could be significant for mre than 2h-hours. . (b) It ppeare that. the altitudes involved in simificant long_range fall-out from high yield weapons are 20,000 feet aa a lower limit on atl, types of bursts, 60,000 feet was raasonable upper limit for water surfice shots and, 80,000 feet should be considered for lami surface shots. Tw ucst intense portica of the fall-out apparently comes from the 20,000 to 69,000 feat interval, however, 15 As noted that the selected limiting altituces 72 £9,COU or 80,COO feet may be a fiunetion of the atmospheric stability a.’ altitude of the tropopause sone which is lLatitute—dependent. (c) Particle sizes iow to at Least 70 microns, ani pos=} sibly to 50 microns, aprerently contributed to the significant fall-out observed. (d) The assumption thet the fall-out intensities resulting from « water surface shot would bo a factor of 10 to 200 less than those of a land surface shot was apparently accurate in part only. Noglocting difn ferences in wind patterns amt the fact that three water surface shots wore detonated in craters of previous shots, a direct comparison of close-in in- tensities (within 20 niles from GZ), inddlested a rough equivalence for the water versus land types. it greater distsnces, there was considerable evi~ dence that the asroscl-type elowd of the water surface shot was highly resia— tant to fall-out and, as a gecnsequence, persisted primarily as a relatively significant serial hasard for 24 to 30 hours. It is conjectured that the Close=in fall-out from the water surface type shot was consiterably sided oy the ecavenging astion of large quantities of liquid water, plus some heavy bottom or suspended material, asscelated with the early close-in fallout, (e) Prior to the operation, data on surface bursts wers 92