PART 2 Interpreting Failure Rates...39 Chapter 4: Realistic Failure Rates and Prediction Confidence...41

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2 Contents Preface...xix Acknowledgements...xxi PART 1 Understanding Reliability Parameters and Costs...1 Chapter 1: The History of Reliability and Safety Technology Failure Data Hazardous Failures Reliability and Risk Prediction Achieving Reliability and Safety-Integrity The RAMS Cycle Contractual and Legal Pressures Chapter 2: Understanding Terms and Jargon Defining Failure and Failure Modes Failure Rate and Mean Time Between Failures The Observed Failure Rate The Observed Mean Time Between Failures The Observed Mean Time to Fail Mean Life Interrelationships of Terms Reliabilty and Failure Rate Reliabilty and Failure Rate as an Approximation Reliabilty and MTBF The Bathtub Distribution Down Time and Repair Time Availability, Unavailability and Probability of Failure on Demand Hazard and Risk-Related Terms Choosing the Appropriate Parameter Chapter 3: A Cost-Effective Approach to Quality, Reliability and Safety Reliability and Optimum Cost Costs and Safety The Need for Optimization Costs and Savings Involved with Safety Engineering The Cost of Quality v

3 PART 2 Interpreting Failure Rates...39 Chapter 4: Realistic Failure Rates and Prediction Confidence Data Accuracy Sources of Data Electronic Failure Rates Other General Data Collections Some Older Sources Data Ranges Using the Ranges Confidence Limits of Prediction Manufacturers Data Overall Conclusions Chapter 5: Interpreting Data and Demonstrating Reliability The Four Cases Inference and Confidence Levels The Chi-Square Test Understanding the Method in More Detail Double-Sided Confidence Limits Reliability Demonstration Sequential Testing Setting Up Demonstration Tests Exercises Chapter 6: Variable Failure Rates and Probability Plotting The Weibull Distribution Using the Weibull Method Curve Fitting to Interpret Failure Data Manual Plotting Using the COMPARE Computer Tool Significance of the Result Optimum Preventive Replacement More Complex Cases of the Weibull Distribution Continuous Processes Exercises PART 3 Predicting Reliability and Risk...85 Chapter 7: Basic Reliability Prediction Theory Why Predict RAMS? Probability Theory The Multiplication Rule The Addition Rule The Binomial Theorem Bayes Theorem...90

4 7.3 Reliability of Series Systems Redundancy Rules General Types of Redundant Configuration Full Active Redundancy (Without Repair) Partial Active Redundancy (Without Repair) Conditional Active Redundancy Standby Redundancy Load Sharing General Features of Redundancy Incremental Improvement Further Comparisons of Redundancy Redundancy and Cost Exercises Chapter 8: Methods of Modeling Block Diagrams and Repairable Systems Reliability Block Diagrams Repairable Systems (Revealed Failures) Repairable Systems (Unrevealed Failures) Systems With Cold Standby Units and Repair Modeling Repairable Systems with Both Revealed and Unrevealed Failures Conventions for Labeling Dangerous, Safe, Revealed and Unrevealed Failures Common Cause (Dependent) Failure What is CCF? Types of CCF Model The BETAPLUS Model Fault Tree Analysis The Fault Tree Calculations Cutsets Computer Tools Allowing for CCF Fault Tree Analysis in Design A Cautionary Note Event Tree Diagrams Why Use Event Trees? The Event Tree Model Quantification Differences Feedback Loops...131

5 Chapter 9: Quantifying the Reliability Models The Reliability Prediction Method Allowing for Diagnostic Intervals Establishing Diagnostic Coverage Modeling Partial Stroke Testing Safe Failure Fraction FMEA (Failure Mode and Effect Analysis) Human Factors Background Models HEART (Human Error Assessment and Reduction Technique) THERP (Technique for Human Error Rate Prediction) TESEO (Empirical Technique to Estimate Operator Errors) Other Methods Human Error Rates Trends in Rigor of Assessment Simulation The Technique Some Packages Comparing Predictions with Targets Exercises Chapter 10: Risk Assessment (QRA) Frequency and Consequence Perception of Risk, ALARP and Cost per Life Saved Maximum Tolerable Risk (Individual Risk) Maximum Tolerable Failure Rate ALARP and Cost per Life Saved Societal Risk Production/Damage Loss Hazard Identification Hazop Hazid HAZAN (Consequence Analysis) Factors to Quantify Reliability Lightning and Thunderstorms Aircraft Impact Earthquake Meteorological Factors Other Consequences...174

