SECTION 5 RADIATION SAFETY AT THE ATMOSPHERIC NUCLEAR TESTS The possible hazards associated with exposure to ionizing radiation were a major concern to the planners of the nuclear tests. Consequently, many of the Nation’s leading experts on the subject were consulted and often served as staff members for each operation. A Health Group consisting of 35 personnel was established for Shot TRINITY, detonated on 16 July 1945 as the first test of a nuclear weapon. The group was headed by Dr. Louis Hempelmann, Medical Director of the Los Alamos National Laboratory; he reported to the test director, Dr. Kenneth T. Bainbridge. Colonel Stafford Warren, medical advisor to the Commanding General of the Manhattan Project, served as a special consultant. The primary function of the group was to provide for the safety of project personnel, as well as offsite citizens. This emphasis on radiation protection was evident throughout the nuclear test program. Some nuclear test participants were exposed to initial radiation (neutron and gamma rays) emitted from the fireball and the cloud column during the first minute after the detonation. Others were exposed to residual radiation, which is emitted primarily by radioactive fission products and other bomb debris in fallout and by neutron-induced radioactivity in the soil and structures in proximity to the detonation. The following sections discuss general protective procedures against initial and residual radiation, with the emphasis on residual radiation. The references are listed in chronological order according to series and given at the end of the chapter. 5.1 PROTECTION AGAINST INITIAL RADIATION. Protection from initial radiation was provided by ensuring that test participants were positioned at a safe distance from the detonation. The safe distance was usually calculated from empirically or theoretically derived equations that considered such factors as the type or design of the nuclear device, the expected yield of the device, environmental conditions including humidity, and any shielding between the detonation and the participant. For several of the CONUS tests, for example, military maneuver and observer troops were situated in trenches that were 3.2 to 4.6 kilometers from ground zero and 143 Le