Critical Systems: a New Approach in Mitigation Control Layer

Abstract The inherent complexity of critical production systems, coupled with policies to preserve people's safety and health, environmental management, and the facilities themselves, and stricter laws regarding the occurrence of accidents, are the motivation to the design of Safety Control Systems that leads the mitigation functionality. According to experts, the concept of Safety Instrumented Systems (SIS) is a solution to these types of issues. They strongly recommend layers of risk reduction based on hierarchical control systems in order to manage risks, preventing or mitigating faults, or to lead the process to a safe state. Additionally some of the safety standards such as IEC 61508, IEC 61511, among others, guide different activities related Safety Life Cycle design of SIS. The IEC 61508 suggests layers of critical fault prevention and critical fault mitigation. In the context of mitigation control system, the standard provides a recommendation of activities to mitigate critical faults, by proposing control levels of mitigation. This paper proposes a method to implement the mitigation layer based on the risk analysis of the plant and the consequences of faults of its critical components. The control architecture, based on distributed and hierarchical control systems in a collaborative way, will make use of the techniques of risk analysis raised and mitigation actions, based on the knowledge of an expert, implemented by fuzzy logic. The mitigation layer therefore seeks to reduce the inherent risk in a process, and besides proposing the mitigation layer, this work aims to a further reduction of process risk on proposing an anticipatory mitigation action through temporal analysis of the evolution of the parameter used to measure the effect of the occurrence of a critical fault.