2.3 On-Site Fall-out Fall-out on Eniwetok and Parry islands was observed only once from devices fired etok Atoll. Approximately two hours after detonation 0 on - m Eberiru Island, an increase in background was noted The fall-out, which was light, continued for approximately one hour. Peak intensity, reached at the end of the fall-out, was 22 mr/hbr. Rain showers later in the day effectively removed most of the contamination. The only significant fall-out observed on Eniwetok and Parry islands during the operation resulted from the vice fired on Bikini Atoll. The fall-out on Eniwetok comm mately nine hours after the device was fired. Two peak intensities in air concentration were observed, as shown in Fig. 2.11. The increase in the background was quite rapid, with a peak of 100 to 120 mr/hr throughout Parry Island. During the fall-out period, which lasted approximately 17 hr, several rain showers occurred; rain samples assayed showed counts in exceas of 5,000,000 disintegrations per minute per liter. The gamma background level fell off quite rapidly once the fall-out ceased. It is to be noted in Fig. 2.11 that the background decay was much more rapid than that. expected from the normal exponential decay until H+48 hr and later. Clean-up operations after the fall-out were conducted around living and recreation areas. As a result of the rain showers, hot spots were found around each building where rain runoff collected. These hot spots, along with other contamination on the surface, were most effectively reduced by using bulldozers, road scrapers, and hand-grading operations to turn the sand. The decontamination efforts were successful in reducing the level to such that no one exceeded the 300 mr/week tolerance level. Most serious effect of the fall-out was delay of the roll-up operations. Initially, personnel from H&N whose dosage records indicated that they were near the limits of 3.9 r were flown out to Bikini to remove them from the contaminated area. Generally, people in this category were urgently required for roll-up, Accordingly, the maximum permissible exposure for the operation was raised to 7 r. This allowed roll-up to proceed without further delay. On the average, the dosage received by any one individual on Eniwetok or Parry islands as a result of the fall-out varied from 2 to 3.5 r, depending on the length of stay of the individual and the type of work in which he was engaged. In general, those working in jobs requiring them to remain outdoors during working hours were at the upper end of the dosage spread. During the actual fall-out period, personnel were requested to remain indoors as much as possible and to take full advantage of shower facilities. Of interest is the fact that no evidence of gross personnel contamination was observed as a result of this fall-out. - 26 -