the test area to monitor exposure rates (1; 10).

Two members of the Site Monitoring Group, a monitor and a physician
with radiological safety training, were assigned to each shelter. The
supervising monitor was stationed at the Base Camp and was in radio
and telephone communication with all three shelters and the offsite
ground and aerial survey teams. Before any personnel were allowed to
leave the shelter areas, a radiological safety monitor and a military
policeman from each shelter advanced along the roads to Broadway to
check radiation levels. They wore respirators to prevent them from
inhaling radioactive material (1; 10).

Since it was expected that any dust from the cloud would fall on one
of the shelter areas within 30 minutes of the shot, plans had been
made to evacuate personnel as soon as the monitors completed their
initial survey. Because the cloud moved to the northeast, the south
shelter (the Control Point) was not completely evacuated, although
nonessential personnel were sent to the Base Camp. The west shelter
was emptied of all personnel except a searchlight crew spotlighting
the cloud as it moved away (1; 10).

Only at the north shelter did an emergency evacuation occur. About 12
minutes after the shot, a detection instrument indicated a rapid rise
in the radiation levels within the shelter. At the same time, a
remote ionization monitoring device detected a rapid increase in
radiation. Because of these two readings, all north shelter personnel
were immediately evacuated to the Base Camp, 25 kilometers to the
south. Film badges worn by personnel stationed at the north shelter,
however, showed no radiation exposure above the detectable level. It
was later discovered that the meter of the detector in the north
shelter had not retained its zero calibration setting, and radiation
at the north shelter had not reached levels high enough to result in
measurable exposures of the personnel who had been positioned there.
However, fallout activity was later detected in the north shelter
area, proof that part of the cloud did head in that direction. This
also explains why the monitoring device detected rising radiation
levels (1; 12).

After ascertaining that radiation levels along the roads leading from
the shelters to Broadway were within acceptable limits, the
radiological safety monitors and military police established
roadblocks at important intersections leading to ground zero. The
north s