IEC 60479-1:2018

IEC 60479-1 ®
Edition 1.0 2018-12
INTERNATIONAL
STANDARD
BASIC SAFETY PUBLICATION
Effects of current on human beings and livestock –
Part 1: General aspects
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IEC 60479-1 ®
Edition 1.0 2018-12
INTERNATIONAL
STANDARD
BASIC SAFETY PUBLICATION
Effects of current on human beings and livestock –

Part 1: General aspects
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.200; 29.020 ISBN 978-2-8322-6295-5

– 2 – IEC 60479-1:2018  IEC 2018
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references . 10
3 Terms and definitions . 10
3.1 General definitions . 10
3.2 Effects of sinusoidal alternating current in the range 15 Hz to 100 Hz . 11
3.3 Effects of direct current . 12
4 Electrical impedance of the human body and livestock . 13
4.1 General . 13
4.2 Internal impedance of the human body (Z ) . 13
i
4.3 Impedance of the skin (Z ) . 13
s
4.4 Total impedance of the human body (Z ) . 13
T
4.5 Factors affecting initial resistance of the human body (R ) . 14
4.6 Values of the total impedance of the human body (Z ) . 14
T
4.6.1 Total body impedance dependence for large, medium and small surface
areas of contact . 14
4.6.2 Sinusoidal alternating current 50/60 Hz for large surface areas of contact . 14
4.6.3 Sinusoidal alternating current 50/60 Hz for medium and small surface
areas of contact . 17
4.6.4 Sinusoidal alternating current with frequencies up to 20 kHz and above . 20
4.6.5 Direct current . 21
4.7 Value of the initial resistance of the human body (R ) . 22
4.8 Characteristics of the impedance of the body of livestock . 22
5 Effects of sinusoidal alternating current in the range of 15 Hz to 150 Hz . 22
5.1 General . 22
5.2 Threshold of perception . 22
5.3 Threshold of reaction . 22
5.4 Immobilization . 22
5.5 Threshold of let-go . 23
5.6 Threshold of ventricular fibrillation . 23
5.7 Other effects related to electric shocks . 23
5.8 Effects of current on the skin . 24
5.9 Description of time/current zones (see Figure 20) . 24
5.10 Application of heart-current factor (F). 25
6 Effects of direct current . 26
6.1 General . 26
6.2 Threshold of perception and threshold of reaction . 26
6.3 Threshold of immobilization and threshold of let-go . 26
6.4 Threshold of ventricular fibrillation . 26
6.5 Other effects of current . 27
6.6 Description of time/current zones (see Figure 22) . 27
6.7 Heart factor . 28
6.8 Effects of anodic versus cathodic DC currents . 45
Annex A (normative) Measurements of the total body impedances Z made on living
T
human beings and on corpses and statistical analysis of the results . 48
Annex B (normative) Influence of frequency on the total body impedance (Z ) . 51
T
Annex C (normative) Total body resistance (R ) for direct current . 52
T
Annex D (informative) Examples of calculations of ZT . 53
Annex E (informative) Theories of ventricular fibrillation . 56
Annex F (informative) Quantities of upper limit of vulnerability (ULV)and lower limit of
vulnerability (LLV) . 57
Annex G (informative) Circuit simulation methods in electric shock evaluation . 58
Annex H (normative) Effects of currents passing through the body of livestock . 61
H.1 General . 61
H.2 Principal consideration of the risk of ventricular fibrillation for livestock . 61
H.3 Characteristics of the impedance of the body of livestock . 62
H.4 Internal impedance of animals (Z ) . 62
i
H.5 Impedance of the hide and skin (Z ) . 63
P
H.6 Impedance (resistance) of the hoof (Z , R ) . 63
h h
H.7 Total body impedance (Z ) . 63
T
H.8 Initial body resistance (R ) . 64
H.9 Values of the total body impedance (Z ) . 64
T
H.10 Values of the initial resistance of the body (R ) . 65
H.11 Effects on livestock of sinusoidal alternating current in the range from 15 Hz
to 100 Hz . 65
H.11.1 General . 65
H.11.2 Threshold of reaction . 66
H.11.3 Threshold of ventricular fibrillation . 66
Bibliography . 69

