Written by Laurence Britton, who has over 20 years' experience in the fields of static ignition and process fire and explosion hazards research, this resource addresses an area not extensively covered in process safety standards or literature: understanding and reducing potential hazards associated with static electricity. The book covers the nature of static electricity, characteristics and effective energies of different static resources, techniques for evaluating static electricity hazards, general bonding, grounding, and other techniques used to control static or prevent ignition, gases and liquids, powders and hybrid mixtures.

Laurence G. Britton is the author of Avoiding Static Ignition Hazards in Chemical Operations: A CCPS Concept Book, published by Wiley.

Preface

Acknowledgments

Introduction

Purpose

1

(3)

Exclusions

4

(1)

Units

5

(1)

Organization of the Book

5

(2)

Fundamentals of Static Electricity

What Is Static Electricity?

7

(4)

Charge Separation

8

(1)

Magnitude of Current and Potential

8

(1)

Concentration of Charged Species

9

(1)

Importance of Trace Contaminants

9

(1)

Hazard Evaluation

10

(1)

Statistics

10

(1)

Charge Generation

11

(2)

Induction Charging

12

(1)

Ionic Charging

13

(1)

Charge Dissipation

13

(3)

Variability of Conductivity

15

(1)

Charge Accumulation

16

(1)

Ignition

17

(3)

Effective Energy

17

(3)

Static Discharges

20

(24)

Corona Discharge

21

(2)

Brush Discharge

23

(9)

Bulking Brush Discharge

32

(3)

Spark Discharge

35

(3)

Propagating Brush Discharge (PBD)

38

(5)

Surface Streamer

43

(1)

Personnel Spark and Shock Hazards

44

(3)

Body Capacitance and Resistance

44

(1)

Voltage (V) and Energy (W) Attained

45

(1)

Human Shock Response

46

(1)

Evaluating the Hazard of Static Electricity

General

47

(1)

Hazard Identification Methods

47

(1)

Decision Trees

48

(1)

Charge Accumulation

48

(1)

Conductive Objects

48

(1)

Nonconductive Objects

49

(1)

Energy Estimates

49

(1)

Charge Sharing

50

(1)

Instrumentation

50

(16)

Charge

50

(4)

Electric Field

54

(3)

Potential

57

(3)

Ignition Energy

60

(3)

Conductivity of Liquids

63

(1)

Resistivity of Solids

64

(1)

Resistance

65

(1)

Direct Observation of Discharges

66

(1)

Radio Frequency Detection of Discharges

66

(1)

Measuring the Effective Energy of Nonspark Discharges

66

(5)

Gas Composition

67

(4)

Controlling electrostatic Hazards

Bonding and Grounding

71

(4)

Definitions

71

(1)

Purpose of Bonding and Grounding

71

(1)

Resistance to Ground

72

(1)

Bonding and Grounding Systems

73

(1)

Ground Rods

73

(1)

Grounding and Cathodic Protection

74

(1)

Control of Charge Relaxation

75

(3)

Increase of Conductivity

75

(1)

Charge Neutralizers

76

(2)

Control of Personnel Charging

78

(3)

Personnel Grounding

78

(2)

Clothing

80

(1)

Gloves

80

(1)

Control of Flammable Atmospheres

81

(2)

Liquid Nitrogen/Liquid Air Hazards

81

(2)

Flammable Liquids, Vapors, and Gases

Ignition Hazards of Liquid Vapor and Mist

83

(13)

Flammable Liquid

83

(3)

Flammable Limits

86

(1)

Liquid Mist

87

(2)

Minimum Ignition Energy (MIE)

89

(6)

Explosion Prevention Systems

95

(1)

Generation and Relaxation (Loss) and Charge in Liquid Systems

96

(10)

Charge Generation

96

(1)

Charge Density

97

(1)

Factors Influencing Charge Generation

97

(1)

Charge Relaxation

98

(3)

Classification of liquids based on Conductivity

101

(3)

Antistatic Additives

104

(2)

Bonding and Grounding

106

(1)

Flow in Pipe, Hose, and Tubing

106

(14)

Metallic Piping Systems

106

(5)

Nonconductive Pipe and Linings

111

(3)

Flexible Hoses

114

(2)

Dip Pipes

116

(1)

Filters and Relaxation Tanks

116

(2)

Suspended Material

118

(1)

Valves and Other Line Restrictions

119

(1)

Filling Criteria for Tank Operations

120

(22)

Storage Tanks

122

(6)

Road Tankers

128

(4)

