MOA 79S OFFICE MEMORANDUM TO: See distribution list below FROM: Merril Bisenbud, Director Health and Sefety Division May 1, 1953 ¢ \\ SUBJs> PROSPECTIVE CHANGES IN mAXIMJm PERMISSIBLE CONCENTRATIONS SYMBOL: HS:idE:srm At the Tripartite Conference on Radiation Doses held in Harriman, N. Y. on March 30 to April 1, the following actions were of particular Significance to New York Operations. The following maximum permissible concentrations were adopted: Radon and Thoron Tho rium ' 10710 curies per liter 500 micrograms per cubic meter With respect to internal dose from alpha emitters, the relative biological effectiveness of alpha with respect to gamma radiation was changed from 20 to 10. This will have the effect of increasing the permissible concentrations of all alpha emitting dusts in air by a factor of two. However, a further increase is likely (perhaps an additional factor of two) by reason of the agreement that the permissible lung dose shall be equivalent in millirem to the dose delivered to the skeleton by O.1 micrograms of radium. 300 millirem per week has previously been used as the maximim permissible dose to lung tissue. 0.1 microgram of radium uniformly distributed throughout the skeleton produces a dose of approximately 70 millirep per week. With the new . RBE of 10, the permissible dose to the lung becomes approximately 700 millirem per week instead of the previous value of 300. The above information should be regarded as an informal summary of the actions taken by the Tripartite Conference which are of direct concern to us. These changes are not as yet official but we can expect ‘them to be incorporated eventually by the official committees which have been established in this country for recommending permissiblé radiation doses. “ete Distribution: R. B. Albert W. B. Harris F. M. Belmore BEST COPY AVAILABLE eis Clarence Karl H. Blatz R. Kirk JW._claus ClausDw. ofBY In.Ulh See" Mason H. B. Fry J. H. Harley pt cg re Gl YF re oe | J. Perry Morgan ae J. Quigley pba ( ORGANIZATION & MANAGEMENT 27382 : Dos AR€HIVES