SLIDE 6 Duration of fallout. Duration of fallout is defined as the time fallout begins up to the time of cessation. This should not be confused with the time fallout begins up to the time of evacuation which is much longer. Peterson's estimated duration of fallout of about 19 hours at Rongelap, appears to be too long relative to the known wind velocity moving the cloud past Rongelap (Cr56) and relative to the first-hand accounts of fallout duration given by the Marshallese evacuated from Rongelap Island (Sh57). Rongerik Atoll was 65 km (40 miles) further away from the detonation than wan Rongelap Atoll. An upper limit of 16 hours duration at Rongerik Atoll was estimated by Sondhaus. Fallout at the location of Sifo Island, Ailingnae Atoll was at the same distance from the detonation site as the Japanese vessel which was contaminated by BRAVO fallout. This fallout was named Bikini Ash by the Japanese. Bikini Ash granule size was visible to the eye (Su56) and was observed to fall for 5 hours (Ts55). Bikini Ash granule size is consistent with reports that fallout was visible at Rongelap, Rongerik and Ailingnae. Fallout would not have been visible at Utirik based on distance vs granule size extrapolations and fall velocity considerations. Visual observations of fallout arrival and cessation time were reported by many persons at each of these locations, (Sh57, Ts55) except Utirik, and were in reasonable agreement with Dunning's values. Lessard estimated duration time based on granule size of Bikini Ash, the relative positions of the atolls and the fishing vessel, and granule fall velocity estimates (Le84b). DURATION OF FALLOUT Hours Location of People Distance from Ground Zero 1956 Sondhaus 1957 Dunning 1981 Peterson Ailingnae Rongelap Rongerik 150 km 210 km 270 km 12 12 12 5.5 5.5 _ 10 19 17 5 7 9 Utirik 570 km 12 3 19 17 11 1984 Lessard