Layers of protection analysis to achieve safety integrity level (SIL), Case study: Hydrogen unit of refinery

Abstract

To identify and evaluate hazard in process industries as oil and gas, there are various methods in which hazard and operability study (HAZOP) and layers of protection analysis (LOPA) are the most common methods. The present study aims to analyze layers of protection to achieve safety integrity level in hydrogen unit of refinery. After performing library studies and data collection of events in refinery, hazards of hydrogen unit as operating nodes and deviations with causes and consequences are identified using HAZOP method. The next stage is presenting corrective solutions by LOPA method and target factor. Then, frequencies are determined for the initiating event by the experts. By completing the sheets of each event, independent layers of protection and integrity level are determined. The results of evaluation of identified risks showed that 11 cases had risk higher than 15 and it is not acceptable. The analysis of consequence of hazards showed that for 6 hazardous points, independent layers of protection can reduce risk as 100% to target factor (10-5) and safety integrity level is fulfilled. Regarding the eighths scenario “elimination of repulsive system of equipment and lines with the high temperature of very hot steam”, layers of protection cannot increase safety integrity level to more than 60% (10-3) and to provide safety to target factor, after eliminating the identified problems, other layers are positioned. In this study, to achieve safety integrity level in hydrogen unit of refiner. A three period plan (short-term, mid-term and long-term) is proposed.