Safety Integrity Level (SIL) of a Chemical Industry for Safer Operations Using LOPA Methodology

Abstract

Safety Integrity Level (SIL) is a criterion that judges the reliability of the safeguards. It speci es or assigns the required safety integrity level to the scenario to identify the level of risk involved in the scenario. International Electro technical Commission (IEC) 61511 has published di erent methods for the determination of SIL in chemical process industries. These methods are categorized based on their approach to determine SIL. Of the three di erent approaches, qualitative, semiquantitative and quantitative, the most commonly used methods for SIL determination are Risk graph and LOPA (Layer Of Protection Analysis) method. Both methods distinctively calculate the required safety integrity level for the given scenario. LOPA, Layer of Protection Analysis, is a simpli ed semi-quantitative risk assessment method used to evaluate the risk of selected accident scenario. The purpose of LOPA is to develop on the information prepared during a qualitative hazard evaluation technique such as HAZOP (Hazard and Operability Study) or PHA (Process Hazard Analysis) to nally identify the Safety Integrity Level (SIL) in an industry. Depending upon the complexity and consequence severity involved in the process, di erent safeguards or line of defenses are provided in an industry. These safeguards however may or may not be able to act independently during the time of event and thereby fail to act as an independent protection layer in an industry. LOPA, in this way, provides a method to test the independence of di erent layers in an industry and rank their ability to protect the industry from an event by assigning a Safety Integrity Level. Safeguards/ independent protection layers upon analysis are added to strengthen or continue to keep the industry intact from any dangers. In this way, the objective is to analyze Carbon black manufacturing facility by applying LOPA method and summarize the results of LOPA method. Usage of this method will lead to determination of hazards, di erent safeguards, risk level of the scenarios, safety integrity level of the scenarios etc. The method proves vital in concluding whether the industry has su cient layers provided. During the analysis, di erent layers were added in cases where urgent attention was required due to intolerable risk present in the scenario. This is discussed in the results and appendix. During analysis, two negative points were also summarized such as LOPA method fails to identify which layers are needed to protect the plant and the results obtained from analysis are dependent on the corporate criteria. Change in these criteria can signi cantly alter the results obtained from LOPA analysis.