Company "B," of the 9812th Technical Service Unit, Army Corps of
Engineers. Military police cleared the test area and recorded the
locations of all personnel before the detonation.

A radiological monitor was assigned to each of the three shelters,
which were located to the north, west, and south of ground zero. Soon
after the detonation, the monitors surveyed the area immediately
around the shelters and then proceeded out the access road to its
intersection with the main road, Broadway. Personnel not essential to
postshot activities were transferred from the west and south shelters
to the Base Camp, about 16 kilometers southwest of ground zero.
Personnel at the north shelter were evacuated when a sudden rise in
radiation levels was detected; it was later learned that the
instrument had not been accurately calibrated and levels had not
increased as much as the instrument indicated. Specially designated
groups conducted onsite and offsite radiological surveys.

Safety Standards and Procedures

The safety criteria established for Project TRINITY were based on
calculations of the anticipated dangers from blast pressure, thermal
radiation, and ionizing radiation. The TR-7 Group, also known as the
Medical Group, was responsible for radiological safety. A limit of 5
roentgens of exposure during a two-month period was established.

The Site and Offsite Monitoring Groups were both part of the Medical
Group. The Site Monitoring Group was responsible for equipping
personnel with protective clothing and instruments to measure
radiation exposure, monitoring and recording personnel exposure
according to film badge readings and time spent in the test area, and
providing for personnel decontamination. The Offsite Monitoring Group
surveyed areas surrounding the test site for radioactive fallout. In
addition to these two monitoring groups, a small group of medical
technicians provided radiation detection instruments and monitoring.

Radiation Exposures at Project TRINITY

Dosimetry information is available for about 815 individuals who
either participated in Project TRINITY activities or visited the test
site between 16 July 1945 and 1 January 1947. The listing does not
indicate the precise military or unit affiliation of all personnel.
Less than six percent of the Project TRINITY participants received
exposures greater than 2 roentgens. Twenty-three of these
individuals received exposures greater than 2 but less t