Static Electricity Static Electricity Understanding, Controlling, Applying Günter Lüttgens, Sylvia Lüttgens, and Wolfgang Schubert Authors All books published by Wiley-VCH are carefully produced. Nevertheless, authors, Günter Lüttgens editors, and publisher do not warrant the Research and Consulting information contained in these books, including Am Berg 27 this book, to be free of errors. Readers are 51519 Odenthal advised to keep in mind that statements, data, Germany illustrations, procedural details or other items may inadvertently be inaccurate. Sylvia Lüttgens Research and Consulting Library of Congress Card No.: applied for Am Berg 27 51519 Odenthal British Library Cataloguing-in-Publication Data Germany A catalogue record for this book is available from the British Library. Wolfgang Schubert SCHUBERT GMD Bibliographic information published by Publicly Appointed and Sworn Expert for the Deutsche Nationalbibliothek Printing Technologies The Deutsche Nationalbibliothek lists this Print-Machines Printability and Runnability publication in the Deutsche Nationalbibliografie; Packaging Print detailed bibliographic data are available on the Independent appraiser for Electrostatics Internet at <http://dnb.d-nb.de>. Weidenweg 15 04425 Taucha © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Germany Boschstr. 12, 69469 Weinheim, Germany Cover material was kindly provided All rights reserved (including those of by the authors translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. 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Print ISBN: 978-3-527-34128-3 ePDF ISBN: 978-3-527-80332-3 ePub ISBN: 978-3-527-80334-7 Mobi ISBN: 978-3-527-80335-4 oBook ISBN: 978-3-527-80333-0 Cover Design Formgeber, Mannheim, Germany Typesetting SPi Global Private Limited, Chennai, India Printing and Binding Printed on acid-free paper v Contents About the Authors xiii Opening Remark xv Preliminary Remark xvii Preface xix 1 Basics of Fire and Explosion: Risk Assessment 1 1.1 Basic Considerations on Fire and Explosion ( T1) 1 1.1.1 Fuel 2 1.1.2 Heat 2 1.1.3 Oxygen 3 1.1.4 Inerting Process 3 1.1.5 Heat versus Oxygen 3 1.2 Explosive Atmosphere 3 1.2.1 Explosion Limits with Flammable Liquids 3 1.2.1.1 Classification of Flammable Liquids 5 1.2.2 Explosion Limits with Combustible Dusts 6 1.2.3 Metal Dusts 6 1.3 Hybrid Mixtures ( P7) 6 1.4 Allocation of Explosion-Endangered Areas and Permissible Equipment ( P6) 7 1.5 Permissible Equipment (Equipment Protection Level) 7 1.5.1 Classification of Equipment Protection Level That Is Currently in the Introductory Stage 8 1.6 Ignition Sources 9 1.6.1 Hot Surfaces 9 1.6.2 Flames and Hot Gases (Including Hot Particles) 9 1.6.3 Mechanically Generated Sparks ( MGS) 10 1.6.4 Electrical Apparatus 10 1.6.5 Cathodic Protection 10 1.6.6 Static Electricity 10 1.6.7 Lightning 10 1.6.8 Electromagnetic Field 10 1.6.9 Electromagnetic Radiation 10 1.6.10 Ionizing Radiation 10 vi Contents 1.6.11 Ultrasonics 11 1.6.12 Adiabatic Compression and Shock Waves 11 1.6.13 Chemical Reactions 11 1.7 Minimum Ignition Energy (MIE) 11 1.8 Imaginary Experiment to Assess the Hazardous Potential of Flammable Liquids 15 PowerPoint Presentations 18 References 18 2 Principles of Static Electricity 19 2.1 Basics 19 2.2 Electrostatic Charging of Solids ( T2) 21 2.3 Triboelectric Series 24 2.4 Surface Resistivity 24 2.4.1 Influence of Surface Texture on Static Charging 28 2.5 Electrostatic Charging of Liquids ( T2, T8) 28 2.5.1 Charge Relaxation with Liquids 30 2.6 Charging by Gases 31 2.7 Electric Field 33 2.8 Electric Induction ( T3) 36 2.8.1 Specification of Electric Induction 36 2.8.2 Image Charge 37 2.9 Capacitance and Capacitor 38 PowerPoint Presentations 38 References 39 3 Metrology 41 3.1 Basics ( T7) 41 3.1.1 “Walking Test” as a Paradigmatic Example 41 3.2 Appropriate Metrology for Electrostatic Safety Measures 44 3.3 Comparison: Electrostatics/Electrical Engineering 44 3.4 