fallout can differ appreciably from that which might be expected from the
direction of surface winds.
b. Automatic Fallout Response.
The rapid onset of fallout, especially from small yields, within a few
kilometers of ground zero of a surface burst requires quick adoption of
The time after burst before onset of fallout near
ground zero will vary, depending on the yield of the nuclear detonation,
weather conditions, and type of terrain. Normally, use of shelter will be
automatic whenever nuclear bursts are observed, since these bursts should be
assumed to be fallout producing until monitoring and the passage of time
prove otherwise. During the period of uncertainty, precautionary measures
consistent with the mission are instituted. See FM 3-3, FM 3-4, and FM 3-
c. Physical Recognition of Fallout.
Fallout particles are often visible during hours of daylight. The arrival
and settling of dust-like particles after a nuclear burst occurs should be
assumed to indicate the onset of fallout unless monitoring shows no
The neutron-induced area is small by comparison with the fallout area
produced by the same yield nuclear weapon. It is often contained within the
area of great destruction and obstacles (tree blowdown, rubble, and fire).
Frequently there will be no need to enter the area. However, if friendly
troops are required to pass through ground zero or occupy positions in the
immediate vicinity of ground zero, induced radiation may be operationally
significant. Total dose predictions are based on actual dose rates obtained
e. Rate of Decay.
The rate of decay must be known to perform meaningful dose-rate or dose
This rate of decay is indicated by the decay exponent (n),
which may vary with time after burst and location of the contamination
within the fallout area.
The true decay exponent generally will not be
accurately determined until several series of dose-rate readings are
available for specific locations within the contaminated area. Therefore, a
decay exponent of n equals 1.2 has been established as standard and is used
by all units unless informed otherwise by higher headquarters.