of a precise overall relationship for timed doses versus biological effects; yet there are sufficient convincing data to permit an attempt at estimating the effect of this phenomenon. ” Blair, Smith, Sacher, Davidsont5, 16, 17, 18, 19 and others have made extensive analyses of existing data on the: effects of timespaced doses for several species of animals. Generally, the recovery rate for larger and longer-lived mammals, such as dogs, is significantly less than for mice. One estimate places the half-time recovery for man as long as four weeks (the time for one-half of the biological damage to be repaired) .+9 Since the estimated rate of biological recovery for man is relatively slow, this factor would have its greatest influence where a given total radiation dose was delivered over long periods of time. This would be the case where the fallout occurred at later times after detonation rather than close-in areas where the fallout is essentially complete in about an hour after the burst, and about onehalf of the total possible dose is delivered in the first 24 hours. NEARBY FALLOUT FROM HIGH YIELD WEAPONS As an exercise during the National Association of Civil Defense Directors meeting in Washington, D. C. on April 15-17, 1957, it was assumed the 4 bombs were dropped simultaneously as follows: 20 megaton on the Union Station Washington, D. C., 5 megaton on the National Airport, 20 megaton on Baltimore, Maryland and 10 megaton co