Selecting the Suitable Measurement Methods 45 3.4.1 Electrical Resistance 45 3.4.2 Fundamental Remarks for the Realization of Resistance Measurements ( T4) 46 3.4.2.1 Volume Resistance and Deriving Volume Resistivity 46 3.4.2.2 Guard Ring Circuit to Measure the Volume Resistance 47 3.4.2.3 Surface Resistance and Deriving Surface Resistivity 48 3.4.2.4 Guard Ring Circuit to Measure the Surface Resistance 49 3.5 Assignment and Summary 49 3.5.1 Additive‐Depleted Surface 50 3.6 Conductivity of Liquids 51 3.7 Bulk Materials 52 3.8 Concerning the Use of Insulating Material in Endangered Areas 52 3.9 Measurement of Electrostatic Charges 52 3.9.1 Voltage Measurement with Electrostatic Voltmeters 53 3.9.2 Charge Measurement by Means of a Faraday Pail 54 Contents vii 3.9.2.1 Faraday Cage 55 3.9.2.2 Charge Measurement on Free‐Falling Objects 55 3.9.3 Measurement of Electric Field Strength 56 3.9.3.1 Induction Electric Field Meters 56 3.9.3.2 Errors When Measuring Field Strength 58 3.9.3.3 Further Types of Electric Field Meters 61 3.9.3.4 Further Applications of Induction Electric Field Meters 65 3.10 Other Measurement Applications 68 3.10.1 Measurement of Surface Charge on Moving Webs 68 3.10.2 Analysis of Protective Textile Clothing (Workwear) 68 3.10.2.1 Triboelectric Test Procedure 69 3.10.2.2 Test Procedures with Electrostatic Influence 69 3.10.3 Test Procedure to Determine Discharge Capacity (Charged Plate Monitor) 71 3.10.4 Test Procedure for Paper 73 3.10.5 Electrostatic Charging of Powdery Bulk Materials 74 3.10.6 Electrostatic Charging with Fluids 75 3.10.7 Electrostatic Charges in Chemical Production 76 3.11 Capacitance 77 3.11.1 Capacitance Measurement (Charging Methods) 77 3.11.2 Measurement of the Permittivity Value 78 3.11.3 Charge Decay Measurement (Relaxation Time) 79 3.12 Themes around Air Humidity 81 3.12.1 Definitions about Climate 81 3.12.2 Fundamental Principles and Definitions 82 3.12.3 Methods of Measuring Atmospheric Humidity 83 3.12.3.1 Dew Point Hygrometry 83 3.12.3.2 Absorption Method 84 3.12.3.3 Hair Hygrometer 84 3.12.3.4 Psychrometer with Wet‐ and Dry‐Bulb Thermometers 84 3.12.3.5 Lithium‐Chloride Hygrometer 85 3.12.3.6 Capacitive Hygrometer 86 3.12.3.7 Resistive Hygrometer 86 3.12.4 Monitoring and Calibrating of Hygrometers 86 PowerPoint Presentations 87 Picture Credits 87 References 88 4 Gas Discharges 89 4.1 Mechanisms of Gas Discharges ( T5) 89 4.2 Electrostatic Gas Discharges 90 4.2.1 Detecting Gas Discharges by Means of Their High‐Frequency Emissions 92 4.3 Types of Gas Discharges 94 4.3.1 Spark Discharge 94 4.3.2 One‐Electrode Discharges 95 4.3.2.1 Corona Discharge 96 viii Contents 4.3.2.2 Brush Discharge 97 4.3.2.3 Cone Discharge (also Referred to as Powder Heap Discharge) 98 4.3.2.4 Propagating Brush Discharge 98 4.4 Consequences of Gas Discharges 102 4.5 Listing of Traces Caused by Gas Discharges (  P11; T8) 102 4.6 How Can Dangerous Gas Discharges Be Avoided? 103 4.6.1 Spark Discharges (V4.1) 104 4.6.2 Corona Discharges 104 4.6.3 Brush Discharges and Super Brush Discharges 104 4.6.4 Cone Discharges 106 4.6.5 Propagating Brush Discharges 107 4.6.5.1 Curiosity When Hydraulic Oil Gradually Flows Out of a Metal Pipe 107 4.6.5.2 Pores at Enameled Containers 108 4.6.6 Simplified Overview of the Occurrence of Different Types of Gas Discharges 108 4.6.7 Assessment of Ignition Dangers Originating from Gas Discharges 108 4.6.8 Electrostatic Shock 111 PowerPoint Presentations 111 Picture Credits 111 Video Credits 111 References 111 5 Preventing Electrostatic Disturbances 113 5.1 Electrostatics: When Sparks Fly 113 5.2 Dielectric Strength 117 5.3 Discharging Charged Surfaces 118 5.3.1 Discharging on Material Webs 119 5.3.1.1 Behavior of Composite Materials 125 5.3.2 Discharging of Sheets 127 5.3.3 Discharging Other Objects 127 5.3.4 Discharging Granules and Similar Particles 129 5.4 Potential Hazards Posed by Discharge Electrodes 134 Picture Credits 136 Video