The 0.3 r per week out~of-doors isodose-rate line might extend to about the same position as the line marked 50 on the map. As one attempts to extrapolate such data to one year after fallout, the analysis becomes still more difficult and uncertain. The data suggest, however, that if return is postponed to one year after fallout, the 50 r effective biological isodose line will have disappeared. On the basis of these conservative estimates, the 1,000 square miles of highest contamination might have an out-of-doors dose rate of about 4 r per week after one year. Similarly, personnel might accumulate a dose of about 100 r for the first year following their return, and an additional 90 r over the next three years, independent of the biological recovery factor. It is to be expected that this factor would be rela- tively great for such long periods of time, thus reducing the effective biological dose below 50 r. The 0.3 r per week out-of-doors isodose- rate line might encompass an area somewhat larger than the line marked 400 on the map. For such effects as genetic, it is the total dose received that is important since biological repair does not enter in such calculations. According to the conservative estimates of weathering and shielding used above, possibly several hundred roentgens might be delivered in the areas of heaviest contamination, from the end of the first year after the fallout occurred until the radioactivity had decreased to essentially zero. However, the foregoing analyses are based on passive factors only, not taking into account the actions of persons themselves in reducing contamination. If, for example, a permanent ee - 16 +