IEC TR 61340-1:2012

Electrostatics - Part 1: Electrostatic phenomena - Principles and measurements

IEC/TR 61340-1:2012 describes the fundamental principles of electrostatic phenomena including charge generation, retention and dissipation and electrostatic discharges. Methods for measuring electrostatic phenomena and related properties of materials are described in a general way. Hazards and problems associated with electrostatic phenomena and principles of their control are outlined. Useful applications of electrostatic effects are summarized. The purpose of this technical report is to serve as a reference for the development of electrostatics related standards, and to provide guidance for their end-users. The contents of the corrigendum of March 2013 and the corrigendum 2 of December 2017 have been included in this copy.

Electrostatique - Partie 1: Phénomènes électrostatiques - Principes et mesures

La CEI/TR 61340-1:2012 qui est un rapport technique, décrit les principes fondamentaux relatifs aux phénomènes électrostatiques, comprenant la génération, le maintien et la dissipation de la charge, et les décharges électrostatiques. Les méthodes de mesure des phénomènes électrostatiques et des propriétés associées des matériaux sont décrites de manière générale. Les dangers et les problèmes liés aux phénomènes électrostatiques ainsi que les principes de leur contrôle sont présentés dans les grandes lignes. Des applications utiles des effets électrostatiques sont résumées. Le présent rapport technique est destinée à servir de référence pour l'élaboration de normes relatives aux phénomènes électrostatiques et de guide pour l'utilisateur final. Le contenu du corrigendum de mars 2013 et de décembre 2017 a été pris en considération dans cet exemplaire.

General Information

• Status: Published
• Publication Date: 09-Jun-2020
• ICS: 17.220.99 - Other standards related to electricity and magnetism
• ICS: 29.020 - Electrical engineering in general
• Technical Committee: TC 101 - Electrostatics
• Current Stage: PPUB - Publication issued
• Start Date: 26-Jun-2012
• Completion Date: 31-Aug-2012

Relations

• Amended By: IEC TR 61340-1:2012/AMD1:2020 - Amendment 1 - Electrostatics - Part 1: Electrostatic phenomena - Principles and measurements
• Effective Date: 05-Sep-2023
• Corrected By: IEC TR 61340-1:2012/COR2:2017 - Corrigendum 1 - Electrostatics - Part 1: Electrostatic phenomena - Principles and measurements
• Effective Date: 05-Sep-2023
• Corrected By: IEC TR 61340-1:2012/COR1:2013 - Corrigendum 1 - Electrostatics - Part 1: Electrostatic phenomena - Principles and measurements
• Effective Date: 05-Sep-2023

Overview

IEC TR 61340-1:2012 - "Electrostatics – Part 1: Electrostatic phenomena – Principles and measurements" is a Technical Report from the IEC that describes the fundamental principles of electrostatic phenomena and gives general guidance on measurement methods. The consolidated Edition 1.1 (2012 + corrigenda and Amendment 1, 2020) serves as a reference for standards development and for end‑users seeking a practical understanding of charge generation, retention, dissipation and electrostatic discharges (ESD).

Key topics

The report covers core electrostatics concepts and measurement-related topics, including:

• Charge generation and contact electrification (triboelectric effects and charge transfer mechanisms)
• Charging by induction and conduction, and retention of charge on materials
• Influence of environmental humidity on charge and charge decay
• Electrostatic discharges: spark, corona, brush, propagating brush and cone discharges; associated energy and ignition potential
• Mechanical forces in electrostatic fields
• ESD failure modes and hazards for electronic components, ignition risks, and human perception
• Common ESD simulation models referenced (human body model, machine model, charged device model) and circuits for discharge simulation
• Measurement concepts: electric field, surface and space potential, surface charge density, charge decay, resistance/resistivity, capacitance and charge transferred in discharges
• General measurement arrangements and practical guidance rather than prescriptive test procedures

Note: IEC TR 61340-1 is a technical report (guidance), not a prescriptive test standard; it provides principles and measurement options rather than mandatory limits.

Applications

IEC TR 61340-1 is useful for organizations and professionals involved in:

• ESD control and prevention programs in electronics manufacturing and assembly
• Product designers and material suppliers selecting packaging, coatings and components with favorable electrostatic properties
• Test laboratories developing measurement methods for surface voltage, charge decay and discharge energy
• Safety and process engineers assessing ignition hazards in flammable atmospheres
• Standards developers and researchers using the document as a reference for developing or harmonizing ESD-related standards

Practical uses include guiding risk assessments, specifying measurement setups, training engineers on ESD phenomena, and informing mitigation strategies (grounding, ionization, humidity control, conductive materials).

Related standards

• Other parts of the IEC 61340 series (Electrostatics) expand on ESD control methods and product‑specific guidance.
• The report references common ESD simulation models (Human Body Model, Machine Model, Charged Device Model) used across industry ESD standards.

Keywords: IEC TR 61340-1:2012, electrostatics, electrostatic discharge, ESD, charge decay, surface voltage, measurement methods, triboelectric, ESD control.

Standards Content (Sample)

IEC TR 61340-1 ®
Edition 1.1 2020-06
CONSOLIDATED VERSION
TECHNICAL
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Electrostatics –
Part 1: Electrostatic phenomena – Principles and measurements

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IEC TR 61340-1 ®
Edition 1.1 2020-06
CONSOLIDATED VERSION
TECHNICAL
REPORT
colour
inside
Electrostatics –
Part 1: Electrostatic phenomena – Principles and measurements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.99; 29.020 ISBN 978-2-8322-8521-3

IEC TR 61340-1 ®
Edition 1.1 2020-06
REDLINE VERSION
colour
inside
Electrostatics –
Part 1: Electrostatic phenomena – Principles and measurements

