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CHAPTER4
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DISCUSSION. AND CONCLUSIONS
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DISCUSSION
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The evaluation of the acute hazard from inhaling radioactive fall-out materials following
atomic explosions requires careful consideration of numerous physical and physiological
phenomena. Among the physical factors the more important are (1) the quantity of radioactive
material produced, governed by (a) type of detonation (high altitude, tower, surface, or subsurface) and (b) yield of the weapon, usually expressed as equivalent kilotons of TNT; (2) the
inhalability of the radioactive material, dependent upon (a) the mean physical density of the
particulate material, (b) the electrical charge on the particles in respect to their tendency to
form aggregates or to remain dispersed, and (c) the amount of radioactivity in fall-out parti-
clea of the respirable particle-size range (0.1 to 5.0 y); (3) the duration of exposure as deter-
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mined by (2) wind speed and direction, (b) distance {rom Ground Zero, and (c) meteorological
“shear” effects; and (4) the effective radiation life span of these inhaled particles as governed
by their chemical nature and derivation from (2) mixed fission products and (b) activation of
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soil, water, or man-made structures at and adjacent to Ground Zero.
The more important physiological factors which are pertinent in evaluating the acute inhatation hazard from fall-out include (1) the filtering effect of the upper respiratory passages
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in preventing large particles from entering the lungs and (2) the physiological defense mechanisms which are involved in clearance of foreign particles from the respiratory passages.
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These include the reflex mechanisms of coughing and sneezing, ciliary activity of cells lining
the respiratory tree, and the phagocytic action of bronchiolar and alveolar histiocytes. In ad-
dition, the dilation of blood vessels in response to irritants results in transudatiun of fluid to
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dissolve and remove by absorption any soluble particles and increased mucous secretion to
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mobilize and float away insolubles.
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Before one can state that 2 certain level of alr-borne radioactivity may present a hazard,
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it 9 necessary to define what is meant by the term “hazard” and to make a distinction between
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criteria were established by the Jangie Feasibility Committee.'' The criteria, applying to the
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short- and long-term hazards. Prior to Operation Buster-Jangle (1951), radiological-safety
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inhalation hazard as well as other aspects of radiological safety, were designed to apply to
peacetime nuclear weapons testing and not to the more serious situation which could be expected in the event of nuclear warfare, The following limiting values applicable to the inhalation of fall-out material were used: (1) The average air concentration of fall-out particles
during the first 24 hr should not exceed 100 pe/m?, (2) any portion of that value which is of
respirable particle size should not exceed { c/m', and (3) no single particle should exceed
107° pe measured at H+4 hr. These limiting values were designed to prevent the public from
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exposure to falI-out which could conceivably result in long-termradiation injury to the lungs
and other internal organs. Studies by the Los Alamos off-site air-sampling group" made dur-
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in particles found in alr samples (cascade-impactor data) are only a few per cent of the ac-
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ing the Nevada tests in 1951 through 1953 have demonstrated that the amounts of radioactivity
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