This book provides an excellent description of the design phase of the SIS safety life cycle as defined in IEC 61511:2016. It focuses on the fundamental concepts, starting with a description of the entire safety life cycle process and then explaining how the design steps - from conceptual design through design verification - fit into that process. The book: Explains the advantages of the performance-based approach to design; Discusses minimum redundancy concepts; Addresses equipment qualification; Provides the theoretical background for the probabilistic calculations that are the foundation of performance verification; Covers recent advances in SIF verification modeling; Provides numerous examples to explain potentially confusing language from IEC 61511 and IEC 61508. This is an excellent reference for professionals designing safety instrumented systems, as well as those who are seeking certification. Each chapter contains questions and answers similar to those found on professional certification exams for functional safety, and the appendices include statistics, probability, failure-rate data tables, and system architectures