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Guidelines forEngineering Design for Process Safety CENTER FOR CHEMICAL PROCESS SAFETY of theAMERICAN INSTITUTE OF CHEMICAL ENGINEERS 345 East 47th Street, New York, New York 10017... Li

Guidelines for

Engineering Design for Process Safety

CENTER FOR CHEMICAL PROCESS SAFETY

of theAMERICAN INSTITUTE OF CHEMICAL ENGINEERS

345 East 47th Street, New York, New York 10017

Copyright O 1993

American Institute of Chemical Engineers

345 East 47th Street

New York, New York 10017

All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission

of the copyright owner.

Library of Congress Cataloging-in Publication Data

Guidelines for engineering design for process safety

It is sincerely hoped that the information presented in this volume will lead to an even more impressive safety record for the entire industry; however, neither the American Institute of Chemical Engineers, its consultants, CCPS and/or its sponsors, its

subcommittee members, their employers, nor their employers' officers and directors warrant or represent, expressly or implied, the correctness or accuracy of the content of the information presented in this conference, nor can they accept liability or responsibility whatsoever for the consequences of its use or misuse by anyone.

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Contents

List of Tables x i

List of Figures xiii

Preface xvii

Glossary xxi

Acronyms and Abbreviations xxix

1 Introduction 1

1.1 Objective 1

1.2 Scope 1

1.3 Applicability 2

1.4 Organization of This Book 2

1.5 References 4

2 Inherently Safer Plants 5

2.1 Introduction 5

2.2 Intensification 11

2.3 Substitution 17

2.4 Attenuation 21

2.5 Limitation of Effects 29

2.6 Simplification and Error Tolerance 37

2.7 Inherent Safety Checklist 40

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2.8 Summary - A Fable 42

Appendix 2A Inherent Process Safety Checklist 44

2.9 References 47

3 Plant Design 53

3.1 Process Safety Review through the Life of the Plant 54

3.2 Process Design 56

3.3 Site Selection and Evaluation 63

3.4 Plant Layout and Plot Plan 66

3.5 Civil Engineering Design 75

3.6 Structural Engineering Design 80

3.7 Architectural Design 86

3.8 Plant Utilities 88

3.9 Plant Modifications 97

3.10 References 97

4 Equipment Design 101

4.1 Introduction 101

4.2 Loading and Unloading Facilities 101

4.3 Material Storage 106

4.4 Process Equipment 117

4.5 References 150

5 Materials Selection 157

5.1 Introduction 157

5.2 Corrosion 162

5.3 Design Considerations 168

5.4 Fabrication and Installation 169

5.5 Corrosion Monitoring and Control Techniques 170

5.6 References 175

Contents vii

This page has been reformatted by Knovel to provide easier navigation 6 Piping Systems 179

6.1 Introduction 179

6.2 Detailed Specification 180

6.3 Specifying Valves to Increase Process Safety 187

6.4 Joints and Flanges 190

6.5 Support and Flexibility 192

6.6 Vibration 197

6.7 Special Cases 199

Appendix 6A: Examples of Safety Design Concerns 202

6.8 References 205

7 Heat Transfer Fluid Systems 211

7.1 Introduction 211

7.2 General Description of Heat Transfer Fluids 212

7.3 System Design Considerations 219

7.4 Heat Transfer Fluid System Components 223

7.5 Safety Issues 230

7.6 References 234

8 Thermal Insulation 237

8.1 Properties of Thermal Insulation 237

8.2 Selection of Insulation System Materials 241

8.3 Corrosion under Wet Thermal Insulation 242

8.4 References 247

9 Process Monitoring and Control 251

9.1 Introduction 251

9.2 Instrumentation 252

9.3 Process Monitoring Using Computer-Based Systems 262

9.4 Alarm Systems Philosophy 273

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9.5 Safety System Maintenance Testing 273

