the surface to 20,000 feet (6.10 km), ment from 20,000 to 70,000 feet and 90,000-foot for each 5,000-foot (1.52-km) 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 Radsafe Of- These were usually defined as locations where significant fallout could occur within 6 hours after detonation. 50-R (10-R for some shots) The plots were delineated by contours based upon the predicted infinite dose.* The radex areas were used to define dangerous areas and to deny entry to task force units into certain areas except by specific authorization. The surface radex area was constructed using the basic forecast hodograph limiting bearings of resultant winds to all significant levels. An additional 15° sector was added to each side of these limiting bearings to allow for diffusion, changes in the forecast wind pattern, and deviation from a point-source origin of fallout. sisted of two sectors. Usually, the radex area con- One defined the low-level trade wind portion of the cloud, and the other defined the midlevels. For all surface radex areas, the radial distance of the sectors was taken as that average distance representing 6 hours of particle fall at 5,000 ft/hr (1.52 km/hr). This established outer limits of surface contamination that considered the fall of particles of all sizes during the 6-hour period. The surface ra- dex was valid from H-hour to H+6 and revised as necessary when forecast winds changed. The forecast air radex areas were constructed in two regions describing the volumes of contaminated air above 10,000 feet (3.05 km) 40,000 feet (12.20 km). and above The first volume was needed for test and service aircraft operating in the shot area to assist them in avoiding contaminated regions. The second volume was primarily for use in cloud-sampling * The infinite dose is the dose from external sources that a person would receive by remaining within fallout contamination until it naturally decayed (that is, infinitely long). 115