DUST EXPLOSIONS

By D. FARAT

1 Combustible Dusts 1 11 Introduction 1 12 Metrics 3 13 Size and Shape 6 14 Size Distribution 9 141 Weighted Distributions 10 142 Number Weighted Distributions 10 143 Volume Weighted Distributions 11 144 Intensity Weighted Distributions 11 145 Size Distribution Statistics 11 15 Why Some Dusts are Combustible 14 16 Common Causes of Dust Explosions and Risk Mitigation 16 161 General 16 162 Explosion Hazard Zones Classifi cation 20 17 Closing Remarks and Defi nitions 21 2 Th e Basics of Dust Explosions 29 21 Conditions for Dust Fires and Explosions 29 211 Explosion Limits 29 22 Primary and Secondary Dust Explosions 39 23 Explosions within Process Equipment 40 231 Baghouse Dust Explosion Case Study 41 232 Blender and Grinder Dust Explosions 44 233 Dryer Dust Explosion Scenarios 46 234 Case Study of an Aluminum Dust Explosion 47 24 Other Examples of Catastrophic Incidents 52 25 Ignition Sensitivity 54 Recommended References 61 3 Factors Infl uencing Dust Explosibility 65 31 Introduction 65 32 Particle Size and Dust Concentration 66 33 Particle Volatility 66 34 Heats of Combustion 68 35 Explosive Concentrations and Ignition Energy 70 36 Classifi cation of Dusts 73 37 Oxidant Concentration 75 38 Turbulence 76 39 Maximum Rate of Pressure Rise 77 310 Presence of Volatile and Flammable Gases 78 311 Limiting Oxygen Concentration 82 312 Important Defi nitions and Concepts 84 Recommended References 91 4 Explosion Prevention in Grain Dust Elevators 93 41 Introduction 93 42 Causes 95 43 Properties of Grain Dusts 98 44 Case Studies 102 441 Toepfer Puerto San Martín Explosion,Argentina, October 2001 102 442 Coinbra Paranaguá Explosion, Brazil, November 2001 102 443 Aca San Lorenzo Explosion, Argentina,April 2002 103 444 Grain Elevator Dust Explosion in Minnesota, August 17, 2012 105 445 De Bruce Grain Elevator in Wichita, KS 1998 105 446 Grain Elevator Explosion in Kansas City, October 29, 2011 105 447 Port Colbourne Elevator in Ontario, Canada, 1952 105 448 Explosions at Various US Facilities 106 449 Other Examples 106 45 Best Industry Practices 107 451 Bucket Elevator Legs 109 46 Osha Grain Handling Standard Audit Questionnaire 120 461 Section (d) Emergency Action Plan 120 462 Section (e) Training 121 463 Section (f) Hot Work Permit 121 464 Section (g) Entry into Grain Handling Structures 122 465 Section (h) Entry into Flat Storage Structures 124 466 Section (i) Contractors 125 467 Section (j) Housekeeping 125 468 Section (k) Grate Openings 126 469 Section (l) Filter Collectors 126 4610 Section (m) Preventive Maintenance 126 4611 Section (n) Grain Stream Processing Equipment 127 4612 Section (o) Emergency Escape Note: Applies only to grain elevators 127 4613 Section (p) Continuous-Flow Bulk Grain Dryers Note: Applies only to grain elevators 127 5 Coal Dust Explosibility and Coal Mining Operations 131 51 Introduction 131 52 Coal as a Fuel 132 53 Heat and Energy 134 54 Coal Dust Suspension, Confi nement, Resuspension and Explosions 135 55 Processing Equipment Explosion Hazards 137 56 Coal Mining Operations and Safety 147 561 Overview 147 562 Origins of Coal Bed Methane and Explosions 148 563 Longwall Mining 153 564 Controlling Explosion Risks at Coal Mine Working Faces 156 565 Stratifi cation 161 566 Use of Portable Methane Detectors 162 567 Summary of Monitoring Principles and Best Practices 164 568 Estimating and Controlling Methane Concentration 169 569 Managing Ignition Sources 175 5610 Case Study – Th e Massey Mine Disaster 176 5611 Other Case Studies 179 5612 Application of Rock Dusting 186 5613 Methane Degasifi cation 190 5614 Prevention, Early Detection and Fire Suppression 196 Recommended References 203 6 Preventing Fires and Explosions Involving Metals 207 61 Introduction 207 62 Combustibility Properties of Metals 208 63 Explosion Temperatures 215 64 Dry Powder (Class D Fires) 216 65 Case Studies 226 651 Combustible Metal Dust Led to Fatal Flash Fire 226 652 Watco Mechanical Services 227 653 Metal Recycling Facility Fire - California 227 654 Other Case Studies 228 66 Good Industry Practices for Prevention and Risk Mitigation 246 661 General Good Practices 246 662 Considerations for Operations and Maintenance 253 663 Assessing and Mitigating Equipment Explosion Hazards 254 67 Risk Screening Guidelines and Resources 265 Recommended References 272 7 Phlegmatization, Diluent Dusts, and the Use of Inert Gases 275 71 Introduction 275 72 Phlegmatization 276 73 Addition of Diluents 279 74 Application of Inert Gases 279 741 Best Practices 282 75 Case Study 289 8 Augmenting Risk Mitigation with Leak Detection and Repair 305 81 Introduction 305 82 Why Ldar Programs are Needed 306 83 Sources of Fugitive Air Discharges 307 84 Good Industry Practices 308