Safety Integrity Level Selection: Systematic Methods Including Layer of Protection Analysis
This book describes a systematic method for selecting safety integrity levels (SILs) for safety instrumented systems (SISs). The method emphasizes accounting for existing layers of protection, and it ensures that the maximum return on risk reduction investments is achieved. This reference demonstrates the application of quantitative risk analysis techniques and tools to the problem of safety integrity level selection. Essential theory is distilled into a format that the average control systems engineer can quickly apply. This is not a generic theoretical dissertation, nor a comprehensive treatment of the topic of quantitative risk analysis. It is a focused process for applying simple, yet powerful, tools of quantitative risk analysis specifically to the problem of selecting safety integrity levels for safety instrumented systems. Congratulations to Ed Marszal and Eric Scharpf for receiving the Thomas G. Fisher Award of Excellence for a Standards-Based Book Publication for their book Safety Integrity Level Selection: Systematic Methods Including Layer of Protection Analysis!
Table of Contents:
Preface xiii
Chapter 1 Selecting Safety Integrity Levels: Introduction 1
1.1 Safety Integrity Level 2
1.2 Safety Instrumented Functions 3
1.3 SIL Selection and Risk 5
1.4 Qualitative versus Quantitative SIL Selection 8
1.5 Benefits of Systematic SIL Selection 12
1.6 Objectives of this Book 13
1.7 Summary 14
1.8 Exercises 15
1.9 References 16
Chapter 2 Safety Life Cycle Context for SIL Selection 17
2.1 Standards and the Safety Life Cycle 17
2.2 SLC Analysis Phase 21
2.3 SLC Realization Phase 23
2.4 SLC Operation Phase 25
2.5 Summary 25
2.6 Exercises 27
2.7 References 27
Chapter 3 Tolerable Risk 29
3.1 Philosophical and Political Basis of Risk Tolerance 30
3.2 Measuring Tolerable Risks (Revealed Values) 32
3.3 Risk Tolerance Decisions Based on Financial Guidelines 33
3.4 Expressions of Risk 35
3.5 Benchmarking Risk Acceptance 41
3.6 Using a Financial Basis for Making Risk Reduction Decisions 45
3.7 Summary 46
3.8 Exercises 47
3.9 References 48
Chapter 4 Identifying Safety Instrumented Functions 49
4.1 General Risk Identification and Hazard Analysis 50
4.2 Identification from PHA Reports 52
4.3 Identification from Engineering Drawings 56
4.4 Summary 57
4.5 Exercises 58
4.6 References 59
Chapter 5 Rules of Probability 61
5.1 Assigning Probability to an Event 61
5.2 Types of Events and Event Combinations 62
5.3 Combining Event Probabilities 65
5.4 Fault Tree Analysis 69
5.5 Failure Rate and Probability 75
5.6 Simplifications and Approximations 81
5.7 Summary 83
5.8 Exercises 85
5.9 References 86
Chapter 6 Consequence Analysis Overview 87
6.1 Introduction to Consequence Analysis 88
6.2 Methods for Performing Consequence Analysis 89
6.3 Consequence Definitions and Measures 92
6.4 Quantitative Analysis of Chemical Releases 95
6.5 Effect Zone and Consequence 106
6.6 Consequence Analysis Tools 109
6.7 Summary 112
6.8 Exercises 113
6.9 References 114
Chapter 7 Likelihood Analysis Overview 117
7.1 Statistical Analysis 117
7.2 Fault Propagation Modeling 118
7.3 Likelihood Analysis: An Example 122
7.4 Summary 128
7.5 Exercises 129
7.6 References 129
Chapter 8 Event Tree Analysis 131
8.1 Introduction to Event Tree Analysis 131
8.2 Initiating Events 132
8.3 Branches 133
8.4 Outcomes 134
8.5 Quantifying Event Trees 135
.6 Average Consequence of Incidents Using Event Trees 137
8.7 Summary 138
8.8 Exercises 139
8.9 References 140
Chapter 9 Layer of Protection Analysis 141
9.1 LOPA Overview 141
9.2 Protection Layers and Mitigating Events 142
9.3 LOPA Quantification 143
9.4 Typical Protection Layers 144
9.5 Multiple Initiating Events 156
9.6 Summary 157
9.7 Exercises 158
9.8 References 159
Chapter 10 SIL Assignment 161
10.1 Correlating Required Risk Reduction and SIL 162
10.2 Hazard Matrix 165
10.3 Risk Graph 169
10.4 Incorporating LOPA into Qualitative Methods 177
10.5 Assignment Based on Frequency 179
10.6 Assignment Based on Individual and Societal Risk 182
10.7 Calibrating Hazard Matrices and Risk Graphs 183
10.8 SIL Assignment Based on Environmental Consequence 186
10.9 SIL Assignment Based on Financial Consequence 192
10.10 Selecting from Multiple Integrity Level Categories 195
10.11 Summary 198
10.12 Exercises 199
10.13 References 203
Appendix A Derivation of Equations 205
A.1 Derivation—SIL Assignment Equation 205
A.2 Derivation—Tolerable Event Frequency 207
A.3 Derivation—Component Average Probability of Failure (Single Mode) 209
Appendix B Acronyms 211
Appendix C Glossary 213
Appendix D Problem Solutions 227
Index 245
