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4 November 2006
This is CHAPTER XII - Biological Effects of The Effects of Nuclear Weapons.
Source: http://www.princeton.edu/~globsec/publications/effects/effects12.pdf (94 pages, 9.4MB)
The full report:
http://www.princeton.edu/~globsec/publications/effects/effects.shtml
Compiled and edited by Samuel Glasstone and Philip J. Dolan
Third Edition
Prepared and published by the UNITED STATES DEPARTMENT OF DEFENSE and the ENERGY RESEARCH AND DEVELOPMENT ADMINISTRATION
1977
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402
When "The Effects of Atomic Weapons" was published in 1950, the explosive energy yields of the fission bombs available at that time were equivalent to some thousands of tons (i.e., kilotons) of TNT. With the development of thermonuclear (fusion) weapons, having energy yields in the range of millions of tons (i.e., megatons) of TNT, a new presentation, entitled "The Effects of Nuclear Weapons," was issued in 1957. A completely revised edition was published in 1962 and this was reprinted with a few changes early in 1964.
Since the last version of "The Effects of Nuclear Weapons" was prepared, much new information has become available concerning nuclear weapons effects. This has come in part from the series of atmospheric tests, including several at very high altitudes, conducted in the Pacific Ocean area in 1962. In addition, laboratory studies, theoretical calculations, and computer simulations have provided a better understanding of the various effects. Within the limits imposed by security requirements, the new information has been incorporated in the present edition. In particular, attention may be called to a new chapter on the electromagnetic pulse.
We should emphasize, as has been done in the earlier editions, that numerical values given in this book are not -- and cannot be -- exact. They must inevitably include a substantial margin of error. Apart from the difficulties in making measurements of weapons effects, the results are often dependent upon circumstances which could not be predicted in the event of a nuclear attack. Furthermore, two weapons of different design may have the same explosive energy yield, but the effects could be markedly different. Where such possibilities exist, attention is called in the text to the limitations of the data presented; these limitations should not be overlooked.
The material is arranged in a manner that should permit the general reader to obtain a good understanding of the various topics without having to cope with the more technical details. Most chapters are thus in two parts: the first part is written at a fairly low technical level whereas the second treats some of the more technical and mathematical aspects. The presentation allows the reader to omit any or all of the latter sections without loss of continuity.
The choice of units for expressing numerical data presented us with a dilemma.
The exclusive use of international (SI) or metric units would have placed a burden on many readers not familiar with these units, whereas the inclusion of both SI and common units would have complicated many figures, especially those with logarithmic scales. As a compromise, we have retained the older units and added an explanation of the SI system and a table of appropriate conversion factors.
Many organizations and individuals contributed in one way or another to this revision of "The Effects of Nuclear Weapons," and their cooperation is gratefully acknowledged. In particular, we wish to express our appreciation of the help given us by L. J. Deal and W. W. Schroebel of the Energy Research and Development Administration and by Cmdr. H. L. Hoppe of the Department of Defense.
Samuel Glasstone Philip J. Dolan
Preparation of this revision of "The Effects of Nuclear Weapons" was made possible by the assistance and cooperation of members of the organizations listed below.
Department of Defense
Headquarters, Defense Nuclear Agency Defense Civil Preparedness Agency Armed Forces Radiobiology Research Institute V. S. Army Aberdeen Research and Development Center, Ballistic Research Laboratories V.S. Army Engineer Waterways Experiment Station Naval Surface Weapons Center
Department of Defense Contractors
Stanford Research Institute General Electric, TEMPO Mission Research Corporation
Department of Commerce National Oceanic and Atmospheric Administration
Atomic Energy Commission
Energy Research and Development Administration
Headquarters Divisions and the laboratories:
Brookhaven National Laboratory Health and Safety Laboratory Lawrence Livermore Laboratory Los Alamos Scientific Laboratory Lovelace Biomedical and Environmental Research Laboratories Oak Ridge National Laboratory Sandia Laboratories
CHAPTER XII - Biological Effects
Characteristics of Acute Whole-Body Radiation Injury
Late Effects of Ionizing Radiation
Long-Term Hazard from Delayed Fallout
Genetic Effects of Nuclear Radiation
Pathology of Acute Radiation Injury
Effects on Farm Animals and Plants
TYPES OF INJURIES
12.01 The three main types of physical effects associated with a nuclear explosion, namely, blast and shock, thermal radiation, and nuclear radiation, each have the potentiality for causing death and injury to exposed persons. Blast injuries may be direct or indirect; the former are caused by the high air pressure and the latter by missiles and by displacement of the body. For a given overpressure, a nuclear device is more effective in producing direct blast injuries than is a conventional, high-explosive weapon because, as will be seen, the human body is sensitive to the duration of the pressure pulse and this is relatively long in a nuclear explosion unless the yield is much less than 1 kiloton. On the whole, indirect blast injuries, especially those caused by missiles such as glass, wood, debris, etc., are similar for nuclear and conventional weapons. However, because of its longer duration, the blast wave from a nuclear explosion produces missile and displacement injuries at much lower overpressures than does a chemical explosion.
12.02 The frequency of burn injuries due to a nuclear explosion is exceptionally high. Most of these are flash burns caused by direct exposure to the pulse of thermal radiation, although individuals trapped by spreading fires may be subjected to flame burns. In addition, persons in buildings or tunnels close to ground zero may be burned by hot gases and dust entering the structure even though they are shielded adequately from direct or scattered thermal radiation. Finally, there are potential harmful effects of the nuclear radiations on the body. These represent a source of casualties entirely new to warfare.
12.03 A nuclear explosion in the air or near the ground will inevitably be accompanied by damage and destruction of buildings, by blast, shock, and fire, over a considerable area. Consequently, a correspondingly larger number of personal casualties is to be expected. However, the actual number, as well as their distribution among the different kinds of injuries mentioned above, will be greatly dependent upon circumstances. As a general rule, for bursts of a given type, e.g., air, surface, or subsurface, the range of each of the major immediate effects -- blast, thermal radiation, and initial nuclear radiation -- increases with the explosive yield of the weapon. But the relative importance of the various effects does not remain the same. The initial nuclear radiation, for example, is much more significant in comparison with blast and thermal radiation for nuclear explosions of low energy yield than it is for those of high yield. In other words, although the total number of casualties will increase with the energy of the explosion, under similar circumstances, the percentage of injuries due to initial nuclear radiation may be expected to decrease whereas the proportions of blast and thermal injuries will increase.
12.04 All other things, including exposure conditions, being the same, the number and distribution of casualties of various kinds for a nuclear explosion of given yield will be determined by the type of burst. Moreover, for an air burst, the height of burst will have an important influence. With other factors constant, there is an optimum height of burst which maximizes the range on the ground for a given overpressure in the blast wave (§ 3.73). This optimum height differs for each yield and for each value of the overpressure. Similarly, there are particular heights of burst, usually different from that for blast damage, which maximize dIe ranges for either thermal radiation or the initial nuclear radiation. It is evident, therefore, that considerable variations are possible both in the number and in the nature of the injuries associated with an air burst.
12.05 The effects of a surface or of a shallow subsurface burst will not be greatly different from those accompanying a low air burst. However, as increasing amounts of contaminated earth and debris are sucked up into the radioactive cloud the hazard from the residual nuclear radiation in the early fallout increases. For an underground burst at a moderate depth, the injuries from blast and from thermal and initial nuclear radiations would be much less than from an air burst or even from a surface burst of the same yield. On the other hand, the effects of ground shock and the delayed nuclear radiation hazard would be greatly increased. In the case of a deep (completely contained) underground burst, casualties would result only from ground shock.
12.06 Apart from the explosion yield and burst conditions, local environmental circumstances can be a significant factor in the casualty potential of a nuclear weapon. Conditions of terrain and weather can influence the injuries caused by blast and by thermal radiation. Structures may have an important, although variable, effect. For example, the shielding in ordinary houses may markedly reduce the range over which significant casualties from flash burns can occur. This is particularly the case for heavier structures extending below as well as above ground; persons properly located in such buildings could be protected from blast and initial nuclear radiations as well as from thermal radiations. On the other hand, in certain buildings the frequency of indirect blast injuries may be greatly increased by the presence of large numbers of missiles.
12.07 As regards direct injuries resulting from the overpressure of the air in the blast wave, the effects of a structure are also quite variable. In some situations it is known that the magnitude of the peak overpressure inside a structure can be appreciably less than the free-field (open terrain) value. On the other hand, there is a possibility that, as a result of reflection at walls, etc., the air overpressure in the interior of a building may be increased twofold or more, depending on the geometry involved (see Chapter IV). There will also be changes in wind velocity inside structures, so that the magnitudes may differ markedly from those existing in the free field as the blast wave spreads outward from the burst point. .Nevertheless, provided people do not lean against the walls or sit or lie on the floor, there is generally a lower probability of injury from direct overpressure effects inside a structure than at equivalent distances on the outside. This results from alterations in the pattern of the overpressure wave upon entering the structure.
JAPANESE CASUALTIES
12.08 The only direct information concerning human casualties resulting from a nuclear explosion is that obtained following the air bursts over Japan and this will be used as the basis for much of the discussion presented here. It should be pointed out, however, that the Japanese experience applies only to the particular heights of burst and yields of the weapons exploded over Hiroshima and Nagasaki (§ 2.24), and to the weather, terrain, and other conditions existing at the times and locations of the explosions. Almost any kind of nuclear explosion in a populated area, except perhaps one deep under the surface, would be accompanied by a large number of deaths and injuries in a short interval of time, but the actual number of casualties and their distribution between blast (and shock), thermal, and nuclear radiation effects could vary markedly with the circumstances.
12.09 The data in Table 12.09 are the best available estimates1 for civilian casualties resulting from all effects of the explosions over Hiroshima and Nagasaki. The population estimates are only for civilians within the affected area in each city and do not include an unknown number of military personnel.
___________________
1 Computed from data in A. W. Oughterson and S. Warren (Editors), "Medical Effects of the Atomic Bomb in Japan," McGraw-Hill Book Co., Inc., Chapter 4, 1956. For further information, see also "Medical Effects of the Atomic Bomb," Report of the Joint Commission for the Investigation of the Effects of the Atomic Bomb in Japan, Office of the Air Surgeon NP-3041; "Medical Report on Atomic Bomb Effects," The Medical Section, Special Committee for the Investigation of the Effects of the Atomic Bomb, National Research Council of Japan, 1953; and the U.S. Strategic Bombing Survey, "The Effects of Atomic Bombs on Hiroshima and Nagasaki," 1946.
Three zones, representing different distances from ground zero, are considered: the first is a circular area of 0.6 mile radius about ground zero, the second is a ring from 0.6 to 1.6 miles from ground zero, and the third is from 1.6 to 3.1 miles from ground zero. In each case there is given the total population in a particular zone, the population density, i.e., number per square mile, and the numbers of killed and injured, in that zone. Also included are the total population "at risk" in the city, the average population density, and the total numbers of killed and injured. The standardized casualty rates are values calculated by proportion on the basis of a population density of one person per 1,000 square feet (or about 28,000 per square mile) of vulnerable area.
12.10 It is important to note that, although the average population densities
in Hiroshima and Nagasaki were 8,500 and 5,800 per square mile, respectively,
densities of over 25,000 per square mile existed in areas close to ground
zero. For comparison, the average population density for the five boroughs
of New York City, based on the 1970 census, is about 24,700 per square mile
and for Manhattan alone it is 68,600 per square mile. The population density
for the latter borough during the working day is, of course, much higher.
The ten next largest U. S. cities have average population densities ranging
from 14,900 to 3,000 persons per square mile.