9.6 Implementing the Process Control System 275

9.7 Summary 290

Appendix 9A Safety Considerations for Monitoring and Control 291

Appendix 9B Instrumentation and Control Checklist 293

9.8 References 294

10 Documentation 299

10.1 Design 300

10.2 Operations 303

10.3 Maintenance 305

10.4 Records Management 309

Appendix 10A: Typical Inspection Points and Procedures 311

10.5 References 313

11 Sources of Ignition 317

11.1 Introduction 317

11.2 Types of Ignition Source 318

11.3 Ignition by Flames 318

11.4 Spontaneous Ignition (Autoignition) 321

11.5 Electrical Sources 326

11.6 Physical Sources 334

11.7 Chemical Reactions 337

11.8 Design Alternatives 342

11.9 References 343

12 Electrical System Hazards 349

12.1 Electrical Equipment Hazards 349

12.2 Lightning Protection 354

Contents ix

This page has been reformatted by Knovel to provide easier navigation 12.3 Bonding and Grounding 360

12.4 References 367

13 Deflagration and Detonation Flame Arresters 371

13.1 Definitions and Explanations of Terms 371

13.2 Introduction 375

13.3 Types of Flame Arresters 380

13.4 Regulatory Use, Testing and Certification 386

13.5 Application Considerations 396

13.6 Special Applications and Alternatives 401

13.7 Conclusions 403

13.8 Future Developments 404

13.9 References 405

14 Pressure Relief Systems 409

14.1 Introduction 409

14.2 Relief Design Scenarios 410

14.3 Pressure Relief Devices 420

14.4 Sizing of Pressure Relief Systems 428

14.5 Design of Relief Devices: Other Considerations 430

14.6 DIERS Methods of Overpressure Protection for Two-Phase Flows 431

14.7 Emergency Depressuring 440

14.8 References 441

15 Effluent Disposal Systems 445

15.1 Flare Systems 446

15.2 Blowdown Systems 465

15.3 Incineration Systems 470

15.4 Vapor Control Systems 482

15.5 References 486

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16 Fire Protection 489

16.1 Introduction 489

16.2 Detection and Alarm Systems 491

16.3 Water-Based Fire Protection Systems 497

16.4 Chemical and Special Agent Extinguishing Systems 502

16.5 Passive Fire Protection 507

16.6 References 515

17 Explosion Protection 521

17.1 Introduction 521

17.2 Energy Release on Noncombustive Vessel Rupture 521

17.3 Flammability 523

17.4 Flame Events 530

17.5 Flammability Control Measures Inside Equipment 538

17.6 Flame Mitigation Inside Equipment 540

17.7 References 554

Index 557

LIST OF TABLES

Table 2-1 Examples of Process Risk Management Strategies 7Table 2-2 Effect of Size on Overpressure Due to Vessel Rupture 12Table 2-3 Effect of Reactor Design on Size and Productivity for a

Gas-Liquid Reaction 14Table 2-4 Effect of Various Options to Reduce Inventory on the Hazard

Zone Resulting from the Rupture of a 500-Foot Chlorine

Transfer Pipe 16Table 2-5 Surface Compactness of Heat Exchangers 17Table 2-6 Some Examples of Solvent Substitutions 20Table 2-7 Vapor Pressure of Aqueous Ammonia and Monomethylamine

Solutions 22Table 2-8 Atmospheric Pressure Boiling Point of Selected Hazardous

Materials 24Table 3-1 Typical Hazard Evaluation Objectives at Different Stages

of a Process Lifetime 55Table 3-2 Typical Material Characteristics 57Table 3-3 Selected Primary Data Sources for Toxic Exposure Limits 61Table 3-4 Methods to Limit Inventory 63Table 3-5 Some Important Safety Considerations in Plant Siting 64Table 3-6 Important Safety Factors in Plant Layout 67Table 3-7 Inter-unit Spacing Requirements for Oil and Chemical Plants 70Table 3-8 Inter-unit [Equipment] Spacing Requirements for Oil and

Chemical Plants 72Table 3-9 Storage Tank Spacing Requirements for Oil

and Chemical Plants 74Table 3-10 1990 Loss Report 82Table 3-11 Possible Utility Failures and Equipment Affected 89Table 4-1 Common Causes of Loss Containment for Different

Process Equipment 119Table 4-2 Basic Considerations for All Fired Equipment 132Table 4-3 Process Vessels: Special Material Concerns 136Table 4-4 Checklist for Design and Operation of Activated Carbon

