The effective range of blast damage is less than thatfrom an air blast because much of the energy istransmitted in the form of a ground or water shock wave.Near ground zero, however, the severity of the shockwave is greater than that of the blast wave. The distanceat which thermal radiation (heat) is hazardous is slightlyless than that from an air blast.Nuclear radiation is of two types—initial andresidual.Initial RadiationInitial radiation occurs within the first minute afteran explosion; residual radiation occurs thereafter. Inmost instances, initial radiation is of little consequencebecause the lethal range of its effects is less than that ofthe blast wave.Residual RadiationResidual radiation for a surface burst is dangerousbecause the large amount of surface material drawn intothe cloud is heavy enough to fall while still highlyradioactive. Additionally, the fallout area of a surfaceblast is much larger than the area affected by heat andshock.SUBSURFACE (UNDERWATER) BURSTIn an underwater burst (fig. 13-4) a fireball isformed. However, it’s smaller than the fireball of an airburst and is not normal. The explosion creates a largebubble (cavity) that rises to the surface where it expelssteam, gases, and debris into the air. Water rushing intothe cavity is thrown upward in the form of a hollowcolumn that may reach a height of several thousand feet.When the column collapses, a circular cloud of mist,called the base surge, is formed around the base of the13-9Student Notes:Figure 13-3.—A surface blast.
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