6 PART 4 Achieving Reliability and Maintainability Chapter 11: Design and Assurance Techniques Specifying and Allocating the Requirement Stress Analysis Environmental Stress Protection Failure Mechanisms Types of Failure Mechanism Failures in Semiconductor Components Discrete Components Complexity and Parts Reduction of Complexity Part Selection Redundancy Burn-In and Screening Maintenance Strategies Chapter 12: Design Review, Test and Reliability Growth Review Techniques Categories of Testing Environmental Testing Marginal Testing High-Reliability Testing Testing for Packaging and Transport Multiparameter Testing Step-Stress Testing Reliability Growth Modeling The CUSUM Technique Duane Plots Exercises Chapter 13: Field Data Collection and Feedback Reasons for Data Collection Information and Difficulties Times to Failure Spreadsheets and Databases Best Practice and Recommendations Analysis and Presentation of Results Manufacturers data Anecdotal Data Examples of Failure Report Forms

7 Chapter 14: Factors Influencing Down Time Key Design Areas Access Adjustment Built-In Test Equipment Circuit Layout and Hardware Partitioning Connections Displays and Indicators Handling, Human and Ergonomic Factors Identification Interchangeability Least Replaceable Assembly Mounting Component Part Selection Redundancy Safety Software Standardization Test Points Maintenance Strategies and Handbooks Organization of Maintenance Resources Maintenance Procedures Tools and Test Equipment Personnel Considerations Maintenance Manuals Spares Provisioning Logistics The User and the Designer Computer Aids to Maintenance Chapter 15: Predicting and Demonstrating Repair Times Prediction Methods US Military Handbook 472 Procedure Checklist Mil 472 Procedure Using a Weighted Sample Demonstration Plans Demonstration Risks US Military Standard 471A (1973) Data Collection Chapter 16: Quantified Reliability Centered Maintenance What is QRCM? The QRCM Decision Process Optimum Replacement (Discard)

8 16.4 Optimum Spares Optimum Proof Test Condition Monitoring Chapter 17: Systematic Failures, Especially Software Programable Devices Software-related Failures Software Failure Modeling Software Quality Assurance (Life Cycle Activities) Organization of Software QA Documentation Controls Programming (Coding) Standards Fault-Tolerant Design Features Reviews Integration and Test Modern/Formal Methods Requirements Specification and Design Static Analysis Test Beds Software Checklists Organization of Software QA Documentation Controls Programming Standards Design Features Code Inspections and Walkthroughs Integration and Test Part 5 Legal, Management and Safety Considerations Chapter 18: Project Management and Competence Setting Objectives and Making Specifications Planning, Feasibility and Allocation Program Activities Responsibilities and Competence Functional Safety Capability Standards and Guidance Documents Chapter 19: Contract Clauses and Their Pitfalls Essential Areas Definitions Environment Maintenance Support Demonstration and Prediction Liability...301

9 19.2 Other Areas Reliability and Maintainability Program Reliability and Maintainability Analysis Storage Design Standards Safety-Related Equipment Pitfalls Definitions Repair Time Statistical Risks Quoted Specifications Environment Liability In Summary Penalties Apportionment of Costs During Guarantee Payment According to Down Time In Summary Subcontracted Reliability Assessments Examples Chapter 20: Product Liability and Safety Legislation The General Situation Contract Law Common Law Statute Law In Summary Strict Liability Concept Defects The Consumer Protection Act Background Provisions of the Act Health and Safety at Work Act Scope Duties Concessions Responsibilities European Community Legislation Management of Health and Safety at Work Regulations Insurance and Product Recall The Effect of Product Liability Trends Some Critical Areas...316

10 Areas of Cover Product Recall Chapter 21: Major Incident Legislation History of Major Incidents Development of major incident legislation CIMAH safety reports Offshore Safety Cases Problem Areas The COMAH Directive (1999 and 2005 Amendment) Rail Corporate Manslaughter and Corporate Homicide Chapter 22: Integrity of Safety-Related Systems Safety-Related or Safety-Critical? Safety-Integrity Levels (SILs) Targets Assessing Equipment Against the Targets Programable electronic systems (PESs) Current guidance IEC International Standard (2010): functional safety of electrical/electronic/programmable electronic safety-related systems: 7 parts IEC International Standard 61511: functional safety safety instrumented systems for the process industry sector Institution of Gas Engineers and Managers IGEM/SR/15: programmable equipment in safety-related applications 5th edition European Standard EN 50126: railway applications the specification and demonstration of dependability, reliability, maintainability and safety (RAMS) UK Defence Standard (Issue 3.0): safety management requirements for defence systems RTCA DO-178B/(EUROCAE ED-12B): software considerations in airborne systems and equipment certification Documents related to machinery Other industry sectors Technis Guidelines, Q124, 2010: demonstration of product/system compliance with IEC Framework for Certification Self-certification Third-party assessment Use of a certifying body...342

