brightness of the fireball does not vary greatly with the yield of the
weapon, the yield does dictate the duration of the fireball. The heat
radiated from the fireball contributes to the overall damage caused by
a nuclear burst by igniting combustibles and thus starting fires in
buildings and forests. These fires may spread rapidly among the
debris produced by the blast. In addition, this heat can cause skin
burns to exposed individuals at great distances from ground zero. The
distance to which this effect will cause injury, however, depends
highly on the weather and the terrain. Conditions of limited
visibility reduce the heat effect significantly from what it would
have been in clear weather.
The fireball formed at the instant of a nuclear detonation is a source
of extremely bright light. This light can cause temporary or
permanent blindness. Temporary blindness from a burst during daylight
should be of very short duration and is not an important consideration
for individuals other than aircraft crewmen. This loss of vision at
night will last for longer periods because the eyes will have adapted
to the dark. Recovery, however, should be complete within 15 minutes.
The light flash can cause permanent injury to the eye because of burns
within the eye itself, but this is likely to occur only in those
individuals who happen to be looking directly at the fireball at the
instant of detonation.
Nuclear radiation is a form of electromagnetic energy that is
beneficial in small doses, such as in medicine. In massive doses, as
Initial Nuclear Radiation.
Radiation emitted within the first minute after detonation is the
gamma rays. Both neutrons and gamma rays, although different in
character, can travel considerable distances through the air and can
produce harmful effects in humans. Gamma rays are invisible rays
similar to X-rays. These penetrating rays interact with the human
body and cause damage to tissues and blood-forming cells. The effects
of neutrons on the body resemble those of gamma rays. The major
problem in protecting against the effects of initial radiation is that
a soldier may receive an incapacitating or lethal dose of radiation
before he can take any protective action.