Rail Cars

132

(1)

Liquid Phase Mixers, Blenders, and Reactors

132

(3)

Liquid-Solid Mixers, Blenders and Reactors

135

(2)

Vaccum Trucks

137

(2)

Plastic Tanks

139

(3)

Sampling, Gauging, and Analysis

142

(2)

Sample Container Cord

142

(1)

Sampling

142

(1)

Gauging

143

(1)

Portable Flammable Gas Analyzers

144

(1)

Tank Cleaning

144

(5)

Water Washing

144

(2)

Solvent Washing

146

(1)

Steam Cleaning

147

(1)

Acid Washing

148

(1)

Grit Blasting

149

(1)

Portable Tanks

149

(1)

Metal Portable Tanks

149

(1)

Plastic Portable Tanks

150

(1)

Portable Containers Less Than 60 Gallons Capacity

150

(7)

All-Steel Drums

151

(2)

Plastic Lined Drums

153

(1)

Plastic Drums

154

(1)

Hand-Held Containers

154

(3)

Wet-Dry Vacuum Cleaners

157

(1)

Miscellaneous Flammable Atmospheres

157

(8)

Clean Rooms

157

(1)

Water and Steam Curtains

158

(1)

Static Electrification in Gas Flow

158

(1)

Ignition of Vented Gas

159

(1)

Hazards of Plastic Sheet and Wrap

160

(1)

Oxidant Enriched Atmospheres

161

(1)

Elevated Temperature and Pressure

162

(1)

Automative and Marine

163

(1)

Aerosol Spray Cans

164

(1)

Cathody Ray Tube Video Display Screens

165

(2)

Cleaning

165

(1)

Screens in Hazardous Locations

165

(1)

Static Dissipating Screen Overlays

166

(1)

Powders and Solids

Flammability of Dust Suspensions

167

(10)

Flammable Limits

169

(1)

Minimum Ignition Energy (MIE) of Dust Suspensions

170

(2)

Hybrid Mixtures

172

(3)

Unstable or Energetic Powders

175

(1)

Effect of Temperature on Ignition Energy

176

(1)

Effect of Moisture on Ignition Energy

177

(1)

Charging Mechanisms

177

(6)

Charge Density

179

(1)

Classification of Powders Based on Conductivity

180

(3)

Pneumatic Conveying

183

(6)

Charging in Pipeline Flow

183

(4)

Special Grounding Cases

187

(2)

Types of Static Discharge in Power Systems

189

(6)

Sparks

190

(3)

Bulking Brush Discharges

193

(1)

Propagating Brush Discharge

194

(1)

General Operations

195

(4)

Vaccum Trucks

197

(1)

Bag Houses

198

(1)

Manual Transfers from Portable Containers

199

(1)

Flexible Intermediate Bulk Containers (FIBCs)

199

(6)

Power Transfers in Air Atmospheres

200

(2)

Power Transfers from FIBC to Flammable Liquids

202

(1)

Conductive and Antistatic FIBCs

202

(2)

Vacuum FIBC Transfers

204

(1)

Appendix A. EXPLANATORY MATERIAL

A-2-6.5 Propagating Brush Discharge

205

(1)

A-4-1.3. Resistance to Ground

206

(3)

A-5-1.4.4. MIE of Liquid Mists

209

(2)

A-5-2.4.1 Hyperbolic Relaxation

211

(2)

A-5.3.5. Filtration

213

(1)

A-5-4. Filling Criteria for Tank Operations

214

(2)

A-5-4.2-1. Effect of Road Tires

216

(1)

A-5-6.1. Potentials during Water Washing of Tanks

217

(2)

A-6-1.2. Effect of Particle Size on Dust MIE

219

(1)

A-6-1.3.1 Ignition Energy of Hybrid Mixtures

219

(1)

A-6.1.5. Effect of Temperature of Powder MIE

220

(3)

Appendix B. DATA TABLES

Flammability Data for Gases and Vapors

223

(4)

Typical Conductivities, Dielectric Constants and Relaxation (or Dissipation) Times of Liquids

227

(7)

Typical Resistivities, Dielectric Constants, and Breakdown Strengths of Solid Dielectrics

234

(3)

Appendix C. FORMULAS AND MATHEMATICAL RELATIONSHIPS (SI UNITS)

C-1. Principal Relationships

237

(1)

C-2. Analysis: Grounded Sphere above Charged Nonconductive Disc

238

(11)

References

249

(12)

Glossary

261

(12)

Index

273

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