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Layer of Protection Analysis: Simplified Process Risk Assessment

ISBN: 978-0-8169-0811-0
292 pages
October 2001
Layer of Protection Analysis: Simplified Process Risk Assessment (0816908117) cover image


Layer of protection analysis (LOPA) is a recently developed, simplified method of risk assessment that provides the much-needed middle ground between a qualitative process hazard analysis and a traditional, expensive quantitative risk analysis. Beginning with an identified accident scenario, LOPA uses simplifying rules to evaluate initiating event frequency, independent layers of protection, and consequences to provide an order-of-magnitude estimate of risk. LOPA has also proven an excellent approach for determining the safety integrity level necessary for an instrumented safety system, an approach endorsed in instrument standards, such as ISA S84 and IEC 61511. Written by industry experts in LOPA, this pioneering book provides all the necessary information to undertake and complete a Layer of Protection Analysis during any stage in a processes' life cycle. Loaded with tables, charts, and examples, this book is invaluable to technical experts involved with ensuring the safety of a process. Because of its simplified, quicker risk assessment approach, LOPA is destined to become a widely used technique. Join other major companies and start your LOPA efforts now by purchasing this book.
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Table of Contents



Acronyms and Abbreviations.

1. Introduction.

1.1 Audience.

1.2 History of LOPA.

1.3 Use of LOPA in the Process Life Cycle.

1.4 Linkage to Other CCPS Publications.

1.5 Annotated Outline of the LOPA book.

2. Overview of LOPA.

2.1 Purpose.

2.2 What is LOPA?

2.3 What LOPA Does.

2.4 When to Use LOPA.

2.5 How LOPA Works.

2.6 How to Implement LOPA.

2.7 Limitations of LOPA.

2.8 Benefits of LOPA.

2.9 Introduction of Continuing Examples.

3. Estimating Consequences and Severity.

3.1 Purpose.

3.2 Consequences of Interest.

3.3 Consequences Evaluation Approaches for LOPA.

3.4 Continuing Examples.

3.5 Link Forward.

4. Developing Scenarios.

4.1 Purpose.

4.2 LOPA Scenarios and Components.

4.3 Identifying and Developing Candidate Scenarios.

4.4 Continuing Examples.

4.5 Link Forward.

5. Identifying Initiating Event Frequency.

5.1 Purpose.

5.2 Initiating Events.

5.3 Frequency Estimation.

5.4 Expression of Failure Rates.

5.5 Continuing Examples.

5.6 Limitations (Cautions).

5.7 Link Forward.

6. Identifying Independent Protection Layers.

6.1 Purpose.

6.2 Definition and Purpose of an IPL.

6.3 IPL Rules.

6.4 LOPA IPL Assessment.

6.5 Example of IPLs.

6.6 Preventive IPLs versus Mitigation IPLs.

6.7 Continuing Examples.

6.8 Link Forward.

7. Determining the Frequency of Scenarios.

7.1 Purpose.

7.2 Quantitative Calculation of Risk and Frequency.

7.3 Look-up Table Determination of Risk of Frequency.

7.4 Calculation of Risk of Frequency with Integer Logarithms.

7.5 Continuing Examples.

7.6 Link Forward.

8. Using LOPA to Make Risk Decisions.

8.1 Purpose.

8.2 Introduction.

8.3 Comparing Calculated Risk to Scenario Risk Tolerance Criteria.

8.4 Expert Judgment.

8.5 Using Cost-Benefit to Compare Alternatives.

8.6 Comparison of Approaches, Pros and Cons.

8.7 Cumulative Risk Criteria versus Scenario Criteria.

8.8 Continuing Examples.

8.9 Cautions.

8.10 Link Forward.

9. Implementing LOPA.

9.1 Purpose.

9.2 Is the Company ready for LOPA?

9.3 What Is the Current Foundation for Risk Assessment?

9.4 What Dare Are Required?

9.5 Will the IPLs Remain in Place?

9.6 How Are the Risk Tolerance Criteria Established?

9.7 When IS LOPA Used?

9.8 Typical Implementation Tasks.

10. Using LOPA for Other Applications.

10.1 Purpose.

10.2 Using LOPA in Capital Improvement Planning.

10.3 Using LOPA in Management of Change.

10.4 Using LOPA in Mechanical Integrity Programs or Risk-Based Inspection/Risk-Based Maintenance Programs.

10.5 Using LOPA in Risk-Based Operator Training.

10.6 Using LOPA in emergency Response Planning.

10.7 Using LOPA to Determine a Credible Design Basis for Overpressure Protection.

10.8 Using LOPA in Evaluating Facility Siting Risks.

10.9 Using LOPA to Evaluate the Need for Emergency Isolation Valves.

10.10 Using LOPA to Evaluate Taking a Safety System Out of Service.

10.11 Using LOPA during Incident Investigations.

10.12 Using LOPA in the Determination of SIL for SIF.

11. Advanced LOPA Topics.

11.1 Purpose.

11.2 Counting Multiple Functions in One BPCS as IPLs in the Same Scenario.

11.3 Summation of Risk for Multiple Scenarios.

11.4 Using LOPA to Develop F/N Curves.

11.5 Operator Response Issues.

11.6 Normal Plant Operations as “Tests: of IPL Components.

11.7 Focused Fault Tree/Event Tree Analysis of IPL Components.

Appendix A. LOPA Summary Sheets for the Continuing Examples.

Appendix B. Worked Examples from CCPS’s Safe Automation Book.

Appendix C. Documentation for a LOPA Study.

Appendix D. Linkage with Other Publications.

Appendix E. Industry Risk Tolerance Criteria Data.

Appendix F. High Initiating Event Frequency Scenarios.

Appendix G. Additional Reading.


Glossary of Terms.


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Author Information

The CENTER FOR CHEMICAL PROCESS SAFETY (CCPS), an industry technology alliance of the American Institute of Chemical Engineers (AIChE), has been a world leader in developing and disseminatinginformation on process safety management and technology since 1985. CCPS has published over 80 books in its process safety guidelines and process safety concepts series. For more information, visit www.ccpsonline.org.
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