Credits 137 References 137 Further Reading 137 6 Description of Demonstration Experiments 139 6.1 Preliminary Remarks 140 6.2 Static Voltmeter 141 6.3 Field Meter 142 6.4 Van de Graaff Generator 142 6.5 Explosion Tube 142 6.6 Electrostatic Force Effects 144 6.6.1 Rolling Pipes 145 Contents ix 6.6.2 Hovering Pipes 146 6.6.3 Electroscope 147 6.6.4 Depicting Electrical Field Lines (in a Classical Way) 148 6.7 Charges Caused by Separating Process 149 6.8 Charging of Particles 150 6.8.1 Charging of Single Particles 150 6.8.2 Charging of Many Particles (Granules) 152 6.9 Electric Induction 153 6.9.1 Basic Experiment 153 6.9.2 Chimes 154 6.9.3 Electric Induction on Isolated Conductive Parts 155 6.10 Dissipating Properties 157 6.11 Experiments with the Explosion Tube 158 6.11.1 Electrostatic Charging of a Person 158 6.11.2 Ignition Voltage 159 6.11.3 Charging by Separation 160 6.12 Gas Discharges 160 6.12.1 Spark Discharges 160 6.12.2 Corona Discharges 161 6.12.3 Brush Discharges 162 6.12.4 Model Experiment: Ignition by Brush Discharges 162 6.12.5 Evidence of Ion Wind 163 6.12.6 Super Brush Discharges 163 6.12.7 Propagating Brush Discharges 164 6.12.7.1 Ignition of Dust 165 6.12.7.2 Short Circuit of a Double‐Layer Charge 166 6.13 Fire and Explosion Dangers 168 6.13.1 Flash Point 168 6.13.2 Effects with Large Surfaces 168 6.13.3 Rich Mixture 169 6.13.4 Progressive Flame Front 170 6.13.5 “Decanting” of Gasoline Vapors 171 6.13.6 Oxygen Demand 172 6.13.7 Extinguishing with Water 173 6.13.8 Burning Handkerchief Does Not Burn Up 174 6.13.9 Inflaming Solid Combustibles 174 6.13.9.1 Gasification Process with Wood 174 6.13.9.2 Inflaming a Dust Heap 175 Reference 175 7 Case Studies 177 7.1 Strategy of Investigation 177 7.1.1 Ignition Sources 178 7.1.2 General Approach 179 7.1.3 Hasty Consequence 179 7.2 Ignitions Due to Brush Discharges 180 7.2.1 Pouring Flaked Product into an Agitator Vessel 180 x Contents 7.2.2 PE Liner Slipping Out of Paper Bag 181 7.2.3 Ignition Caused by an Antistatic PE Bag 182 7.2.4 Shaking Fine Dust Out of a PE Bag (Hybrid Mixture) 183 7.2.5 Pumping Polluted Toluene 185 7.2.6 Impregnation of a Glass Fiber Fabric 186 7.2.7 Filling Pipe Blocked with Sulfur Leading to Ignition of Methanol 187 7.2.8 Ion Exchanger Resin in Toluene 188 7.2.9 Two Explosions in Big Storage Tanks 189 7.2.9.1 Explosion in a Floating Roof Tank Followed by Fire (2014) 189 7.2.9.2 Explosion Disaster Near Bitburg (1954) 190 7.3 Case Studies Related to Propagating Brush Discharges 192 7.3.1 Explosion in a Railcar Bulk Container 192 7.3.2 Metal Drum with Inner Liner 193 7.3.3 Plastic Drum with Inner Liner 195 7.3.4 Failed Attempt to Eliminate Electrostatic Nuisances 195 7.3.5 Fire in a Spray‐Bed Dryer 197 7.3.6 Ignition in a Micronizer Jet Mill 200 7.3.7 Explosion During Rotational Molding 201 7.3.8 Explosion in a Mixing Silo for Plastic Granules 202 7.3.9 Curiosity During Outflow of Liquid from a Metal Pipe 202 7.4 Case Histories Related to Spark Discharges 204 7.4.1 Powder Explosion in a Metal Drum 204 7.4.2 Dust Removal from Pharmaceutical Pills 205 7.4.3 Sparks at a Throttle Valve (V4.1) 206 7.4.4 Filling n‐Hexane into Metal Drums ( P 15) 207 7.4.5 Hose Filter 208 7.4.6 Water Flowing Through PVC Hose 210 7.4.7 Lost and Found 211 7.4.8 Miraculous Earthing Clamp 212 7.5 Ignition Caused by Cone Discharges 212 7.6 Doubts with Electrostatic Ignitions 213 7.6.1 Fire in a Polyethylene Drum 213 7.6.2 Fire in a Solvent Cleaning Area 215 7.6.3 Burst of a Glass Pipe 218 7.7 Act with Relevant Experience 219 7.7.1 Basic Information 219 PowerPoint Presentations 220 Video 221 References 221 8 Targeted Use of Charges 223 8.1 Applications 223 8.2 Examples of the Creative Implementation of Applications 226 8.2.1 Adhesive Bonding – Blocking 226 8.2.2 Adhesion of an Insert on a Variable Base 227 8.2.3 Blocking a Number of Paper Webs or Film Webs in One Ribbon 229 8.2.4 Adhesion of a Melt Layer on the Chill Roll 230