Adsorbers 149Table 5-1 Metal Failure Frequency for Various Forms of Corrosion 163Table 5-2 Corrosion Inhibitors 172Table 7-1 Typical Industrial Uses of Heat Transfer Fluids 212Table 7-2 Commercially Available Heat Transfer Fluids 213

Table 7-3 Factors in Design of Heat Transfer Fluid Systems 220Table 7-4 Analysis of Heat Transfer Fluids 221Table 8-1 Design Practices to Reduce Corrosion Under Insulation 245Table 9-1 Ranking of Process Operability and Process Safety 259Table 9-2 Characterization of Process Sensitivity and Process Hazard 260Table 9-3 Comparison of Instrument Type Features 261Table 9-4 Process Control Terminology 264Table 10-1 Elements of Chemical Process Safety Management 299Table 10-2 Typical Design Documents 301Table 10-3 Typical Nondestructive Examination Techniques 307Table 12-1 Typical Hazardous Locations 350Table 12-2 NEMA Definitions of Enclosures 352Table 13-1 Deflagration Flame Arrester Test Standards 389Table 13-2 Detonation Flame Arrester Test Standards 390Table 13-3IMO and USCG Endurance Burn Requirements 392Table 13-4 Comparison of Published MESG Values 394Table 14-1 Advantages and Disadvantages of Pilot Operated Valves 424Table 14-2 Advantages and Disadvantages of Rupture Disks 426Table 14-3 Vessel Flow Models 433Table 14-4 Summary of SAFIRE Emergency Relief System Input Data

Requirements 438Table 15-1 Incineration System Components 472Table 17-1 Gases Supporting Decomposition Flames 526Table 17-2 Fundamental Burning Velocity of Selected Hydrocarbons

in Air 531Table 17-3 Properties of Shock Fronts in Air 534Table 17-4 Detonation Characteristics of Select Stoichiometric

Gas-Air Mixtures 535Table 17-5 Combustible-Dependent Constants

for Low-Strength Enclosures 552

LIST OF FIGURES

Figure 2-1 Typical layers of protection in a modern chemical plant 10 Figure 2-2 A large batch reactor to manufacture a product 13 Figure 2-3 A tubular reactor to manufacture the product of Figure 2-2 13 Figure 2-4 Relative hazard zones for anhydrous and aqueous

monomethylamine releases—relative distances within which a

specified concentration of monomethylamine is exceeded upon

rupture of a 1-inch liquid pipe at summer ambient temperature for(A) anhydrous monomethylamine and (B) aqueous

monomethylamine 23

Figure 2-5 Effect of ase conditions on vapor release rate for a 6-inch

propane line: (A) gas phase release, (B) refrigerated liquid

release, (C) two-phase release 25

Figure 2-6 Relative hazard zones for ambient and refrigerated storage of

monomethylamine releases—relative distances within which a

specified concentration of monomethylamine is exceeded upon

rupture of a 1-inch liquid pipe containing liquid anhydrous

monomethylamine (A) at summer ambient temperature and (B)

refrigerated to its atmospheric pressure boiling point 26

Figure 2-7 A chlorine storage system 27 Figure 2-8 Influence of particle size on explosion properties of

combustible dusts 28

Figure 2-9 Manufacturing strategy options for a chemical Strategy B is

inherently safer because it eliminates the need to transport a

hazardous material from Plant 1 to Plant 2 30

Figure 2-10 A feed tank designed to prevent simultaneously filling and

emptying 32

Figure 2-11 A feed tank modified to limit the amount of materials it can

hold 33

Figure 2-12 Effect of dike design on a flammable vapor cloud from a 250

Ib/sec propane spill (A) Unconfined, (B) confined to a 30 X 30 footsump inside a 200 X 200 foot dike 34

Figure 2-13 A liquefied gas storage facility 35 Figure 2-14 A chlorine storage system with collection sump with vapor

containment 36

Figure 2-15 A diking design for a flammable liquid 36 Figure 2-16 A chemical process totally contained in a large pressure

vessel 37

Figure 2-17 Alternate arrangements for digital output signals from a

DCS Digital Output Mode (DOM) to a group of pumps

Arrangement (B) is more failure tolerant 41

Figure 2-18 (A)Poor distribution of analog signals to a DCS analog input

module (AIM) (B) An improved signal distribution, which is morefailure tolerant 42