12.11 The numbers in Table 12.09 serve to emphasize the high casualty potential of nuclear weapons. There are several reasons for this situation. In the first place, the explosive energy yield is very much larger than is possible with conventional weapons, so that both the area and degree of destruction are greatly increased. Second, because of the high energy yields, the duration of the overpressure (and winds) associated with the blast wave, for a given peak overpressure, is so long that injuries occur at overpressures which would not be effective in a chemical explosion. Third, the proportion of the explosive energy released as thermal radiation is very much greater for a nuclear weapon; hence there is a considerably larger incidence of flash burns. Finally, nuclear radiation injuries, which are completely absent from conventional explosions, add to the casualties.
12.12 The data in the table also show that more than 80 percent of the population within 0.6 mile (3170 feet) from ground zero were casualties. In this area the blast wave energy, thermal exposure, and initial nuclear radiation were each sufficient to cause serious injury or death. Beyond about 1.6 miles, however, the chances of survival were very greatly improved. Between 0.6 and 1.6 miles from ground zero a larger proportion of the population would probably have survived if immediate medical attention had been available. Although the particular distances mentioned apply to the yield and conditions of the Japanese explosions, it is to be expected quite generally that close to ground zero the casualty rate will be high, but it will drop sharply beyond a certain distance which scales with the energy yield of the explosion.
CAUSES OF FATALITIES
12.13 There is no exact information available concerning the relative significance of blast, burn, and nuclear radiation injuries as a source of fatalities in the nuclear bombings of Japan. It has been estimated that some 50 percent of the deaths were caused by burns of one kind or another, but this figure is only a rough estimate. Close to two-thirds of those who died at Hiroshima during the first day after the explosion were reported to have been badly burned. In addition, there were many deaths from burns during the first week.
12.14 The high incidence of flash burns caused by thermal radiation among both fatalities and survivors in Japan was undoubtedly related to the light and scanty clothing being worn, because of the warm summer weather prevailing at the time of the attacks. If there had been an appreciable cloud cover or haze below the burst point, the thermal radiation would have been attenuated somewhat and the frequency of flash burns would have been much less. Had the weather been cold, fewer people would have been outdoors and they would have been wearing more extensive clothing. Both the number of people and individual skin areas exposed to thermal radiation would then have been greatly reduced and there would have been fewer casualties from flash burns.
12.15 None of the estimates of the causes of death bear directly on the incidence of those blast effects which result in early death, e.g., air (emboli) in the arteries, lung damage, and heart injury which tolerate very little post-injury activity, various bone fractures, severing of major blood vessels by sharp missiles, violent impact, and others. One of the difficulties in assessing the importance of injuries of various types lies in the fact that many people who suffered fatal blast injuries were also burned. As seen earlier, within about half a mile of ground zero in the Japanese explosions, either blast, burns, or nuclear radiation injury alone was lethal in numerous instances.
12.16 As a result of various circumstances, however, not everyone within a radius of half a mile was killed immediately. Among those who survived the first few days after the explosions at Hiroshima and Nagasaki, a number died two or more weeks later with symptoms which were ascribed to nuclear radiation injuries (see § 12.113 el seq.). These were believed to represent from 5 to 15 percent of the total fatalities. A rough estimate indicates that about 30 percent of those who died at Hiroshima had received lethal doses of nuclear radiation, although this was not always the immediate cause of death.
12.17 The death rate in Japan was greatest among individuals who were in the open at the time of the explosions; it was less for persons in residential (wood-frame and plaster) structures and least of all for those in concrete buildings. These facts emphasize the influence of circumstances of exposure on the casualties produced by a nuclear weapon and indicate that shielding of some type can be an important factor in survival. For example, within a range of 0.6 mile from ground zero over 50 percent of individuals in Japanese-type homes probably died of nuclear radiation effects, but such deaths were rare among persons in concrete buildings within the same range. The effectiveness of concrete structures in providing protection from injuries of all kinds is apparent from the data in Table 12.17; this gives the respective average distances from ground zero at which there was 50-percent survival (for at least 20 days) among the occupants of a number of buildings in Hiroshima. School personnel who were indoors had a much higher survival probability than those who were outdoors at the times of the explosions.
CAUSES OF INJURIES AMONG SURVIVORS
12.18 From surveys made of a large number of Japanese, a fairly good idea has been obtained of the distribution of the three types of injuries among those who became casualties but survived the nuclear attacks. The results are quoted in Table 12.18; the totals add up to more than 100 percent, since many individuals suffered multiple injuries.
12.19 Among survivors the proportion of indirect blast (mechanical) injuries
due to flying missiles and motion of other debris was smallest outdoors and
largest in certain types of industrial buildings. Patients were treated for
lacerations received out to 10,500 feet (2 miles) from ground zero in Hiroshima
and out to 12,500 feet (2.2 miles) in Nagasaki. These distances correspond
roughly to those at which moderate damage occurred to wood-frame houses,
including the shattering of window glass.
12.20 An interesting observation made among the Japanese survivors was the relatively low incidence of serious mechanical injuries. For example, fractures were found in only about 4 percent of survivors. In one hospital there were no cases of fracture of the skull or back and only one fractured femur among 675 patients, although many such injuries must have undoubtedly occurred. This was attributed to the fact that persons who suffered severe concussion or fractures were rendered helpless, particularly if leg injuries occurred, and, along with those who were pinned beneath the wreckage, were trapped and unable to seek help or escape in case fire ensued. Such individuals, of course, did not survive.
CASUALTIES AND STRUCTURAL DAMAGE
12.21 For people who were in buildings in Japan, the overall casualties were related to the extent of structural damage, as well as to the type of structure (§ 12.17). The data in Table 12.21 were obtained from a study of 1,600 Japanese who were in reinforced-concrete buildings, between 0.3 and 0.75 mile from ground zero, when the nuclear explosions occurred. At these distances fatalities in the open ranged from about 90 to 100 percent, indicating, once more, that people were safer inside buildings, even when no special protective action was taken because of the lack of warning. There may have been an increase of casualties in buildings from debris etc., but this was more than compensated by the reduction due to shielding against the initial nuclear radiation and particularly from the thermal pulse.
12.22 In two concrete buildings closest to ground zero, where the mortality
rate was 88 percent, about half the casualties were reported as being early
and the other half as delayed. The former were attributed to a variety of
direct and indirect blast injuries, caused by overpressure, structural collapse,
debris, and whole-body translation, whereas the latter were ascribed mainly
to burns and initial nuclear radiation. Minor to severe but nonfatal blast
injuries no doubt coexisted and may have contributed to the delayed lethality
in many cases. At greater distances, as the threat from nuclear radiation
decreased more rapidly than did that from air blast and thermal radiation,
the proportion of individuals with minor injuries or who were uninjured increased
markedly. The distribution of casualties of different types in Japanese buildings
was greatly influenced by where the people happened to be at the time of
the explosion. Had they been forewarned and knowledgeable about areas of
relative hazard and safety, there would probably have been fewer casualties
even in structures that were badly damaged.
12.23 The shielding effect of a particular building is not only different for blast, the thermal pulse, and nuclear radiation, but it may also depend on the distance from the explosion and the height of burst. Furthermore, the locations and orientations of individuals in the building are important in determining the extent of the shielding. Hence, the protection offered by structures is quite variable. This fact must be kept in mind in considering the data in Table 12.21. Although the table indicates a general correlation between structural damage and the frequency of casualties, the numbers cannot be used to estimate casualties from the degree of structural damage. In an actual situation, the effects would depend on many factors, including the type of structure, the yield of the nuclear explosion, the height of burst, the distance from the explosion point, the locations and orientations of people in the building, and the nature of prior protective action.
DIRECT BLAST INJURIES: BIOLOGICAL FACTORS
12.24 Blast injuries are of two main types, namely, direct (or primary) injuries associated with exposure of the body to the environmental pressure variations accompanying a blast wave, and indirect injuries resulting from impact of penetrating and non-penetrating missiles on the body or as the consequences of displacement of the body as a whole. There are also miscellaneous blast injuries, such as burns from the gases and debris, and irritation and possibly suffocation caused by airborne dust. The present section will treat direct injuries, and indirect blast effects will be discussed later.
12.25 The general interactions of a human body with a blast wave are somewhat similar to that of a structure as described in Chapter IV. Because of the relatively small size of the body, the diffraction process is quickly over, the body being rapidly engulfed and subjected to severe compression. This continues with decreasing intensity for the duration of the positive phase of the blast wave. At the same time the blast wind exerts a drag force of considerable magnitude which contributes to the displacement hazard.
12.26 The sudden compression of the body and the inward motion of the thoracic and abdominal walls cause rapid pressure oscillations to occur in the air-containing organs. These effects, together with the transmission of the shock wave through the body, produce damage mainly at the junctions of tissues with air-containing organs and at areas between tissues of different density, such as where cartilage and bone join soft tissue. The chief consequences are hemorrhage and occasional rupture of abdominal and thoracic walls.
12.27 The lungs are particularly prone to hemorrhage and edema (accumulation of fluid causing swelling), and if the injury is severe, air reaches the veins of the lungs and hence the heart and arterial circulation. Death can occur in a few minutes from air embolic obstruction of the vessels of the heart or the brain or from suffocation caused by lung hemorrhage or edema. Fibrin emboli in the blood may also affect the brain and other critical organs. The emboli, apparently associated with severe hemorrhagic damage to the lungs, are a consequence of the disturbance of the blood-clotting mechanism. Damage to the brain due to air blast overpressure alone is improbable, but indirect damage may arise from injury to the head caused by missiles, debris, or displacement of the body. Bodily activity after blast damage to the heart and lungs is extremely hazardous and lethality can result quickly where recovery might otherwise have been expected. The direct blast effect was not specifically recognized as a cause of fatality in Japan, but it no doubt contributed significantly to early mortality even though most of the affected individuals may also have received mortal injury from debris, displacement, fire, or thermal and nuclear radiations.
12.28 Primary blast casualties have been reported after large-scale air attacks with conventional high-explosive bombs, mainly because of the provision of medical care for those who otherwise would have suffered the early death that is characteristic of serious blast injury to the lungs. However, persons who spontaneously survive for 24 to 48 hours in the absence of treatment, complications, and other injury usually recover and show little remaining lung hemorrhage after 7 to 10 days. In very severe injuries under treatment, recurring lung hemorrhage has been reported as long as 5 to 10 days after injury. In view of such facts and overwhelming disruptive effects of the Japanese bombings on medical and rescue services, it can be concluded that individuals with significant direct blast injuries did not survive. Those with relatively minor blast injuries who did survive, did so without getting into medical channels, or if they did require medical care it was for post-blast complications, e.g., pneumonitis, or for causes other than blast injury to the lungs. For these reasons primary blast effects, except for eardrum rupture, were not commonly seen among Japanese survivors.
12.29 Many persons who apparently suffered no serious injury reported temporary loss of consciousness. This symptom can be due to the direct action of the blast wave, resulting from transient disturbance of the blood circulation in the brain by air emboli. However, it can also be an indirect effect arising from impact injury to the head caused by missiles or by violent displacement of the body by the air pressure wave.
12.30 A number of cases of ruptured eardrums were reported among the survivors
in Hiroshima and Nagasaki, but the incidence was not high even for those
who were fairly close to ground zero. Within a circle of 0.31 mile (I ,640
feet) radius about 9 percent of a group of 44 survivors in Nagasaki had ruptured
eardrums, as also did some 8 percent of 125 survivors in the ring from 0.31
to 0.62 mile from ground zero. In Hiroshima the incidence of ruptured eardrums
was somewhat less. In both cities very few cases were observed beyond 0.62
mile.