– 2 – IEC TR 61340-1:2012+AMD1:2020 CSV
© IEC 2020
CONTENTS
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Fundamentals of static electricity . 10
4.1 General . 10
4.2 Contact electrification . 11
4.3 Charging by induction . 12
4.4 Charge transfer by conduction . 13
4.5 Retention of charge . 13
4.6 Influence of environmental humidity . 15
4.6.1 General . 15
4.6.2 In situ measurements . 15
4.7 Electrostatic discharges . 15
4.7.1 General . 15
4.7.2 Spark discharges . 15
4.7.3 Corona discharges . 16
4.7.4 Brush discharges . 16
4.7.5 Propagating brush discharges . 16
4.7.6 Cone discharges . 17
4.8 Mechanical forces in an electrostatic field . 17
5 Electrostatic problems and hazards . 18
5.1 General . 18
5.2 Electronic components and systems . 18
5.2.1 General . 18
5.2.2 Types of failure . 18
5.2.3 Problems and threats at different life cycle periods . 19
5.3 Electrostatic ignition – Hazards . 20
5.3.1 General . 20
5.3.2 Spark discharges from conducting objects . 20
5.3.3 Corona discharges from conducting objects . 20
5.3.4 Brush discharges from insulating surfaces . 20
5.3.5 Propagating brush discharges from insulating surfaces . 21
5.3.6 Discharges from people . 21
5.3.7 Ignition potential of electrostatic discharges . 21
5.4 Physiological sensation . 23
5.5 Simulation of electrostatic discharges. 24
5.5.1 General . 24
5.5.2 Capacitive discharges for ignition energy measurements . 25
5.5.3 Human body model . 25
5.5.4 Machine model . 25
5.5.5 Charged device model . 25
6 General solutions to problems and hazards . 26
6.1 General . 26
6.2 Common approaches. 26
7 Useful applications of electrostatic effects . 27
8 General aspects of measurements . 28

© IEC 2020
8.1 General . 28
8.2 Electric field . 28
8.2.1 General . 28
8.2.2 Application . 29
8.3 Potential . 29
8.3.1 General . 29
8.3.2 Surface voltage . 30
8.3.3 Space potential . 30
8.4 Charge . 31
8.5 Charge density . 31
8.5.1 Surface charge density . 31
8.5.2 Volume charge density . 32
8.6 Charge decay . 32
8.7 Resistance and resistivity . 33
8.8 Chargeability . 33
8.9 Current . 34
8.10 Energy in capacitive discharges . 34
8.11 Ignition energy . 35
8.11.1 General . 35
8.11.2 Equivalent energy . 35
8.12 Charge transferred in electrostatic discharges . 36
8.12.1 General . 36
8.12.2 Discharge electrode . 37
8.12.3 Measuring circuit . 38
8.12.4 Alternative charge transfer measuring arrangements . 38
8.13 Capacitance . 38
8.14 Electric strength . 39

Figure 1 – Charging by induction . 13
Figure 2 – Charge transfer by conduction when objects 1 and 2 are conductors. 13
Figure 3 – Equivalent electrical circuit for an electrostatically charged conductor . 14
Figure 4 – Examples of brush discharge waveforms measured with a fast digital
storage oscilloscope . 23
Figure 5 – Circuit for simulation of electrostatic discharges . 24
Figure 6 – Basic arrangements for measuring charge transferred in electrostatic
discharges with alternative measuring circuits . 37
Figure 7 – Oscilloscope voltage/time traces . 38

Table 1 – Example of triboelectric series. 12
Table 2 – Typical electrical capacitances . 16
Table 3 – Typical perception levels and physical responses of people to discharges
based on a body capacitance of 200 pF . 24
Table 4 – Typical values used in ESD simulation models . 26

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© IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
ELECTROSTATICS –
Part 1: Electrostatic phenomena –
Principles and measurements
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
This consolidated version of the official IEC Standard and its amendment has been
prepared for user convenience.
IEC TR 61340 edition 1.1 contains the first edition (2012-06) [documents 101/344/DTR
and 101/355/RVC] and its corrigenda 1 (2013-03) and 2 (2017-12), and its amendment 1
(2020-06) [documents 101/598/DTR and 101/604/RVDTR].
In this Redline version, a vertical line in the margin shows where the technical content
is modified by amendment 1. Additions are in green text, deletions are in strikethrough
red text. A separate Final version with all changes accepted is available in this
publication.
© IEC 2020
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC TR 61340-1, which is a technical report, has been prepared by IEC technical committee
101: Electrostatics.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 61340 series, published under the general title Electrostatics,
can be found on the IEC website.
The committee has decided that the contents of the base publication and its amendment will
remain unchanged until the stability date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC TR 61340-1:2012+AMD1:2020 CSV
© IEC 2020
INTRODUCTION
Static electricity has been known for around 2 500 years but until recently had little impact on
humankind. More recently in the last century the nature of static electricity became better
understood and the principles of charge separation and accumulation could be described.
Despite this improved understanding, it remains difficult to predict with certainty the polarity
and magnitude of charges built up in any situation due to the many factors involved, and to,
many electrostatics remains a “black art” rather than a science.
The development of modern materials, especially polymers, and their nearly ubiquitous
application in fields such as floor materials, furnishings, clothing and engineering materials,
has made static electricity an everyday phenomenon. In some industries, such as electronics
manufacture and processes using flammable materials, unintended and invisible electrostatic
discharges can lead to substantial component damage or unreliability, or fires or explosions.
In everyday life, experience of electrostatic shocks to personnel has become commonplace.
This has led to increasing need to understand such phenomena, and to specify materials,
equipment and procedures for use in preventing and controlling electrostatic problems in the
human environment.
This technical report gives an overview of the field of electrostatics and has been prepared to
give the user a view of the background, principles, methods of measurement and industrial
applications prepared in conformity with IEC TC101 publications.

© IEC 2020
ELECTROSTATICS –
Part 1: Electrostatic phenomena –
Principles and measurements
1 Scope
This part of IEC 61340, which is a technical report, describes the fundamental principles of
electrostatic phenomena including charge generation, retention and dissipation and
electrostatic discharges.
Methods for measuring electrostatic phenomena and related properties of materials are
described in a general way.
Hazards and problems associated with electrostatic phenomena and principles of their control
are outlined.
Useful applications of electrostatic effects are summarized.
The purpose of this technical report is to serve as a reference for the development of
electrostatics related standards, and to provide guidance for their end-users.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60079-10-1, Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas
atmospheres
IEC 60079-10-2, Explosive atmospheres – Part 10-2: Classification of areas – Combustible
dust atmospheres
IEC TS 60079-32-1:2013, Explosive atmospheres – Part 32-1: Electrostatic hazards, guidance
IEC 60079-32-2, Explosive atmospheres – Part 32-2: Electrostatic hazards – Tests
IEC 61000-4-2, Electromagnetic compatibility (EMC) – Part 4-2: Testing and measurement
techniques – Electrostatic discharge immunity test
IEC 61340-5-1, Electrostatics – Part 5-1: Protection of electronic devices from electrostatic
phenomena – General requirements
IEC TR 61340-5-2, Electrostatics – Part 5-2: Protection of electronic devices from
electrostatic phenomena – User guide
IEC 61340-6-1, Electrostatics – Part 6-1: Electrostatic control for healthcare – General
requirements for facilities
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© IEC 2020
IEC 60243-1, Electrical strength of insulating materials – Test methods – Part 1: Tests at
power frequencies
IEC 60243-2, Electric strength of insulating materials – Test methods – Part 2: Additional
requirements for tests using direct voltage
IEC 61241-2-3, Electrical apparatus for use in the presence of combustible dust – Part 2:
Test methods – Section 3: Method for determining minimum ignition energy of dust/air
mixtures
BS EN 13821, Potentially explosive atmospheres. Explosion prevention and protection.
Determination of minimum ignition energy of dust/air mixtures
ISO/IEC 80079-20-2, Explosive atmospheres – Part 20-2: Material characteristics –
Combustible dusts test methods
ISO 80079-36:2016, Explosive atmospheres – Part 36: Non-electrical equipment for explosive
atmospheres – Basic method and requirements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
antistatic additive
antistatic filler, antistatic treatment
substance added to, or process applied to a liquid or solid in order to reduce its tendency to
acquire a charge by contact and rubbing, or to promote more rapid charge migration and so to
reduce its ability to retain significant charge when in contact with earth
3.2
antistatic
refers to the property of a material that inhibits or limits triboelectric charging
3.3
bonding
electrical connection between two or more conducting objects that reduces the potential
difference between them to an insignificant level
3.4
breakdown
failure, at least temporarily, of the insulating properties of an insulating medium under electric
stress
3.5
breakdown voltage
voltage at which breakdown occurs, under prescribed conditions of test or use
3.6
charge decay
neutralization or migration of charge across or through a material leading to a reduction of
charge density or surface potential at the point where the charge is deposited
3.7
charge decay time
charge relaxation time
time taken for charge to decay from a specified value to a specified lower value