Figure 2-19 A complex batch reactor conducting a multistep process 43 Figure 2-20 The same process as Figure 2-19, conducted in a series of

simpler vessels 43

Figure 3-1 Effects of timing of design changes 53 Figure 3-2 Hazards evaluation 54 Figure 3-3 Some reactivity hazards of chemical materials 58 Figure 3-4 Seismic zone map of the United States, used to assign seismic

zone factor Z 81

Figure 3-5 Minimum basic wind speeds in miles per hour, used to

determine design wind pressure 83

Figure 3-6 Single module UPS with bypass 91 Figure 3-7 Rectifier input type UPS 92 Figure 3-8 Parallel redundant hot-tie type UPS 93 Figure 4-1 Pressurized inert gas forces liquid from tank at left into one at

and pressurized reservoir Upon seal failure, the buffer liquid

(rather than the toxic process liquid) leaks, the liquid in the

reservoir drops, and the pump motor shuts off 142

Figure 5-1 Cathodic protection of an underground tank using impressed

Figure 7-3 Typical expansion tank (A) Suggested inert gas arrangemt

ofr expansion tank (B) Suggested cold seal trap arrangement forexpansion tank 224

Figure 7-4 Heat transfer system using the heat-transfer medium in the

vapor phase 227

Figure 7-5 Views of failed tube showing bulging and plug 231 Figure 8-1 Areas where corrosion under insulation is likely to occur 244

Figure 9-1 Schematic diagram of the structure of a programmable

Electronic System (PES) Whatever their size and role in a

particular installation, PESs all have the same basic structure 263

Figure 9-2 Layers of protection in a modern chemical plant 268 Figure 9-3 Sequence of steps in establishing SIS requirements 271 Figure 9-4 Process hazard analysis activities during the process life cycle 278 Figure 9-5 Linkage of process risk to SIS integrity classifications 279 Figure 9-6 Examples of SIS structures 285 Figure 9-7 Schematic chain of elements that must perform for

successful interlock action (lift weight on demand) 286

Figure 9-8 Two examples of inconsistent interlock chains 286 Figure 9-9 Example of Integrity Level 3 SIS function 289 Figure 11-1 Schematic autoignition temperature-pressure diagram 323 Figure 11-2 Illustration of ignition energy ranges) 327 Figure 12-1 Lightning formation 356 Figure 12-2 Mean annual days of thunderstorm activity in

the United States 357

Figure 12-3 (a) Single mast zone of protection, (b) Overhead

ground wires 358

Figure 12-4 Structural lightning protection using air terminals 359 Figure 12-5 Typical grounding system 362 Figure 12-6 Charge separation in a pipe 363 Figure 12-7 Charge generation during tank truck loading 364 Figure 12-8 Vessel fill pipe/dip leg arrangement to avoid static

electricity problems 365

Figure 12-9 Filling tank truck through open dome 366 Figure 13-1 (A)Deflagration (B) Detonation 373 Figure 13-2 End-of-line flame arrester 378 Figure 13-3 Vapor recovery system with detonation arresters applied 379 Figure 13-4 Types of arresters: (a) crimped ribbon; (b) parallel plate; (c)

expanded metal cartridge 382

Figure 13-5 (A) Liquid seal arrester; (B) Linde hydraulic valve arrester;

(C) packed bed arrester 383

Figure 13-6 Flame of run-up distance on maximum allowable

pressure—restricted end deflagrations 391

Figure 14-1 Typical conventional safety relief valve 420 Figure 14-2 Typical bellows type balanced relief valve For corrosion

isolation, an unbalanced bellows safety relief valve is available 421

Figure 14-3 Typical piston type balanced relief valve 422 Figure 14-4 Typical pilot-operated relief valve 423 Figure 14-5 Typical rupture disk 425 Figure 15-1 Typical elevated fire installation 448 Figure 15-2 Open ground flare 450

