Abstract:

Based on a system accident model where an accident occurs due to the loss of safety control actions, this paper proposes a simple method to obtain accident conditions of a complex system with interactions among human, software and hardware. For the accident to occur, two fundamental conditions are necessary: (1) a disturbance path can cause a deviation leading to the system accident, and (2) safety control actions related to the disturbance path fail to prevent or mitigate it. To obtain these failure conditions objectively, the proposed method utilizes a global system model, which clearly shows the relations between the physical behavior and safety control actions. While a formal approach using bond graphs is applied to the analysis of physical behaviour, information flow analysis is applied to safety control actions including operator actions such as monitoring and diagnosis. As long as the design assumptions and the evaluation of the safety control actions are correct, the consistency of accident conditions is guaranteed.
Received on September 29, 2004