(db) Significant fall-out was expected to cocur duriag the fires twalve hours. Past experienee inthis matter scened to fawr & six-hour period for significant fall; however, since the off-site fxll-cud aspects of IVY MIKE were not know, the value of twelve hours ws ssvuned. for @ margin of safety. BRAVO and ROMEO experierse revised this essumption. Tt became apparent that scmething om the order of at least eighteen and possibly twenty-four hours wuld te more realistic, especially for surface land burete. fs a consequence, the new technique was developed (Incl 2 of Tab D) to approximate the significant fall-cot area (significant fall-out area wae defined as that ares inside the lor infinity 1sc-dose Line) for the first twenty-four hour period. No besie change was nade in the fall-cot foreeasting techniques as planned and used price to BRAVO (Inel 1 of Tab D), rather the new method was usedand presented et briefings to eugnent and modify results from the original msthode. (5) Tne method of plotting infinity dose envelopes ty elliptical approximations (as proposed by ARIC Report "Radicactive Fall—cut fram Atomio Banbe", dated Novesber 1953) wae plamed and used on the CASTILE series. This method is an empirical solution to the fall-out pattern based on the great amount of data from low yield shots at the NPG. Due to the great differenses in yield and cloud heights for NPG and FPG shots, a strict application of thesystem on C/STLE wes acecapanied by£1 ectrenely low confidence factor, perticoular'y for the first shot. There «ry re no real aseurances that ‘he vuyntem described the high yleli fol us cochanian at all, For exemplu. the trapping characteristice of <ho tirnponause could only be conjectured, and if it ws sssumed to diarsgau tise “ropopause 57