Communicating Risk Concepts to Subject Expert. S. T. F. Bott and S. W. Eisenhawer, Probabilistic Risk and Hazard Analysis Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
This paper discusses communication issues encountered in using subject experts to provide input to quantitative safety assessment. In many technical fields, safety analysts must make extensive use of a narrow cadre of specialists to gain subject matter knowledge. Because of a paucity of relevant test data, calculations, and experience, expert judgment is often required. These experts tend to think in deterministic terms and have been accustomed to handling safety questions in a different manner. The safety analyst encounters some viewpoints among these experts that can significantly complicate the extraction of useful information. Issues discussed include a historical view of probability and statistics in which events that have not been observed are often considered essentially impossible; experts internally screening accident sequences they consider incredible; unconscious risk acceptance where the consequences of an accident remain unarticulated; intuitive beliefs in thresholds that imply that probability density functions are truncated; unstated considerations of the likelihood of events that precede those explicitly included in the elicitation; and sensitivity about human performance to the extent that procedure violations are excluded a priori. During the course of the analysis, interim results are often communicated to the experts to ensure that their input has been interpreted properly. This phase of the analysis gives rise to a host of new communications issues. The subject experts possess considerable expertise in the technical aspects of the systems being analyzed but are accustomed to viewing system safety from a much different perspective and may find a probabilistic approach alien and incomprehensible. Some of the experts’ preconceived notions may make it difficult for the analysts to communicate the meaning of their analysis to the experts. Communications issues encountered during this phase of the safety analysis included the compatibility of estimates based on expert input with their a priori risk perception; uncertainty and its role in the analysis; demonstrating that quantitative safety analysis has value in expanding a qualitative understanding of the process; and helping the experts understand frequency estimates in concrete terms. Each these issues are discussed and examples from nuclear weapons applications are presented.