Contents
Preface xi
Chapter 1 Introduction 1
General Safety Criteria: Protection of People, Property,
and the Community 2
Safety Philosophy and Principles 5
Electrical and Control System Safety Incidents 6
Acronyms and Abbreviations 7
Chapter 2 Process Units for Electrical and Process
Control Safety 9
Process Conditions That Influence Safety 9
Process Operations 11
Plant Layout: Physical Facilities 12
Chapter 3 Hazardous (Classified) Locations:
Area Classification 14
National Electrical Code Terminology 14
Flammability Characteristics 18
Leak and Release Sources 20
Ventilation 21
Process Conditions 22
Vapor Barriers 22
Nonelectrical Ignition Sources 22
Electrical Classification Practice 22
Analytical Approach to Classification 24
Electrical Classification versus EPA
and Toxicity Requirements 27
Reducing Classified Locations 28
Division 3 28
Probability Concepts: Division 0 29
vii
viii CONTENTS
Electrical Classification: Special Cases 30
Conclusion 33
References 34
Chapter 4 Electrical Equipment in Class I Locations 35
Electrical Facilities Outside Classified Locations 38
National Electrical Code 37
Explosionproof Apparatus 39
Sealing Process-Connected Instrumentation 41
Purging and Pressurization 45
Advantages of Purging and Pressurization 49
Intrinsic Safety 50
Oil Immersion 58
Conclusion 59
References 60
Chapter 5 Dust Electrical Safety in ChemicalProcessing
Facilities 61
Dust Explosions and Fires 61
Electrical Causes of Dust Ignition 62
Characteristics of Dust Explosion 62
National Electrical Code and Combustible Dusts 64
Classification of Dust Locations 68
Conclusion 70
References 70
Chapter 6 Electrical Safety in Chemical Processes 71
Electrocution and Personnel Safety 72
Lightning Protection for Chemical-Process Facilities 75
Static Electricity as an Ignition Source 85
Protection of Electrical Systems 96
Electrical Power Reliability and Quality 122
Cable Systems for Chemical-Process Facilities 139
Conclusion 143
References 145
Chapter 7 Measurement and Final Control Elements 148
Instrumentation Flow Diagrams 148
Process Measuring Elements 149
Final Control Elements 154
Alternating Current Versus Direct Current Drives 156
Conclusion 157
References 158
Chapter 8 Process Control Safety 159
History of Process Control 160
Distributed Control Systems 162
Alarm Systems 164
Interlock Systems 167
Safety Interlock Systems 168
Electrical Protection of Control Systems 171
Conclusion 177
References 178
CONTENTS ix
Chapter 9 Electrical and Process Control Safety Standards
for Chemical Processes 180
National Standards Organizations 181
International Standards 190
Conclusion 193
Chapter 10 Safety in Maintenance 194
Preventive Maintenance 195
Design for Maintainability 195
Electrical and Process Control System
Maintenance Practices 196
Surveys and Inspections 197
Testing 198
References 200
Chapter 11 Safety in Work Practices 201
Electrical and Process Control Safety
Work Practices 201
Hot Work 204
Maintenance in Hazardous (Classified) Locations 204
Hot Work in Hazardous (Classified) Locations 205
Appendix An Illustrated Guide to Electrical Safety 207
Index 239
Preface
This text is about electrical and instrumentation safety for chemical processes.
It covers a wide area of electrical and electronic phenomena and how
they have and can significantly affect the safety of chemical processes. The
importance of the subject is well known to anyone involved in the operation
of chemical processes.
Lightning strikes can explode storage tanks, shut down electrical power
systems, and shut down or damage computer and instrument systems.
Static electricity can ignite flammable materials and damage sensitive electronic
process control equipment. Electrical power system failures or interruptions
can produce unsafe process conditions. Chemical processes use
flammable and combustible vapors, gases, or dusts that can be exploded by
electrical equipment and wiring. Even low-energy equipment like flashlights
can ignite a flammable vapor. Interlock and equipment protection systems
can cause safety problems.
How important is electrical and process control safety? A survey on
“How Safe is Your Plant?”, in the April 1988 issue of Chemical Engineering
magazine, provided some answers. Among the results of this survey of
chemical processes, it was found that over 800 respondents believed instrumentation
and controls, shutdown systems, equipment interlocks, and
other protection systems to be the least safe aspect of chemical industries.
The survey also indicated that complying with OSHA and other regulations,
process control software security, inspections, audits, and safety
training are important safety issues.
Electrical and Instrumentation Safety for Chemical Processes covers the
areas mentioned in the Chemical Engineering magazine survey, as well as
many other important issues, including: hazardous areas; combustible dust
safety; computer power and grounding; power system reliability for chemical
processes; and process control safety.
