Introduction to Best Engineering Practices Applied to Safety Instrumented Systems Management: A Sil Approach

The proposed methodology aims to present best engineering practices related to the management of the instrumented safety systems on process industries, through the classification of these safety functions in terms of required integrity safety levels (SIL classification), application of reliability techniques to project definition and functions architecture in order to attempt to the required SIL (implementation phase), definition of the operational criteria, maintenance, tests strategy, verification, validation e safety instrumented systems audits, with focus on process safety. The main aspects are: the risks and the necessity of safety integrity levels (SIL), SIL definition (qualitative and quantitative methodologies, life cycle approach and costs, based on IEC 61508 / 61511.

Many accidents on process industry occurred due to deficient safety management system, which allows systematic failures leading the process since the safe operational conditional until catastrophic releases. A SIS represents a protection layer, among others, that can be used to keep the process on safe condition. Integrity and functionality are essential performance attributes for the SIS, but the excess of attention on requirements can lead to loss of focus on other important issues. The SIS ability to reach a SIL requirement is in general limited by human against the practices and procedures. Independency, reliability, auditability and change management are aspects that must receive sufficient attention. These essential attributes support the SIS over its life cycle, ensuring the appropriate focus on reducing human failure impacts on the SIS performance. The lack of a rigorous management system can cause discrepancies among the required functionality and integrity, that's really reached during operation.