Figure 15-3 Enclosed ground flare 451 Figure 15-4 Typical enclosed ground flare 452 Figure 15-5 Typical flare knockout drum 460 Figure 15-6 Typical flare stack seal drum 461 Figure 15-7 Typical condensable blowdown drum 468 Figure 15-8 Condensable blowdown tank solvent service 469 Figure 15-9 Typical rotary kiln incineration unit 474 Figure 15-10 Typical multiple hearth incineration unit 476 Figure 15-11 Typical fluidized bed incineration unit 477 Figure 15-12 Modified wet air oxidation 480 Figure 15-13 Typical marine vapor control system incorporating

U.S Coast Guard regulations 485

Figure 16-1 Average property damage losses greater than $10 million in

the hydrocarbon processing industries 490

Figure 16-2 Frequency of losses greater than $10 million in the

hydrocarbon processing industries 491

Figure 16-3 Comparison of methods to test fireproof ing 510 Figure 17-1 Frequency distribution of types of equipment involved in

polyethylene dust in air 527

Figure 17-5 Typical pressure versus time data for closed-vessel

deflagration 533

Figure 17-6 Ideal blast wave overpressure versus scaled distance 537 Figure 17-7 Backflash interruptor 543 Figure 17-8 Explosion detector and isolation valve in a pipe 544 Figure 17-9 Dust suppression in a spherical vessel: Pressure-time plot

of a closed-vessel dust cloud deflagration 546

Figure 17-10 Schematic of a deflagration suppression system 548 Figure 17-11 Pressure-time plot for suppressed dust cloud deflagration 548 Figure 17-12 Pressure-time characteristics of vented and unvented

deflagrations form initially closed vessels 550

The Center for Chemical Process Safety (CCPS) was established in 1985 by theAmerican Institute of Chemical Engineers (AIChE) for the express purpose ofassisting the Chemical and Hydrocarbon Process Industries in avoiding ormitigating catastrophic chemical accidents To achieve this goal, CCPS hasfocused its work on four areas:

• establishing and publishing the latest scientific and engineering practices(not standards) for prevention and mitigation of incidents involving toxicand/or reactive materials;

• encouraging the use of such information by dissemination through lications, seminars, symposia and continuing education programs forengineers;

pub-• advancing the state-of-the-art in engineering practices and technical agement through research in prevention and mitigation of catastrophicevents; and

man-• developing and encouraging the use of undergraduate education ricula which will improve the safety knowledge and consciousness ofengineers

cur-The current book, Guidelines for Engineering Design for Process Safety, is the

result of a project begun in 1989 in which a group of volunteer professionalsrepresenting major chemical, pharmaceutical and hydrocarbon processingcompanies, worked with engineers of the Stone & Webster Engineering Cor-poration The intent was to produce a book that presents the process safetydesign issues needed to address all stages of the evolving design of the facility.This book discusses the impact that various engineering design choices willhave on the risk of a catastrophic accident, starting with the initial selection ofthe process and continuing through its final design This book is concernedwith engineering design for process safety It does not focus on operations,maintenance, transportation, storage or personnel safety issues, althoughimproved process safety can benefit each area Detailed engineering designsare outside the scope of the work, but the authors have provided an extensiveguide to the literature to assist the designer who wishes to go beyond safetydesign philosophy to the specifics of a particular design

The book has been organized so as to treat basic design issues first The firstdesign question addressed is the issue of "Inherently Safer Plants." Thisreflects the authors' strong belief that the optimum way to achieve processsafety is to design safety into the initial design The latter portion of the book

moves to reducing risk through the use of passive and then active devices toprevent and mitigate catastrophic events.

ACKNOWLEDGMENTS

The American Institute of Chemical Engineers (AIChE) wishes to thank theCenter for Chemical Process Safety (CCPS) and those involved in its operation,including its many sponsors whose funding made this project possible; themembers of its Technical Steering Committee who conceived of and sup-ported this Guidelines project and the members of its Engineering PracticesSubcommittee for their dedicated efforts, technical contributions, and en-thusiasm

The members of the Engineering Practices Subcommittee were

Stanley S Grossel, Hoffmann-LaRoche, Inc (Chairman)

Dane Brashear, Martin Marietta Energy Systems

Laurence G Britton, Union Carbide Corp.

