PREFACE The May 1973 report of the Advisory Committee on Civil Defense of the National Academy of Sciences (ACCD/NAS), which discusses various aspects of the fallout hazard, is considered to be of sufficient importance to warrant further distribution. For this reason, and with the ACCD/NAS concurrence, this report is herein reissued in the format of a DCPA Research Report. There is a further advantage in that an opportunity is provided for the addition of notes and comments to help define the implications of the report. These notes and comments by Jack C. Greene of DCPA, listed by Part I is the. ren chapter, appear as Part II of this Research Report. ACCD Subcommittee document in its original form.