Hiroshima Peace Memorial Museum Outline



August 6, 1945

Hiroshima in ruins

The atomic bomb was dropped at 8:15 a.m. August 6, 1945. It exploded with a blinding flash approximately 580 meters above the center of the city. The white-hot fireball was described as a small sun. It is estimated that about 350,000 people were in Hiroshima at the time. This number included some tens of thousands of Koreans and Chinese, including forced laborers. Exchange students from Southeast Asia and American prisoners of war were also among the victims.

One second after detonation, the fireball was 280 meters in diameter. The temperature at the center was over one million degrees centigrade. The heat emitted by that fireball raised surface temperatures near the hypocenter to 3,000 to 4,000 degrees centigrade.

Five hundred meters from the hypocenter, the blast pressure was 19 tons per square meter. The maximum wind speed was 440 meters per second. This blast simply crushed all wooden buildings within a radius of two kilometers.

The fire that swept the city after the heat, blast and radiation left nothing but burnt rubble. By the end of December that year, 140,000 victims were dead. This panorama is a 1000-to-1 scale model of Hiroshima extending out to a radius of 2,750 meters from the hypocenter. As you can see, the vast majority of buildings were crushed and burned. The cloud that billowed up after the explosion climbed 12,000 meters into the sky. In this model, the cloud would be 12 meters high. Under that giant mushroom cloud, tens of thousands of lives were lost instantly to the complex interaction of heat, blast, and radiation, followed by a city-wide fire. Destruction spread on an unprecedented scale.