Figure 1 – Impedances of the human body . 28
Figure 2 – Internal partial impedances Z of the human body . 29
ip
Figure 3 – Simplified schematic diagram for the internal impedances of the human
body . 30
Figure 4 – Total body impedance Z (50 %) for a current path hand to hand, for large
T
surface areas of contact in dry, water-wet and saltwater-wet conditions for a percentile
rank of 50 % of the population for touch voltages U = 25 V to 700 V, AC 50/60 Hz . 31
T
Figure 5 – Dependence of the total impedance Z of one living person on the surface
T
area of contact in dry conditions and at touch voltage (50 Hz) . 32
Figure 6 – Dependence of the total body impedance Z on the touch voltage U for a current
T T
path from the tips of the right to the left forefinger compared with large surfaceareas of
contact from the right to the left hand in dry conditions measured on one living person, touch
voltage range U = 25 V to 200 V, AC 50 Hz, duration of current flow max. 25 ms . 33
T
th
Figure 7 – Dependence of the total body impedance Z for the 50 percentile rank of
T
a population of living human beings for large, medium and small surface areas of
2 2 2
contact (order of magnitude 10 000 mm , 1 000 mm and 100 mm respectively) in
dry conditions at touch voltages U = 25 V to 200 V AC 50/60 Hz . 34
T
th
Figure 8 – Dependence of the total body impedance Z for the 50 percentile rank of
T
a population of living human beings for large, medium and small surface areas of
2 2 2
contact (order of magnitude 10 000 mm , 1 000 mm and 100 mm respectively) in
water-wet conditions at touch voltages U = 25 V to 200 V, AC 50/60 Hz . 35
T
th
Figure 9 – Dependence of the total body impedance Z for the 50 percentile rank of
T
a population of living human beings for large, medium and small surface areas of
2 2 2
contact (order of magnitude 10 000 mm , 1 000 mm and 100 mm respectively) in
saltwater-wet conditions at touch voltages U = 25 V to 200 V, AC 50/60 Hz . 36
T
– 4 – IEC 60479-1:2018  IEC 2018
Figure 10 – Values for the total body impedance Z measured on 10 living human
T
beings with a current path hand to hand and large surface areas of contact in dry
conditions at a touch voltage of 10 V and frequencies from 25 Hz to 20 kHz . 37
Figure 11 – Values for the total body impedance Z measured on one living human
T
being with a current path hand to hand and large surface areas of contact in dry
conditions at a touch voltage of 25 V and frequencies from 25 Hz to 2 kHz . 37
Figure 12 – Frequency dependence of the total body impedance Z of a population for
T
a percentile rank of 50 % for touch voltages from 10 V to 1 000 V and a frequency
range from 50 Hz to 150 kHz for a current path hand to hand or hand to foot, large
surface areas of contact in dry conditions . 38
Figure 13 – Statistical value of total body impedances Z and body resistances R for
T T
a percentile rank of 50 % of a population of living human beings for the current path
hand to hand, large surface areas of contact, dry conditions, for touch voltages up to
700 V, for AC 50/60 Hz and DC . 38
Figure 14 – Dependence of the alteration of human skin condition on current density
i and duration of current flow . 39
T
Figure 15 – Electrodes used for the measurement of the dependence of the
impedance of the human body Z on the surface area of contact . 40
T
Figure 16 – Oscillograms of touch voltages U and touch currents I for AC, current
T T
path hand to hand, large surface areas of contact in dry conditions taken from
measurements . 41
Figure 17 – Occurrence of the vulnerable period of ventricles during the cardiac cycle . 42
Figure 18 – Triggering of ventricular fibrillation in the vulnerable period – Effects on
electro-cardiogram (ECG) and blood pressure . 42
Figure 19 – Fibrillation data for dogs, pigs and sheep from experiments and for
persons calculated from statistics of electrical accidents with transversal direction of
current flow hand to hand and touch voltages U = 220 V and 380 V AC with body
T
impedances Z (5 %) . 43
T
Figure 20 – Conventional time/current zones of effects of AC currents (15 Hz to
100 Hz) on persons for a current path corresponding to left hand to feet (see Table 11) . 44
Figure 21 – Oscillogram of touch voltages U and touch current I for DC, current path
T T
hand to hand, large surface areas of contact in dry conditions . 44
Figure 22 – Conventional time/current zones of effects of DC currents on persons for
a longitudinal upward current path (see Table 13) . 45
Figure 23 – Let-go currents for 60 Hz sinusoidal current . 45
Figure 24 – Effects of anodic versus cathodic DC currents . 46
Figure 25 – Pulsed DC stimulation of single heart cells . 47
Figure G.1 – Electric shock in electrical model by Hart [33] including startle reaction
effect . 59
Figure H.1 – Current flow and impedances of the relevant parts of the body of a cow
for current path from the nose to the legs. 62
Figure H.2 – Diagrams for an animal, for a current path from the nose to the four legs
(path A) and from the forelegs to the hindlegs (path B) . 62
Figure H.3 – Diagram for the total body impedance for cattle for a percentage of 5 %
of the population . 65
Figure H.4 – Ventricular fibrillation for sheep . 66
Figure H.5 – Minimum fibrillating currents of sheep as a function of weight for a shock
duration of 3 s [55] . 67
Figure H.6 – Minimum fibrillating currents (averages) of various species of livestock as
a function of weight for a shock duration of 3 s [53] . 68
Table 1 – Total body impedances Z for a current path hand to hand AC 50/60 Hz, for
T
large surface areas of contact in dry conditions . 15

