In less than one second, the fireball had expanded to 900 feet. The blast wave shattered windows for a distance of ten miles and was felt as far away as 37 miles. Over two-thirds of Hiroshima's buildings were demolished. The hundreds of fires, ignited by the thermal pulse, combined to produce a firestorm that had incinerated everything within about 4.4 miles of ground zero.
To the crew of the Enola Gay, Hiroshima had disappeared under a thick, churning foam of flames and smoke. The co-pilot, Captain Robert Lewis, commented, "My God, what have we done?"
About 30 minutes after the explosion, a heavy rain began falling in areas to the northwest of the city. This "black rain" was full of dirt, dust, soot and highly radioactive particles that were sucked up into the air at the time of the explosion and during the fire. It caused contamination even in areas that were remote from the explosion.