2.3
On-Site call-out
Fall-out on Entwetok and Parry islands was observed only once from
devices fired at Eniwetok Atoll. Approximately two hours after detonation of
thef_ Mohawk}device on Eberiru Island, an increase in background was noted
on Parry fsland. The fall-out, which waa light, continued for approximately
one hour, Penk Intensity, reached at the end of the fall-out, was 22 mr/hr.
Ruin showers later tn the day effectively removed most of the contamination.
The onlv significant fall-out observed on Eniwetok and Parry islands
during the operation resulted from the (__ TEWA
“device fired on Bikini
Atoll, The fall-out on Eniwetok commenced approxffmately nine hours after
the device was fired. Two peak Intensities in air concentration were ob-
served, ay 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 oc-
curred; rain samples assayed showed counts in excess of 5,000,000 disintegrations per minute per Hter.
The gamma background Ievel fell off quite rapidly once the fall-out
ceased. It Is to be noted in Fig. 2.12 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 tall-out were conducted around living and
recreation areas.
As a result of the rain showers, hot spots were found
around cach building where rain runoff collected. These hot spots, along
with other contamination on the surface, were most effectively reduced by
using bulldozers, read scrapers, and hand-grading operations to turn the sand.
The decontamination efforts were successful in reducing the level to such
that no ons exceeded the 300 mr/weck 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 Ilmits of 3.9 > were flown out to Bikini to remove them fror. 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 tndividual on Eniwetok
or Parry Islands as a result of the fall-out varied from 2 to 3.5 r, depend-
ing 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 houra were at the upper end of the dosage spread.
During the actual fall-out period, personnel were requested to remain
indoors ag much as possible and to take full advantage of shower facllitics.
Of interest is the fact that no evidence of grossa personnel contamination was
observed as a result of this fall-out.
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