Table 2 – Total body impedances Z for a current path hand to hand AC 50/60 Hz, for
T
large surface areas of contact in water-wet conditions . 16
Table 3 – Total body impedances Z for a current path hand to hand AC 50/60 Hz, for
T
large surface areas of contact in saltwater-wet conditions . 17
Table 4 –Total body impedances Z for a current path hand to hand for medium
T
surface areas of contact in dry conditions at touch voltages U = 25 V to 200 V AC
T
50/60 Hz (values rounded to 25 Ω) . 18
Table 5 – Total body impedances Z for a current path hand to hand for medium
T
surface areas of contact in water-wet conditions at touch voltages U = 25 V to 200 V
T
AC 50/60 Hz (values rounded to 25 Ω) . 19
Table 6 – Total body impedances Z for a current path hand to hand for medium
T
surface areas of contact in saltwater-wet conditions at touch voltages U = 25 V to
T
200 V AC 50/60 Hz (values rounded to 5 Ω) . 19
Table 7 – Total body impedances Z for a current path hand to hand for small surface
T
areas of contact in dry conditions at touch voltages U = 25 V to 200 V AC 50/60 Hz
T
(values rounded to 25 Ω) . 19
Table 8 – Total body impedances Z for a current path hand to hand for small surface
T
areas of contact in water-wet conditions at touch voltages U = 25 V to 200 V AC
T
50/60 Hz (values rounded to 25 Ω) . 20
Table 9 – Total body impedances Z for a current path hand to hand for small surface
T
areas of contact in saltwater-wet conditions at touch voltages U = 25 V to 200 V AC
T
50/60 Hz (values rounded to 5 Ω) . 20
Table 10 – Total body resistances R for a current path hand to hand, direct current,
T
for large surface areas of contact in dry conditions . 21
Table 11 – Time/current zones for AC 15 Hz to 100 Hz for hand to feet pathway –
Summary of zones of Figure 20 . 25
Table 12 – Heart-current factor F for different current paths . 26
Table 13 – Time/current zones for direct current for hand to feet pathway – Summary
of zones of Figure 22 . 28
Table A.1 – Total body impedances Z , electrodes type A for dry conditions and
T
deviation factors F (5 % and 95 %) . 48
D
Table A.2 – Total body impedances Z , electrodes type B for dry, water-wet and
T
saltwater-wet conditions and deviation factors F (5 % and 95 %) . 48
D
Table A.3 – Total body impedances Z for dry, water-wet and saltwater-wet conditions
T
and deviation factors F (5 % and 95 %) . 48
D
Table A.4 – Deviation factors F (5 %) and F (95 %) for dry and water-wet conditions
D D
in the touch voltage range U = 25 V up to 400 V for large, medium and small surface
T
areas of contact . 50
th
Table D.1 – 50 percentile values for the total body impedance for a current path
hands-feet, medium surface area of contact for hands, large for feet, reduction factor
0,8, dry conditions, touch currents I and electrophysiological effects . 54
T
Table G.1 – Body impedance examples (uncompensated) . 59
Table H.1 – Impedance (resistance) of the hooves of cattle (Z , R ) for AC voltages up
h h
to 230 V, 50/60 Hz . 63
Table H.2 – Total body impedances Z for AC 50/60 Hz for cattle for touch voltages up
T
to 230 V . 64
Table H.3 – Initial body resistance R for cattle . 65
Table H.4 – Threshold of ventricular fibrillation for AC 50/60 Hz [53] [54] for different
species of livestock, for a shock duration of 3 s . 67

