Preventing recurrence of industrial control system accident using assurance case

Lessons learned from accident experiences in safety-critical infrastructures are valuable not only for the organizations operating the infrastructures but also for third-party organizations developing or operating similar safety-critical infrastructure systems. While such accident knowledge is often reported after rigorous investigations of the accidents, learning from the knowledge and applying them to improve other systems is not a trivial issue, since the report is not structured for such a purpose. In this paper, we present a method to elucidate the accident knowledge by assurance case consisting of structured arguments and evidence. We introduce a new assurance case pattern and create a post-failure safety case that argues over the avoidance of a similar accident. The effectiveness of the proposed method is evaluated through a case study concerning the PG&E accident in SCADA system.