Chemical process safety : fundamentals with applications

1 Introduction 1 Safety Programs 2 Engineering Ethics 4 Accident and Loss Statistics 4 Acceptable Risk 12 Public Perceptions 14 The Nature of the Accident Process 15 Inherent Safety 20 Four Significant Disasters 23 Flixborough, England 23 Bhopal, India 25 Seveso, Italy 26 Pasadena, Texas 27 Suggested Reading 29 Problems 30 2 Toxicology 35 2-1 How Toxicants Enter Biological Organisms 36 Gastrointestinal Tract 37 Skin 37 Respiratory System 38 2-2 How Toxicants Are Eliminated from Biological Organisms 39 2-3 Effects of Toxicants on Biological Organisms 40 2-4 Toxicological Studies 41 2-5 Dose versus Response 42 vi Contents 2-6 Models for Dose and Response Curves 48 2-7 Relative Toxicity 54 2-8 Threshold Limit Values 54 Suggested Reading 59 Problems 59 3 Industrial Hygiene 63 3-1 Government Regulations 64 Laws and Regulations 64 Creating a Law 64 Creating a Regulation 64 OSHA: Process Safety Management 68 EPA: Risk Management Plan 71 3-2 Industrial Hygiene: Identification 74 Material Safety Data Sheets 74 3-3 Industrial Hygiene: Evaluation 78 Evaluating Exposures to Volatile Toxicants by Monitoring 79 Evaluation of Worker Exposures to Dusts 83 Evaluating Worker Exposures to Noise 84 Estimating Worker Exposures to Toxic Vapors 85 3-4 Industrial Hygiene: Control 94 Respirators 96 Ventilation 97 Suggested Reading 103 Problems 104 Source Models 109 4-1 Introduction to Source Models 109 4-2 Flow of Liquid through a Hole 112 4-3 Flow of Liquid through a Hole in a Tank 116 4-4 Flow of Liquids through Pipes 121 2-K Method 124 4-5 Flow of Vapor through Holes 130 4-6 Flow of Gases through Pipes 136 Adiabatic Flows 136 Isothermal Flows 143 4-7 Flashing Liquids 151 4-8 Liquid Pool Evaporation or Boiling 157 4-9 Realistic and Worst-Case Releases 159 4-10 Conservative Analysis 159 Suggested Reading 161 Problems 162 Contents vii 5 Toxic Release and Dispersion Models 171 5-1 Parameters Affecting Dispersion 172 5-2 Neutrally Buoyant Dispersion Models 176 Case 1: Steady-State Continuous Point Release with No Wind 180 Case 2: Puff with No Wind 181 Case 3: Non-Steady-State Continuous Point Release with No Wind 182 Case 4: Steady-State Continuous Point Source Release with Wind 183 Case 5: Puff with No Wind and Eddy Diffusivity Is a Function of Direction 183 Case 6: Steady-State Continuous Point Source Release with Wind and Eddy Diffusivity Is a Function of Direction 184 Case 7: Puff with Wind 184 Case 8: Puff with No Wind and with Source on Ground 185 Case 9: Steady-State Plume with Source on Ground 185 Case 10: Continuous Steady-State Source with Source at Height Hr above the Ground 186 Pasquill-Gifford Model 186 Case 11: Puff with Instantaneous Point Source at Ground Level, Coordinates Fixed at Release Point, Constant Wind Only in x Direction with Constant Velocity u 190 Case 12: Plume with Continuous Steady-State Source at Ground Level and Wind Moving in x Direction at Constant Velocity u 191 Case 13: Plume with Continuous Steady-State Source at Height Hr above Ground Level and Wind Moving in x Direction at Constant Velocity u 192 Case 14: Puff with Instantaneous Point Source at Height Hr above Ground Level and a Coordinate System on the Ground That Moves with the Puff 193 Case 15: Puff with Instantaneous Point Source at Height Hr above Ground Level and a Coordinate System Fixed on the Ground at the Release Point 194 Worst-Case Conditions 194 Limitations to Pasquill-Gifford Dispersion Modeling 194 5-3 Dense Gas Dispersion 195 5-4 Toxic Effect Criteria 199 5-5 Effect of Release Momentum and Buoyancy 212 5-6 Release Mitigation 213 Suggested Reading 214 Problems 215 6 Fires and Explosions 225 6-1 The Fire Triangle 225 6-2 Distinction between Fires and Explosions 227 - - - - - viii Contents 6-3 Definitions 227 6-4 Flammability Characteristics of Liquids and Vapors 229 Liquids 230 Gases and Vapors 233 Vapor Mixtures 233 Flammability Limit Dependence on Temperature 235 Flammability Limit Dependence on Pressure 236 Estimating Flammability Limits 236 6-5 Limiting Oxygen Concentration and Inerting 238 6-6 Flammability Diagram 240 6-7 Ignition Energy 248 6-8 Autoignition 249 6-9 Auto-Oxidation 249 6-10 Adiabatic Compression 249 6-11 Ignition Sources 251 6-12 Sprays and Mists 252 6-13 Explosions 252 Detonation and Deflagration 253 Confined Explosions 255 Blast Damage Resulting from Overpressure 265 TNT Equivalency 269 TNO Multi-Energy Method 271 Energy of Chemical Explosions 274 Energy of Mechanical Explosions 276 Missile Damage 279 Blast Damage to People 279 Vapor Cloud Explosions 281 Boiling-Liquid Expanding-Vapor Explosions 282 Suggested Reading 282 Problems 283 7 Designs to Prevent Fires and Explosions 291 7-1 Inerting 292 Vacuum Purging 292 Pressure Purging 295 Combined Pressure-Vacuum Purging 297 Vacuum and Pressure Purging with Impure Nitrogen 