IEC/TS 60479-1

SLOVENSKI STANDARD
01-september-2006
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Effects of current on human beings and livestock - Part 1: General aspects
Effets du courant sur l'homme et les animaux domestiques - Partie 1: Aspects généraux
Ta slovenski standard je istoveten z: IEC/TS 60479-1
ICS:
13.200 3UHSUHþHYDQMHQHVUHþLQ Accident and disaster control
NDWDVWURI
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

Edition 4.0 2005-07
TECHNICAL
SPECIFICATION
SPÉCIFICATION
TECHNIQUE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ
Effects of current on human beings and livestock –
Part 1: General aspects
Effets du courant sur l'homme et les animaux domestiques –
Partie 1: Aspects généraux
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XA
CODE PRIX
ICS 13.200; 29.020 ISBN 2-8318-8096-3

– 2 – TS 60479-1 © IEC:2005
CONTENTS
FOREWORD.6
INTRODUCTION.9

1 Scope.11
2 Normative references .12
3 Terms and definitions .12
3.1 General definitions .12
3.2 Effects of sinusoidal alternating current in the range 15 Hz to 100 Hz .13
3.3 Effects of direct current .14
4 Electrical impedance of the human body.14
4.1 Internal impedance of the human body (Z ) .14
i
4.2 Impedance of the skin (Z ).15
s
4.3 Total impedance of the human body (Z ) .15
T
4.4 Factors affecting initial resistance of the human body (R ) .15
O
4.5 Values of the total impedance of the human body (Z ).15
T
4.6 Value of the initial resistance of the human body (R ) .23
O
5 Effects of sinusoidal alternating current in the range of 15 Hz to 100 Hz.23
5.1 Threshold of perception.23
5.2 Threshold of reaction.23
5.3 Immobilization .23
5.4 Threshold of let-go .23
5.5 Threshold of ventricular fibrillation.24
5.6 Other effects related to electric shocks.24
5.7 Effects of current on the skin.25
5.8 Description of time/current zones (see Figure 20).26
5.9 Application of heart-current factor (F) .26
6 Effects of direct current .27
6.1 Threshold of perception and threshold of reaction .27
6.2 Threshold of immobilization and threshold of let-go .27
6.3 Threshold of ventricular fibrillation.27
6.4 Other effects of current .28
6.5 Description of time/current zones (see Figure 22).29
6.6 Heart factor .29

Annexes .48
Annex A (normative) Measurements of the total body impedances Z made on living
T
human beings and on corpses and the statistical analysis of the results .49
Annex B (normative) Influence of frequency on the total body impedance (Z ) .52
T
Annex C (normative) Total body resistance (R ) for direct current .53
T
Annex D (informative) Examples of calculations of Z .54
T
Bibliography.58

TS 60479-1 © IEC:2005 – 3 –
Figure 1 – Impedances of the human body.29
Figure 2 – Internal partial impedances Z of the human body .30
ip
Figure 3 – Simplified schematic diagram for the internal impedances of the human body.31
Figure 4 – Total body impedances 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, a.c. 50/60 Hz.32
T
Figure 5 – Dependence of the total impedance Z of one living person on the surface
T
area of contact in dry condition and at touch voltage (50 Hz) .
Figure 6 – Dependence of the total body impedance Z on the touch voltage U for a
T T
current path from the tips of the right to the left forefinger compared with large surface
areas 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, a.c. 50 Hz, duration of current flow
T
max. 25 ms .34
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 a.c. 50/60 Hz.35
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, a.c. 50/60 Hz.36
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, a.c. 50/60 Hz .37
T
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 .38
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.38
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 2 kHz for a current path hand to hand or hand to foot, large
surface areas of contact in dry conditions .39
Figure 13 – Statistical value of total body impedances Z and body resistances R for a
T T
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 a.c. 50/60 Hz and d.c.40
Figure 14 – Dependence of the alteration of human skin condition on current density i
T
and duration of current flow (for detailed description of zones, see 5.7) .41
Figure 15 – Electrodes used for the measurement of the dependence of the
impedance of the human body Z on the surface area of contact .42
T
– 4 – TS 60479-1 © IEC:2005
Figure 16 – Oscillograms of touch voltages U and touch currents I for a.c., current
T T
path hand to hand, large surface areas of contact in dry conditions taken from
measurements .43
Figure 17 – Occurrence of the vulnerable period of ventricles during the cardiac cycle .44
Figure 18 – Triggering of ventricular fibrillation in the vulnerable period – Effects on
electro-cardiogram (ECG) and blood pressure .44
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 a.c. with body
T
impedances Z (5 %) .45
T
Figure 20 – Conventional time/current zones of effects of a.c. currents (15 Hz to
100 Hz) on persons for a current path corresponding to left hand to feet (for
explanation see Table 11).46
Figure 21 – Oscillogram of touch voltages U and touch current I for d.c., current path
T T
hand to hand, large surface areas of contact in dry conditions .46
Figure 22 – Conventional time/current zones of effects of d.c. currents on persons for
a longitudinal upward current path (for explanation see Table 13).47
Figure 23 – Let-go currents for 60 Hz sinusoidal current .47

