Fallout from the stem starts building after about 10 minutes. This is the prime threat to rescue crews. The affected area would have a radius of about 6.5 miles with a hot spot a distance downwind that depends on the wind velocity (the dashed circle). If there is a 15-mph wind from the southwest, an area of about 1 square mile—the solid ellipse shown–would cause an average exposure of 300 rems in the first hour. The larger toned ellipse shows an area of 150 rems in the first hour.