© IEC 2020
Note 1 to entry: The specified lower value is commonly one tenth or 1/e of the starting value (e = 2,718).
3.8
conductivity
−1
ability of the substance to conduct electrical current expressed as S×m
3.9
conductor or conductive material
object or material providing a sufficiently high conductivity so that potential differences over
any parts of it are not sufficiently large as to be of practical significance
Note 1 to entry: In general this is a material having a resistance below about but different standards may
10 Ω
define different resistance ranges for this term.
3.10
dissipative material
material which allows charge to migrate over its surface and/or through its volume in a time
that is short compared to the timescale of the actions creating the charge or that will cause an
electrostatic problem
5 11
Note 1 to entry: In general a material having a resistance approximately 10 Ω and below approximately 10 Ω is
considered to be dissipative. Different standards may disagree on the exact values of the limits.
3.11
earth, earthing, grounding
ground
electrical connection (bonding) of a conductor to the main body of the earth to ensure that it is
at earth potential
3.12
electrostatic discharge
ESD
transfer of charge by direct contact or by breakdown from a material or object at a different
electrical potential to its immediate surroundings
3.13
explosion groups
flammable gaseous atmospheres subdivided into explosion groups I, IIA, IIB and IIC to define
their inflammability
Note 1 to entry: The most sensitive explosion group is Group IIC.
Note 2 to entry: See [9] to [11] [10] for definitions of classification method.
3.14
flammable substance
substance in the form of gas, liquid, solid or mixture of these, capable of propagating
combustion when subjected to a sufficiently strong ignition source
3.15
hazard threshold voltage
minimum electrical potential of capacitive stored charge that may give rise to an electrostatic
hazard
3.16
hazardous area
area in which flammable substance is, or may be expected to be, present in quantities such
as to require special precautions against ignition
___________
References in square brackets refer to the bibliography.

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© IEC 2020
Note 1 to entry: Hazardous area zones are defined in IEC 60079-10-1 and IEC 60079-10-2.
3.17
insulator
insulative material
material with very low mobility of charge so that any charge on the surface will remain there
for long time
Note 1 to entry: Connecting an insulator to earth does not help charge migration.
3.18
minimum ignition energy
MIE
smallest amount of energy released in a capacitive electrical spark that can ignite a mixture of
a specified flammable material with air or oxygen, according to a defined procedure
3.19
relaxation of charge
migration or neutralization of charge over and/or through a solid, liquid or gaseous material
causing a reduction in surface charge density and energy
Note 1 to entry: If the potential of a surface is defined then this is also reduced.
3.20
surface charge density
σ
s
net quantity of charge per unit area of surface of a solid or liquid
3.21
surface resistivity
Ω
resistance between opposing sides of a square on the surface of a material
3.22
triboelectric charging
electrical charging process in which charge is generated by the contact and separation of two
surfaces which may be solid, liquid or particle-carrying gases
3.23
volume charge density
σ
v
net quantity of charge per unit volume of a solid, liquid or gas
3.24
volume resistivity
Ω×m
resistance between opposing sides of 1 m of the material
4 Fundamentals of static electricity
4.1 General
Generally, electrostatic charge on a material, product or object is the result of:
• contact and rubbing;
• charge transfer;
• induction in an electric field;
• effect of polarization;
© IEC 2020
• photoelectric effect;
• pyroelectric effect;
• piezoelectric effect;
• ionization and ions adsorption;
• electrochemical processes.
However, the primary source of electrostatic charge is triboelectric charging. If two previously
uncharged substances come into contact, charge transfer will, in general, occur at their
common boundary. If a gas containing solid particles or liquid droplets in suspension becomes
charged by contact and separation, then the gas can be seen as carrying an electrostatic
charge. On separation, each surface will carry an additional charge of equal magnitude but of
opposite polarity. Conducting or dissipative objects can become charged by induction if they
reside in an electric field produced by other charged objects or conductors at high potential in
their vicinity. Any object can become charged if charged particles or molecules accumulate on
it.
It is very important to have some appreciation of these phenomena in order to enable the
proper implementation of test procedures and unambiguous interpretation of the resultant
data. It is also important with regard to choice of electrodes, protection of current measuring
devices from the initial capacitive surge and the time at which the value is recorded. The latter
should, of course, be appropriate to meet the practical circumstance for which the data are
required. Further comments are included in this technical report with the descriptions of the
individual test methods, where considered necessary.
4.2 Contact electrification
Contact electrification can occur at solid/solid, liquid/liquid or solid/liquid interfaces. Clean
gases cannot charge materials in this way. If a gas contains solid particles or liquid droplets in
suspension, however, these may be charged by contact so that such a gas can carry an
electrostatic charge by virtue of these particles.
In the case of solids of different materials, initially uncharged and normally at earth potential,
charge is transferred from one material to the other when they make contact. When they
separate, a net positive charge remains on the one surface and a net negative charge on the
other surface. The quantity of charge is increased by the size of the contact areas and the
size is affected by the contact pressure. Additional rubbing also increases the effective
contact area.
The relative amounts and polarity of charge transferred between materials can be presented
as a list, referred to as the triboelectric series. A material is expected to charge positively
against materials lower in the series, and negatively against materials higher in the series. It
should be noted that the position of a material in the triboelectric series is an approximation,
dependent on test conditions, and that two samples of the same material rubbed against each
other can result in quite strong charging.
Examples of triboelectric series are shown in Table 1.