Table 1 – Total body impedances Z for a current path hand to hand a.c. 50/60 Hz, for
T
large surface areas of contact in dry conditions .16
Table 2 – Total body impedances Z for a current path hand to hand a.c. 50/60 Hz, for
T
large surface areas of contact in water-wet conditions .17
Table 3 – Total body impedances Z for a current path hand to hand a.c. 50/60 Hz, for
T
large surface areas of contact in saltwater-wet conditions.18
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 a.c.
T
50/60 Hz (values rounded to 25 Ω) .19
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
a.c. 50/60 Hz (values rounded to 25 Ω).20
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 a.c. 50/60 Hz (values rounded to 5 Ω).20
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 a.c. 50/60 Hz
T
(values rounded to 25 Ω) .20
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 a.c.
T
50/60 Hz (values rounded to 25 Ω) .21

TS 60479-1 © IEC:2005 – 5 –
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 a.c.
T
50/60 Hz (values rounded to 5 Ω) .21
Table 10 – Total body resistances R for a current path hand to hand, d.c., for large
T
surface areas of contact in dry conditions .22
Table 11 – Time/current zones for a.c. 15 Hz to 100 Hz for hand to feet pathway :
Summary of zones of Figure 20 .26
Table 12 – Heart-current factor F for different current paths.27
Table 13 – Time/current zones for d.c. for hand to feet pathway – Summary of zones of
Figure 22 .29
Table A.1 – Total body impedances Z , electrodes type A for dry condition and
T
deviation factors F (5 % and 95 %) .49
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 %) .49
D
Table A.3 – Total body impedances Z for dry, water-wet and saltwater-wet conditions
T
and deviation factors F (5 % and 95 %).50
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 .51
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.56
T
– 6 – TS 60479-1 © IEC:2005
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
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.

TS 60479-1 © IEC:2005 – 7 –
IEC 60479-1, which is a technical specification, has been prepared by IEC technical
committee 64: Electrical installations and protection against electric shock.
This fourth edition cancels and replaces the third edition, published as a technical report in
1994, and constitutes a technical revision.
The main changes with respect to the previous edition are listed below:
th
– Dependence of the total body impedance Z for 50 percentile rank of a population of
T
living human beings for large, average and small surface areas of a contact in dry, water-
wet and saltwater-wet conditions at touch voltage U = 25 V to 200 V a.c. 50/60 Hz.
T
– Oscillograms of touch voltages U and touch currents I for a.c., current path hand-to-
T T
hand, large surface areas of contact in dry condition taken from measurements given in
Figure 16 with the relevant explanations in the main text.
– Fibrillation data for dogs, pigs and sheep obtained 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 to 380 V a.c.with body impedances Z (5%)
T T
given in Figure 19 with the relevant explanations in the main text.
– Change of Curve B in Figure 20 from 10 mA to 5 mA: conventional time/current zones of
effects of a.c. current (15 Hz to 100 Hz) on persons with the relevant explanations in
themain text.
– Let-go currents for 60 Hz sinusoidal current given in Figure 23 with the relevant
explanations in the main text.
– new structure to the body of the standard.
This technical specification has the status of a basic safety publication in accordance with IEC
Guide 104.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
64/1427/DTS 64/1463/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above Table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 60479 consists of the following parts under the general title Effects of current on human
beings and livestock
Part 1: General aspects
Part 2: Special aspects:
Chapter 4: Effects of alternating current with frequencies above 100 Hz
Chapter 5: Effects of special waveforms of current
Chapter 6: Effects of unidirectional single impulse currents of short duration
Part 3: Effects of currents passing through the bodies of livestock
Part 4: Effects of lightning strokes on human beings and livestock

– 8 – TS 60479-1 © IEC:2005
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of October 2006 have been included in this copy.

