An Approach towards Safety Using Safety Instrumented Systems: A Case Study

In industrial globalization “safety” is emerging as most noticing and valued factor. The main intention of this design of safety systems is to avoid unexpected accidents and to achieve reduction in dangerous environment according to health and property risk. The different safety functions considered to increase the relative safety of the plant are combinable and all together named as safety instrumented system. These systems works in response to its inputs, when pre-included the safety functions fails which includes operator faults, system hardware failures and environmental changes. This paper is focused on these systems. This paper will introduce you different concepts related to safety analysis like safety life cycle model, ALARP principle, LOPA concept, probability of failure on demand (pfd) and mean time to failure (MTTF) along with small review of safety standards iec61508 and IEC 61511. After a preliminary introduction of the SIL (safety integrity level) concept in accordance with iec61508 / iec61511, a case study concerning the evaluation of both the mean time to failure (MTTF) and the probability of failure on demand (pfd) to select an appropriate SIL for a basic process safety control system for a tank is considered.