– 6 – IEC 60479-1:2018  IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EFFECTS OF CURRENT ON HUMAN BEINGS
AND LIVESTOCK –
Part 1: General aspects
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
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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.
International Standard IEC 60479-1 has been prepared by IEC technical committee 64:
Electrical installations and protection against electric shock.
This first edition cancels and replaces IEC TS 60479-1:2005, Amendment 1:2016 and
IEC TR 60479-3:1998. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to
IEC TS 60479-1 and IEC TR 60479-3:
• The contents of IEC TR 60479-3 relating to aspects unique to the effects of current
passing through the bodies of livestock have been incorporated into a new Annex H
(normative).
It has the status of a basic safety publication in accordance with IEC Guide 104.

The text of this International Standard is based on the following documents:
CDV Report on voting
64/2275/CDV 64/2343/RVC
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60479 series, published under the general title Effects of current
on human beings and livestock, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

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.
– 8 – IEC 60479-1:2018  IEC 2018
INTRODUCTION
In order to avoid errors in the interpretation of this document, it should be emphasized that
the data given herein is mainly based on experiments with animals as well as on information
available from clinical observations. Only a few experiments with shock currents of short
duration have been carried out on living human beings.
On the evidence available, mostly from animal research, the values are so conservative that
this document applies to persons of normal physiological conditions including children,
irrespective of age and weight.
There are, however, other aspects which should be taken into account, such as probability of
faults, probability of contact with live or faulty parts, ratio between touch voltage and fault
voltage, experience gained, technical feasibilities, and economics. These parameters should
be considered carefully when establishing safety requirements, for example, operating
characteristics of protective devices for electrical installations.
The form of the document, as has been adopted, summarizes results so far achieved which
are being used by technical committee 64 as a basis for establishing requirements for
protection against shock. These results are considered important enough to justify an IEC
publication which may serve as a guide to other IEC committees and countries having need of
such information.
This document applies to the threshold of ventricular fibrillation which is the main cause of
deaths by electric current. The analysis of results of recent research work on cardiac
physiology and on the fibrillation threshold, taken together, has made it possible to better
appreciate the influence of the main physical parameters and, especially, of the duration of
the current flow.
This document contains information about body impedance and body current thresholds for
various physiological effects. This information can be combined to derive estimates of AC and
DC touch voltage thresholds for certain body current pathways, contact moisture conditions,
and skin contact areas.
This document refers specifically to the effects of electric current. When an assessment of the
harmful effects of any event on human beings and livestock is being made, other non-electric
phenomena, including falls, heat, fire, or others should be taken into account. These matters
are beyond the scope of this document, but may be extremely serious in their own right.
Further experimental data are under consideration, such as recent ongoing experimental work
on "current induced heart fibrillation by excitation with discrete Fourier spectra" which is
intended to contribute to frequency factor data.
The characteristics of the impedance of the body of livestock and the effects of sinusoidal
alternating currents are described in Annex H.

