Protecting the People

The Medical Group was divided into two monitoring groups, the Site Monitoring Group, which was responsible for onsite monitoring, and the Offsite Monitoring Group.

Continuing The First Atomic Bomb,
our selection from Project Trinity 1945-1946 by Carl Maag and by Steve Rohrer published in 1982. The selection is presented in nine installments for 5-minute daily reading. For works benefiting from the latest research see the “More information” section at the bottom of these pages.

Previously in The First Atomic Bomb.

Time: July 16, 1945
Place: Old McDonald Ranch House, New Mexico

Chapter 3 Radiation Protection at Project Trinity

The TR-7 or Medical Group, shown in the figure 1-5 organizational chart, was responsible for radiological safety at Project TRINITY. Many of the physicians and scientists in the Medical Group had worked with radioactive materials before and were trained in radiological safety procedures. The Chief of the Medical Group supervised the radiological safety operations and reported to the TRINITY director. In addition to providing medical care to TRINITY personnel, this group established radiological safety programs to:

• Minimize radiation exposure of personnel on the test site and in offsite areas
• Provide monitors to conduct radiological surveys onsite and offsite
• Provide and maintain radiation detection instruments
• Provide protective clothing and equipment.

An exposure limit of 5 roentgens during a two-month period was established. Personnel were provided with radiation detection instruments to determine their exposures. [1]

3.1 Organization

The Medical Group consisted of physicians, scientists, and administrators, as well as radiological monitors. Many of these personnel were nonmilitary, but all worked on the Manhattan Project under the administration of the Army Corps of Engineers Manhattan Engineer District.

The Medical Group was divided into two monitoring groups, the Site Monitoring Group, which was responsible for onsite monitoring, and the Offsite Monitoring Group. Each reported to the Chief of the Medical Group, and each communicated with the other during the monitoring activities. In addition to these two groups, a small group of medical technicians provided radiation detection instruments to Medical Group personnel. [1; 10]

3.2 Site Monitoring Group

The Site Monitoring Group consisted of a chief monitor, three other monitors, and several medical doctors. This group had the following functions: [1; 10]

• Conduct ground surveys of the test area and mark areas of radioactivity
• Conduct surveys of the Base Camp and roads leading into the test area
• Provide protective clothing and equipment, including film badges and pocket dosimeters, to personnel
• Monitor all personnel for radioactive contamination and provide for their decontamination
• Maintain a record of radiation exposures received by personnel.

The Site Monitoring Group monitored the radiation exposures of personnel in the test area. The time spent by personnel in radiation areas was limited, and radiation detection instruments were provided to permit continuous monitoring of exposure rates. In many cases, a monitor from the Site Monitoring Group accompanied project personnel into 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 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 first checked the roadblock at Pennsylvania Avenue and Broadway. Next they drove to the roadblock at Vatican Road and Broadway. Upon the chief monitor’s arrival, the west shelter monitor traveled about nine kilometers west on Vatican Road to monitor Guard Post 1 so that the military police could reoccupy the post. The monitoring excursion to Guard Post 1 continued until the chief monitor had returned from Guard Post 2, located 17 kilometers northwest of the Vatican Road roadblock on Broadway. [1; 18]

SOURCES CITED ON THIS PAGE

[1. Aebersold, Paul. July 16th Nuclear Explosion-Safety and Monitoring of Personnel (U). Los Alamos Scientific Laboratory, Atomic Energy Commission. Los Alamos, NM.: LASL. LA-616. January 9, 1947. 170 Pages.]

[10. Hempelmann, L. H., M.D. {Extracts from: “Preparation and Operational Plan of Medical Group (TR-7) for Nuclear Explosion 16 July 1945.”} Los Alamos Scientific Laboratory, Atomic Energy Commission. Los Alamos, NM.: LASL. LA-631(Deleted). June 13, 1947. 32 Pages.]

[12. Lamont, Lansing. Day of TRINITY. New York, NY.: Atheneum. 1965. 331 Pages.]

[18. Warren, S. L., COL, USA; Hempelmann, L. H., M.D. Extracts from: Personal Notes, Subject: Events in Camp Immediately Following Shot–July 16, 1945. 1945. 2 Pages.]

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