James B Byrne, E I duPont de Nemours, Inc.

Stephen E Cloutier, UOP

Gus L Constan, Dow Corning Corp.

William E (Skip) Early, Stone & Webster Engineering Corp.

(Project Manager)

Kenneth W Under, Industrial Risk Insurers

Ann B May, Stone & Webster Engineering Corp (Technical Editor)

Al J McCarthy, The M W Kellogg Co.

Joseph B Mettalia, Jr., CCPS Staff

Carl S Schiappa, Dow Chemical USA

Former members were

Stanley M Englund, Dow Chemical USA

Walter B Howard, Process Safety Consultant

Howard E Huckins, Jr., CCPS Staff

Russell J Kerlin, Dow Corning Corp.

Paul Koppel, Fluor Daniel, Inc.

Philip MacVicar, W.R Grace & Co.

Marvin F Specht, Hercules Inc.

Technical Contributors and Reviewers were

Fred H Babet, Babet Engineering

Paul R Chaney, Mobil Chemical Company

Daniel A Crowl, Michigan Tech University

Elisabeth M Drake, M I T Energy Lab; CCPS Staff

Harold G Fisher, Union Carbide Corp.

Rudolph Frey, The M W Kellogg Co.

Raymond R Grehofsky, E I duPont de Nemours, Inc.

Russell J Kerlin, Dow Chemical Corp.

Trevor Knittel, Westech Corp.

Stanley S Schechter, Rohm and Haas Company

Robert W WaIz, ABB Lummus Crest Inc.

Lester H Wittenberg, CCPS Staff

A considerable number of other Stone & Webster Engineering Corporationpersonnel contributed; among them were:

The Engineering Practices Subcommittee is particularly indebted to Dennis

C Hendershot of the Rohm and Haas Company for Chapter 2, Inherently Safer

Plants, to Raymond P Grehofsky of E I duPont de Nemours, Inc for Section

9.6 of Chapter 9, Process Control, to Laurence G Britton of the Union Carbide Corporation for Chapter 11, Sources of Ignition, and Chapter 13, Deflagration

and Detonation Flame Arresters, to Kenneth Linder of Industrial Risk Insurers

for Chapter 16, Fire Protection, to Harold Fisher of the DIERS Committee for assistance with the section on two-phase venting in Chapter 14, Pressure Relief

Systems, and to Joseph A Senecal of Fenwal Safety Systems for Chapter 17, Explosion Protection.

Lastly we wish to express our appreciation to Thomas W Carmody andHoward E Huckins of the CCPS staff for their support and guidance

Administrative Controls: Procedural mechanisms, such as lockout/tagoutprocedures, for directing and/or checking human performance on planttasks

Autoignition Temperature: The autoignition temperature of a substance,whether solid, liquid, or gaseous, is the minimum temperature required

to initiate or cause self-sustained combustion, in air, with no other source

of ignition

Basic Event: An event in a fault tree that represents the lowest level ofresolution in the model such that no further development is necessary(e.g., equipment item failure, human failure, or external event)

Boiling-Liquid-Expanding-Vapor Explosion (BLEVE): A type of rapid phasetransition in which a liquid contained above its atmospheric boiling point

is rapidly depressurized, causing a nearly instantaneous transition fromliquid to vapor with a corresponding energy release A BLEVE is oftenaccompanied by a large fireball if a flammable liquid is involved, since anexternal fire impinging on the vapor space of a pressure vessel is acommon BLEVE scenario However, it is not necessary for the liquid to beflammable to have a BLEVE occur

Bonding: The permanent joining of metallic parts to form an electricallyconductive path which will assure electrical continuity and the capacity

to safely conduct any current likely to be imposed

Basic Process Control System (BPCS): The control equipment which is stalled to support normal production functions

in-Catastrophic Incident: An incident involving a major uncontrolled emission,fire or explosion with an outcome effect zone that extends offsite into thesurrounding community

Combustible: A term used to classify certain liquids that will burn on the basis

of flash points Both the National Fire Protection Association (NFPA) andthe Department of Transportation (DOT) define "combustible liquids" ashaving a flash point of 10O0F (37.80C) or higher See also, "Flammable."