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© IEC 2020
Table 1 – Example of triboelectric series
Item Charge
Rabbit fur Positive
Glass
Human hair
Polyamide (nylon)
Wool
Fur
Silk
Aluminum
Paper
Cotton
Steel
Wood
Rubber Negative
Acetate rayon
Polyethylene (PE) and polypropylene (PP)
PET
PVC
Polyurethane
PTFE
The two materials are oppositely charged and consequently there is an electric field between
them. If the materials are then separated, measures shall be taken to overcome the attraction
between the opposing charges and the potential difference between them increases linearly
with distance. This higher potential difference tends to drive charge back to any point of
residual contact. In the case of two conductors, the recombination of charges is virtually
complete and no significant amount of charge remains on either material after separation. If
one material, or both, is a non-conductor, the recombination cannot take place completely and
the separating materials retain part of their charge. There may only be a small amount of
charge involved but, because the distance between the charges when the surfaces are in
contact is extremely small, the potential generated on separation can easily reach many
kilovolts. Realistic surfaces are usually rough and so the charging is enhanced if the contact
and separation involves rubbing and/or pressure, since the area of real contact is increased
by these actions. Note that the real area of contact can be quite different in size from the
appearing area of contact. They can differ by a magnitude or more.
Contact electrification in liquids is essentially the same process but it can depend on the
presence of ions or sub-microscopic charged particles (the latter are usually less important).
Ions (or particles) of one polarity may be absorbed at the interface and they then attract ions
of opposite polarity which form a diffuse layer of charge in the liquid, close to the surface. If
the liquid is then moved relative to the interface, it carries away some of this diffuse layer,
thereby bringing about separation of the opposing charges. As in the case of solids, a high
voltage is generated because of the work done to bring about separation, provided that the
liquid is sufficiently non conducting to prevent recombination. Such processes can occur at
both solid/liquid and liquid/liquid interfaces.
4.3 Charging by induction
There is an electric field around any charged object. A conductor or dissipative material
introduced into this field changes the distribution of electric field in its vicinity and at the same
time there is a redistribution of charges in the material under the influence of the field (see

© IEC 2020
Figure 1a). If it is isolated from earth, the conductor takes up a potential, dependent upon its
position in the field. The material is capable of producing an electrostatic discharge by virtue
of this potential.
1 2 1 2 2
IEC  1190/12 IEC  1191/12 IEC  1192/12

Figure 1a) – Move the charged Figure 1b) – Connect the Figure 1c) – Remove the earth
object (1) close to an uncharged object (2) to ground connection and then the first
uncharged object (2) momentarily. The uncharged object; the conductor remains
object is charged, but assumes charged (negatively in this
ground potential example)
Figure 1 – Charging by induction
If, while it is in the field, the material is momentarily earthed, its potential is reduced to zero
and an imbalance of charge remains on it (Figure 1b). When the electrical field is removed
from the object the net charge remains (Figure 1c). If the material is isolated from earth and
the electric field is removed, the material then has a charge available to provide an
electrostatic discharge. The conducting object after this process is said to be charged by
induction. A discharge from such an object can be hazardous, for example in the case of an
isolated person moving in the area of electrostatically charged materials.
4.4 Charge transfer by conduction
Whenever a charged object makes contact with another object (Figure 2), the total charge is
shared between them to the extent that their conductance and capacitance allow. This is a
potent source of electrostatic charging and examples include charged sprays, mists or dusts
impinging or settling on solid objects. A similar transfer of charge can also take place when a
stream of gaseous ions is incident upon an object.

1 2 1 2
IEC  1193/12 IEC  1194/12
Figure 2a) – A charged object has contact Figure 2b) – Charged objects will be
with an uncharged object. Positive charge separated
transfer to the uncharged object
Figure 2 – Charge transfer by conduction when objects 1 and 2 are conductors
4.5 Retention of charge
Even after separation in the charging process, electrostatic charges will quickly re-combine
either directly or via the earth unless they are prevented from doing so. If a charge is on a
non-conductor, it is retained by virtue of the resistance of the material itself. To retain charge
on a conductor it has to be isolated from other conductors and from earth.
Pure gases, like air, under normal conditions are non-conductors and the suspended particles
or droplets in dust clouds, mists or sprays can often retain their charges for very long periods,
irrespective of the conductivity of the particles themselves.

– 14 – IEC TR 61340-1:2012+AMD1:2020 CSV
© IEC 2020
The charge leaks away at a rate determined by the resistances of the non-conductors in the
system and the capacitances of the conductors. This process is known as relaxation. The
resistance, resistivity, conductivity or charge decay rate values which are needed to produce
an electrostatic problem depend greatly upon the system under consideration.
In many industrial processes there is often a continuous generation of static charge that
accumulates on an insulator or an isolated conductor. Examples are when a steady stream of
charged liquid or powder flows into an isolated metal container, or a person walks across an
insulating floor covering. The potential on the isolated conductor is then the result of a
balance between the rate of input of charge and the rate of dissipation. The equivalent
electrical circuit is shown in Figure 3 and the potential of the conductor is given by the
equation:
−t −t
RC R×C
V= V × e + I× R×(1− e ) (1)
o
where
V is the potential of the conductor (V);
is the initial potential;
V
R is the resistance to ground (Ω);

T is the time from the commencement of charging (s);

C is its capacitance (F).
The maximum potential is reached when t >> RC, and is given by:
V = I× R (2)
max
V
I
C R
IEC  1195/12
Figure 3 – Equivalent electrical circuit for an electrostatically charged conductor
The capacitance of an isolated object and its “resistance to ground” or the rate of charge
dissipation can be measured to establish if significant charges can accumulate. This cannot
be done for dusts and mists while suspended in air.
There is an inherent assumption here that the resistance, or the charge relaxation rate, of an
insulating material is single valued. This is not always the case. The value of resistance for a
given potential difference can vary with time and, similarly, the rate of charge dissipation can
be a function of the electric stress (or amount of charge). These effects can also be greatly
influenced by the temperature and the ambient humidity.

