Two types of burns were observed. These are generally differentiated
as flame or fire burn and so-called flash burn.
The early appearance of the flame burn as reported by the Japanese, and
the later appearance as observed, was not unusual.
The flash burn presented several distinctive features. Marked redness
of the affected skin areas appeared almost immediately, according to
the Japanese, with progressive changes in the skin taking place over a
period of a few hours. When seen after 50 days, the most distinctive
feature of these burns was their sharp limitation to exposed skin areas
facing the center of the explosion. For instance, a patient who had
been walking in a direction at right angles to a line drawn between him
and the explosion, and whose arms were swinging, might have burns only
on the outside of the arm nearest the center and on the inside of the
other arm.
Generally, any type of shielding protected the skin against flash
burns, although burns through one, and very occasionally more, layers
of clothing did occur in patients near the center. In such cases, it
was not unusual to find burns through black but not through white
clothing, on the same patient. Flash burns also tended to involve
areas where the clothes were tightly drawn over the skin, such as at
the elbows and shoulders.
The Japanese report the incidence of burns in patients surviving more
than a few hours after the explosion, and seeking medical attention, as
high as 95%. The total mortalities due to burns alone cannot be
estimated with any degree of accuracy. As mentioned already, it is
believed that the majority of all the deaths occurred immediately. Of
these, the Japanese estimate that 75%, and most of the reports estimate
that over 50%, of the deaths were due to burns.
In general, the incidence of burns was in direct proportion to the
distance from X. However, certain irregularities in this relationship
result in the medical studies because of variations in the amount of
shielding from flash burn, and because of the lack of complete data on
persons killed outright close to X.
The maximum distance from X at which flash burns were observed is of
paramount interest. It has been estimated that patients with burns at
Hiroshima were all less than 7,500 feet from the center of the
explosion at the time of the bombing. At Nagasaki, patients with burns
were observed out to the remarkable distance of 13,800 feet.