only after hundreds of rep were accumulated and tumors only after 1500 or more," The permissible level referred to is that recom- mended by the NCRP for industrial workers, The Committee noted that although "some children have accumulated a measurable amount of radioastive strontium in their bodies, the amount is quite small--a thousandth of what is considered a permissible dose, Committee concluded, "then, that Strontium-90 is not a current The threat, but if there were any substantial increase in the rate of contamination in the atmosphere, it could become one." Committee on Metesroiogizal Aspects of Atomiz Radiation Chairman - Harry Wexle> ~_U, S, Weather Breau In this part of the report there is the fullest discus- Bicn of fallout from nuclear weapons, They distinguisn between kilcton burats when the cloud does not penetrate to the stratosphere ard megaton bursts where the zloud does, They estimate that with surface bursts, i,e,, whare the firebali touches the . ground 70-80% of the residuel radisastivity falls ozt nearby, i.e., with small weapons a few miles, with larger cnes up to 300 miles or more, They emphasize the ease of predicting this "nearby" fallout pattern after the fast and the problem of predicting its precise pattern prior to detsnation, They speak of intermediate fallout, i.e., material of small particle size released below the stratosphere and some 80% of which falls cut within three which it originated and tending with rainfall and wind patterns general latitude as that of its weeks in the same hemisphere in to uneven distribution associated along a broad band in the same origin, Finally, they refer to delayed fallout cf materiel whish has gained entry into the strato- sphere, It is slow with an average storage time in the stratosphere of 10 years, plus or minus five years, AEC believes the latter \ figure - five years - is the more likely, This delayed fallout tends to distribute itself more or less uniformly over the surface of the earth over the years. NAS They state that "at present, the amcunt cf Sr 90 in the stratosphere from nuclear weapons tests is far too small to approach maximum permissible concentration even if it were all deposited now," They urged a continuing pregram to check on the amount of radioactivity in the stratosphere as necessary so that if there were to be a greatly increased rate of thermonuclear weapons testing activi-~ ties we would know at the earliest moment when it was time to slow down in terms of potential hazard from Sr 90 to man, There is also a discussion of the radicactivity from fall- out of the intermediate and delayed varisty. They point out that it