© IEC 2020
4.6 Influence of environmental humidity
4.6.1 General
Materials absorb atmospheric water to some degree and in the case of insulators this can
increase the rate of charge dissipation greatly. Water absorbed on the surface of materials is
the principal cause of a surface conductivity that is different from that in the bulk of the
material. The effect, well observed but still poorly understood, is that the conductivity
increases with the amount of water absorbed, i.e. in practical terms, the conductivity
increases with increasing relative humidity. The effect is observed even under relatively dry
(RH < 20 %) conditions where the water can only be present in molecular form and no free
liquid water layer exists.
4.6.2 In situ measurements
When making measurements under practical conditions, it is often not possible to control
humidity. As the results are likely to be influenced by environmental humidity, it is important to
record the environmental conditions at the time of measurement.
4.7 Electrostatic discharges
4.7.1 General
An electrostatic discharge occurs when the electric field exceeds the breakdown strength of
the atmospheric gas, which is usually air. As a guide, the breakdown strength for flat or large
radius surfaces 10 mm or more apart is about 3 MV/m (30 kV/cm) under normal ambient
conditions.
Electrostatic discharges vary greatly in type and depend in a detailed way on the system in
which the discharge is initiated. The several types of discharges can be classified as
described in 4.7.2 to 4.7.6, although the differentiation between the various types is not
completely definite.
4.7.2 Spark discharges
A spark is an electrical discharge between two conductors at different potentials. It is
characterized by a well-defined luminous discharge channel carrying a high density current.
Ionization of gas in the channel is complete over its whole length. The discharge is very rapid
and can give rise to an audible “crack”. The discharge observed between a person’s finger
and a large metal object is a typical example.
The potential difference between the conductors necessary to produce a field which exceeds
the electric strength of the ambient atmosphere depends upon both the shape and the
distance between the conductors.
The current passing in a spark is limited only by the impedance in the external circuit and so
nearly all the charge on the electrodes is drawn into the discharge. The spark in most
practical cases, therefore, dissipates almost all the available energy which is given by:
1 1 1 Q
W= × Q× V= CV =  (3)
2 2 2 C
where
W is the energy dissipated (J),
Q is the quantity of charge on the conductor (C),
V is its potential (V);
C is the capacitance to earth (F).

– 16 – IEC TR 61340-1:2012+AMD1:2020 CSV
© IEC 2020
This is the maximum amount of available energy. Any resistance in the discharging circuit
reduces the energy in the spark and increases its duration. Typical values for the
capacitances of conductors are given in Table 2.
Table 2 – Typical electrical capacitances
-12
Object Capacitance ×10 F
Very small metal items (screw, nail) 1 to 10
Small metal items (scoop, hose nozzle) 10 to 20
Small containers (bucket, 50 l drum) 10 to 100
Medium containers (250 l to 500 l) 50 to 300
Human body 100 to 300
Major plant items (reaction vessels) closely surrounded by earthed structure 100 to 1 000
Cars 800 to 1 200
4.7.3 Corona discharges
This type of discharge is associated with conductors with sharp points or edges. They can
occur when such a conductor is earthed and moved towards a highly charged object or,
alternatively, if the conductor is raised to a high potential. The discharges arise due to the fact
that the electric field located at the sharp surface is very high and above the breakdown
stress (3 MV/m). Since the field away from the conductor decreases rapidly with distance, the
region of ionization does not extend far from it. It may be directed towards the charged object
or, in the case of a high potential conductor, it may simply be directed into space.
Corona discharges are difficult to see, but under subdued lighting a glow can be seen
adjacent to the point. Outside this ionized region ions can drift away, their polarity being
dependent on the field direction.
The field from a charged surface producing co
...

IEC/TR 61340-1 ®
Edition 1.0 2012-06
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
Electrostatics –
Part 1: Electrostatic phenomena – Principles and measurements

Electrostatique –
Partie 1: Phénomènes électrostatiques – Principes et mesures

IEC/TR 61340-1:2012
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IEC/TR 61340-1 ®
Edition 1.0 2012-06
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
Electrostatics –
Part 1: Electrostatic phenomena – Principles and measurements

Electrostatique –
Partie 1: Phénomènes électrostatiques – Principes et mesures

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 17.200.99; 29.020 ISBN 978-2-83220-195-4

– 2 – TR 61340-1  IEC:2012
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Fundamentals of static electricity . 11
4.1 General . 11
4.2 Contact electrification . 12
4.3 Charging by induction . 13
4.4 Charge transfer by conduction . 14
4.5 Retention of charge . 14
4.6 Influence of environmental humidity . 16
4.6.1 General . 16
4.6.2 In situ measurements . 16
4.7 Electrostatic discharges . 16
4.7.1 General . 16
4.7.2 Spark discharges . 16
4.7.3 Corona discharges . 17
4.7.4 Brush discharges . 17
4.7.5 Propagating brush discharges . 17
4.7.6 Cone discharges . 18
4.8 Mechanical forces in an electrostatic field . 18
5 Electrostatic problems and hazards . 19
5.1 General . 19
5.2 Electronic components and systems . 19
5.2.1 General . 19
5.2.2 Types of failure . 19
5.2.3 Problems and threats at different life cycle periods . 20
5.3 Electrostatic ignition – Hazards . 21
5.3.1 General . 21
5.3.2 Spark discharges from conducting objects . 21
5.3.3 Corona discharges from conducting objects . 21
5.3.4 Brush discharges from insulating surfaces . 21
5.3.5 Propagating brush discharges from insulating surfaces . 22
5.3.6 Discharges from people . 22
5.3.7 Ignition potential of electrostatic discharges . 22
5.4 Physiological sensation . 24
5.5 Simulation of electrostatic discharges. 25
5.5.1 General . 25
5.5.2 Capacitive discharges for ignition energy measurements . 26
5.5.3 Human body model . 26
5.5.4 Machine model . 26
5.5.5 Charged device model . 26
6 General solutions to problems and hazards . 27

TR 61340-1  IEC:2012 – 3 –
6.1 General . 27
6.2 Common approaches. 27
7 Useful applications of electrostatic effects . 28
8 General aspects of measurements . 29
8.1 General . 29
8.2 Electric field . 29
8.2.1 General . 29
8.2.2 Application . 30
8.3 Potential . 30
8.3.1 General . 30
8.3.2 Surface voltage . 30
8.3.3 Space potential . 31
8.4 Charge . 31
8.5 Charge density . 32
8.5.1 Surface charge density . 32
8.5.2 Volume charge density . 32
8.6 Charge decay . 33
8.7 Resistance and resistivity . 34
8.8 Chargeability . 34
8.9 Current . 35
8.10 Energy in capacitive discharges . 35
8.11 Ignition energy . 36
8.11.1 General . 36
8.11.2 Equivalent energy . 36
8.12 Charge transferred in electrostatic discharges . 37
8.12.1 General . 37
8.12.2 Discharge electrode . 38
8.12.3 Measuring circuit . 39
8.12.4 Alternative charge transfer measuring arrangements . 39
8.13 Capacitance . 39
8.14 Electric strength . 40
Bibliography . 41

