Spurious activation of safety instrumented systems in the oil and gas industry: Basic concepts and formulas

Spurious activation of safety instrumented systems in the oil and gas industry may lead to production loss, stress on affected components and systems, and hazards during system restoration. This article defines and clarifies concepts related to spurious activation. A clear distinction is made between spurious operation, spurious trip, and spurious shutdown. The causes and effects of spurious activation are discussed and related to the concepts used in IEC 61508, IEC 61511, and OREDA. A new set of formulas for calculating the spurious activation rate is presented, and compared with formulas that are frequently used in the oil and gas industry. The new approach is illustrated in a simple case study.