11 Chapter 23: A Case Study: The Datamet Project Introduction The Datamet Concept The Contract Detailed Design Syndicate Study Hints Chapter 24: A case study: gas detection system Safety-Integrity Target Random Hardware Failures ALARP Architectures Life-Cycle Activities Functional Safety Capability Chapter 25: A Case Study: Pressure Control System The Unprotected System Protection System Assumptions Reliability Block Diagram Failure Rate Data Quantifying the Model Proposed Design and Maintenance Modifications Modeling Common Cause Failure (Pressure Transmitters) Quantifying the Revised Model ALARP Architectural Constraints Appendix 1: Glossary A1.1 Terms Related to Failure A1.1.1 Failure A1.1.2 Failure Mode A1.1.3 Failure Mechanism A1.1.4 Failure Rate A1.1.5 Mean Time Between Failures and Mean Time to Fail A1.1.6 Common Cause Failure A1.1.7 Common Mode Failure A1.2 Reliability Terms A1.2.1 Reliability A1.2.2 Redundancy A1.2.3 Diversity A1.2.4 Failure Mode and Effect Analysis A1.2.5 Fault Tree Analysis...365

12 A1.2.6 Cause Consequence Analysis (Event Trees) A1.2.7 Reliability Growth A1.2.8 Reliability Centered Maintenance A1.3 Maintainability Terms A1.3.1 Maintainability A1.3.2 Mean Time to Repair (MTTR) A1.3.3 Repair Rate A1.3.4 Repair Time A1.3.5 Down Time A1.3.6 Corrective Maintenance A1.3.7 Preventive Maintenance A1.3.8 Least Replaceable Assembly (LRA) A1.3.9 Second-Line Maintenance A1.4 Terms Associated with Software A1.4.1 Software A1.4.2 Programable Device A1.4.3 High-Level Language A1.4.4 Assembler A1.4.5 Compiler A1.4.6 Diagnostic Software A1.4.7 Simulation A1.4.8 Emulation A1.4.9 Load Test A Functional Test A Software Error A Bit Error Rate A Automatic Test Equipment (ATE) A Data Corruption A1.5 Terms Related to Safety A1.5.1 Hazard A1.5.2 Major Hazard A1.5.3 Hazard Analysis A1.5.4 HAZOP A1.5.5 LOPA A1.5.6 Risk A1.5.7 Consequence Analysis A1.5.8 Safe Failure Fraction A1.5.9 Safety-Integrity A Safety-Integrity level A1.6 General Terms A1.6.1 Availability (Steady State) A1.6.2 Unavailability (PFD) A1.6.3 Burn-In...370

13 A1.6.4 Confidence Interval A1.6.5 Consumer s Risk A1.6.6 Derating A1.6.7 Ergonomics A1.6.8 Mean A1.6.9 Median A PFD A Producer s Risk A Quality A Random A FRACAS A RAMS Appendix 2: Percentage Points of thechi-square Distribution Appendix 3: Microelectronics Failure Rates Appendix 4: General Failure Rates Appendix 5: Failure mode percentages Appendix 6: Human Error Probabilities Appendix 7: Fatality rates Appendix 8: Answers to Exercises Chapter Chapter Chapter Chapter Chapter Notes Chapter Chapter : Protection System : Reliability Block Diagram : Quantifying the Model Revised diagrams: ALARP Architectural Constraints Appendix 9: Bibliography Appendix 10: Scoring Criteria for BETAPLUS Common Cause Model A10.1 Checklist and Scoring for Equipment Containing Programable Electronics...413

14 A10.2 Checklist and Scoring for Non-Programable Equipment For Programable Electronics For Sensors and Actuators Appendix 11: Example of HAZOP A11.1 Equipment Details A11.2 HAZOP Worksheets A11.3 Potential Consequences Worksheet Appendix 12: HAZID Checklist Appendix 13: Markov Analysis of Redundant Systems Index...433