DIRECT BLAST INJURIES: PHYSICAL FACTORS
12.31 Tests with animals have demonstrated that five parameters of the blast wave can affect the extent of the direct injuries to the body; they are (1) the ambient pressure, (2) the "effective" peak overpressure, (3) the rate of pressure rise (or "rise time") at the blast wave front, (4) the character and "shape" of the pressure pulse, and (5) the duration of the positive phase of the blast wave and the associated wind (see Chapter III). These parameters will be considered below as they arise.
12.32 The biologically effective peak overpressure depends on the orientation of the individual to the blast wave. If the subject is against a reflecting surface, e.g., a wall, the effective overpressure for direct blast injury is equal to the maximum reflected overpressure, which may be a few times the incident peak overpressure. On the other hand, in the open at a substantial distance from a reflecting surface, the effective overpressure is the sum of the peak incident overpressure and the associated peak dynamic pressure if the subject is perpendicular to the direction of travel of the blast wave and to the peak overpressure alone if the subject is parallel to this direction. Consequently, for a given incident overpressure, the blast injury is expected to be greatest if the individual is close to a wall and least if he is at a distance from a reflecting surface and is oriented with his body parallel to the direction in which the blast wave is moving.
12.33 The body, like many other structures, responds to the difference between the external and internal pressures. As a consequence, the injury caused by a certain peak overpressure depends on the rate of increase of the pressure at the blast wave front. For wave fronts with sufficiently slow pressure rise, the increase in internal pressure due to inward movement of the body wall and air flow in the lungs keeps pace (to some extent) with the external pressure. Consequently, quite high incident overpressures are tolerable. In contrast, if the rise time is short, as it is in nuclear explosions under appropriate terrain and burst conditions, the damaging effect of a given overpressure is greater. The increase in internal pressure of the body takes a finite time and the response is then to the maximum possible pressure differential. Thus, a sharply rising pressure pulse will be more damaging than if the same peak overpressure is attained more slowly. In precursor formation (§ 3.79 et seq.), for example, the blast pressure increases at first slowly and then quite rapidly; the injury potential of a given peak overpressure is thus decreased.
12.34 An individual inside a building but not too close to a wall would be subject to multiple reflections of the blast wave from the ceiling, floor, and walls as well as to the incident wave entering the structure. Since the reflected waves would reach him at different times, the result would be a step loading, although the rise time for each step might be quite short. In such cases, where the initial blast pressure is tolerable and the subsequent pressure increase is not too great or occurs in stages (or slowly), a certain peak overpressure is much less hazardous than if it were applied in a single sharp pulse. Apparently the reason for the decreased blast injury potential in these situations is that the early stage of the pressure pulse produces an increase in the internal body pressure, thereby reducing the pressure differential associated with the later portion of the pulse. In a manner of speaking, a new and higher "ambient" pressure is imposed on the body by the early part of the pressure pulse and tolerance to the later rise in overpressure is enhanced. A higher peak overpressure is then required to cause a certain degree of blast injury.
12.35 Clearly, for a given peak incident overpressure, the geometry2 in which an individual is exposed inside a structure may have a significant effect on his response to air blast. A location against a wall is the most hazardous position because the effective peak overpressure, which is the maximum reflected overpressure, is high and is applied rapidly in a single step. A location a few feet from a wall is expected to decrease the direct blast injury, although the hazard arising from displacement of the body may be increased. Apart from the effects just described, oscillating pressures, for which no adequate biomedical criteria are available, often exist inside structures due to reverberating reflections from the inside walls.
___________________
2 The word "geometry" is used here as a general term to describe the location of an individual in relation to the details of the environment that may affect the blast wave characteristics.
12.36 The duration of the positive phase of the blast wave is a significant factor for direct blast injuries. Up to a point, the increase in the duration increases the probability of injury for a given effective peak overpressure. Beyond this point, which may be of the order of several tens to a few hundred milliseconds, depending on the body size, it is only the magnitude of the overpressure that is important. The duration of the positive phase, for a given peak overpressure, varies with the energy yield and the height of burst (§ 3.75 et seq.). But for most conditions, especially for energy yields in excess of about 10 kilotons, the duration of the positive phase of the blast wave is so long -- approaching a second or more -- that the effective peak overpressure is the main factor for determining the potential for direct injury from a fast-rising pressure pulse.
12.37 A given peak pressure in the blast wave from conventional high explosives is less effective than from a nuclear explosion -- except perhaps at unusually low yields -- mainly because of the short duration of the positive phase in the former case. From observations made with small charges of chemical explosives, it has been estimated that deaths in humans would require sharp-rising effective overpressures as high as 200 to 400 (or more) pounds per square inch when the positive phase durations are less than a millisecond or so. These pressures may be compared with values of roughly 50 (or less) to about 100 pounds per square inch, with positive phase durations of the order of a second, for nuclear explosions.
12.38 Tentative criteria, in terms of effective peak overpressure as defined in § 12.32, for lung damage, lethality, and eardrum rupture caused by a fast-rising pressure pulse of long duration (0.1 second or more) are given in Table 12.38. The values for lung damage and lethality are average pressures obtained by extrapolation from animal data to man; the variability of the results is indicated by the numbers in parentheses. Rupture of the normal eardrum is apparently a function of the age of the individual as well as of the effective blast pressure. Failures have been recorded at overpressures as low at 5 pounds per square inch ranging up to 40 or 50 pounds per square inch. The values in Table 12.38 of the effective peak overpressures for eardrum rupture are based on relatively limited data from man and animals.
INDIRECT BLAST INJURIES
12.39 Indirect blast injuries are associated with (1) the impact of missiles, either penetrating or non-penetrating (secondary effects), and (2) the physical displacement of the body as a whole (tertiary effects). The wounding potential of blast debris depends upon a number of factors; these include the impact (or striking) velocity, the angle at which impact occurs, and the size, shape, density, mass, and nature of the moving objects. Furthermore, consideration must be given to the portion of the body involved in the missile impact, and the events which may occur at and after the time of impact, namely, simple contusions and lacerations, at one extreme, or more serious penetrations, fractures, and critical damage to vital organs, at the other extreme.
12.40 The hazard from displacement depends mainly upon the time and distance over which acceleration and deceleration of the body occur. Injury is more likely to result during the latter phase when the body strikes a solid object, e.g., a wall or the ground. The velocity which has been attained before impact is then significant. This is determined by certain physical parameters of the blast wave, as mentioned below, as well as by the orientation of the body with respect to the direction of motion of the wave. The severity of the damage depends on the magnitude of the impact velocity, the properties of the impact surface, and the particular portion of the body that has received the decelerative impact, e.g., head, back, extremities, thoracic and abdominal organs, body wall, etc.
DISPLACEMENT VELOCITIES
12.41 Because the effects of both missiles and body displacement depend on the velocity attained before impact, it is convenient to consider the relationships between displacement velocity and the blast parameters for objects as small as tiny pieces of glass and as large as man. The significant physical factors in all cases are the magnitude and duration of the blast overpressure and the accompanying winds, the acceleration coefficient of the displaced object.3 ground shock, gravity, and the distance traveled by the object. The latter is important because, as a result of the action of the blast wave, the velocity of the object increases with the time and distance of travel until it attains that of the blast wind. Subsequently, the velocity falls because of negative winds or impact with the ground or other material.
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3 The acceleration coefficient is the product of the projected area presented to the blast wave and the drag coefficient (§ 4.19) divided by the mass of the object.
12.42 As a result of the interaction of the various factors, large and heavy objects gain velocity rather slowly and attain a maximum velocity only after most of the blast wave has passed. The velocity is consequently determined by the duration of the overpressure and winds. In contrast, small and light objects reach their maximum velocity fairly quickly, often after a small proportion of the blast wave has passed over them. The maximum velocity is thus not too sensitive to the duration of the overpressure and winds, but depends largely on the effective peak overpressure (cf. § 12.32). As a consequence of this fact, it has been found possible to relate the velocities attained by the fragments produced by the breakage of glass window panes to the effective overpressure. The results for glass panes of different thicknesses can be expressed in a fairly simple graphical manner as will be shown in § 12.238.
12.43 The variations of the overpressure and dynamic pressure with time (§ 3.57 et seq.) at the location of interest also have a bearing on the behavior of a displaced object. Data were obtained at nuclear weapons tests under such conditions that the blast wave was approximately ideal in behavior. Some of the median velocities, masses, and spatial densities (number of fragments per square foot) of window glass, from houses exposed to the blast, and of natural stones are summarized in Table 12.43. For glass, the velocities refer to those attained after 7 to 13 feet of travel; for the stones the distances are not known, but the velocities given in the table may be regarded as applicable to optimum distances of missile travel.
12.44 Studies have also been made of the displacement of anthropomorphic dummies weighing 165 pounds by the blast from a nuclear explosion. A dummy standing with its back to the blast attained its maximum velocity, about 21 feet per second, after a displacement of 9 feet within 0.5 second after the arrival of the blast wave. The free-field overpressure at the test location was 5.3 pounds per square inch. The dummy traveled 13 feet before striking the ground and then slid or rolled another 9 feet. A prone dummy, however, did not move under the same conditions. The foregoing results were obtained in a situation where the blast wave was nearly ideal, but in another test, at a peak overpressure of 6.6 pounds per square inch, where the blast wave was non ideal (§ 3.79), both standing and prone dummies suffered considerably greater displacements. Even in such circumstances, however, the displacement of over 125 feet for the prone dummy was much less than that of about 250 feet for the standing one. The reason for the greater displacement of the standing dummy is that it acquired a higher velocity.
12.45 In order to study the displacements of moving objects, field tests have been made by dropping animal cadavers, including guinea pigs, rabbits, goats, and dogs, and stones and concrete blocks onto a flat, hard surface from a vehicle traveling between 10 and 60 miles per hour (14.7 to 88 feet per second). For a given initial velocity, the stopping distance for the animals increased somewhat with the mass, and a relationship was found to represent the stopping distance as a function of velocity applicable to the animals over a wide range of mass (§ 12.239). One reason for the consistency of the data is probably that all the animals assumed a rolling position about their long axis regardless of the initial orientation. The animals remained relatively low to the ground and bounced very little. By contrast, stones and concrete blocks bounced many times before stopping; the data were not sensitive to mass, depended more on orientation, and were more variable than the results obtained with animals. On the whole, the stopping distances of the blocks and stones were greater for a given initial velocity. One of the conclusions drawn from the foregoing tests was that a person tumbling over a smooth surface, free from rocks and other hard irregularities, might survive, even if the initial velocity is quite high, if he could avoid head injury and did not flail his limbs.
MISSILE AND DISPLACEMENT INJURY CRITERIA
12.46 Velocity criteria for the production of skin lacerations by penetrating missiles, e.g., glass fragments, are not known with certainty. Some reliable information is available, however, concerning the probability of penetration of the abdominal wall by glass. The impact velocities, for glass fragments of different masses, corresponding to 1, 50, and 99 percent penetration probability are recorded in Table 12.46.
12.47 The estimated impact velocities of a to-gram (0.35-ounce) glass missile required to produce skin lacerations and serious wounds are summarized in Table 12.47. The threshold value for skin lacerations is recorded as 50 feet per second and for serious wounds it is 100 feet per second.
