Deriving Major Accident Failure Frequencies with a Storybuilder Analysis of Reportable Accidents

Quantitative Risk Assessment (QRA) is used in the Netherlands and the UK for site permitting and land-use planning around industries with dangerous substances. For example, individual risk contours resulting from a QRA determine where houses and other types of constructions may exist. Therefore, both industry and regulators ask for models and data that are up to date. Data used for input includes the failure frequency of failure scenarios. In the past, updating frequencies required costly one-time investigations. As major hazard accidents are investigated by the Labor Inspectorate by decree, a possibility arises to use these accident investigation data for a continuing updating scheme. Recent major accidents in the UK and in the Netherlands were analyzed with the Storybuilder method. Underlying failure causes at operational and management levels were investigated and stored in a structured database. The amount of equipment present at plants was explored using various paths. Failure scenarios and frequencies can be updated on a regular basis by combining the accident data with the equipment data.