberated by the reaction which produces the explosion escape from the environment of the bomb. The neutrons have a capability of producing radioisotopes just as neutrons do in a reactor. There are present in the air and sea and in the ground elements which are susceptible to neutrons. Nitrogen and sodium are important elements, in this category; other examples are aluminum, silicon, and manganese. Their radioisotopes have short half lives but can cause high initial activity; and hazardous dose rates may exist. Because of the short half lives, the decay progresses rapidly, more rapidly than in fallout. VARIATIONS DUE TO HEIGHT OF BURST In a war situation all the effects may not appear at a point in the order in which they have been discussed today; that is, the order in which we would normally expect them at a test. An obvious departure would be the appearance of fallout only whether from one or more detonations. Another would be the arrival of fallout from a distant explosion followed sometime later by the immediate effects, and possibly fallout, from a nearby explosion. But it is proper to remember that there are no known fallout casualties among the 220,000 Japanese hurt and killed in Hiroshima and Nagasaki. The conditions of burst influence the effects quantitatively. There is no single condition of burst which maximizes the severity or range of all the effects. An analysis has been prepared to show the variations which may be expected from different conditions of burst for weapons of similar energy yield. It deals with the light, heat, initial nuclear radiation, ground shock, air blast, and early fallout. (See fig. C-2.) Mr. CORSBIE. The number of marks provides a rough indication of the relative importance of the indicated effect to a ground observer. Four marks imply that the effect is the most extensive for the given burst type; a blank space means that the effect is negligible or absent. For the high-altitude burst the light is intense and the heat moderate, decreasing as the height of burst increases. There would be little initial nuclear radiation and airblast. Ground shock and fallout would be of little immediate concern. For the airburst the light is intense, although less than for the high altitude burst. The heat is intense, as is the initial nuclear radiation. The range at which the heat is dangerous is much greater than the range at which the initial radiation is dangerous from the larger weapons. Except in the case of low airbursts, the ground shock is not a serious problem; airblast, on the other hand, is serious over a large area. The early fallout is negligible. The surface or near surface burst is the source of the wartime fallout hazard. The light and heat from a surface burst, though less than the light and heat from the airburst, are considerable. The initial nuclear radiation is important, but less intense than from an airburst. Ground shock may be damaging to structures out to about three crater radii. The airblast effect will be greater at the close-in distance than would be the case with an airburst; however, the lower pressures do not extend to ranges at which they are significant for airburst weapons. Whether the weapon is detonated on the ground or on water, the severity of the effects are about the same, although there will be somewhat more light from the water surface burst. The confined subsurface detonation where the surface, either of ground or water, is not penetrated produces no significant hazard except ground or water shock. EFFECTS ON PERSONNEL In the data in "Effects of Nuclear Weapons" on personnel the numbers are in the main based on free field conditions. These are the sort of conditions which existed for many of the experiments conducted during weapons tests. The shock wave, for example, traveled across the test site generally unperturbed by structures. In a city the reaction of the blast with the buildings would produce local variations of turbulence and higher and lower pressures. The extent of injury and the rate of recovery, as we know, are related to one's orientation with respect to the effect, to the state of his health, to conditions in the environment and to the medical attention he receives. If an individual receives more than one type of injury, the future course of his health may be quite different and more complicated. For example, recovery from burns is impeded if the individual also receives a substantial radiation dose. While there is a desire for great precision in diagnosis of multiple injuries, the situations are complex, and we must settle for a somewhat less than complete forecast of injury. EYE DAMAGE The light from a nuclear explosion is dangerous to the human eye at ranges of many miles in the event of bursts low in the atmosphere or on the surface, varying with visibility. At the test sites highdensity goggles were provided to the observers of nuclear tests, and there was an extensive warning system to prevent eye injury. Injury may range from a temporary flash blindness to burns on the retina. In the event of high-altitude explosions of megaton bombs, that is, at 20 miles or so, the data from experiments during the tests above Johnston Island in 1958 show that burns to the retina can occur as far away as 300 nautical miles, or 345 statute miles. In such high-altitude explosions the light pulse is emitted very rapidly-much of it less than 0.015 second, the time required for the blinking of the eye. If one were looking in the direction of a very high altitude burst, the injury would be produced before the blink reflex could react to protect the eye. BURN INJURY The second-degree burn is not the only burn hazard. First-degree burns of the bare skin of unprotected persons can occur over large areas which become increasingly large as the yield increases. Firstdegree burns, comparable to sunburn, represent a nonincapacitating though uncomfortable injury. For air bursts in clear atmosphere first-degree burns can occur as far as 13 miles from 1-megaton, 36 miles from 10-megaton, and 49 miles from 20-megaton bursts. The need for warning of attack and for protective action thus extends far beyond the confines of what we may be apt to think of as a target. If we can recover easily from first-degree burns and accept them when necessary, we must be careful with the hazard of second-degree and the more serious third-degree burns. As stated, the second-degree burn can occur about 32 miles from the 20-megaton bursts. At about 25 miles there would be sufficient thermal energy to produce thirddegree burns if no evasive action were taken. At still closer ranges sufficient heat would be delivered with such rapidity as to produce burns even with evasive action. INJURIES FROM BLAST It has been estimated that 70 percent of the Japanese survivors suffered mechanical injuries, that is, injuries derived from the blast effects. Blast produces injuries in three ways: First there is the effect of the overpressure itself; second there are the effects of missiles, such as fragments of glass, set in motion by the blast; and third, there is the displacement effect in which men may be injured by being set in motion by the blast and stopped or decelerated by impact with a hard object—a building, a tree, the ground. The human body is quite tolerant to high pressure if we think of it as a pressure slowly applied without missiles or displacement. Survival of the blast effects would be common in regions having overpressures sufficient to damage severely all but especially constructed buildings if it were only a matter of overpressure; that is, increase in atmospheric pressure or primary blast. Indeed among the survivors in Japan are those who were in buildings in the 30- to 40pounds-per-square-inch range. Missiles, which is the designation used for pieces of flying debris, produce large numbers of seriously injured persons. Flying bits of glass can penetrate the body, and larger pieces of material-a brick, a timber, a piece of furniture-cause injury by striking the body a heavy blow. If we were to assign a casualty-producing value of 1 to the effect of overpressure, we should assign a value of 2 to the missile effect. And we should assign a value of 3 to the displacement effect. It is the displacement effect-the decelerative impact that causes many deaths and injuries in automobile accidents. During the 1957 test series we conducted an experiment in which anthropometric dummies were exposed to blast. A standing dummy exposed in an ideal pressure region to a maximum of 5.3 pounds per square inch was blown about 22 feet downwind; it reached a velocity of 21 feet per second, or 14 miles per hour, in one-half second after 9 feet of travel. A prone dummy at the same location did not move. A standing dummy exposed to 6.6 pounds per square inch in a nonideal pressure region was displaced 256 feet downwind, veering 44 feet off course; a prone dummy at this position was displaced 125 feet downwind and veered 20 feet. At about 3-pounds-per-square-inch pressure, for larger yields, displacement begins to become a major problem. At 3 pounds per square inch the accompanying blast winds have speeds of the order 73266-61--11 |