reasonable agreement. These last two approaches were different from each other in that Sondhaus derived the estimate of whole-body dose from actual measurements of total exposure (film badges at Rongerik) and exposure rate, while the estimate using Bikini ash depended upon measurements of the composition of fallout and exposure rate. The approach used by Peterson depended on upper-air wind level patterns and the fallout was estimated by him to drift back in a southerly fashion. This was not in agreement with assumptions regarding wind level patterns which were used in three previous and independent approaches (Ha79). The Peterson results for whole-body dose were radically different from other esti- mates for Rongerik and Utirik people and do not coincide with measured values for exposure and exposure rate (Sh57). 3. Duration of Fallout. Duration of fallout is defined as the time fall_out begins up to the time of cessation (not to be confused with the time of evacuation, which was much later). Peterson's estimated duration of fallout (see Table 3) of about 19 hours at Rongelap appears to be too long relative to the reported 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). An upper limit of 16 hours' duration at Rongerik Atoll, estimated by Sondhaus, was based on the assumption of a constant rate-of-rise of exposure rate. The exposure-rate datum used to indicate cloud passage was the offscale reading of >100 mR h7! at 7 hours and 22 minutes post~detonation 270 km (170 miles) away from Bikini Atoll. Estimates of fallout duration time by Peterson, Sondhaus, and Dunning and those estimated by us are tabulated in Table 3 for comparison. Sifo Island, Ailingnae Atoll, was the same distance from the detonation site as the Japanese vessel contaminated by Bikini ash (BRAVO fallout). Bikini ash was observed to fall for 5 hours (Ts55). Bikini ash granule size was visible to the eye ($u56), which at this location was consistent with reports that fallout was visible at Rongelap, Rongerik, and Ailingnae. Visual observations of Table 3 Duration of Fallout, Hours Location of People Ailingnae Ronge lap Rongerik Utirik Distance From the Detonation Site, km 150 210 270 570 Fallout Duration Estimated by Sondhaus 1955 (S055) 12 12 12 12 Fallout Duration Estimated by Dunning 1957 (JCAES7) 5.5 5.5 17 Fallout Duration Estimated by Peterson 1981 Fallout Duration Estimated Here 1984 (Pe81) (This Report) 10 19 17 3 5 7 9 19