DNA 1240H-2 hazard of the base surge is considered unimportant compared with air- blast and fallout hazards from bursts in this category. Very-Shaliow bursts are those for which the bubble breaks the sur~ face during the first cycle while bubble pressure is greater than atmospheric pressure, causing blowout of fission products. Shallow bursts are those for which the bubble vents during the first cycle, but at a time when bubble pressure has dropped to atmospheric pressure or less. Deep pursts are those for which the bubble completes at least one oscillation (expansion and contraction) before breaking through the surface. Very Deep bursts are so deep that the bubdbdle breaks up before reaching the surface. The minimum burst depth for thia category is taken as that at which the bubble completes three expansion-contraction eycles before breaking through the surface. Although the physical category into which a burst falls may be influenced by bottom depth as well &s burst depth, the influence of the bottom is not considered in this model. For bursts close to the dividing line between two categories, it is suggested 8 that an appropriately weighted average of the results for these categories be used. C. Base Surge Forms The two geometrical forms of the base surge used in the model were suggested by photographic and radiological data, and are shown in Fig. 17-10. It is emphasized that the geometrical forms used for computation purposes, which yield transit-dose-rate and dose values in agreement with test data, are not necessarily the actual visible shape of the surge. Very Shallow and Shallow. The form is a right-circular hollow truncated cone, with the lower interior angles of both inner and outer faces equal to 70°. radius. The inner radius is taken as 2/3 of the outer Deep and Very Deep. The form is s solid right circular truncated cone with the lower interior angle of the face equal to 60°. In both forms, the height of the base surge, Z, as a function of time t (sec) is the same: 17-44 Aoa a ae ee en = ee ee = - ne SR ce nee ce a a “ ee