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 letgo
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.
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