4. DAMAGE FROM HEAT RAYS

At the moment of the explosion a fireball was generated with a center which reached a temperature of several million degrees Celsius. The heat rays released in all directions had a strong effect on the ground for about three seconds, starting approximately 1/100 second after the detonation. Due to the heat rays, the temperature in the hypocenter area is believed to have reached 3,000-4,000 degrees Centigrade (Iron melts at 1,536 degrees).

Up to approximately 600 meters from the hypocenter, the heat rays caused bubbles to form in ceramic roof tiles. The surface of granite stones within one kilometer were bleached white and became rough from the popping of quartz in the stone.

About 1.8-2.0 km from the hypocenter, clothes of persons outdoors and laundry drying in the sun spontaneously combusted. Railroad ties and wooden fences along railroads up to 2.1 km from the hypocenter spontaneously ignited and burned. Thatched roofs caught fire and went up in flames up to about 2.5 km from the hypocenter. There was also spontaneous combustion of trees in parks and other locations. Many old and huge trees burnt from the inside, and were left standing with only the exterior of the trunks remaining.

Shadow of Rail on Yorozuyo Bridge
The heat rays cast a permanent shadow of the bridge's rail on the asphalt. Shadows of carts and people were also left behind. (850 meters from hypocenter. Photograph by U.S. Army, around November 1945.)

Person's Shadow on Stone
This shadow was made by a person sitting on the steps in front of the bank entrance waiting for it to open. The victim was probably hit by the flash from the front. dying on-the-spot. The surface of the surrounding stone was significantly whitened by exposure to the bombs heat rays, but the place where the person sat remained dark.

(Approximately 260 meters from hypocenter. Courtesy of the Hiroshima Branch of the sumitomo Bank.)