12.48 Little is known concerning the relationship between mass and velocity of non-penetrating missiles that will cause injury after impact with the body. Studies with animals showed that fairly high missile velocities are required to produce lung hemorrhage, rib fractures, and early mortality, but quantitative data for man are lacking. No relationship has yet been developed between mass and velocity of non-penetrating missiles that will cause injury as a result of impacts with other parts of the body wall, particularly near the spine, kidney, liver, spleen and pelvis. It appears, however, that a missile with a mass of 10 pounds striking the head at a velocity of about 15 feet per second or more can cause skull fracture. For such missiles it is unlikely that a significant number of dangerous injuries will occur at impact velocities of less than 10 feet per second. The impact velocities of a 10-pound missile for various effects on the head are given in Table 12.48.
12.49 Although there may be some hazard associated with the accelerative phase of body displacement (translation) by a blast wave, the deceleration, particularly if impact with a solid object is involved, is by far the more significant. Since a hard surface will cause a more serious injury than a softer one, the damage criteria given below refer to perpendicular impact of the displaced body with a hard, flat object. From various data it is concluded that an impact velocity of 10 feet per second is unlikely to be associated with a significant number of serious injuries; between 10 and 20 feet per second some fatalities may occur if the head is involved; and above 20 feet per second, depending on trauma to critical organs, the probabilities of serious and fatal injuries increase rapidly with increasing displacement velocity. Impact velocities required to produce various indirect (tertiary) blast effects are shown in Table 12.49. The curves marked "translation near structures" in Fig. 12.49 may be used to estimate ground distances at which 1 percent and 50 percent casualties would be expected, as functions of height of burst, for a 1-kiloton explosion.5 Based on tests with animals, the criteria for 1 and 50 percent casualties were somewhat arbitrarily set at impact velocities of 8 and 22 feet per second, respectively. The results in Fig. 12.49 may be extended to other burst heights and yields by using the scaling law given in the example facing the figure.
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5 In this connection, a casualty is defined as an individual so injured that he would probably be a burden on others. Some of the casualties would prove fatal, especially in the absence of medical care.
12.50 Evaluation of human tolerance to decelerative tumbling during translation in open terrain is more difficult than for impact against a rigid surface described above. Considerably fewer data are available for decelerative tumbling than for body impact, and there is virtually no human experience for checking the validity of extrapolations from observations on animal cadavers. Tests have been made with goats, sheep, and dogs, but for humans the information required to derive reliable hazards criteria for decelerative tumbling are still not adequate. The initial velocities at which 1 and 50 percent of humans are expected to become casualties as a result of decelerative tumbling have been tentatively estimated to be 30 and 75 feet per second, respectively. The curves in Fig. 12.49 marked "translation over open terrain" are approximate, but they may be used to provide a general indication of the range within which casualties might occur from decelerative tumbling due to air blast from surface and air bursts. The curves in Fig. 12.49 show 50 percent and 1 percent casualties resulting from translation near structures and over open terrain as a function of ground distance and height of burst for a 1 KT explosion in a standard sea-level atmosphere. The results apply to randomly oriented, prone personnel exposed to the blast wave in the open. The curves for translation over open terrain (decelerative tumbling) are approximate (§ 12.50).
Scaling. The required relationships are
d/d1 = h/h1 = W0.4
where d, and h1 are the distance from ground zero and height of burst, respectively, for 1 KT; and d and h are the corresponding distance and height of burst for W KT.
Example
Given: A 50 KT explosion at a height of 860 feet over open terrain.
Find: The ground distance at which translational effects would produce 50 percent casualties among prone personnel.
Solution: The corresponding burst height for I KT is
h1 = h/W0.4 = 860/(50)0.4 = 180 feet.
From Fig. 12.49, at a height of burst of 180 feet, the ground distance at which 50 percent casualties among personnel in the open will occur is roughly 660 feet. The corresponding ground distance for 50 KT is then given approximately as
d = d1 W0.4 = 660 X (50)0.4
= 3,150 feet. Answer
CLASSIFICATION OF BURNS
12.51 Thermal radiation can cause burn injuries either directly, i.e., by absorption of the radiant energy by the skin, or indirectly by heating or ignition of clothing, or as a result of fires started by the radiation. The direct burns are often called "flash burns," since they are produced by the flash of thermal radiation from the fireball. The indirect (or secondary) burns are referred to as "contact burns" or "flame burns"; they are identical with skin burns that result from touching a hot object or those that would accompany (or be caused by) any large fire no matter what its origin. In addition, individuals in buildings or tunnels close to ground zero may be burned from hot debris, gases, and dust (§ 12.02).
12.52 A skin burn is an injury caused by an increase in skin temperature resulting from direct absorption of thermal radiation, which varies with skin color, or from the transference of heat through clothing. The severity of the burn depends on the amount of the temperature increase and on the duration of the increase. For example, a skin temperature of 70°C (155°F) for a fraction of a second will produce the same type of burn as a temperature of 48°C (118°F) for a few minutes. Skin burns are generally classified as first, second, or third degree, in order of increasing severity of the burn. Pain associated with skin burns occurs when the temperature of certain nerve cells near the surface is raised to 43°C (109°F) or more. If the temperature is not sufficiently high or does not persist for a sufficient length of time, pain will cease and no injury will occur. The amount of pain is not directly related to the severity of the burn injury, but it can serve a useful purpose in warning an individual to evade part of the thermal pulse from a nuclear explosion.
12.53 First-degree burns, which are the mildest, are characterized by immediate pain and by ensuing redness of the affected area. The pain continues even after the temperature of the skin has returned to normal. The first-degree burn is a reversible injury; that is to say, healing is complete with no scar formation. Sunburn is the classic example of first-degree burn.
12.54 Second-degree burns result from skin temperatures that are higher and/or of longer duration than those causing first-degree skin burns. The injury is characterized by pain which persists, and may be accompanied either by no immediate visible effect or by a variety of skin changes including blanching, redness, loss of elasticity, swelling, and development of blisters. After 6 to 24 hours, a scab will form over the injured area. The scab may be flexible and tan or brown, if the injury is moderate, or it may be thick, stiff, and dark, if the injury is more severe. The wounds will heal within one to two weeks unless they are complicated by infection. Second-degree burns do not involve the full thickness of the skin, and the remaining uninjured cells may be able to regenerate normal skin without scar formation.
12.55 If skin temperatures become sufficiently high and/or are of long duration, third-degree burns will be produced. Pain is experienced at the peripheral, less injured areas only, since the nerve endings in the centrally burned areas are damaged to the extent that they are unable to transmit pain impulses.
Immediately after suffering the burn, the skin may appear either normal, scalded, or charred, and it may lose its elasticity.
The healing of third-degree burns takes several weeks and will always result in scar formation unless new skin is grafted over the burned area. The scar results from the fact that the full thickness of the skin is injured, and the skin cells are unable to regenerate normal tissue.
12.56 The distribution of burns into three groups obviously has certain limitations since it is not possible to draw a sharp line of demarcation between first- and second-degree, or between second- and third-degree burns. Within each class the burn may be mild, moderate, or severe, so that upon preliminary examination it may be difficult to distinguish between a severe burn of the second degree and a mild third-degree burn. Subsequent pathology of the injury, however, will usually make a distinction possible. In the following discussion, reference to a particular degree of burn should be taken to imply a moderate burn of that type.
12.57 The depth of the burn is not the only factor in determining its effect on the individual. The extent of the area of the skin which has been affected is also important. Thus, a first-degree burn over the entire body may be more serious than a third-degree burn at one spot. The larger the area burned, the more likely is the appearance of symptoms involving the whole body. Furthermore, there are certain critical, local regions, such as the hands, where almost any degree of burn will incapacitate the individual.
12.58 Persons exposed to nuclear explosions of low or intermediate yield may sustain very severe burns on their faces and hands or other exposed areas of the body as a result of the short pulse of directly absorbed thermal radiation. These burns may cause severe superficial damage similar to a third-degree burn, but the deeper layers of the skin may be uninjured. Such burns would heal rapidly, like mild second-degree burns. Thermal radiation burns occurring under clothing or from ignited clothing or other tinder will be similar to those ordinarily seen in burn injuries of non-nuclear origin. Because of the longer duration of the thermal pulse from an air burst weapon in the megaton range, flash burns on exposed skin and burns of non-nuclear origin may also be similar.
BURNS UNDER CLOTHING
12.59 Skin burns under clothing, which depend on the color, thickness, and nature of the fabric, can be produced in the following ways: by direct transmittance through the fabric if the latter is thin and merely acts as an attenuating screen; by heating the fabric and causing steam or volatile products to impinge on the skin; by conduction from the hot fabric to the skin; or the fabric may ignite and hot vapors and flames will cause burns where they impinge on the skin. Burns beneath clothing can arise from heat transfer for some time after the thermal pulse ends. These burns generally involve deeper tissues than the flash burns produced by the direct thermal pulse on bare skin. Flame burns caused by ignited clothing also result from longer heat application, and thus will be more like burns due to conventional conflagrations.
12.60 First- and second-degree burns of the uncovered skin and burns through thin clothing occur at lower radiant exposures (§ 7.35) than those which ignite clothing (Table 7.36). Because of these factors, first- and second-degree burns in exposed persons would involve only those body areas that face the explosion. Where the direct thermal pulse produces third-degree burns and clothing ignition takes place, persons wearing thin clothing would have such burns over parts of the body facing the burst. Persons wearing heavy clothing could suffer third-degree burns over the whole body if the ignited clothing could not be removed quickly. This phenomenon is typically seen in persons whose clothing catches fire by conventional means.
INCAPACITATION FROM BURNS
12.61 Burns of certain areas of the body, even if only of the first degree, will frequently result in incapacitation because of their critical location. Any burn surrounding the eyes that causes occluded vision, e. g., because of swelling of the eyelids, will be incapacitating. Burns of the elbows, knees, hands, and feet produce immobility or limitation of motion as the result of swelling, pain, or scab formation, and will cause ineffectiveness in most cases. The occurrence of burns of the face, neck, and hands are probable because these areas are most likely to be unprotected. Second- or third-degree burns in excess of 20 percent of the surface area of the body should be considered major burns and will require special medical care in a hospital. If the nose and throat are seriously involved and obstructive edema (§ 12.27) occurs, breathing may become impossible and tracheotomy may be required as a life-saving measure.
12.62 Shock is a term denoting a generalized state of serious circulatory inadequacy. If serious, it will result in incapacitation and unconsciousness and if untreated may cause death. Third-degree burns of 25 percent of the body and second-degree burns of 30 percent of the body will generally produce shock within 30 minutes to 12 hours and require prompt medical treatment. Such treatment is complicated and causes a heavy drain on medical personnel and supply resources.
RADIANT EXPOSURES FOR BURNS ON EXPOSED SKIN
12.63 The critical radiant exposure for a skin burn depends on the duration of the radiation pulse and the thermal energy spectrum; both of these quantities vary with the yield and height of burst. Hence, although the radiant exposure is known as a function of distance and yield (see Chapter VII), it is not a simple matter to predict distances at which burns of different types may be expected from a given explosion. Apart from radiant exposure, the probability and severity of the burns will depend on several factors. One of the most important is the absorptive properties of the skin for thermal radiation. In a normal population, the fraction of the radiation energy absorbed may vary by as much as 50 percent because of differences in skin pigmentation.
12.64 For thermal radiation pulses of 0.5 second duration or more, as is the case for explosions with yields exceeding I kiloton, the energy absorbed by the skin, rather than the radiant exposure, determines the extent of the burn injury. The spectral absorptance of the skin, i.e., the fraction of the incident radiation energy (or radiant exposure) that is absorbed, depends on the skin pigmentation. The curves in Fig. 12.64 have been derived from thermal energy spectra of nuclear explosions in the lower part of the atmosphere and measured values of the absorptance of different skin types. By considering explosions in the lower atmosphere, the height of burst variable is largely eliminated. The results in the figure are applicable to exposed skin when no evasive action is taken and there is no protection from structures or clothing. It is seen that the radiant exposure required to produce a given degree of burn injury varies significantly with skin pigmentation. In fact, people with very dark skins could receive burns from approximately two-thirds the incident radiant energy that will cause similar burns in very light-skinned people.