EFFECTS OF CURRENT ON HUMAN BEINGS
AND LIVESTOCK –
Part 1: General aspects
1 Scope
This part of IEC 60479 provides basic guidance on the effects of shock current on human
beings and livestock.
For a given current path through the human body, the danger to persons depends mainly on
the magnitude and duration of the current flow. However, the time/current zones specified in
the following clauses are, in many cases, not directly applicable in practice for designing
measures of protection against electrical shock. The necessary criterion is the admissible limit
of touch voltage (i.e. the product of the current through the body called touch current and the
body impedance) as a function of time. The relationship between current and voltage is not
linear because the impedance of the human body varies with the touch voltage, and data on
this relationship is therefore required. The different parts of the human body (such as the skin,
blood, muscles, other tissues and joints) present to the electric current a certain impedance
composed of resistive and capacitive components.
The values of body impedance depend on a number of factors and, in particular, on current
path, on touch voltage, duration of current flow, frequency, degree of moisture of the skin,
surface area of contact, pressure exerted and temperature.
The impedance values indicated in this document result from a close examination of the
experimental results available from measurements carried out principally on corpses and on
some living persons.
Knowledge of the effects of alternating current is primarily based on the findings related to the
effects of current at frequencies of 50 Hz or 60 Hz which are the most common in electrical
installations. The values given are, however, deemed applicable over the frequency range
from 15 Hz to 100 Hz, threshold values at the limits of this range being higher than those at
50 Hz or 60 Hz. Principally the risk of ventricular fibrillation is considered to be the main
mechanism of death of fatal electrical accidents.
Accidents with direct current are much less frequent than would be expected from the number
of DC applications, and fatal electrical accidents occur only under very unfavourable
conditions, for example, in mines. This is partly due to the fact that with direct current, the let-
go of parts gripped is less difficult and that for shock durations longer than the period of the
cardiac cycle, the threshold of ventricular fibrillation is considerably higher than for alternating
current.
This basic safety publication is primarily intended for use by technical committees in the
preparation of standards in accordance with the principles laid down in IEC Guide 104 and
lSO/lEC Guide 51. It is not intended for use by manufacturers or certification bodies.
One of the responsibilities of a technical committee is, wherever applicable, to make use of
basic safety publications in the preparation of its publications. The requirements, test
methods or test conditions of this basic safety publication will not apply unless specifically
referred to or included in the relevant publications.

– 10 – IEC 60479-1:2018  IEC 2018
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC Guide 104:2010, The preparation of safety publications and the use of basic safety
publications and group safety publications
ISO/IEC Guide 51:2014, Safety aspects – Guidelines for their inclusion in standards
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 General definitions
3.1.1
longitudinal current
current flowing lengthwise through the trunk of the human body such as from hand to feet
3.1.2
transverse current
current flowing across the trunk of the human body such as from hand to hand
3.1.3
internal impedance of the human body
Z
i
impedance between two electrodes in contact with two parts of the human body, neglecting
skin impedances
Note 1 to entry: For the body of livestock, the impedance of the hooves, if any, are also neglected.
3.1.4
impedance of the skin
Z
s
impedance between an electrode on the skin and the conductive tissues underneath
3.1.5
total impedance of the human body
Z
T
vectorial sum of the internal impedance and the impedances of the skin
Note 1 to entry: For the body of livestock, Z is the vectorial sum of the internal impedance and the impedances
T
of the hide, skin and hooves, if any (see Figure H.1).
SEE: Figure 1.
3.1.6
impedance of the hide and skin
Z
P
impedance between an electrode on the hide and/or skin and the conductive tissues
underneath
3.1.7
impedance of the hoof
Z
h
impedance between an electrode under the hoof and the conductive tissues above it
3.1.8
initial resistance of the human body

R
resistance limiting the peak value of the current at the moment when the touch voltage occurs
Note 1 to entry: For the body of livestock the resistance of the hide, if any, is neglected, but the resistance of the
hooves, if any, are included.
3.1.9
dry condition
condition of the skin of a surface area of contact with regard to humidity of a living person
being at rest under normal indoor environmental conditions
3.1.10
water-wet condition
condition of the skin of a surface area of contact being exposed for 1 min to water of public
water supplies (average resistivity ρ = 3 500 Ωcm, pH = 7 to 9)
3.1.11
saltwater-wet condition
condition of the skin of a surface area of contact being exposed for 1 min to a 3 % solution of
NaCl in water (average resistivity ρ = 30 Ωcm, pH = 7 to 9)
Note 1 to entry: It is assumed that saltwater-wet condition simulates the condition of the skin of a sweating person
or a person after immersion in seawater. Further investigations are necessary.
3.1.12
deviation factor
F
D
total body impedance Z for a given percentile rank of a population divided by the total body
T
impedance Z for a percentile rank of 50 % of a population at a given touch voltage
T
Z (X%, U )
T T
F (X%, U ) =
D T
Z (50%, U )
T T
3.2 Effects of sinusoidal alternating current in the range 15 Hz to 100 Hz
3.2.1
threshold of perception
minimum value of touch current which causes any sensation for the person through which it is
flowing
3.2.2
threshold of reaction
minimum value of touch current which causes involuntary muscular contraction

