The General Effects of the Atomic Bombs produced flash burns on victims. The flash of the explosion, which was extremely brief, emitted radiant heat travelling at the speed of light. Flash burns thus followed the explosion instantaneously. The fact that relatively few victims suffered burns of the eyeballs should not be interpreted as an indication that the radiant heat followed the flash, or that time was required to build up to maximum heat intensity. The explanation is simply that the structure of the eye is more resistant to heat than is average human skin, and near ground zero the recessed position of the eyeball offered protection from the overhead explosion. Peak temperatures lasted only momentarily.
Survivors in the two cities stated that people who were in the open directly under the explosion of the bomb were so severely burned that the skin was charred dark brown or black and that they died within a few minutes or hours.…
Because of the brief duration of the flash wave and the shielding effects of almost any objects—leaves and clothing as well as buildings—there were many interesting cases of protection. The radiant heat came in a direct line like light, so that the area burned corresponded to this directed exposure. Persons whose sides were toward the explosion often showed definite burns of both sides of the back while the hollow of the back escaped. People in buildings or houses were apparently burned only if directly exposed through the windows. The most striking instance was that of a man writing before a window. His hands were seriously burned but his exposed face and neck suffered only slight burns due to the angle of entry of the radiant heat through the window.
Flash burns were largely confined to exposed areas of the body, but on occasion would occur through varying thicknesses of clothing. Generally speaking, the thicker the clothing the more likely it was to give complete protection against flash burns. One woman was burned over the shoulder except for a T-shaped area about one-fourth inch in breadth; the T-shaped area corresponded to an increased thickness of the clothing from the seam of the garment. Other people were burned through a single thickness of kimono but were unscathed or only slightly affected underneath the lapel. In other instances, skin was burned beneath tightly fitting clothing but was unburned beneath loosely fitting portions. Finally, white or light colors reflected heat and afforded some protection; people wearing black or dark-colored clothing were more likely to be burned.
…Comparatively few instances were reported of arms or legs being torn from the body by flying debris. Another indication of the rarity of over-pressure is the scarcity of ruptured eardrums. Among 106 victims examined by the Japanese in Hiroshima on 11 and 12 August, only three showed ruptured eardrums.…
Injuries produced by falling and flying debris were much more numerous, and naturally increased in number and seriousness nearer the center of the affected area. The collapse of the buildings was sudden, so that thousands of people were pinned beneath the debris. Many were able to extricate themselves or received aid in escaping, but large numbers succumbed either to their injuries or to fire before they could be extricated. The flimsiness of Japanese residential construction should not be allowed to obscure the dangers of collapse; though the walls and partitions were light, the houses had heavy roof timbers and heavy roof tiles. Flying glass from panels also caused a large number of casualties, even up to 15,000 feet from ground zero.
The number of burns from secondary fires was slight among survivors, but it was probable that many of the deaths in both cities came from the burning of people caught in buildings. Eyewitness accounts agree that many fatalities occurred in this way, either immediately or as a result of the lack of care for those who did extricate themselves with serious burns. There are no references, however, to people in the streets succumbing either to heat or to carbon monoxide as they did in Tokyo or in Hamburg, Germany. A few burns resulted from clothing set afire by the flash wave, but in most cases people were able to beat out such fires without serious injury to the skin. The flash burns produced by the General Effects of the Atomic Bombs were indeed of immense consequence.