Hazard Management for Safety Critical Systems Philip Benjamin Supervised by: Dr. David Hemer Computer Science Department University Of Adelaide

Abstract of talk Safety critical systems increasingly used in industries Regulated by safety standards Require tool support for hazard management Existing tools have limitations Aim to address these limitations Data model for hazard management Existing model New improved model Require tracking and managing hazards Lots of data Complex inter-relationships

Talk Outline Terminology: Hazards, risk, safety integrity levels, etc Existing tools HazLog Cassandra Explain the existing data model for HazLog and the proposed conceptual data model

Reference Material Def(Aust) 5679 Australian Defense Standard for Procurement of Computer-Based Safety Critical Systems UK MOD Safety Management Requirements for Defense Systems, U.K. Ministry of Defense Neil Storey Safety Critical Computer Systems HazLog Tool support for hazard management, Australian Workshop on Industrial Experience with Safety Critical Systems

Terms in Safety Critical Systems Accident: An unintended event or sequence of events that causes death, injury, or damage Hazard: A situation in which there is actual or potential danger to people or the environment Risk: A combination of the frequency or probability of a specified hazardous event, and its consequence Risk Assessment: Assessed by providing levels of integrity and levels of trust to the systems

Hazard Analysis Range of techniques that provides insight into characteristics of the system under investigation Event tree analysis (ETA) Start with all possible outcomes and work forward to determine their outcomes Fault tree analysis (FTA) Start with all identified hazards and work backward to determine their possible causes Logical operators are used to combined the effect of events Data from other earlier accidents/incidents from similar system in service can be used as starting point

Existing Tools Cassandra Supports Def Stan 00-56, MIL-STD-882C Has one kind of risk Safety Integrity Level’s (SIL) HazLog Supports Def(Aust) 5679 Two levels of hazards System Hazard Component Hazard Risk allocation Level Of Trust (LOT) Safety Integrity Level’s (SIL)

HazLog: Initial Data Model

HazLog Limitations Incompatibility of this tool with standards other than Def(Aust) 5679 e.g. Two separate risk allocations Only supports two levels of hazards May want to support more levels e.g. Systems of systems

New Conceptual Data Model

Analysis of the new Data Model There is one type of generic hazard - can be either system or component hazard Cutsets model relationships between hazards parent or child The occurrence of a loop in the model could result in a graph Child node can also become a parent node of another parent node above its level

Project Plan Week 1 to 6: Initial report Week 7: Presentation with a 15 min talk Milestones: 1st Milestone: (Week 9) Initial requirements and analysis (What the tool must be doing) 2nd Milestone: (Week 11) Initial Design (Drawing entity- relationship diagrams) 3rd Milestone: (Week 3 Semester 2) Prototype 4th Milestone: (Week 5 Semester 2) Case Study to work out the gaps using “aircraft safety” 5th Milestone: (Week 7 Semester 2) Final Design Final Presentation (1 week) Final Report (Last 4 weeks of Semester 2)

Conclusion Safety critical software require hazard management Tool required Current tools have limitations Aim to address these limitations by redesigning existing HazLog tool