298 Advantages and Disadvantages of the Various Pressure and Vacuum Tnerting Procedures 299 Sweep-Through Purging 299 Siphon Purging 301 Using the Flammability Diagram To Avoid Flammable Atmospheres 301 7-2 Static Electricity 307 Fundamentals of Static Charge 307 -- Contents ix Charge Accumulation 308 Electrostatic Discharges 309 Energy from Electrostatic Discharges 311 Energy of Electrostatic Ignition Sources 312 Streaming Current 313 Electrostatic Voltage Drops 316 Energy of Charged Capacitors 316 Capacitance of a Body 321 Balance of Charges 324 7-3 Controlling Static Electricity 330 General Design Methods To Prevent Electrostatic Ignitions 333 Relaxation 332 Bonding and Grounding 332 Dip Pipes 333 Increasing Conductivity with Additives 336 Handling Solids without Flammable Vapors 337 Handling Solids with Flammable Vapors 337 7-4 Explosion-Proof Equipment and Instruments 337 Explosion-Proof Housings 339 Area and Material Classification 339 Design of an XP Area 340 7-5 Ventilation 340 Open-Air Plants 340 Plants Inside Buildings 341 7-6 Sprinkler Systems 343 7-7 Miscellaneous Designs for Preventing Fires and Explosions 347 Suggested Reading 347 Problems 348 8 Introduction to Reliefs 353 8-1 Relief Concepts 354 8-2 Definitions 356 8-3 Location of Reliefs 357 8-4 Relief Types 360 8-5 Relief Scenarios 364 8-6 Data for Sizing Reliefs 365 8-7 Relief Systems 368 Relief Installation Practices 368 Relief Design Considerations 368 Horizontal Knockout Drum 371 Flares 375 Scrubbers 376 Condensers 376 Suggested Reading 376 Problems 377 x Contents 9 Relief Sizing 383 9-1 Conventional Spring-Operated Reliefs in Liquid Service 384 9-2 Conventional Spring-Operated Reliefs in Vapor or Gas Service 389 9-3 Rupture Disc Reliefs in Liquid Service 394 9-4 Rupture Disc Reliefs in Vapor or Gas Service 394 9-5 Two-Phase Flow during Runaway Reaction Relief 395 Simplified Nomograph Method 401 9-6 Deflagration Venting for Dust and Vapor Explosions 404 Vents for Low-Pressure Structures 406 Vents for High-Pressure Structures 408 9-7 Venting for Fires External to Process Vessels 411 9-8 Reliefs for Thermal Expansion of Process Fluids 415 Suggested Reading 418 Problems 420 10 Hazards Identification 429 10-1 Process Hazards Checklists 432 10-2 Hazards Surveys 432 10-3 Hazards and Operability Studies 448 10-4 Safety Reviews 454 10-5 Other Methods 459 Suggested Reading 460 Problems 460 11 Risk Assessment 471 11-1 Review of Probability Theory 472 Interactions between Process Units 474 Revealed and Unrevealed Failures 480 Probability of Coincidence 484 Redundancy 486 Common Mode Failures 486 11-2 Event Trees 486 11-3 Fault Trees 491 Determining the Minimal Cut Sets 494 Quantitative Calculations Using the Fault Tree 497 Advantages and Disadvantages of Fault Trees 498 Relationship between Fault Trees and Event Trees 498 11-4 QRA and LOPA 499 Quantitative Risk Analysis 499 Layer of Protection Analysis 500 Consequence 503 Frequency 503 Suggested Reading 507 Problems 508 Contents xi Accident Investigations 515 12-1 Learning from Accidents 515 12-2 Layered Investigations 516 12-3 Investigation Process 518 12-4 Investigation Summary 519 12-5 Aids for Diagnosis 521 Fires 522 Explosions 522 Sources of Ignition in Vessels 523 Pressure Effects 523 Medical Evidence 525 Miscellaneous Aids to Diagnosis 525 12-6 Aids for Recommendations 528 Control Plant Modifications 528 User-Friendly Designs 529 Block Valves 529 Double Block and Bleed 530 Preventive Maintenance 530 Analyzers 531 Suggested Reading 532 Problems 532 13 Case Histories 535 13-1 Static Electricity 536 Tank Car Loading Explosion 536 Explosion in a Centrifuge 536 Duct System Explosion 537 Conductor in a Solids Storage Bin 537 Pigment and Filter 536 Pipefitter's Helper 536 Lessons Learned 536 13-2 Chemical Reactivity 540 Bottle of Isopropyl Ether 540 Nitrobenzene Sulfonic Acid Decomposition 540 Organic Oxidation 541 Lessons Learned 541 13-3 System Designs 546 Ethylene Oxide Explosion 546 Ethylene Explosion 546 Butadiene Explosion 546 Light Hydrocarbon Explosion 547 Pump Vibration 547 Pump Failure 547 Ethylene Explosion (1) 548 xii Contents Ethylene Explosion (2) 548 Ethylene Oxide Explosion 548 Lessons Learned 549 13-4 Procedures 551 Leak Testing a Vessel 552 Man Working in Vessel 552 Vinyl Chloride Explosion 552 Dangerous Water Expansion 553 Phenol-Formaldehyde Runaway Reaction 553 Conditions and Secondary Reaction Cause Explosion 554 Fuel-Blending Tank Explosion 555 Lessons Learned 556 13-5 Conclusion 556 Suggested Reading 557 Problems 557 Appendix A: Unit Conversion Constants 561 Appendix B: Flammability Data for Selected Hydrocarbons 565 Appendix C: Detailed Equations for Flammability Diagrams 571 Equations Useful for Placing Vessels into and out of Service 576 Appendix D: Formal Safety Review Report for Example 10-4 581 Appendix E: Saturation Vapor Pressure Data 591