[en] Systematic methods for reviewing and evaluating improved emergency procedure guidelines are presented. The deficiencies of existing event-oriented emergency procedures are discussed and the industry efforts to produce improved guidelines in the aftermath of TMI are summarized. It is concluded that the function- or symptom-oriented approaches which have evolved since TMI have, in theory, the potential to produce effective guidelines. However, when attention is focused on a limited number of critical safety functions (or symptoms indicative of the performance of these functions), the concern arises that diverse accident conditions which exhibit common or similar symptoms can result in ambiguous operator diagnosis and ineffective response. Methods for systematically examining potential accident sequences using operator action event trees are developed in this first volume which can help ensure that functional or symptomatic guidance can, in reality, lead to unambiguous and effective diagnosis and response regardless of the specific failure events