Figure 1 – Charging by induction . 14
Figure 2 – Charge transfer by conduction when objects 1 and 2 are conductors. 14
Figure 3 – Equivalent electrical circuit for an electrostatically charged conductor . 15
Figure 4 – Examples of brush discharge waveforms measured with a fast digital
storage oscilloscope . 24
Figure 5 – Circuit for simulation of electrostatic discharges . 25
Figure 6 – Basic arrangements for measuring charge transferred in electrostatic
discharges with alternative measuring circuits . 38
Figure 7 – Oscilloscope voltage/time traces . 39

– 4 – TR 61340-1  IEC:2012
Table 1 – Example of triboelectric series. 13
Table 2 – Typical electrical capacitances . 17
Table 3 – Typical perception levels and physical responses of people to discharges
based on a body capacitance of 200 pF . 25
Table 4 – Typical values used in ESD simulation models . 27

TR 61340-1  IEC:2012 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
ELECTROSTATICS –
Part 1: Electrostatic phenomena –
Principles and measurements
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 61340-1, which is a technical report, has been prepared by IEC technical committee
101: Electrostatics.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
101/344/DTR 101/355/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.

– 6 – TR 61340-1 © IEC:2012
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 61340 series, published under the general title Electrostatics,
can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
The contents of the corrigenda 1 (March 2013) and 2 (December 2017) have been included
in this copy.
TR 61340-1  IEC:2012 – 7 –
INTRODUCTION
Static electricity has been known for around 2 500 years but until recently had little impact on
humankind. More recently in the last century the nature of static electricity became better
understood and the principles of charge separation and accumulation could be described.
Despite this improved understanding, it remains difficult to predict with certainty the polarity
and magnitude of charges built up in any situation due to the many factors involved, and to,
many electrostatics remains a “black art” rather than a science.
The development of modern materials, especially polymers, and their nearly ubiquitous
application in fields such as floor materials, furnishings, clothing and engineering materials,
has made static electricity an everyday phenomenon. In some industries, such as electronics
manufacture and processes using flammable materials, unintended and invisible electrostatic
discharges can lead to substantial component damage or unreliability, or fires or explosions.
In everyday life, experience of electrostatic shocks to personnel has become commonplace.
This has led to increasing need to understand such phenomena, and to specify materials,
equipment and procedures for use in preventing and controlling electrostatic problems in the
human environment.
This technical report gives an overview of the field of electrostatics and has been prepared to
give the user a view of the background, principles, methods of measurement and industrial
applications prepared in conformity with IEC TC101 publications.

– 8 – TR 61340-1  IEC:2012
ELECTROSTATICS –
Part 1: Electrostatic phenomena –
Principles and measurements
1 Scope
This part of IEC 61340, which is a technical report, describes the fundamental principles of
electrostatic phenomena including charge generation, retention and dissipation and
electrostatic discharges.
Methods for measuring electrostatic phenomena and related properties of materials are
described in a general way.
Hazards and problems associated with electrostatic phenomena and principles of their control
are outlined.
Useful applications of electrostatic effects are summarized.
The purpose of this technical report is to serve as a reference for the development of
electrostatics related standards, and to provide guidance for their end-users.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60079-10-1, Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas
atmospheres
IEC 60079-10-2, Explosive atmospheres – Part 10-2: Classification of areas – Combustible
dust atmospheres
IEC 61000-4-2, Electromagnetic compatibility (EMC) – Part 4-2: Testing and measurement
techniques – Electrostatic discharge immunity test
IEC 61340-5-1, Electrostatics – Part 5-1: Protection of electronic devices from electrostatic
phenomena – General requirements
IEC 61340-5-2, Electrostatics – Part 5-2: Protection of electronic devices from electrostatic
phenomena – User guide
IEC 60243-1, Electrical strength of insulating materials – Test methods – Part 1: Tests at
power frequencies
IEC 60243-2, Electric strength of insulating materials – Test methods – Part 2: Additional
requirements for tests using direct voltage

TR 61340-1 © IEC:2012 – 9 –
IEC 61241-2-3, Electrical apparatus for use in the presence of combustible dust – Part 2:
Test methods – Section 3: Method for determining minimum ignition energy of dust/air
mixtures
BS EN 13821, Potentially explosive atmospheres. Explosion prevention and protection.
Determination of minimum ignition energy of dust/air mixtures
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
antistatic additive
antistatic filler, antistatic treatment
substance added to, or process applied to a liquid or solid in order to reduce its tendency to
acquire a charge by contact and rubbing, or to promote more rapid charge migration and so to
reduce its ability to retain significant charge when in contact with earth
3.2
antistatic
refers to the property of a material that inhibits or limits triboelectric charging
3.3
bonding
electrical connection between two or more conducting objects that reduces the potential
difference between them to an insignificant level
3.4
breakdown
failure, at least temporarily, of the insulating properties of an insulating medium under electric
stress
3.5
breakdown voltage
voltage at which breakdown occurs, under prescribed conditions of test or use
3.6
charge decay
neutralization or migration of charge across or through a material leading to a reduction of
charge density or surface potential at the point where the charge is deposited
3.7
charge decay time
charge relaxation time
time taken for charge to decay from a specified value to a specified lower value
Note 1 to entry: The specified lower value is commonly one tenth or 1/e of the starting value (e = 2,718).
3.8
conductivity
−1
ability of the substance to conduct electrical current expressed as S×m

– 10 – TR 61340-1 © IEC:2012
3.9
conductor or conductive material
object or material providing a sufficiently high conductivity so that potential differences over
any parts of it are not sufficiently large as to be of practical significance
Note 1 to entry: In general this is a material having a resistance below about but different standards may
10 Ω
define different resistance ranges for this term.
3.10
dissipative material
material which allows charge to migrate over its surface and/or through its volume in a time
that is short compared to the timescale of the actions creating the charge or that will cause an
electrostatic problem
5 11
Note 1 to entry: In general a material having a resistance approximately 10 Ω and below approximately 10 Ω is
considered to be dissipative. Different standards may disagree on the exact values of the limits.
3.11
earth, earthing, grounding
ground
electrical connection (bonding) of a conductor to the main body of the earth to ensure that it is
at earth potential
3.12
electrostatic discharge
ESD
transfer of charge by direct contact or by breakdown from a material or object at a different
electrical potential to its immediate surroundings
3.13
explosion groups
flammable gaseous atmospheres subdivided into explosion groups I, IIA, IIB and IIC to define
their inflammability
Note 1 to entry: The most sensitive explosion group is Group IIC.
Note 2 to entry: See [9] to [11] for definitions of classification method.
3.14
flammable substance
substance in the form of gas, liquid, solid or mixture of these, capable of propagating
combustion when subjected to a sufficiently strong ignition source
3.15
hazard threshold voltage
minimum electrical potential of capacitive stored charge that may give rise to an electrostatic
hazard
3.16
hazardous area
area in which flammable substance is, or may be expected to be, present in quantities such
as to require special precautions against ignition
Note 1 to entry: Hazardous area zones are defined in IEC 60079-10-1 and IEC 60079-10-2.
___________
References in square brackets refer to the bibliography.

