Temporal Logic for System Safety Properties and Hazard Monitoring

In recent years, there has been a growing interest in the use of temporal logic (TL) in a variety of technical areas, such as robotics and safety-critical computational system. TL provides a formal language for the verification of requirements and for specification logic, to ensure the desired performance and behavior of the system. In this work we propose the application of temporal logic for risk analysis and system safety and in support of accident prevention and risk mitigation. We first provide an introduction to temporal logic and the use of temporal operators. We then examine the types of properties that can be expressed in TL and provide a set of four safety principles, formulated at a high-level of abstraction, based on the notions of accident sequence and hazard level/escalation. These safety properties, once expressed in TL, can be monitored during the design and operation of systems for compliance and be verified on-line and off-line. The verification of whether the system satisfies or violates the TL safety properties along with the monitoring of emerging hazards provide an important feedback for designers and operators to recognize the need for and trigger safety interventions. The present work augments the traditional perspective in risk analysis and its reliance on (conditional) probabilities as the basic modeling ingredient with the notion of temporal contingency, a novel dimension by which hazards are prioritized and ranked based on the temporal vicinity of their associated accident(s) to being released. This approach offers novel capabilities, complementary to PRA, and rich possibilities for further contributions toward accident prevention and improved risk management.