– 12 – IEC 60479-1:2018  IEC 2018
3.2.3
threshold of let-go
maximum value of touch current at which a person holding electrodes can let go of the
electrodes
3.2.4
threshold of immobilization
minimum value of current through the body of the influenced human being or livestock (or part
of the human body or livestock) which causes such muscular reaction that the person or
livestock cannot move voluntarily, as long as the current flows
3.2.5
threshold of ventricular fibrillation
minimum value of touch current through the body of the human being or livestock which
causes ventricular fibrillation
3.2.6
heart-current factor
F
factor which relates the electric field strength (current density) in the heart for a given current
path to the electric field strength (current density) in the heart for a touch current of equal
magnitude flowing from left hand to feet
Note 1 to entry: In the heart, the current density is proportional to the electric field strength.
3.2.7
vulnerable period
comparatively small part of the cardiac cycle during which the heart fibres are in an
inhomogeneous state of excitability and ventricular fibrillation occurs if they are excited by an
electric current of sufficient magnitude
Note 1 to entry: The vulnerable period corresponds to the first part of the T-wave in the electrocardiogram which
is approximately 10 % of the cardiac cycle (see Figures 17 and 18).
3.3 Effects of direct current
3.3.1
total body resistance
R
T
sum of the internal resistance of the human body and the resistances of the skin
3.3.2
DC/AC equivalence factor
k
ratio of direct current to its equivalent RMS value of alternating current having the same
probability of inducing ventricular fibrillation
Note 1 to entry: As an example for shock durations longer than the period of one cardiac cycle and 50 %
probability for ventricular fibrillation, the equivalence factor for 10 s is approximately:
I
300 mA
DC-fibrillation
3, 75
k = (see Figures 20 and 22).
I 80 mA
AC-fibrillation (RMS)
3.3.3
upward current
direct touch current through the human body for which the feet represent the positive polarity
==
3.3.4
downward current
direct touch current through the human body for which the feet represent the negative polarity
4 Electrical impedance of the human body and livestock
4.1 General
The values of body impedance depend on a number of factors and, in particular, on current
path, on touch voltage, duration of current flow, frequency, degree of moisture of the skin,
surface area of contact, pressure exerted and temperature.
A schematic diagram for the impedance of the human body is shown in Figure 1.
NOTE A modelling circuit for the human body is given in Annex G.
4.2 Internal impedance of the human body (Z )
i
The internal impedance of the human body can be considered as mostly resistive. Its value
depends primarily on the current path and, to a lesser extent, on the surface area of contact.
NOTE 1 Measurements indicate that a small capacitive component exists (dashed lines in Figure 1).
Figure 2 shows the internal impedance of the human body for its different parts expressed as
percentages of that related to the path hand to foot.
For current paths hand to hand or hand to feet, the impedances are mainly located in the
limbs (arms and legs). If the impedance of the trunk of the body is neglected, a simplified
circuit diagram can be established which is shown in Figure 3.
NOTE 2 In order to simplify the circuit diagram, it is assumed that the impedance of arms and legs have the same
values.
4.3 Impedance of the skin (Z )
s
The impedance of the skin can be considered as a network of resistances and capacitances.
Its structure is made up of a semi-insulating layer and small conductive elements (pores). The
skin impedance falls when the current is increased. Sometimes current marks are observed
(see 4.7).
The value of the impedance of the skin depends on voltage, frequency, duration of the current
flow, surface area of contact, pressure of contact, the degree of moisture of the skin,
temperature and type of skin.
For lower touch voltages the value of the impedance of the skin varies widely, even for one
person, with surface area of contact and condition (dry, wet, perspiration), temperature, rapid
respiration, etc. For higher touch voltages the skin impedance decreases considerably and
becomes negligible when the skin breaks down.
As regards the influence of frequency, the impedance of the skin decr
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