the surface to 20,000 feet (6.10 km), for each 5,000-foot ment from 20,000 to 70,000 feet and 90,000-foot (1.52-4km) incre=- (6.10 to 21.30 km), and for the [80,000- (24.40- and 27.40—-km) levels. Radex Areas Radiological exclusion fice. (radex) areas were determined by the These were usually defined as locations where significan could occur within 6 hours after detonation. adsafe Offallout The plots were delfineated by 50-R (10-R for some shots) contours based upon the predicted inffinite dose.* The radex areas were used to define dangerous areas and to deny ntry to task force units into certain areas except by specific authoriz ion. The surface radex area was constructed using the basic fore st hodo- graph limiting bearings of resultant winds to all significant lefels. An additional 15° sector was added to each side of these limiting bBarings to allow for diffusion, changes in the forecast wind pattern, an tion from a point-source origin of fallout. sisted of two sectors. Usually, the radex deviarea con- One defined the low-level trade wind porfion of the cloud, and the other defined the midlevels. For all surface] radex areas, the radial distance of the sectors was taken as that aver ge distance representing 6 hours of particle fall at 5,000 ft/hr (1.52 km/hr). This established outer limits of surface contamination that cons dered the fall of particles of all sizes during the 6-hour period. The su fface ra- dex was valid from H-hour to H+6 and revised as necessary when fprecast winds changed. The forecast air radex areas were constructed in two regions describ- ing the volumes of contaminated air above 10,000 feet (3.05 km) 40,000 feet (12.20 km). The first volume was needed for test an nd above service aircraft operating in the shot area to assist them in avoiding cq ntaminated regions. The second volume was primarily for use in cloud; sampling * The infinite dose is the dose from external sources that a per on would receive by remaining within fallout contamination until it nat rally decayed (that is, infinitely long). 115 40