= The YAGH,O was stationed 40 miles due north of ground zero, out arrived shortly after H # 7 hours. Fali- The washdown was not activated until a build-up of about 20 mr/hr on deck was reached, This occurred 1 3/4 hours after the first indications of fallout arrival. The fallout ceased at approximately H # 21; the total time that the ship was in the fallout was 13 hours. | The total dose under the washdown was approximately 150 mr, compared with 34 r in the non-washed area, The relative effectiveness of the wash- down for this event is 96 to 97 percent far dose rate and 93 percent for accumulated dose, Discussion ~ Washdown The nature of the fallout material is considerably different from, r that of tne(2220) shot, i.e., considerably less mass and averag= v ing smaller size, 30 micron diameter or less, and arriving in liquid droplets of high salt content. The significant difference is that the fallout material consisted of very small, solj@, in aqueous suspension whereas —. radioactive particles of bomb debris I(zuNt) material was mostly agglomer= ate material heavy and much larger in size.