Types of Postulated Initiating events available in SAFRAN. The user can select between PIEs grouped in different categories: Internal, External natural and External human induced. An event identified during design as capable of leading to anticipated operational occurrences or accident conditions. The primary causes of postulated initiating events may be credible equipment failures and operator errors (both within and external to the facility) or human induced or natural events. (IAEA Safety Glossary. Terminology used in Nuclear Safety and Radiation Protection 2007 Edition)