TR 61340-1 © IEC:2012 – 11 –
3.17
insulator
insulative material
material with very low mobility of charge so that any charge on the surface will remain there
for long time
Note 1 to entry: Connecting an insulator to earth does not help charge migration.
3.18
minimum ignition energy
MIE
smallest amount of energy released in a capacitive electrical spark that can ignite a mixture of
a specified flammable material with air or oxygen, according to a defined procedure
3.19
relaxation of charge
migration or neutralization of charge over and/or through a solid, liquid or gaseous material
causing a reduction in surface charge density and energy
Note 1 to entry: If the potential of a surface is defined then this is also reduced.
3.20
surface charge density
σ
s
net quantity of charge per unit area of surface of a solid or liquid
3.21
surface resistivity
Ω
resistance between opposing sides of a square on the surface of a material
3.22
triboelectric charging
electrical charging process in which charge is generated by the contact and separation of two
surfaces which may be solid, liquid or particle-carrying gases
3.23
volume charge density
σ
v
net quantity of charge per unit volume of a solid, liquid or gas
3.24
volume resistivity
Ω×m
resistance between opposing sides of 1 m of the material

4 Fundamentals of static electricity
4.1 General
Generally, electrostatic charge on a material, product or object is the result of:
• contact and rubbing;
• charge transfer;
• induction in an electric field;

– 12 – TR 61340-1  IEC:2012
• effect of polarization;
• photoelectric effect;
• pyroelectric effect;
• piezoelectric effect;
• ionization and ions adsorption;
• electrochemical processes.
However, the primary source of electrostatic charge is triboelectric charging. If two previously
uncharged substances come into contact, charge transfer will, in general, occur at their
common boundary. If a gas containing solid particles or liquid droplets in suspension becomes
charged by contact and separation, then the gas can be seen as carrying an electrostatic
charge. On separation, each surface will carry an additional charge of equal magnitude but of
opposite polarity. Conducting or dissipative objects can become charged by induction if they
reside in an electric field produced by other charged objects or conductors at high potential in
their vicinity. Any object can become charged if charged particles or molecules accumulate on
it.
It is very important to have some appreciation of these phenomena in order to enable the
proper implementation of test procedures and unambiguous interpretation of the resultant
data. It is also important with regard to choice of electrodes, protection of current measuring
devices from the initial capacitive surge and the time at which the value is recorded. The latter
should, of course, be appropriate to meet the practical circumstance for which the data are
required. Further comments are included in this technical report with the descriptions of the
individual test methods, where considered necessary.
4.2 Contact electrification
Contact electrification can occur at solid/solid, liquid/liquid or solid/liquid interfaces. Clean
gases cannot charge materials in this way. If a gas contains solid particles or liquid droplets in
suspension, however, these may be charged by contact so that such a gas can carry an
electrostatic charge by virtue of these particles.
In the case of solids of different materials, initially uncharged and normally at earth potential,
charge is transferred from one material to the other when they make contact. When they
separate, a net positive charge remains on the one surface and a net negative charge on the
other surface. The quantity of charge is increased by the size of the contact areas and the
size is affected by the contact pressure. Additional rubbing also increases the effective
contact area.
The relative amounts and polarity of charge transferred between materials can be presented
as a list, referred to as the triboelectric series. A material is expected to charge positively
against materials lower in the series, and negatively against materials higher in the series. It
should be noted that the position of a material in the triboelectric series is an approximation,
dependent on test conditions, and that two samples of the same material rubbed against each
other can result in quite strong charging.
Examples of triboelectric series are shown in Table 1.

TR 61340-1  IEC:2012 – 13 –
Table 1 – Example of triboelectric series
Item Charge
Rabbit fur Positive
Glass
Human hair
Polyamide (nylon)
Wool
Fur
Silk
Aluminum
Paper
Cotton
Steel
Wood
Rubber Negative
Acetate rayon
Polyethylene (PE) and polypropylene (PP)
PET
PVC
Polyurethane
PTFE
The two materials are oppositely charged and consequently there is an electric field between
them. If the materials are then separated, measures shall be taken to overcome the attraction
between the opposing charges and the potential difference between them increases linearly
with distance. This higher potential difference tends to drive charge back to any point of
residual contact. In the case of two conductors, the recombination of charges is virtually
complete and no significant amount of charge remains on either material after separation. If
one material, or both, is a non-conductor, the recombination cannot take place completely and
the separating materials retain part of their charge. There may only be a small amount of
charge involved but, because the distance between the charges when the surfaces are in
contact is extremely small, the potential generated on separation can easily reach many
kilovolts. Realistic surfaces are usually rough and so the charging is enhanced if the contact
and separation involves rubbing and/or pressure, since the area of real contact is increased
by these actions. Note that the real area of contact can be quite different in size from the
appearing area of contact. They can differ by a magnitude or more.
Contact electrification in liquids is essentially the same process but it can depend on the
presence of ions or sub-microscopic charged particles (the latter are usually less important).
Ions (or particles) of one polarity may be absorbed at the interface and they then attract ions
of opposite polarity which form a diffuse layer of charge in the liquid, close to the surface. If
the liquid is then moved relative to the interface, it carries away some of this diffuse layer,
thereby bringing about separation of the opposing charges. As in the case of solids, a high
voltage is generated because of the work done to bring about separation, provided that the
liquid is sufficiently non conducting to prevent recombination. Such processes can occur at
both solid/liquid and liquid/liquid interfaces.
4.3 Charging by induction
There is an electric field around any charged object. A conductor or dissipative material
introduced into this field changes the distribution of electric field in its vicinity and at the same
time there is a redistribution of charges in the material under the influence of the field (see

– 14 – TR 61340-1  IEC:2012
Figure 1a). If it is isolated from earth, the conductor takes up a potential, dependent upon its
position in the field. The material is capable of producing an electrostatic discharge by virtue
of this potential.
1 2 1 2 2
IEC  1190/12 IEC  1191/12 IEC  1192/12

