-Tevent has been a guiding principle in the establishment and conduct of long range scientific studies in seismology for the particular penefit of safety. In approaching the question of safety from the effects of underground nuclear explosions, one is easily tempted to think in terms of the effects of earthquakes. Much of the popular reaction to proposed test events by AEC arises from popular older reports of catastrophic natural events where losses in life and property are great. reaction is not unnatural. This popular Public opinion is influenced by these con- siderations and difficult to change with hard facts, logic and reason. Understanding of the principles of seismology is not easy to come by. The problem of those responsible for safety at AEC is thus to present images, models and pictures which are readily grasped by the public, which give a high degree of assurance that the planners at AEC know what they are doing, that they are able to say with reliability and aBsurance that no planned event will endanger the lives and property of people. These assurances are made from time to time by the Nevada Operations Office of the Commission, expressed in terms understood by the public and based upon the most exhaustive array of deductions that can be made. A brief account of these procedures will bring us to the end of this discussion and the papers to follow. really a big problem. The safety of live is not WNo nuclear detonation underground has BoE ABCEivE people so much that it injured or could injure a human being or animal. If the predicted motion of the ground is great enough that some such possibility exists the manager of the test event makes sure that everyone 27