that provided considerable shielding. Unshielded participants were customarily positioned much further away from ground zero. 5.2 PROTECTION AGAINST RESIDUAL RADIATION. Procedures for protection against residual radiation were more complex because operations in a contaminated environment involved potential exposure to radiation sources both external to and inside the body, the latter resulting primarily from inhalation or ingestion of radioactive material. The next sections address these protective measures. 5.2.1 Identification and Control of Radiation Areas. The fundamental approach for protection against residual radiation was to control access to contaminated areas. Obviously, the first step was the identification of the radiation areas and quantification of the radiation therein. In all cases, authorized entry into a radiation area was made through a control point and preceded by some form of survey by trained radiation monitors using state-of-the-art radiation detection and measurement equipment. In the case of a military maneuver, radiation monitors preceded the advancing troops to steer them away from radiation areas contaminated above pre-established limits. Re-entry into the shot area by scientific project personnel or military troops visiting a display area normally was delayed until a "Recovery Hour" was declared after completion of an initial radiation survey of the area. The initial survey team used radiation detectors to locate and mark various radiation intensities approaching the detonation site. In some cases, early entry was authorized for certain scientific project personnel; however, these personnel were accompanied by their own radiation monitors. The radiation levels measured by these monitors were used to determine the amount of time the participants could remain in the area. "Stay times" were calculated and observed to ensure that external gamma radiation exposure limits were not exceeded. Only gamma radiation was considered for this purpose since normal clothing provided adequate protection against external alpha and beta radiation exposure. 144 6/