Immediately after the shot, Medical Group personnel began the radiological monitoring activities described in section 3.1.2. At 0815, when most of the monitoring activities were completed, preparations began for entrance into the ground zero area. To regulate entry into the area, a "Going-in Board" was established, consisting of Dr. Bainbridge, the Chief of the Medical Group, and a special scientific consultant. Its purpose was to determine whether a party had a valid reason for entering the ground zero area. The board functioned for three days. Military police at Guard Post 4 and at three roadblocks set up along Broadway controlled entry into the area. Guard Posts 3, 5, 6, and 7 were within 3,000 meters of ground zero and thus remained unmanned. At the south shelter, the Medical Group set up a "going-in" station where personnel were required to stop to put on protective clothing (coveralls, booties, caps, and cotton gloves) and pick up monitoring equipment before entering the ground zero area. Since it was not known how much radioactive material might be suspended in the air, all personnel entering the ground zero area wore complete protective covering and respirators for the first three days after the detonation. Figure 2-6 shows two Project TRINITY personnel wearing protective clothing (1). On the day of the shot, five parties entered the ground zero area. One party consisted of eight members of the earth-sampling group. They obtained samples by driving to within 460 meters of ground zero in a tank specially fitted with rockets to which retrievable collectors were fastened in order to gather soil samples from a distance. This group made several sampling excursions on 16 and 17 July. The tank carried two personnel (a driver and a passenger) each trip. No member of this party received a radiation exposure of more than 1 roentgen (1). Five other men from the earth-sampling group entered the ground zero area in a second tank, lined with lead for radiation protection. The tank, carrying the driver and one passenger, made five trips into the ground zero area to retrieve soil samples on 16 and 17 July. On two trips, the tank passed over ground zero; on the others, it approached to within about 90 meters of ground zero. The men scooped up soil samples through a trap door in the bottom of the tank. One driver who made three trips into the ground zero area received the highest exposure, 15 roentgens (1). This lead-lined tank was also used by ten men to observe the radiation area. These men, traveling two at a time, made five trips into the area on shot-day but never approached closer than 1,370 meters to ground zero. The highest exposure among these ten men was 0.3 roentgens (1).