Determination of Safety Integrity Level (SIL) using LOPA method in the Emergency Shutdown system (ESD) of Hydrogen unit.

Iraj Alimohamdadi, Majid Jalilian, Mansour Nadi


Petrochemical plants are high risk, high parameter, and high-energy units, with the potential risks of fire, explosion and poisoning. The severe accidents at Bhopal, Mexico City, Samton, Brazil, Panipat, Mumbai and many others have increased the public awareness of the health, property and environmental risks posed by chemical installations. The recent years have seen a convergence of scenario-based Hazard and Operability (HAZOP) studies, Layer of Protection Analyses (LOPAs), and Safety Integrity Level (SIL) determinations. The aim of the research was to study the hazardous scenario identified in the hydrogen unit of petrochemical plant and to determine the SIL for ESD system. 20 hazardous scenarios identified by HAZOP study and determined by SIL by applying the LOPA method for ESD system, were used to control the hazardous scenarios. KS-1, KS-2 and KS-3are three ESD systems applied in the hydrogen unit. The maximum SIL determined for ESD system was SIL3. Since the rise in SIL can be quite costly for the industry, adding other layers of protection can reduce the level of SIL for ESD (SIS).



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Adam S, Markowski and M, Sammanan. ExSys-LOPA for the chemical process industry. 2010; 23(6): 688-696.

Faisali, Khan .S, A, Abbasi. Opt-HAZOP an effective and optimum approach for HAZOP study.1997; 10(3): 191-204.

Feng Wang. Yajun Chen. Haochen Wang. Cunyin Chen. Bin Shi. The Intrinsic Safety Engineering Design Method for the Petrochemical Plant. 2012; 43: 156 – 161.

U.S. Department of Energy Washington. DC.20585. Chemical Process Hazards Analysis. 1996.

Angela Summers. William Vogtmann. Steven Smolen. Improving PHA/LOPA b consistent consequence severity estimation. 2011; 24(6):879-885.

Arthur M, Dowell. Dennis C, Hendershot. Simplified Risk Analysis-Layer of Protection Analysis (LOPA). 2002; 281a.

Andrew Franks. Lines of Defense/Layers of Protection Analysis in the COMAH Context.1999.

Christopher A, Lassen. Layer of protection analysis (LOPA) for determination of safety integrity level (SIL). 2008.

Arthur M, Dowell. Layer of protection analysis for determining safety integrity level. 1998; 37(3): 155-165.

Robert W, Johanson. Beyond-compliance uses of HAZOP/LOPA studies. 2010; 23(6): 727-733.

Yillin Liu. Marvin Rausand. Reliability assessment of safety instrumented systems subject to different demand modes. 2011; 24(1): 49-56.

Chunyang Weia. William J, Rogersb. M, Sam Mannanb. Layer of protection analysis for reactive chemical risk assessment. 2008; 159(1): 19–24.

Clementina Ramírez-Marengoa. Julio de Lira-Floresa. Antioco López-Molinaa. Richart Vázquez-Romána. Victor Carreto-Vázquezb. M. Sam Mannanb. A formulation to optimize the risk reduction process based on LOPA. 2013; 26(3): 489–494.

IEC 61508. Functional safety of electrical/ electronic/programmable electronic Safety-related systems International Electro technical Commission. 2003; Geneva.

Iranian Journal of Health, Safety and Environment e-ISSN: :2345-5535 Iran university of Medical sciences, Tehran, Iran