Lesson 2/Learning Event 2
specific nuclear burst, special monitoring reports will be required to determine H-hour. Information
necessary to determine H-hour is obtained from a series of monitoring reports from several selected
locations. When these series of monitoring reports are required, each dose rate must be taken with the
radiacmeter placed at the same position within the selected location. Generally, each of these series
should consist of at least six reports spaced over at least a 2 1/2-hour period, followed by a series of
hourly reports. The locations at which these series of readings should be taken are carefully selected by
the NBCE based upon the length of time a unit is likely to remain in its present location and the status of
training of the unit. The locations should be selected so that the soil, vegetation, and other general
features of the area are typical of the contaminated area. Further development of information depends
upon the H-hour determination; therefore, it is essential that these series of monitoring reports be
properly and promptly accomplished with the information precisely determined.
more accurate evaluation of the hazard. For induced contamination, the soil type, known or assumed
(type II), will determine the decay rate. For fallout, the assumed decay rate (n = 1.2) is used until a
series of monitoring reports as described in the previous paragraph provides sufficient data for the valid
determination of the actual decay rate. Determination of decay rate was discussed in Learning Event 1.
Time of Completion of Fallout. The time in which fallout will be complete can be estimated. The time
(T) in hours after detonation by which fallout will be completed at any specified point is approximately
one and one-quarter the time of arrival (in hours after detonation) of fallout plus the time in hours
required for the nuclear cloud to pass over. This is expressed by the formula:
The cloud diameter is obtained from NBC 1 (Nuclear) Reports. Determination of effective wind speed
is a function of the NBCE. For an example of the method of estimating the time of completion of
fallout, consider a given location with the following information available:
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