12.65 Figure 12.65 shows radiant exposures for the various probabilities of burn occurrence, again assuming no evasive or protective action. The solid lines represent the conditions under which it is probable that 50 percent of an average exposed population will receive skin burns of the indicated degree. The broken lines divide the burn probability distributions into ranges for three degrees of burn severity with average probabilities of 18 percent and 82 percent assigned within the various ranges. For example, from Fig. 12.65 it is expected that, if a normal population is exposed to the thermal pulse from a I-megaton explosion in the lower atmosphere, at distances where the radiant exposures are between 4.5 and 6 cal/cm2, 18 percent of the population will receive second-degree burns and the remainder first-degree burns to the exposed (unprotected) skin.
12.66 With the aid of the yield-distance relationships for various radiant exposures given in Chapter VII, the curves in Fig. 12.65 may be used to determine the approximate distances from ground zero at which given burn probabilities may be experienced. Suppose that, in the example given above, the 1-megaton weapon is detonated at a height of 10,000 feet, which is within the lower atmosphere. According to Fig. 7.42, for air bursts below 20,000 feet and 12-mile visibility, the specified radiant exposure between 4.5 and 6 cal/cm2, would be received at slant ranges of from 9 to 10 miles. Since these ranges are substantially greater than the height of burst (about 2 miles), they may be taken as the distances to ground zero to the accuracy of Fig. 7.42. Hence, within the radii of 9 and 10 miles from ground zero, it is probable that 18 percent of an average population subjected to the whole thermal pulse will receive second-degree burns and 82 percent first-degree burns to their exposed (unprotected) skin.
12.67 As already noted, the burn criteria given above are based on the supposition that no evasive action is taken. For air bursts with yields less than about 100 kilotons, the main part of the thermal energy arrives too quickly for people to react and take some protective action. Evasion of part of the thermal energy that would be effective in reducing burn injuries is possible, however, for yields of 100 kilotons or more in the lower atmosphere. The length of the thermal pulse is then such that the pain could initiate a reaction which, if appropriate, might allow a person to obtain sufficient protection to decrease the severity of the potential burn (§ 7.87). The ability to react in this manner can apparently be improved by appropriate training.
BURN INJURIES IN JAPAN
12.68 Among the survivors of the nuclear explosions in Japan, the incidence of flame burns appeared to be very small. In fact, they constituted not more than 5 percent of the total burn injuries. This was the case because most of those who suffered flame burns did not survive, since they were caught in burning buildings and could not escape. The character of the flame burns was similar to that of burns caused by other conflagrations. The clothing usually caught fire and then large parts of the body suffered flame burns. By contrast, as will be seen below, flash burns were generally restricted to exposed skin areas, i.e., face, arms, hands, and legs.
12.69 One of the most striking consequences of the nuclear bombings of Japan was the large number of casualties due to flash burns caused by the thermal radiation. The situation was aggravated by the clear atmosphere and warm weather which prevailed at the time (§ 12.14). It was estimated that 20 to 30 percent of the fatal casualties in Hiroshima and Nagasaki were caused by flash burns. In the former city alone, about 42,000 burn cases were reported and of those some 24,500 were recorded as being serious. Unless protected by heavy clothing, thermal radiation burns, apart from other injuries, would have been fatal to nearly all unshielded persons in the open at distances up to 6,000 feet (1.1 miles) or more from ground zero. Even as far out as 12,000 to 14,000 feet (2.3 to 2.6 miles), there were instances of such burns which were bad enough to require treatment.
THERMAL RADIATION BURNS IN JAPAN
12.70 A distinctive feature of the thermal radiation (flash) burns was their sharp limitation to exposed areas of the skin facing the center of the explosion. For this reason they are sometimes called "profile burns" (Fig. 12.70). The phenomenon occurred because most of the radiation received had traveled in a straight line from the fireball and so only regions that were directly exposed were affected. A striking illustration of this behavior was that of a man writing before a window. His hands were seriously burned, but his face and neck, which were not covered, suffered only slight burns because the angle of entry of the thermal radiation through the window was such as to place them in partial shadow.
12.71 Although flash burns were largely confined to exposed parts of the body, there were a few cases where such burns occurred through one, and very occasionally more, layers of clothing. Instances of this kind were observed when the radiant exposure was large enough to overcome the protective effect of the particular fabric. When burns did occur through clothing, they frequently involved regions where the clothes were in contact with the skin, at the elbows and shoulders, for example. Such burns may have been due to heat transmitted from the hot fabric, rather than to the direct effect of radiation. Areas over which the clothing fitted loosely, so that an air space separated it from the skin, were generally unharmed by the thermal radiation (Fig. 12.71).
12.72 There were many instances in which burns occurred through black clothing, but not through white material worn by the same individual (Fig. 12.72). This was attributed to the reflection of thermal radiation by white or other light-colored fabrics, whereas materials of dark color absorbed radiation, became hot, and so caused contact burns. In some cases black outer clothing actually burst into flame and ignited the undergarments, so that flame burns resulted. It should be mentioned, however, that white clothing does not always necessarily provide protection against thermal radiation. Some materials of this kind transmit enough radiation to permit flash burning of the skin to occur.
12.73 The frequency of flash burns was, of course, greatest among persons who were in the open. Nevertheless, there were a surprising number of such burns among individuals who were indoors. This was largely because many windows, especially in commercial structures, were uncurtained or were wide open on account of the summer weather. Hence, many persons inside buildings were directly exposed to thermal radiation. In addition to the protection afforded by clothing, particularly if light in color, some shielding was provided by the natural promontories of the body, e.g., the nose, supraorbital (eye socket) ridges, and the chin.
GENERAL CHARACTERISTICS OF FLASH BURNS
12.74 In spite of the thousands of flash burns experienced after the nuclear attacks on Japan, only their general features were reported. However, this information has been supplemented by observations made, especially on anesthetized pigs, both in the laboratory and at nuclear test explosions. The skin of white pigs has been found to respond to thermal radiation in a manner which is in many respects similar to, and can be correlated with, the response of human skin.
12.75 Severity of the flash burns in Japan ranged from mild erythema (reddening) to charring of the outermost layers of the skin. Among those who were within about 6,000 feet (1.1 miles) from ground zero, the burn injuries were depigmented lesions (light in color), but at greater distances, from 6,000 to 12,000 feet (1.1 to 2.3 miles), the initial erythema was followed by the development of a walnut coloration of the skin, sometimes called the "mask of Hiroshima."
12.76 Burns of moderate second degree (and milder) usually healed within four weeks, but more severe burns frequently became infected so that the healing process was much more prolonged. Even under the best conditions, it is difficult to prevent burns from becoming infected, and after the nuclear bombings of Japan the situation was aggravated by inadequate care, poor sanitation, and general lack of proper facilities. Nuclear radiation injury may have been a contributory factor in some cases because of the decrease in resistance of the body to infection.
12.77 Experimental flash burns have been produced both in the laboratory and in nuclear tests which were apparently quite similar to those reported from Hiroshima and Nagasaki. In the more severe cases of circular experimental burns there was a central charred region with a white outer ring surrounded by an area of erythema. A definite demarcation both in extent and depth of the burns was noted, so that they were unlike contact burns which are generally variable in depth. The surface of the flash burns became dry without much edema or weeping of serum.
12.78 Another phenomenon, which appeared in Japan after the healing of some of the more severe burns, was the formation of keloids, that is, thick overgrowths of scar tissue. It was suggested, at one time, that they might have been due to nuclear radiation, but this view is no longer accepted. The degree of keloid formation appears to have been influenced by infections, which complicated healing of the burns, and by malnutrition. A secondary factor is the known disposition for keloid formation to occur among the Japanese and other dark-skinned people as a racial characteristic. Many spectacular keloids, for example, were formed after the healing of burns produced in the incendiary bomb attacks on Tokyo. There is a tendency, however, for keloids to disappear gradually in the course of time.
EFFECTS OF THERMAL RADIATION ON THE EYES
12.79 It is of interest that, among the survivors in Hiroshima and Nagasaki, eye injuries directly attributable to thermal radiation appeared to be relatively unimportant. There were many instances of temporary blindness, occasionally lasting up to 2 or 3 hours, but only one case of retinal injury was reported.
12.80 The eye injury known as keratitis (an inflammation of the cornea) occurred in some instances. The symptoms, including pain caused by light, foreign-body sensation, lachrymation, and redness, lasted for periods ranging from a few hours to several days. Among 1,000 cases, chosen at random, of individuals who were in the open, within some 6,600 feet (1.25 miles) of ground zero at the time of the explosions, only 42 gave a history of keratitis coming on within the first day. Delayed keratitis was reported in 14 additional cases, with symptoms appearing at various times up to a month or more after the explosion. It is possible that nuclear radiation injury, which is associated with delayed symptoms, as will be seen below, may have been a factor in these patients.
12.81 Investigators have reported that in no case, among 1,400 examined, was the thermal radiation exposure of the eyes apparently sufficient to produce permanent opacity of the cornea. This observation is not surprising since the cornea is transparent to the major portion of the thermal energy which is received in the visible and longer wavelength (infrared) parts of the spectrum. In approximately one-quarter of the cases studied there had been facial burns and often singeing of the eyebrows and eyelashes. Nevertheless, some 3 years later the corneas were found to be normal.
12.82 Several reasons have been suggested for the scarcity of severe eye injuries in Japan. For example, the detonations occurred in the morning in broad daylight when the eye pupil would be expected to be small. Another possible explanation is that the recessed position of the eyes and, in particular, the overhanging upper lids served to decrease the direct exposure to thermal radiation. Furthermore, on the basis of probability, it is likely that only a small proportion of individuals would be facing the explosions in such a way that the fireball would actually be in their field of vision.
12.83 Exposure of the eye to the bright flash of a nuclear detonation can produce two possible injuries: flashblindness and retinal burns. Flashblindness (dazzle) is a temporary impairment of vision caused by a bleaching of the light-sensitive elements (rods and cones) in the retina of the eye. It may be produced by scattered light and does not necessarily require the eye to be focused on the fireball. Flashblindness will normally blank out the entire visual field of view with a bright afterimage. The effects persist only a short time and recovery is complete.
12.84 During the period of flashblindness (several seconds to minutes) useful vision is lost. This may preclude effective performance of activities requiring constant, precise visual function. The severity and time required for recovery of vision are determined by the intensity and duration of the flash, the viewing angle from the burst, the pupil size, brightness of the object being viewed and its background, and the visual complexity of the object. Flashblindness would be more severe at night since the pupil is larger and the objects and background are usually dimly illuminated.
12.85 A retinal burn is a permanent eye injury that occurs whenever the retinal tissue is heated excessively by the image of the fireball focused in the eye. The underlying pigmented cells absorb much of the light (radiation) energy and the temperature is increased in that area. A temperature elevation of 12 to 20°C (22 to 36°F) in the eye produces a thermal injury that involves both the pigmented layer and the adjacent rods and cones, so that visual capacity is permanently lost in the burned area. The natural tendency of people to look directly at the fireball would increase the incidence of retinal burns. A retinal burn normally will not be noticed by the individual concerned if it is off the central axis of vision, but very small burned areas may be noticeable if they are centrally located. A person generally will be able to compensate for a small retinal burn by learning to scan around the burned area.
