. Sx IWoI SF [EP ag different heights, it is impossible to apply a@ single fallout pattern to all detonations, The area of signif icdnt contamination will be largely dependen: upon the yield of the bé@mb. Its location, with regard to ground zero, and its widih and length, will be determined by the resultant direction andivelocity of the winds at various heights and distances. In generg@l terms it will be an elongated cigar-shaped area extending "downwind" from the point of burst. It i8 obvious that dimensions depend upon Bo many uncertainties as to preclude precise predictions.| Realistic assumptions, however, based on experimental data From the Pacific Proving Grounds provide an adequate basis for civil defense planning for operational preparedness. The thermonuclear bomb fired at the Bikin¥ Atoll on March 1, 1954, resulted in an area of contamination (1@0 roentgens or more cumulative dose 24-48 hours after the detonation) of nearly 14,000 square miles with the heaviest concentratJon falling on the central portion of the ellipse extending som@ the point of burst. distance from Some of the early fallout fgom this explosion occurred in the form of a fine dust which lookedJlike snow. On the inhabited islandgabout 170 miles down-wind,Jthe fallout began about eight hours after the detonation and contigued for several hours, On the basis of gamma dose radiation effeBt, the March 1, 1954 explosion heavily contaminated (500 roentgehhs or more cumulative dose 24-48 hours after the detonation) extending approximately 160 miles down-wind and width. an area bp to 40 miles in On the same basis and with the assumptidh of no shelter or other protective measures, it has been estimated that in a down- Wind belt about 140 miles long and up to 20 milds wide the residual radiation would have been fatal to neawly all persons 8 Ubeadr SFISD DOE ARCHIVES