Effects of current on human beings and livestock - Part 1: General aspects (IEC 60479-1:2018, identical)

2Scope / Description

The present part of IEC 60479 addresses the principal guidelines concerning the effects of electric shock current on human beings and livestock. For current passing through the human body, the risk to a person depends primarily on the magnitude and duration of the current. However, the time-current zones presented in subsequent sections cannot be applied directly in many cases to the development of effective electric-shock protection measures. The essential criterion is the permissible touch voltage (i.e., the product of the touch current, which is the current flowing through the body, and the body's apparent resistance), as a function of time. The relationship between current and voltage is not linear because the apparent resistance of the human body varies with the touch voltage; therefore, appropriate data are required.

Different parts of the human body (such as skin, blood, muscles, other tissues, and joints) exhibit different impedances to electric current, comprising both resistive and capacitive components. The value of the body's apparent resistance depends on several factors, notably the current path, touch voltage, duration of current, frequency, degree of skin moisture, size of the contact surface, applied pressure, and temperature. The apparent resistance values presented in this document are based on a careful analysis of test measurement results obtained on cadavers and on some living human subjects.

Knowledge of the effects of alternating current is based primarily on data obtained on the effects of current at frequencies of 50 Hz and 60 Hz, which are the most common in electrical installations. Nevertheless, the values given are considered applicable across a frequency range from 15 Hz to 100 Hz, with threshold values at the boundaries of this range being higher than those at 50 Hz or 60 Hz. Ventricular fibrillation is, in principle, regarded as the primary cause of fatal electrical accidents.

For direct current, electrical accidents are far fewer than might be inferred from the number of DC applications. Fatal accidents occur only under very adverse conditions, such as in mines. This is partly explained by the fact that it is easier to release a grasp when subjected to DC, and for durations longer than the cardiac cycle, the threshold for ventricular fibrillation is significantly higher with DC than with AC.

This document is intended primarily for use by technical committees in the preparation of standards, in accordance with the principles set out in IEC Guide 104 and ISO/IEC Guide 51. It is not intended for use by manufacturers or certification bodies. One of the responsibilities of a technical committee is to utilize safety-related publications wherever possible in the development of its own publications. The requirements, test methods, or test conditions of these safety publications shall not be applied without explicit reference thereto or incorporation into the relevant publication.