12.86 Retinal burns can be produced at great distances from nuclear detonations, because the probability of their occurrence does not decrease as the square of the distance from the detonation, as is true of many other nuclear weapons effects. Theoretically, the optical process of image formation within the eye should keep the energy per unit area on the retina a constant, regardless of the distance. However, meteorological conditions and the fact that the human eye is not a perfect lens, all contribute toward reducing the retinal burn hazard as the distance is increased between the observer and the detonation.
12.87 Explosions with yields of more than about 1 megaton at heights greater than some 25 miles may produce retinal burns as far out as the horizon on clear nights. If the burst height is greater than some 50 miles, the short pulse of thermal energy from the early-time weapon debris, as well as that from the X-ray pancake, can be effective in this respect (§ 7.91). Bursts above 90 miles altitude probably will not cause retinal burns in persons on the ground, unless the yield is greater than 10 megatons. The eye's blink reflexes are sufficiently fast (roughly 0.25 second) to provide some protection against weapons of more than 100 kilotons yield detonated below about 25 miles. The blink time is too slow to provide any appreciable protection from smaller weapons or from bursts at higher altitudes. When people have adequate warning of an impending nuclear burst, evasive action, including closing or shielding the eyes, will prevent both flashblindness and retinal burns.
12.88 Safe separation distances from ground zero, i.e., distances beyond which persons on the ground would not receive incapacitating eye injuries, are shown in Figs. 12.88a and b as a function of weapon yield for two heights of burst (HOB). The curves in Fig. 12.88a are for a clear day; for a cloudy day the safe separation distances would be reduced to about half. The curves in Fig. 12.88b are for night conditions. The distances for retinal burns are those for which such burns will not occur provided the eye can blink within 0.25 second. A faster blink time will not change the values appreciably, but a slower time would increase them. Data for the complete absence of flashblindness are not available and the distances in Figs. 12.88a and b are those within which a visual loss for about 10 seconds may be expected, to a degree sufficient to preclude the performance of a precision task under conditions of dim light, e.g., a pilot reading instruments at night.
12.89 The flashblindness and retinal burn safe separation distances do not bear a constant relationship to one another as the yield changes. In circumstances that require determination of complete eye safety (bearing in mind the 10-second visual loss criterion for flashblindness), the effect that occurs at the greater distance from the burst is the critical one. For example, for a height of burst of 50,000 feet at night, it is seen from Fig. 12.88b that for yields up to about 3 megatons, flashblindness is the important factor in determining the distance at which there will be no. incapacitating eye effects. For larger yields, retinal burn becomes the limiting factor. Where only permanent eye damage is of interest and the temporary loss of vision from flashblindness is of little concern, the retinal burn curves should be used to estimate safe distances no matter what the explosion energy yield.
INTRODUCTION
12.90 The injurious effects of nuclear radiations from a nuclear explosion represent a phenomenon which is completely absent from conventional explosions. For this reason, the subject of radiation injury (or sickness) will be described at some length. It should be understood, however, that the extended discussion does not necessarily imply that nuclear radiation would be the most important source of casualties in a nuclear explosion. This was certainly not the case in Japan where the detonations occurred at heights of approximately 1,870 feet (Hiroshima) and 1,640 feet (Nagasaki) above the ground. Such injuries as were caused by nuclear radiation were due to the initial radiation. The effect of the residual radiation, in the form of early fallout and induced radioactivity, was negligible. However, as was seen in Chapter IX, the situation could be very different in the event of a surface burst.
12.91 It has long been known that exposure to radiations, such as X rays, alpha and beta particles, gamma rays, and neutrons, which are capable of producing ionization, either directly or indirectly (§§ 8.21, 8.58), can cause injury to living organisms. After the discovery of X rays and radioactivity, toward the end of the nineteenth century, it became increasingly apparent that an element of danger was associated with exposure to ionizing radiations.6 In spite of the growing awareness by both scientists and physicians of the hazards inherent in many radiation sources, there were some excessive exposures. In the course of time, however, recommendations for preventing overexposures were adopted and radiation injuries became less frequent. Nevertheless, occasional overexposures have occurred among personnel operating radiographic equipment, powerful X-ray machines in industrial laboratories and hospitals, cyclotrons, and experimental nuclear reactors, or working with radioactive materials.
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6 The more general expression "ionizing radiations" is often employed instead of nuclear radiations, since this permits the inclusion of radiations of non-nuclear origin, e.g., X rays, having similar biological effects.
12.92 The harmful effects of nuclear radiations appear to be caused by the ionization (and excitation) produced in the cells composing living tissue. As a result of ionization, some of the constituents, which are essential to the normal functioning of the cells, are altered or destroyed. In addition, the products formed may act as poisons. Among the observed consequences of the action of ionizing radiations on cells are breaking of the chromosomes, swelling of the nucleus and of the entire cell, increase in viscosity of the cell fluid, increased permeability of the cell membrane, and destruction of cells. In addition, the process of cell division (or "mitosis") is delayed by exposure to radiation. Frequently, the cells are unable to undergo mitosis, so that the normal cell replacement occurring in the living organism is inhibited.
RADIATION DOSE UNITS
12.93 The radiation unit known as the roentgen was described in § 8.17. By definition, it is applicable only to gamma rays or X rays. and not to other types of ionizing radiation, such as alpha and beta particles and neutrons. Since the roentgen refers to a specific result in air accompanying the passage of an amount of radiation through the air, it does not imply any effect that it would produce in a biological system. The roentgen is thus a measure of the "exposure" to gamma rays and X rays. The effect on a biological system, such as the whole body or a particular organ, however, depends on the amount of radiation energy that has been absorbed by the body or organ. The unit of absorbed dose, which applies to all kinds of ionizing radiations, including alpha and beta particles and neutrons, is the rad, as defined in § 8.18.
12.94 Although all ionizing radiations are capable of producing similar biological effects, the absorbed dose (measured in rads) which will produce a certain effect may vary appreciably from one type of radiation to another. This difference in behavior is expressed by means of the "relative biological effectiveness" (or RBE) of the particular nuclear radiation. The RBE of a given radiation is defined as the ratio of the absorbed dose in rads of gamma radiation (of a specified energy)7 to the absorbed dose in rads of the given radiation having the same biological effect. The value of the RBE for a particular type of nuclear radiation depends upon several factors, including the dose rate, the energy of the radiation, the kind and degree of the biological damage, and the nature of the organism or tissue under consideration.
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7 Gamma rays from cobalt-60 have been commonly specified for this purpose.
12.95 The "biological dose," also called the "RBE dose," that provides a direct indication of the expected effects of any ionizing radiation on the body (or organ), is stated in terms of the "rem," an abbreviation of "roentgen equivalent (in) man." It is equal to the absorbed dose in rads multiplied by the RBE for the particular radiation (or radiations) absorbed; thus,
Dose in rems = Dose in rads x RBE.
An advantage of the rem is that it is possible to express the total biological effect that might result from the absorption of more than one kind of ionizing radiation. The absorbed dose in rads of each radiation type is multiplied by the appropriate RBE and the results are added. (In connection with radiological protection in peacetime activities, the "dose equivalent" in rems is defined as the absorbed dose in rads multiplied by a "quality factor," and sometimes by other modifying factors. The quality factor, which depends on the nature and energy of the absorbed radiation, replaces the RBE.) 12.96 All radiations capable of producing ionization (or excitation) directly or indirectly, e.g., alpha and beta particles, X rays, gamma rays, and neutrons, cause radiation injury of the same general type. Although the effects are qualitatively similar, the various radiations differ in the depth to which they penetrate the body and in the degree of injury corresponding to a specified amount of energy absorption. As seen above, the latter difference is expressed by means of the RBE.
12.97 The RBE for gamma rays is approximately unity, by definition, although it varies somewhat with the energy of the radiation. For beta particles, the RBE is also close to unity; this means that for a given amount of energy absorbed in living tissue, beta particles produce about the same extent of injury within the body as do X rays or gamma rays.8 The RBE for alpha particles from radioactive sources that have been taken into the body is in the range from 10 to 20, more specifically for the development of bone cancers. The RBE for neutrons varies with the energy and the type of injury. For the neutron energy spectrum of nuclear weapons, the RBE for immediate (acute) radiation injury is close to 1.0. But it is significantly larger (4 to 10) for the occurrence of opacities of the eye lens (cataracts), leukemia, and genetic changes (§ 12. 144 et seq., § 12.201 et seq.). For these biological effects, a certain amount of energy absorbed from exposure to neutrons is much more damaging than the same amount of energy (in rads) absorbed from gamma rays.9
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8 Beta particles from sources on or near the body can also cause skin lesions. called "beta burns" (§ 12.155 et seq.).9 The curves in Chapter VIII that show the neutron dose in rads at a particular location relative 10 a nuclear explosion calculated by considering the contributions of neutrons in various energy ranges al that location for typical weapons spectra. Multiplication of these doses by the appropriate RBE gives the corresponding biological dose in rems.
GENERAL CHARACTERISTICS OF RADIATION EFFECTS
12.98 In considering the possible effects on the body of ionizing radiations from external sources, it is necessary to distinguish between an "acute" (or "one-shot") exposure and a "chronic" (or extended) exposure. In an acute exposure the whole radiation dose is received in a relatively short interval of time. This is the case, for example, in connection with the initial nuclear radiation. It is not possible to define an acute dose precisely, but it may be somewhat arbitrarily taken to be the dose received during a 24-hour period. Although the delayed radiations from early fallout persist for longer times, the main exposure would be received during the first day and so it is regarded as being acute. On the other hand, an individual entering a fallout area after the first day or so and remaining for some time would be considered to have been subjected to a chronic exposure.
12.99 The importance of making a distinction between acute and chronic exposures lies in the fact that, if the dose rate is not too large, the body can achieve partial recovery from many (but perhaps not all) of the consequences of nuclear radiations. For example, an acute dose of 50 rems will generally cause changes in the constituents of the blood (§ 12.113), but the same dose spread over a period of years (or even less) will produce only minor effects on the blood cells. In an extreme case, an acute dose exceeding 600 rems would cause serious illness and in the great majority of instances death could occur within a few weeks. On the other hand, a chronic dose of the same total magnitude accumulated gradually over 20 years might have no observable effect.
12.100 The injury caused by a certain dose (and dose rate) of radiation will depend upon the extent and part of the body that is exposed. One possible reason is that when the exposure is restricted, the unexposed regions may be able to contribute to the recovery of the injured area. But if the whole body is exposed, many organs are affected and recovery is much more difficult.
12.101 Different portions of the body show different sensitivities to ionizing radiations, and there are variations in degree of sensitivity among individuals. In general, the most radio-sensitive cells are found in the lymphoid tissue, bone marrow, spleen, organs of reproduction, and gastrointestinal tract. Of intermediate sensitivity are the skin, lungs, and liver, whereas muscle, nerve, and adult bones are the least sensitive.
EFFECTS OF ACUTE RADIATION DOSES
12.102 Before the nuclear bombings of Hiroshima and Nagasaki relatively little was known of the phenomena associated with acute whole-body exposure to ionizing radiation. In Japan, however, a large number of individuals received whole-body doses of radiation ranging from insignificant quantities to amounts which proved fatal. The effects were often complicated by other injuries and shock, so that the symptoms of acute radiation injury could not always be isolated. Because of the great numbers of patients and the lack of facilities after the explosions, it was impossible to make detailed observations and keep accurate records. Nevertheless, certain important conclusions have been drawn from Japanese experience with regard to the effects of nuclear radiation on the human organism.
