6.1 6.11 Introduction Significance of the 1 March Shot The events following the first shot detonated at the Pacific proving grounds in 1954, described in this report, served to emphasize new problems resulting. from the use of atomic weapons. These different effects, the importance of which was only vaguely appreciated before, were brought into sharp focus by the present episode. In this chapter the medical problems associated with the use of atomic weapons or nuclear reactor accidents will be discussed. In particular, the problems associated with large scale fallout, as they were brought out in the present experience and as they may pertain to the thinking and planning of civil defense, the military and industries employing nuclear power will be discussed. Human radiation injury resulting from exposure to fallout and other nuclear radiations will be described, as well as current thought on the diagnosis and treatment of the disease states resulting from exposure to these radiations. dent reported here are not necessarily typical of potential fallout situations in the future. It is clear, however, that the cardinal effects to be expected from fallout radiations, as exemplified by the events described in this report, are clearcut and can be predicted with a reasonable degree of assurance. In particular, this accident has emphasized the particulate nature of the fallout material that renderedit visible in many areas. It should not be inferred that serious fallout will necessarily be visible under other conditions of detonation. Also, the chemical nature of the material (calcium oxide) will be encountered in only limited areas of the world. Although, as stated in Chapter IIT, the chemical action of the fallout material was considered to have contributed little or none to the effects seen, the degree of adhesiveness of the material to skin and hair might be quite different with different fallout material, and in a colder climate where sweating would be minimal. Extrapolation of the Present Findings to More General Situations 6.2 It must be emphasized that the large experimental nuclear device, the detonation of which led to the exposure of humanbeingsto fallout radiations, was exploded close to the ground on a tropical coral atoll under geologic and geographic conditions that are significantly different from most populated areas of the world. Eachof these conditions, i. e., size of weapon, height of burst, type of terrain, weather conditions, presence or absence of water under or nearthe burst will obviously influence markedly the rate and extent of contamination by fallout, and the particle size and chemical nature of the fallout material. These factors have been discussed in official releases (1-4). It follows, therefore, that the events observed in the acci- 6.21 6.12 The Effects of Kiloton Weapons Blast and Thermal Effects Before the problemsof fallout associated with megaton weapons are discussed in detail, the medical effects of kiloton weapons will be reviewed briefly for contrast. The effects of such weapons have been considered chiefly in the context of the nominal or 20 KT weapondetonated high in theair. (5). The blast and heat effects have been treated thoroughly by Oughtersen et al. (6) and little additional comment is required here. Blast and heat accounted for the vast majority of serious casualties in the Hiroshima and Nagasaki incidents. It should be pointed out, however,that in cities with more substantial dwellings than were present in 95