Figure 1a) – Move the charged Figure 1b) – Connect the Figure 1c) – Remove the earth
object (1) close to an uncharged object (2) to ground connection and then the first
uncharged object (2) momentarily. The uncharged object; the conductor remains
object is charged, but assumes charged (negatively in this
ground potential example)
Figure 1 – Charging by induction
If, while it is in the field, the material is momentarily earthed, its potential is reduced to zero
and an imbalance of charge remains on it (Figure 1b). When the electrical field is removed
from the object the net charge remains (Figure 1c). If the material is isolated from earth and
the electric field is removed, the material then has a charge available to provide an
electrostatic discharge. The conducting object after this process is said to be charged by
induction. A discharge from such an object can be hazardous, for example in the case of an
isolated person moving in the area of electrostatically charged materials.
4.4 Charge transfer by conduction
Whenever a charged object makes contact with another object (Figure 2), the total charge is
shared between them to the extent that their conductance and capacitance allow. This is a
potent source of electrostatic charging and examples include charged sprays, mists or dusts
impinging or settling on solid objects. A similar transfer of charge can also take place when a
stream of gaseous ions is incident upon an object.

1 2 1 2
IEC  1193/12 IEC  1194/12
Figure 2a) – A charged object has contact Figure 2b) – Charged objects will be
with an uncharged object. Positive charge separated
transfer to the uncharged object
Figure 2 – Charge transfer by conduction when objects 1 and 2 are conductors
4.5 Retention of charge
Even after separation in the charging process, electrostatic charges will quickly re-combine
either directly or via the earth unless they are prevented from doing so. If a charge is on a
non-conductor, it is retained by virtue of the resistance of the material itself. To retain charge
on a conductor it has to be isolated from other conductors and from earth.
Pure gases, like air, under normal conditions are non-conductors and the suspended particles
or droplets in dust clouds, mists or sprays can often retain their charges for very long periods,
irrespective of the conductivity of the particles themselves.

TR 61340-1  IEC:2012 – 15 –
The charge leaks away at a rate determined by the resistances of the non-conductors in the
system and the capacitances of the conductors. This process is known as relaxation. The
resistance, resistivity, conductivity or charge decay rate values which are needed to produce
an electrostatic problem depend greatly upon the system under consideration.
In many industrial processes there is often a continuous generation of static charge that
accumulates on an insulator or an isolated conductor. Examples are when a steady stream of
charged liquid or powder flows into an isolated metal container, or a person walks across an
insulating floor covering. The potential on the isolated conductor is then the result of a
balance between the rate of input of charge and the rate of dissipation. The equivalent
electrical circuit is shown in Figure 3 and the potential of the conductor is given by the
equation:
−t −t
RC R×C
V= V × e + I× R×(1− e ) (1)
o
where
V is the potential of the conductor (V);
V is the initial potential;
R is the resistance to ground (Ω);

T is the time from the commencement of charging (s);

C is its capacitance (F).
The maximum potential is reached when t >> RC, and is given by:
V = I× R (2)
max
V
I
C R
IEC  1195/12
Figure 3 – Equivalent electrical circuit for an electrostatically charged conductor
The capacitance of an isolated object and its “resistance to ground” or the rate of charge
dissipation can be measured to establish if significant charges can accumulate. This cannot
be done for dusts and mists while suspended in air.
There is an inherent assumption here that the resistance, or the charge relaxation rate, of an
insulating material is single valued. This is not always the case. The value of resistance for a
given potential difference can vary with time and, similarly, the rate of charge dissipation can
be a function of the electric stress (or amount of charge). These effects can also be greatly
influenced by the temperature and the ambient humidity.

– 16 – TR 61340-1 © IEC:2012
4.6 Influence of environmental humidity
4.6.1 General
Materials absorb atmospheric water to some degree and in the case of insulators this can
increase the rate of charge dissipation greatly. Water absorbed on the surface of materials is
the principal cause of a surface conductivity that is different from that in the bulk of the
material. The effect, well observed but still poorly understood, is that the conductivity
increases with the amount of water absorbed, i.e. in practical terms, the conductivity
increases with increasing relative humidity. The effect is observed even under relatively dry
(RH < 20 %) conditions where the water can only be present in molecular form and no free
liquid water layer exists.
4.6.2 In situ measurements
When making measurements under practical conditions, it is often not possible to control
humidity. As the results are likely to be influenced by environmental humidity, it is important to
record the environmental conditions at the time of measurement.
4.7 Electrostatic discharges
4.7.1 General
An electrostatic discharge occurs when the electric field exceeds the breakdown strength of
the atmospheric gas, which is usually air. As a guide, the breakdown strength for flat or large
radius surfaces 10 mm or more apart is about 3 MV/m (30 kV/cm) under normal ambient
conditions.
Electrostatic discharges vary greatly in type and depend in a detailed way on the system in
which the discharge is initiated. The several types of discharges can be classified as
described in 4.7.2 to 4.7.6, although the differentiation between the various types is not
completely definite.
4.7.2 Spark discharges
A spark is an electrical discharge between two conductors at different potentials. It is
characterized by a well-defined luminous discharge channel carrying a high density current.
Ionization of gas in the channel is complete over its whole length. The discharge is very rapid
and can give rise to an audible “crack”. The discharge observed between a person’s finger
and a large metal object is a typical example.
The potential difference between the conductors necessary to produce a field which exceeds
the electric strength of the ambient atmosphere depends upon both the shape and the
distance between the conductors.
The current passing in a spark is limited only by the impedance in the external circuit and so
nearly all the charge on the electrodes is drawn into the discharge. The spark in most
practical cases, therefore, dissipates almost all the available energy which is given by:
1 1 1 Q
W = ×Q ×V = CV =  (3)
2 2 2 C
where
W is the energy dissipated (J),
Q is the quantity of charge on the conductor (C),
V is its potential (V);
C is the capacitance to earth (F).

TR 61340-1  IEC:2012 – 17 –
This is the maximum amount of available energy. Any resistance in the discharging circuit
reduces the energy in the spark and increases its duration. Typical values for the
capacitances of conductors are given in Table 2.
Table 2 – Typical electrical capacitances
-12
Object
Capacitance ×10 F
Very small metal items (screw, nail) 1 to 10
Small metal items (scoop, hose nozzle) 10 to 20
Small containers (bucket, 50 l drum) 10 to 100
Medium containers (250 l to 500 l) 50 to 300
Human body 100 to 300
Major plant items (reaction vessels) closely surrounded by earthed st
...