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 shelter monitor and military police set up a post where the
North Shelter Road ran into Broadway. The west shelter monitor and a
military policeman blocked Vatican Road where it intersected Broadway.
The south shelter monitor and military police set up a roadblock where
Broadway intersected Pennsylvania Avenue (1).

The monitor assigned to Guard Post 4 surveyed the Mockingbird Gap area
to ensure that it was safe for the guards to return to their post.
This position controlled access to the McDonald Ranch Road, which led
directly to ground zero (1).

At 0540 hours, the chief monitor departed from the Base Camp with a
military policeman to monitor the entire length of Broadway. They