A safety instrumented system is a high-reliability system comprised of sensors, logic solver(s) and final elements. It includes a number of safety instrumented functions (SIFs), each designed to provide a specified risk reduction. The necessary risk reduction is assigned as a safety integrity level that establishes the reliability requirements for the SIF.
A clear understanding of the failure rate, failure mode and failure effects for devices as well as implementation of a management program to effectively identify and correct failures on a routine basis are essential for achieving the needed reliability.
This article from our sister website Chemical Processing will review failure rate and failure mode basics, proof test frequency and effectiveness, the robustness of the maintenance program, information collected during a proof test, and tips for analyzing data to ensure continued reliability.