Guidelines for Combustible Dust Hazard Analysis

This book describes how to conduct a Combustible Dust Hazard Analysis (CDHA) for processes handling combustible solids. The book explains how to do a dust hazard analysis by using either an approach based on compliance with existing consensus standards, or by using a risk based approach. Worked examples in the book help the user understand how to do a combustible dust hazards analysis.

Table of Contents:
List of Tables xiii List of Figures xv Acronyms and Abbreviations xvii Glossary xix Acknowledgments xxiv Preface xxvii 1. Introduction 1 1.1 Purpose of Book 1 1.2 Book Road Map 2 1.3 References 4 2. Background 5 2.1 Nature of the Dust Fire and Explosion Problem 5 2.1.1 Dust Explosion Statistics 5 2.1.2 Case Study: Hoeganaes Corporation 5 Findings and Lessons 10 2.2 Requirements for Dust Fires and Explosions 11 2.2.1 Layer Fire. 12 2.2.2 Flash Fires and Explosions 12 2.3 Combustibility and Explosivity Parameters 15 2.3.1 Explosibility Screening Test 15 2.3.2 Deflagration Index, KSt (bar-m/sec) 18 2.3.3 Maximum Pressure, Pmax (Bar) 18 2.3.4 Minimum Explosible Concentration, MEC (g/m3) 19 2.3.5 Minimum Ignition Energy, MIE (mJoules, mJ) 19 2.3.6 Minimum Auto Ignition Temperature, Cloud, MAIT (°C) 20 2.3.7 Layer Ignition Temperature, LIT (°C) 20 2.3.8 Limiting Oxygen Concentration, LOC (vol% O2) 20 2.3.9 Volume Resistivity (Ohm-m) 20 2.4 Comparison to Combustible Vapors 21 2.5 Effect of Parameters 22 2.6 Summary 22 2.7 References 23 3. The Hazards Within – Dust Inside Equipment 25 3.1 Methods of Prevention, Protection, Mitigation 25 3.1.1 Ignition Control 26 3.1.2 Inerting/Oxidant Control 28 3.1.3 Combustible Concentration Control 28 3.1.4 Deflagration Venting 28 3.1.5 Deflagration Suppression 29 3.1.6 Containment 29 3.1.7 Deflagration Isolation 30 3.2 Issues 30 3.2.1 Air/Material Separators 32 3.2.2 Size Reduction Equipment (grinders, mills, etc.) 34 3.2.3 Dryers 35 3.2.4 Silos/Hoppers 36 3.2.5 Portable Containers 37 3.2.6 Conveyors 38 3.2.7 Blenders/Mixers 41 3.2.8 Feeding into Vessels Having Flammable Vapor Atmospheres 41 3.3 Summary 42 3.4 References 42 4. Hazards of Dust External to Equipment 45 4.1 Case Study – Imperial Sugar 45 4.2 Issues Inside a Room or Building 48 4.3 Methods of Prevention and Protection 49 4.3.1 Control of Dust Deposits Outside of Equipment 49 4.3.2 Ignition Control 52 4.3.3 Damage Limiting Construction 52 4.4 Summary 52 4.5 References 53 5. Traditional Approach to Hazard Assessment and Control 55 5.1 Introduction 55 5.1.1 Process Safety Information (PSI) 55 5.1.2 Competent Team 56 5.2 Steps to the Traditional Approach 56 5.2.1 Step 1 – Is a combustible dust involved? 57 5.2.2 Step 2 – Determine Which Standards Apply 58 5.2.3 Step 3 - Determine Where Fire/Explosion Hazards Exist 62 5.2.4 Step 4 – Review Unit Operation vs. Standard Requirements for Prevention and Mitigation of Fires/Explosions 63 5.2.5 Step 5 – Make Recommendations 65 5.2.6 Step 6 – Document the DHA 65 5.2.7 Step 7 – Implement the Recommendations 66 5.3 Summary 67 5.4 References 68 6. Risk-based Approach to Dust Hazard Analysis 69 6.1 Introduction 69 6.2 Technique for a Risk-based DHA 70 6.2.1 Step 1: Identify Failure Scenarios 70 6.2.2 Step 2: Evaluate the Consequences 70 6.2.3 Step 3: Are the Consequences Tolerable? 73 6.2.4 Step 4: Estimate Likelihood and Risk 73 6.2.5 Step 5: Is the Risk Tolerable 78 6.2.6 Step 6: Recommend and Evaluate Solutions 80 6.2.7 Step 7: Is the Mitigated Risk Tolerable? 81 6.2.8 Step 8: Document Results 81 6.3 DHA Risk Assessment, Additional Requirements 82 6.3.1 DHA Leader Competency 83 6.3.2 Documentation 83 6.4 Managing Change and Updating Risk Assessment 83 6.5 Summary 83 6.6 References 84 7. Special Considerations: Combustible Dust Issues in Existing Facilities 87 7.1 Introduction 87 7.2 Existing Facilities and Combustible Dusts 87 7.2.1 Potential Issues 87 7.2.2 Issues Impact 91 7.2.3 Precautions 92 7.3 Summary 92 7.4 References 93 8. Worked Examples 95 8.1 Introduction 95 8.2 Example 1 95 8.2.1 Process Description – Example 1 95 8.2.2 Traditional DHA – Example 1 95 8.2.3 Risk-based DHA – Example 1 112 8.2.4 Comparison of Traditional vs. Risk-based Approach – Example 1 167 8.3 Example 2 169 8.3.1 Process Description 2 169 8.3.2 Traditional DHA 171 8.3.3 Risk-based DHA 173 8.3.4 Comparison of Traditional vs. Risk-based Approach – Example 2 176 8.4 Example 3 177 8.4.1 Process Description – Example 3 177 8.4.2 Traditional DHA – Example 3 179 8.4.3 Risk-based DHA – Example 3 181 8.5 Summary 188 8.6 References 188 Appendix A Regulations and Codes 191 A.1 Regulations 191 A.1.1 U.S. 191 A.1.2 International 191 A.2 Codes 192 References 195 Appendix B Additional Resources 197 B.1 Books 197 B.2 U.S. Chemical Safety Board Reports 197 B.3 Journal Articles 198 B.4 Other 199 Appendix C Data for Risk-based DHA 201 C.1 Probability Assessment of Process Unit Fire or Dust Explosion 201 C.1.1 Initiating Event Frequencies 204 C.1.2 Ignition Probabilities 205 C.1.3 Protection Layer PFDs 207 C.2 References 209 Appendix D Good Practices 211 D.1 Self Assessment 211 D.2 Housekeeping 213 D.2.1 Combustible Dust Housekeeping Inspection Checklist 215 D.3 Explosion Protection Methods 217 Appendix E DHA Roadmap 219 Notes for Figure E.1 221 Index 223

About the Author :
Since 1985, the Center for Chemical Process Safety (CCPS) has been the global leader in developing and disseminating information on process safety management and technology. CCPS, an industry technology alliance of the American Institute of Chemical Engineers (AIChE), has published over 100 books in its process safety guidelines and process safety concepts series, and over 100 training modules through its Safety in Chemical Engineering Education (SACHE) series.