TS 60479-1 © IEC:2005 – 9 –
INTRODUCTION
This technical specification provides basic guidance on the effects of shock current on human
beings and livestock, for use in the establishment of electrical safety requirements.
In order to avoid errors in the interpretation of this specification, it must 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
the standard applies to persons of normal physiological conditions including children,
irrespective of age and weight.
There are, however, other aspects to 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 have to be
considered carefully when fixing safety requirements, for example, operating characteristics of
protective devices for electrical installations.
The form of the specification as has been adopted summarizes results so far achieved which
are being used by technical committee 64 as a basis for fixing 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 technical specification 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.
IEC 60479-1 contains information about body impedance and body current thresholds for
various physiological effects. This information can be combined to derive estimates of a.c.
and d.c. touch voltage thresholds for certain body current pathways, contact moisture
conditions, and skin contact areas. Information about touch voltage thresholds for
physiological effects is contained in the IEC 61201.
This specification 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 specification, but may be extremely serious in their own
right.
Recent research work has also been conducted on the other physical accident parameters,
especially the waveform and frequency of the current and the impedance of the human body.
This fourth revision of IEC 60479-1 should be viewed as the logical development and
evolution of the third edition.
Clause 2 of IEC 60479-1 (third edition) on the impedance of the human body contained little
information on the dependence of the impedance on the surface area of contact and then only
for dry conditions.
– 10 – TS 60479-1 © IEC:2005
Therefore measurements were carried out on 10 persons using medium and small surface
areas of contact in dry, water-wet and saltwater-wet conditions, current path hand to hand, at
a touch voltage of 25 V a.c. 50 Hz. The impedance values for a percentile rank of 5 %, 50 %
and 95 % have been calculated from these measurements.
Due to unpleasant sensations and the possibility of inherent danger, measurements using
large surface areas of contact (order of magnitude 10 000 mm ) in dry, water-wet and
saltwater-wet conditions and with medium and small surface areas of contact (order of
2 2
magnitude 1 000 mm and 100 mm ) in dry condition at touch voltages from 25 V up to and
including 200 V a.c. have only been carried out on one person. By the use of deviation factors
it was nevertheless possible to derive values of the total body impedance Z for a percentile
T
rank of 5 %, 50 % and 95 % of a population of persons. With the same one person
measurements were also made with still smaller surface areas of contact (10 mm and
1 mm ) and between fingertips.
For the calculation of total body impedance Z for a percentile rank of 5 %, 50 % and 95 % of
T
a population of persons for large surface areas of contact for touch voltages above 200 V up
to 700 V and higher up to the asymptotic values the method to adapt values of Z measured
T
on corpses to those of persons used for the second edition of IEC 60479-1 was improved by
taking account of the different temperature of the corpses during measurements and the
temperature of 37 °C for persons.
The present state of knowledge of a.c. impedance Z of the human body for large, medium
T
and small surface areas of contact in dry, water-wet and salt-water-wet conditions and of the
d.c.-resistance R of the human body for large areas of contact in dry conditions are
T
presented.
It should be mentioned that the thresholds as order of magnitude are valid for all persons
(men, women and children) independent of their state of health. Often concerns are
expressed in that respect but if the background of such objections is examined it is found that
such objections represent just opinions without experimental evidence. Some measurements
indicate that the thresholds of perception and let-go for women are lower than for men. This
may also be the case for children.
Furthermore in Clause 5 a heart-current factor F for the current path foot to foot has been
introduced. This is important for electrical risks caused by step voltages.

TS 60479-1 © IEC:2005 – 11 –
EFFECTS OF CURRENT ON HUMAN BEINGS
AND LIVESTOCK –
Part 1: General aspects
1 Scope
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 technical specification 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 d.c. 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.
NOTE The IEC 60479 series contains information about body impedance and body current thresholds for various
physiological effects. This information can be combined to derive estimates of a.c. and d.c. touch voltage
thresholds for certain body current pathways, contact moisture conditions, and skin contact areas. Information
about touch voltage thresholds for physiological effects is contained in IEC 61201.

– 12 – TS 60479-1 © IEC:2005
2 Normative references
The following referenced documents are indispensable for the application 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 61201:1992, Extra-low voltage (ELV) – Limit values
Guide 104:1997, The preparation of safety publications and the use of basic safety
publications and group safety publications
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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
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 (see Figure 1)
3.1.6
initial resistance of the human body
R
resistance limiting the peak value of the current at the moment when the touch voltage occurs
3.1.7
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

TS 60479-1 © IEC:2005 – 13 –
3.1.8
water-wet condition
condition of the skin of a surface area of contact being exposed for 1min to water of public
water supplies (average resistivity ρ = 3 500 Ωcm, pH = 7 to 9)
3.1.9
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 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.
3.1.10
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
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 ventricular fibrillation
minimum value of touch current through the body which causes ventricular fibrillation
3.2.5
heart-current factor
F
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 In the heart, the current density is proportional to the electric field strength.
3.2.6
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 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).