12.103 Information on this subject has also been gathered from other sources. These include a few laboratory accidents involving a small number of human beings, irradiation used in treating various diseases and malignancies, and extrapolation to man of observations on animals. In addition, detailed knowledge has been obtained from a careful study of over 250 persons in the Marshall Islands, who were accidentally exposed to nuclear radiation from fallout following the test explosion on March 1, 1954 (§ 9.104 et seq.). The exposed individuals included both Marshallese and a small group of American servicemen. The whole-body radiation doses ranged from relatively small values (14 rems), which produced no obvious symptoms, to amounts (175 rems) that caused prompt marked changes in the blood-forming system (§ 12.124).
12.104 No single source of data directly yields the relationship between the physical dose of ionizing radiation and the clinical effect in man. Hence, there is no complete agreement concerning the effect associated with a specific dose or dose range. Attempts in the past have been made to relate particular symptoms to certain narrow ranges of exposure; however, the data are incomplete and associated with many complicating factors that make interpretation difficult. For instance, the observations in Japan were very sketchy until 2 weeks following the exposures, and the people at that time were suffering from malnutrition and pre-existing bacterial and parasitic infections. Consequently, their sickness was often erroneously attributed to the effects of ionizing radiation when such was not necessarily the case. The existing conditions may have been aggravated by the radiation, but to what extent it is impossible to estimate in retrospect.
12.105 In attempting to relate the acute radiation dose to the effect on man, it should be mentioned that reliable information has been obtained for doses up to 200 rems. As the dose increases from 200 to 600 rems, the data from exposed humans decrease rapidly and must be supplemented more and more by extrapolations based on animal studies. Nevertheless, the conclusions drawn can be accepted with a reasonable degree of confidence. Beyond 600 rems, however, observations on man are so sporadic that the relationship between dose and biological effect must be inferred or conjectured almost entirely from observations made on animals exposed to ionizing radiations. Such observations have been made in recent years at extremely high doses.
12.106 Individuals receiving acute whole-body doses of ionizing radiation may show certain signs and symptoms of illness. The time interval to onset of these symptoms, their severity, and their duration generally depend on the amount of radiation absorbed, although there may be significant variations among individuals. Within any given dose range the effects manifested can be divided conveniently into three time phases: initial, latent, and final.
12.107 During the initial phase, exposed individuals may experience nausea, vomiting, headache, dizziness, and a generalized feeling of illness. The onset time decreases and the severity of these symptoms increases with increasing dose. During the latent phase exposed individuals will experience few, if any, symptoms and most likely will be able to perform useful tasks. The final phase is characterized by illness that requires hospitalization of people receiving the higher doses. In addition to the recurrence of the symptoms noted during the initial phase, skin hemorrhages, diarrhea, and loss of hair may appear, and, at higher doses, seizures and prostration may occur. The final phase is consummated by recovery or death.
12.108 With the foregoing in mind, Table 12.108 is presented as the best available summary of the effects of various whole-body dose ranges of ionizing radiation on human beings. Results of radio-biological studies are generally reported in terms of the (vertical) midline tissue dose in rads. This dose is lower than the dose that would be measured by instruments (and the dose that would be absorbed by tissue) near the surface of the body by a factor that depends upon the energy of the radiation and the size of the individual. The nuclear radiation data presented in Chapters VIII and IX refer to the absorbed dose in tissue at the surface of an individual that is nearest the burst, and thus they also correspond to the expected instrument readings. For consistency, the data in Table 12.108 are the doses (in rems) equivalent to the absorbed doses (in rads) in tissue at the surface of the individual. For gamma rays, these absorbed doses are essentially equal to the exposures in roentgens (§ 8.18). For nuclear weapon radiation, the midline tissue doses for average size adults would be approximately 70 percent of the doses in the table.
12.109 As shown in Table 12.108, below 100 rems the response is almost completely subclinical; that is to say, there is no sickness requiring special attention. Changes may, nevertheless, be occurring in the blood, as will be seen later. Between 100 and 1,000 rems is the range in which therapy, i.e., proper medical treatment, will be successful at the lower end and may be successful at the upper end. The earliest symptoms of radiation injury are nausea and vomiting, which may commence within about 15 minutes to 6 hours of exposure, depending on the dose, accompanied by discomfort (malaise), loss of appetite, and fatigue. The most significant, although not immediately obvious effect in the range under consideration, is that on the hematopoietic tissue, i.e., the organs concerned with the formation of blood. An important manifestation of the changes in the functioning of these organs is leukopenia, that is, a decline in the number of leukocytes (white blood cells). Loss of hair (epilation) will be apparent about 2 weeks or so after receipt of a dose exceeding 300 rems.
12.110 Because of the increase in the severity of the radiation injury and the variability in response to treatment in the range from 100 to 1,000 rems, it is convenient to subdivide this range into three subsections, as shown in Table 12.108. For whole-body doses from 100 to 200 rems, hospitalization is generally not required, but above 200 rems admission to a hospital is necessary so that the patient may receive such treatment as may be indicated. Up to 600 rems, there is reasonable confidence in the clinical events and appropriate therapy, but for doses in excess of this amount there is considerably uncertainty and variability in response.
12.111 Beyond 1,000 rems, the prospects of recovery are so poor that therapy may be restricted largely to palliative measures. It is of medical interest, however, to subdivide this lethal range into two parts in which the characteristic major clinical effects are different. Although the dividing line has been somewhat arbitrarily set at 5,000 rems in Table 12.108, human data are so limited that this dose level might well have any value from 2,000 to 6,000 rems. In the range from 1,000 to (roughly) 5,000 rems, pathological changes in the gastrointestinal tract, which are apparent at lower doses, become very marked. Above 5,000 rems, the central nervous system also exhibits the consequences of major injury.
12.112 The superposition of radiation effects upon injuries from other causes may be expected to result in an increase in the number of cases of shock. For example, the combination of sublethal nuclear radiation exposure and moderate thermal burns will produce earlier and more severe shock than would the comparable burns alone. The healing of wounds of all kinds will be retarded because of the susceptibility to secondary infection accompanying radiation injury and for other reasons. In fact, infections, which could normally be dealt with by the body, may prove fatal in such cases.
DOSES OF 25 TO 100 REMS: NO ILLNESS
12.113 Single doses in the range of from 25 to 100 rems over the whole body will produce some changes in the blood (§ 12.124). These changes do not usually occur below this range and are not produced consistently unless the dose is 50 rems or more. Disabling sickness does not occur and exposed individuals should be able to proceed with their usual duties.
DOSES OF 100 TO 200 REMS: SLIGHT OR NO ILLNESS
12.114 A whole-body dose in the range of 100 to 200 rems will result in a certain amount of illness but it will rarely be fatal. Doses of this magnitude were common in Hiroshima and Nagasaki, particularly among persons who were at some distance from the nuclear explosion. Of the 267 individuals accidentally exposed to fallout in the Marshall Islands following the test explosion of March 1, 1954, a group of 64 received radiation doses in this range. The exposure of these individuals was not strictly of the acute type, since it extended over a period of some 45 hours. More than half the dose, however, was received within 24 hours and the observed effects were similar to those to be expected from an acute exposure of the same amount.
12.115 The illness from radiation doses in this range does not present a serious problem since most patients will suffer little more than discomfort and fatigue and others may have no symptoms at all. There may be some nausea and vomiting on the first day or so following irradiation, but subsequently there is a latent period, of up to 2 weeks or more (§ 12.107). The usual symptoms, such as loss of appetite and malaise, may reappear, but if they do, they are mild. The changes in the character of the blood, which accompany radiation injury, become significant during the latent period and persist for some time. If there are no complications, due to other injuries or infection, there will be recovery in essentially all cases. In general, the more severe the early stages of the radiation sickness, the longer will be the process of recovery. Adequate care and the use of antibiotics, as may be indicated clinically, can greatly expedite complete recovery of the small proportion of more serious cases.
DOSES OF 200 TO 1,000 REMS: SURVIVAL POSSIBLE
12.116 For doses between 200 and 1,000 rems the probability of survival is good at the lower end of the range but poor at the upper end. The initial symptoms are similar to those common in radiation sickness, namely, nausea, vomiting, diarrhea, loss of appetite, and malaise. The larger the dose, the sooner will these symptoms develop, generally during the initial day of the exposure. After the first day or two the symptoms disappear and there may be a latent period of several days to 2 weeks during which the patient feels relatively well, although important changes are occurring in the blood. Subsequently, there is a return of symptoms, including fever, diarrhea, and a steplike rise in temperature which may be due to accompanying infection.
12.117 Commencing about 2 or 3 weeks after exposure, there is a tendency to bleed into various organs, and small hemorrhages under the skin (petechiae) are observed. This tendency may be marked. Particularly common are spontaneous bleeding in the mouth and from the lining of the intestinal tract. There may be blood in the urine due to bleeding in the kidney. The hemorrhagic tendency depends mainly upon depletion of the platelets in the blood, resulting in defects in the bloodclotting mechanism (see § 12.129). Loss of hair, which is a prominent consequence of radiation exposure, also starts after about 2 weeks, i.e., immediately following the latent period, for doses over 300 rems (Fig. 12.117).
12.118 Susceptibility to infection of wounds, burns, and other lesions, can be a serious complicating factor. This would result to a large degree from loss of the white blood cells, and a marked depression in the body's immunological process. For example, ulceration about the lips may commence after the latent period and spread from the mouth through the entire gastrointestinal tract in the terminal stage of the sickness. The multiplication of bacteria, made possible by the decrease in the white cells of the blood and injury to other immune mechanisms of the body, allows an overwhelming infection to develop.
12.119 Among other effects observed in Japan was a tendency to spontaneous internal bleeding toward the end of the first week. At the same time, swelling and inflammation of the throat was not uncommon. The development of severe radiation illness among the Japanese was accompanied by an increase in the body temperature, which was probably due to secondary infection. Generally there was a steplike rise between the fifth and seventh days, sometimes as early as the third day following exposure, and usually continuing until the day of death.
12.120 In addition to fever, the more serious cases exhibited severe emaciation and delirium, and death occurred within 2 to 8 weeks. Examination after death revealed a decrease in size of and degenerative changes in testes and ovaries. Ulceration of the mucous membrane of the large intestine, which is generally indicative of doses of 1,000 rems or more, was also noted in some cases.
12.121 Those patients in Japan who survived for 3 to 4 months, and did not succumb to tuberculosis, lung diseases, or other complications, gradually recovered. There was no evidence of permanent loss of hair, and examination of 824 survivors some 3 to 4 years later showed that their blood composition was not significantly different from that of a control group in a city not subjected to nuclear attack.
LARGE DOSE (OVER 1,000 REMS): SURVIVAL IMPROBABLE
12.122 Very large doses of wholebody radiation (approximately 5,000 rems or more) result in prompt changes in the central nervous system. The symptoms are hyperexcitability, ataxia (lack of muscular coordination), respiratory distress, and intermittent stupor. There is almost immediate incapacitation for most people, and death is certain in a few hours to a week or so after the acute exposure. If the dose is in the range from 1,000 to roughly 5,000 rems, it is the gastrointestinal system which exhibits the earliest severe clinical effects. There is the usual vomiting and nausea followed, in more or less rapid succession, by prostration, diarrhea, anorexia (lack of appetite and dislike for food), and fever. As observed after the nuclear detonations in Japan, the diarrhea was frequent and severe in character, being watery at first and tending to become bloody later; however, this may have been related to preexisting disease.
12.123 The sooner the foregoing symptoms of radiation injury develop the sooner is death likely to result. Although there may be no pain during the first few days, patients experience malaise, accompanied by marked depression and fatigue. At the lower end of the dose range, the early stages of the severe radiation illness are followed by a latent period of 2 or 3 days (or more), during which the patient appears to be free from symptoms, although profound changes are taking place in the body, especially in the blood-forming tissues. This period, when it occurs, is followed by a recurrence of the early symptoms, often accompanied by delirium or coma, terminating in death usually within a few days to 2 weeks.
