The atomic explosion created the super-high pressure of several hundred thousand atmospheres. The surrounding air expanded enormously,generating a powerful blast. 　The blast comprised a shock wave （the leading edge moving at supersonic speed）and the blast wind that fol- lowed it. Approximately 10 seconds after detonation, the blast had traveled 3.7 kilmeters. The pressure was im- mense, 15 tons per square meter as far away as 500 meters from the hypocenter. 　When the blast subsided, the air pressure in the center area was extremely low, and air rushed back from sur- rounding areas toward the point of explosion. 　In the area from the hypocenter out to a 2-kilometer radius, wooden structures were mostly destroyed. Though ferro-concrete structures remained standing, they were severely damaged, all windows shattered, interiors com- pletely gutted by fire. 　Many people were knocked unconscious and injured when lifted and blown through the air. Others were crushed under collapsing buildings.