– 14 – TS 60479-1 © IEC:2005
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
d.c./a.c. equivalence factor
k
ratio of direct current to its equivalent r.m.s. value of alternating current having the same
probability of inducing ventricular fibrillation
NOTE 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
d.c.−fibrillation
k = = = 3,75 (see Figures 20 and 22)
I 80 mA
a.c.−fibrillation (r.m.s.)
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
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.
4.1 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.
TS 60479-1 © IEC:2005 – 15 –
4.2 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 the 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 decreases when the
frequency increases.
4.3 Total impedance of the human body (Z )
T
The total impedance of the human body consists of resistive and capacitive components.
For lower touch voltages, there are considerable variations in the impedance of the skin Z
S
and the total impedance of the human body Z similarly varies widely. For higher touch
T
voltages, the total impedance depends less and less on the impedance of the skin and its
value approaches that of the internal impedance Z . See Figures 4 to 9.
i
As regards the influence of frequency, taking into account the frequency dependence of the
skin impedance, the total impedance of the human body is higher for direct current and
decreases when the frequency increases.
4.4 Factors affecting initial resistance of the human body (R )
At the moment when the touch voltage occurs, capacitances in the human body are not
charged. Therefore skin impedances Z and Z are negligible and the initial resistance R
S1 S2 0
is approximately equal to the internal impedance of the human body Z (see Figure 1). The
i
initial resistance R depends mainly on the current path and to a lesser extent on the surface
area of contact.
The initial resistance R limits the current peaks of short impulses (e.g. shocks from electric
fence controllers).
4.5 Values of the total impedance of the human body (Z )
T
th
The dependence of the total body impedance Z for the 50 percentile rank of a population of
T
living human beings for large, medium and small surface areas of contact (order of magnitude
2 2 2
10 000 mm , 1 000 mm and 100 mm respectively) in dry, water-wet and saltwater-wet
conditions at touch voltages U = 25 V a.c. to 200 V a.c. is shown in Figures 7, 8 and 9.
T
4.5.1 Sinusoidal alternating current 50/60 Hz for large surface areas of contact
The values of the total body impedances in Tables 1, 2 and 3 are valid for living human
beings and a current path hand to hand for large surface areas of contact (order of magnitude
10 000 mm ) in dry (Table 1), water-wet (Table 2) and saltwater-wet (Table 3) conditions.

– 16 – TS 60479-1 © IEC:2005
The range of the total body impedances for touch voltages up to 700 V for large surface areas
of contact in dry, water-wet and saltwater-wet conditions for a percentile rank of 50 % of the
population is presented in Figure 4.
The values for Tables 1, 2 and 3 represent the best knowledge on the total body impedances
Z for living adults. On the knowledge at present available the total body impedance Z for
T T
children is expected to be somewhat higher but of the same order of magnitude.
Table 1 – Total body impedances Z for a current path hand to hand a.c. 50/60 Hz, for
T
large surface areas of contact in dry conditions
Touch voltage
Values for the total body impedances Z (Ω) that are not exceeded for
T
V
5 % of the population 50 % of the population 95 % of the population
25 1 750 3 250 6 100
50 1 375 2 500 4 600
75 1 125 2 000 3 600
100 990 1 725 3 125
125 900 1 550 2 675
150 850 1 400 2 350
175 825 1 325 2 175
200 800 1 275 2 050
225 775 1 225 1 900
400 700 950 1 275
500 625 850 1 150
700 575 775 1 050
1 000 575 775 1 050
Asymptotic value 575 775 1 050
= internal impedance
NOTE 1 Some measurements indicate that the total body impedance for the current path hand to foot is somewhat
lower than for a current path hand to hand (10 % to 30 %).
NOTE 2 For living persons the values of Z correspond to a duration of current flow of about 0,1 s. For longer
T
durations Z values may decrease (about 10 % to 20 %) and after complete rupture of the skin Z approaches the
T T
internal body impedance Z .
i
NOTE 3 For the standard value of the voltage 230 V (network-system 3N ∼ 230/400 V) it may be assumed that the
values of the total body impedance are the same as for a touch voltage of 225 V.
NOTE 4 Values of Z are rounded to 25 Ω.
T
TS 60479-1 © IEC:2005 – 17 –
Table 2 – Total body impedances Z for a current path hand to hand a.c. 50/60 Hz, for
T
large surface areas of contact in water-wet conditions
Touch voltage
Values for the total body impedances Z (Ω) that are not exceeded for
T
V
5 % of the population 50 % of the population 95 % of the population
25 1175 2 175 4 100
50 1100 2 000 3 675
75 1025 1 825 3 275
100 975 1 675 2 950
125 900 1 550 2 675
150 850 1 400 2 350
175 825 1 325 2 175
200 800 1 275 2 050
225 775 1 225 1 900
400 700 950 1 275
500 625 850 1 150
700 575 775 1 050
1 000 575 775 1 050
Asymptotic value 575 775 1 050
=internal impedance
NOTE 1 Some measurements indicate that the total body impedance for the current path hand to foot is somewhat
lower than for a current path
...