Importance: Combustible liquid vapors do not ignite as easily as flammable

liquids; however, combustible vapors can be ignited when heated andmust be handled with caution Class II liquids have flash points at orabove 10O0F, but below 14O0F Class III liquids are subdivided into twosubclasses

Class UIA: Those having flash points at or above 14O0F but below 20O0F

Class IHB: Those having flash points at or above 20O0F

Common Mode Failure: An event having a single external cause with ple failure effects which are not consequences of each other.

multi-Continuous Reactors: Reactors that are characterized by a continuous flow ofreactants into and a continuous flow of products from the reaction system.Examples are the Plug Flow Reactor and the Continuous-flow StirredTank Reactor

Distributed Control System: A system which divides process control tions into specific areas interconnected by communications (normallydata highways) to form a single entity It is characterized by digital

func-controllers and typically by central operation interfaces

Distributed control systems consist of subsystems that are functionallyintegrated but maybe physically separated and remotely located from oneanother Distributed control systems generally have at least one sharedfunction within the system This maybe the controller, the communicationlink or the display device All three of these functions may be shared

A system of dividing plant or process control into several areas ofresponsibility, each managed by its own Central Processing Unit, with thewhole interconnected to form a single entity usually by communicationbuses of various kinds

Deflagration: The chemical reaction of a substance in which the reaction frontadvances into the unreacted substance at less than sonic velocity Where

a blast wave is produced that has the potential to cause damage, the term

explosive deflagration may be used.

Detonation: A release of energy caused by the extremely rapid chemicalreaction of a substance in which the reaction front advances into theunreacted substance at equal to or greater than sonic velocity

Design Institute for Emergency Relief Systems (DIERS): Institute under theauspices of the American Institute of Chemical Engineers founded toinvestigate design requirements for vent lines in case of two-phase vent-ing

Design Institute for Physical Property Data (DIPPR): Institute under theauspices of the American Institute of Chemical Engineers, founded tocompile a database of physical, thermodynamic, and transport propertydata for most common chemicals

Dow Fire and Explosion Index (F&EI): A method (developed by Dow cal Company) for ranking the relative fire and explosion risk associatedwith a process Analysts calculate various hazard and explosion indexesusing material characteristics and process data

Chemi-Emergency Shutdown (ESD) System: The safety control system which rides the action of the basic control system when predetermined condi-tions are violated

over-Equipment Reliability: The probability that, when operating under statedenvironment conditions, process equipment will perform its intendedfunction adequately for a specified exposure period.

ExplosionrA release of energy that causes a pressure discontinuity or blastwave

Fail-Safe: Design features which provide for the maintenance of safe ing conditions in the event of a malfunction of control devices or aninterruption of an energy source (e.g., direction of failure of a motoroperated valve on loss of motive power)

operat-Features incorporated for automatically counteracting the effect of ananticipated possible source of failure A system is fail-safe if failure of acomponent, signal, or utility initiates action that return the system to asafe condition

Failure: An unacceptable difference between expected and observed mance

perfor-Fire Point: The temperature at which a material continues to burn when theignition source is removed

Fireball: The atmospheric burning of a fuel-air cloud in which the energy ismostly emitted in the form of radiant heat The inner core of the fuelrelease consists of almost pure fuel whereas the outer layer in whichignition first occurs is a flammable fuel-air mixture As buoyancy forces

of the hot gases begin to dominate, the burning cloud rises and becomesmore spherical in shape

Flammability Limits: The range of gas or vapor amounts in air that will burn

or explode if a flame or other ignition source is present Importance: The

range represents an unsafe gas or vapor mixture with air that may ignite

or explode Generally, the wider the range the greater the fire potential.See also Lower Explosive Limit/Lower Flammable Limit and UpperExplosive Limit/Upper Flammable Limit

Flammable: A "Flammable Liquid" is defined by NFPA as a liquid with a flashpoint below 10O0F (37.80C)

Importance: Flammable liquids provide ignitable vapor at room

tempera-tures and must be handled with caution Precautions such as bonding andgrounding must be taken Flammable liquids are: Class I liquids and may

GLOSSARY xxiii