Yunju Jung, Seungjune Choi, and En Sup Yoon

1. Chemical Process Risk Analysis Using Layer of Protection Analysis and a Study on the Establishment about Proper Protection Layers Yunju Jung, Seungjune Choi, and En Sup Yoon School of Chemical Engineering, Seoul National University Process system and safety laboratory

2. What is IPL? • IPL : Independent Protection Layer • Features of IPL • Criteria : Specificity, Independence, Dependability, Auditability • 3D : Detect, Decide, Deflect • 3E : Fast Enough, Strong Enough, Big Enough • Big I : Independent • All IPLs are safeguards, but not all safeguards are IPLs. Process system and safety laboratory

3. Classification of IPLs • Passive IPLs : dike, underground drainage system, open vent(no valve), Fire proofing, blast wall/bunker, inherently safe design, flame/detonation arrestors • Active IPLs : relief valve, rupture disc, basic process control system, interlocks • sensor(instrument, mechanical, or human) • decision making process(logic solver, relay, mechanical device, human) • action(instrument, mechanical, or human) Process system and safety laboratory

4. Protection Layers of the Process Process system and safety laboratory

5. Facility Design Operation & Maintenance SIS Design New or Existing Process Develop Safety Requirement Specs Establish Operations & Maintenance Process Perform PHA & Risk Assessment Conceptual SIS Design Pre-Startup Safety Review Specs Met? Apply Non-SIS Protection Layers to Reduce Risk Operations, Testing, & Maintenance No Yes Modify or Decommission SIS Required No Perform Detail SIS Design Yes Define Target SIL SIS Installation & Commissioning SIS Decommissioning Installation PHA The safety Life Cycle Process system and safety laboratory

6. What is LOPA? • LOPA : Layer of Protection Analysis • LOPA is a semi-quantitative methodology that can be used to identify safeguards that meet the independent protection layer (IPL) criteria. • LOPA provides specific criteria and restrictions for the evaluation of IPLs. • LOPA is limited to a single cause-consequence pair as a scenario. Process system and safety laboratory

7. Use of LOPA • LOPA is used all around the process life cycle. • Research, process development, process design, operations & maintenance modification, decommissioning • provide guidelines in process design • Decide the safety critical • Identify operator actions & responses • LOPA is typically applied after a qualitative hazard analysis has been completed. • It is cost effective that LOPA is used during or after the HAZOP review or revalidation. Process system and safety laboratory

8. Task of LOPA How safe is safe enough? How many protection layers are needed? How much risk reduction should each layer provide? LOPA Providing rational, semi-quantitative, risk-based answers Reducing emotionalism Providing clarity and consistency Documenting the basis of the decision Process system and safety laboratory

9. Step 1 : Identify the consequence to screen the scenario Step 2 : Select an accident scenario Step 3 : Identify the initiating event & determine the initiating event frequency Step 4 : Identify the IPLs & estimate PFD of each IPL Step 5 : Estimate the risk Step 6 : Evaluate the risk The steps to the LOPA process Process system and safety laboratory

10. Benefits of LOPA • LOPA takes less time than quantitative risk analysis. • LOPA provides better risk decision basis. • LOPA is more defensible for more rigorous documentation and specific value than qualitative method. • LOPA identifies operations and practices. LOPA is simple numerical qualitative methodology! Process system and safety laboratory

11. Case Study • Hexane Storage Tank Overflow – spill not contained by the dike • Initiating event • The inventory control system fails. • A truck arrives at the tank with insufficient space in the tank. • Probability : due to an error in ordering, or unit shutdown after the truck was ordered, once a year Process system and safety laboratory

12. Case Study (Continued) • IPLs in place • Human action to check level prior to filling (PFD for human response = 1X10-1) • This procedure is an IPL because it meets the criteria of: Effectiveness – if it is performed correctly, The level is read correctly the operator does not initiate loading an overflow will not occure Independence, Auditability • Dike (PFD = 1X10-2) • Total PFD for the IPLs in place = 1X10-1 X1X10-2 = 1X10-3 Process system and safety laboratory

13. Case Study (Continued) • Safeguards that are not IPLs for LOPA • The BPCS level control loop • Human action other than response to a BPCS alarm is not an IPL Process system and safety laboratory

14. Case Study (Continued) • IPLs proposed • BPCS and operators are involved with either the initiating event or existing IPLs. • Thus, additional equipment must be added to reduce the risk. • SIF(Safety Instrumented Function) (PFD of SIF candidate = 1X10-2) • Total PFD for the IPLs in place = 1X10-1 X1X10-2 X 1X10-2 = 1X10-5 Process system and safety laboratory

15. Discussion • LOPA is a methodology for hazard evaluation and risk assessment, and lies between simple qualitative and more elaborate quantitative analysis techniques. • In decision-making process, LOPA helps to decide the propriety of protection layers that exist or are suggested to prevent accidents, so ideally matches the risk-decision criteria of the company. • LOPA is a recognized technique that can establish a proper safety integrity level (SIL) of the process. • Using LOPA, we need to set up proper protection layers that evaluate, analyze, and decease the risk in chemical process. Process system and safety laboratory