Evaluation of safety instrumented system using “HAZOP-LOPA-FTA” methodology

Following the IEC 61508 standard, this paper presents a combined "HAZOP-LOPA-FTA" method for evaluating the safety level of a High Integrity Pressure Protection System (HIPPS) which is a type of SIS. The technique combines hazard and operability analysis (HAZOP), layers of protection analysis (LOPA), and fault tree analysis (FTA). This paper aims to confirm that a safety instrumented system achieves the intended safety integrity level as per IEC 61508. If not, suggest upgrading the safety instrumented system to lessen the effects of the scenario under study. The technique was used in the C-63 distillation column at RA1K Skikda refinery. HAZOP identified important causes and effects. According to LOPA, a minimum safety level was determined. The real SIL rating was calculated using the Tree module in the GRIF software.