EFFECTS OF RADIATION ON BLOOD CONSTITUENTS
12.124 Among the biological consequences of exposure of the whole body to an acute dose of nuclear radiation, perhaps the most striking and characteristic are the changes which take place in the blood and blood-forming organs. Normally, these changes will be detectable only for doses greater than 25 rems. Much information on the hematological response of human beings to nuclear radiation was obtained after the nuclear explosions in Japan and also from observations on victims of laboratory accidents. The situation which developed in the Marshall Islands in March 1954, however, provided the opportunity for a very thorough study of the effects of small and moderately large doses of radiation (up to 175 rems) on the blood of human beings (§ 12.103). The descriptions given below, which are in general agreement with the results observed in Japan, are based largely on this study.
12.125 One of the most striking hematological changes associated with radiation injury is in the number of white blood cells. Among these cells are the neutrophils, formed chiefly in the bone marrow, which are concerned with resisting bacterial invasion of the body. During the course of certain types of bacterial infection, the number of neutrophils in the blood increases rapidly to combat the invading organisms. Loss of ability to meet the bacterial invasion, whether due to radiation or any other injury, is a very grave matter, and bacteria which are normally held in check by the neutrophils can then multiply rapidly; the consequences are thus serious. There are several types of white blood cells with different specialized functions, but which have in common the general property of resisting infection or removing toxic products from the body, or both.
12.126 After the body has received a radiation dose in the sublethal range, i.e., about 200 rems or less, the total number of white blood cells may show a transitory increase during the first 2 days or so, and then decrease below normal levels. Subsequently the white count may fluctuate and possibly rise above normal on occasions. During the seventh or eighth weeks, the white cell count becomes stabilized at low levels and a minimum probably occurs at about this time. An upward trend is observed in succeeding weeks but complete recovery may require several months or more.
12.127 The neutrophil count parallels the total white blood cell count, so that the initial increase observed in the latter is apparently due to increased mobilization of neutrophils. Complete return of the number of neutrophils to normal does not occur for several months.
12.128 In contrast to the behavior of the neutrophils, the number of lymphocytes, produced in parts of the lymphatic tissues of the body, e.g., lymph nodes and spleen, shows a sharp drop soon after exposure to radiation. The lymphocyte count continues to remain considerably below normal for several months and recovery may require many months or even years. However, to judge from the observations made in Japan, the lymphocyte count of exposed individuals 3 or 4 years after exposure was not appreciably different from that of unexposed persons.
12.129 A significant hematological change also occurs in the platelets, a constituent of the blood which plays an important role in blood clotting. Unlike the fluctuating total white count, the number of platelets begins to decrease soon after exposure and falls steadily and reaches a minimum at the end of about a month. The decrease in the number of platelets is followed by partial recovery, but a normal count may not be attained for several months or even years after exposure. It is the decrease in the platelet count which partly explains the appearance of hemorrhage and purpura in radiation injury.
12.130 The red blood cell (erythrocyte) count also undergoes a decrease as a result of radiation exposure and hemorrhage, so that symptoms of anemia, e.g., pallor, become apparent. But the change in the number of erythrocytes is much less striking than that in the white blood cells and platelets, especially for radiation doses in the range of 200 to 400 rems. Whereas the response in these cells is rapid, the red cell count shows little or no change for several days. Subsequently, there is a decrease which may continue for 2 or 3 weeks, followed by a gradual increase in individuals who survive.
12.131 As an index of severity of radiation exposure, particularly in the sublethal range, the total white cell or neutrophil counts are of limited usefulness because of the wide fluctuations and the fact that several weeks may elapse before the maximum depression is observed. The lymphocyte count is of more value in this respect, particularly in the low dose range, since depression occurs within a few hours of exposure (§ 12.224). However, a marked decrease in the number of lymphocytes is observed even with low doses and there is relatively little difference with large doses.
12.132 The platelet count, on the other hand, appears to exhibit a regular pattern, with the maximum depression being attained at approximately the same time for various exposures in the sublethal range. Furthermore, in this range, the degree of depression from the normal value is roughly proportional to the estimated whole-body dose. It has been suggested, therefore, that the platelet count might serve as a convenient and relatively simple direct method for determining the severity of radiation injury in the sublethal range. The main disadvantage is that an appreciable decrease in the platelet count is not apparent until some time after exposure.
GENERAL CONSIDERATIONS
12.133 Thus far, blast, thermal, and (ionizing) radiation injuries have been considered separately, but combined injuries, from two or more of these causes, would probably be common as a result of a nuclear explosion. Combined injuries might be received almost simultaneously, e.g., from a single detonation without fallout, or separated in time by minutes to days, e.g., from a single detonation followed by fallout or from multiple detonations. Injuries may consist of any combination of blast, thermal, and radiation effects. Furthermore, such injuries may be influenced by other conditions that might be expected during or after a nuclear attack, e.g., malnutrition, poor sanitation, fatigue, and various other environmental factors. Current knowledge concerning combined injuries is derived mainly from studies of the Japanese victims of nuclear bombs and from laboratory and field tests with a variety of animals.
12.134 The contribution of combined injuries to overall mortality and morbidity in Japan has never been determined adequately, but two general impressions have emerged: the combination of mechanical (blast) and thermal injuries was responsible for the majority of deaths that occurred within the first 48 hours after the attacks, and delayed mortality was higher and complications were more numerous among burned people exposed to ionizing radiation than would have been anticipated in the absence of such radiation. In Hiroshima and Nagasaki, among those who survived for 20 days or more, about 50 percent of the people within 1.25 miles of ground zero received combined injuries, whereas the incidence was roughly 25 percent at distances from 1.25 to 3 miles from ground zero.
12.135 It should be recognized that the incidences of combined injuries in the two Japanese cities apply only to the particular circumstances of the nuclear explosions. The number and types of combined injuries will depend on the yield, height of burst, and the conditions of exposure. Air bursts, unaccompanied by fallout, with yields less than about 10 kilotons, would cause combinations of mechanical, thermal, and initial-radiation injuries. On the other hand, larger yields would be expected to produce a greater proportion of combined burn and mechanical injuries; initial-radiation injuries would be less significant in the surviving population. A nuclear explosion near (above or below) the surface would maximize radiation injuries due to fallout and in a large proportion of the casualties such injuries would be combined with mechanical and thermal effects. People who are outdoors and unshielded would have a greater probability of sustaining initial and/or fallout (residual) radiation injury in combination with flash burns than would those within buildings. In the latter case, burns would be minimized and combinations of mechanical and radiation injuries might be dominant.
12.136 No reliable criteria for incapacitation are known for persons receiving combined injuries. The available data do indicate, however, that individuals suffering such injuries that occur nearly simultaneously are unlikely to become casualties within a few hours, provided the individual injuries would not produce casualties if administered separately. Consequently, it is not unreasonable to make early casualty predictions for a single nuclear detonation on the basis of the most significant injury. If there is a substantial probability of another injury, this could contribute to combined injury and might result in increased casualties at later times.
12.137 The effects of combined injuries may be synergistic, additive, or antagonistic. That is to say, the overall response may be greater than, equal to, or less than, respectively, what would be predicted based on the assumption that the various injuries act independently of one another in producing casualties. Quantitative data from laboratory experiments suggests that in situations where a combined effect has been observed, the interaction of the various forms of injury has resulted in enhanced early as well as delayed mortality, although from the limited data available the latter seems to be the more common.
RADIATION AND THERMAL INJURIES
12.138 Exposure of laboratory animals to external ionizing radiation while subjected to thermal burn has been found to cause a substantial increase in mortality over that expected from the insults received separately. The extent of the increase depends on the radiation dose and the severity of the burn. Severely burned subjects exhibit some anemia and the body is less able to cope with this stress if the immune mechanism and the activity of the bone marrow are depressed by the ionizing radiation. The enhanced mortality from the thermal burns combined with radiation exposure was not observed for doses of 25 rems or less and it is improbable that the synergistic effect would occur unless the dose is large enough to produce at least minimal effect on the immunologic and hematologic systems. Very little information is available on fallout (internal) radiation in combination with thermal or any other form of injury.
MECHANICAL AND RADIATION INJURIES
12.139 Mechanical and radiation injuries can be expected to be frequent, particularly if fallout is present. Studies indicate that there is a delay in wound healing with doses in excess of 300 rems, and that wounds in irradiated subjects are considerably more serious if treatment is delayed for more than 24 hours. In addition, missile and impact injuries that result in disruption of the skin and damage to the soft tissues provide a portal of entry for infection, and thus may be extremely hazardous to irradiated people. Injuries that are associated with significant blood loss would be more serious in those who have received a radiation dose large enough to interfere with normal blood clotting mechanisms.
12.140 One week after exposure to an external radiation dose which would by itself have resulted in 45 percent mortality within 30 days, animals (rats) were subjected to a blast overpressure which would normally produce 5 percent early lethality. As a result, early lethality associated with blast-induced hemorrhage and lung injury was increased four fold and the delayed mortality was almost double that expected from the radiation alone. In these tests, ionizing radiation and blast were clearly synergistic in causing both early and delayed mortality.
THERMAL AND MECHANICAL INJURIES
12.141 Burns and mechanical injuries in combination are often encountered in victims of conventional explosions. Increased numbers of delayed complications, shorter times-to-death, and enhanced mortality rate are frequent occurrences. However, few quantitative data are available on this form of combined injury.
INTRODUCTION
12.142 There are a number of consequences of nuclear radiation which may not appear for some years after exposure. Among them, apart from genetic effects, are the formation of cataracts, non-specific life shortening, leukemia, other forms of malignant disease, and retarded development of children in utero at the time of the exposure. Information concerning these late effects has been obtained from continued studies of various types, including those in Japan made chiefly under the direction of the Atomic Bomb Casualty Commission.10
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10 The Atomic Bomb Casualty Commission (ABCC) of the U.S. National Academy of Sciences-National Research Council was sponsored by the U.S. Atomic Energy Commission (now the Energy Research and Development Administration) and administered in cooperation with the Japanese National Institute of Health. One of its purposes was to study the long-term effects of human exposure to nuclear radiation. In 1975, the ABCC was superseded by the Radiation Effects Research Foundation which is supported equally by Japan and the United States.
12.143 The effects which occur later in life, like the acute reactions observed within a few weeks or months after irradiation, arise from changes in cells and tissues at the time of exposure. If an exposed individual survives the acute reaction, cell replacement may be complete, but the cells may not necessarily be quite normal; however, the causes for the late effects are largely unknown although many theories have been proposed.
CATARACTS
12.144 The term "cataract" is commonly used to describe any detectable change in the normal transparency of the lens of the eye. Cataracts may range from small lesions, which cause only minor impairment of vision, to extensive opacification that results in total blindness. The vast majority of natural cataracts in man are of the senile form of arthritis known as ankylosing spondylitis. Three main types of leukemia are induced by radiation, namely, acute and chronic granulocytic and acute lymphocytic forms; the occurrence of chronic lymphocytic leukemia is not significantly increased by radiation. The development of leukemia as a result of an overexposure to radiation is associated with a latent period varying from one to 20 years or more. The disease is generally fatal, no matter what its cause.
12.148 The first evidence of an increased incidence of leukemia among the survivors of the Hiroshima and Nagasaki explosions appeared in 1947. The occurrence of the disease reached a peak in 1951 and 1952 and it has been declining since then. By the end of 1966, the frequency of acute granulocytic anemia was approaching the normal value for Japan. Children who were exposed to radiation when they w