Body resistance

In electrical engineering , body resistance is understood to be the electrical resistance of a human or animal body. This resistance largely determines the limit values for the prevention of electrical accidents . Other areas of application for measuring body resistance are in the area of body fat scales and lie detectors .

General

The human or animal body is an ionic conductor (second type of conductor ). The body resistance consists of the skin resistance and the resistance of the rest of the body. It is a complex resistor made up of R and C and depends on various parameters such as the voltage applied , the frequency , the contact area, the electrode location, the degree of moisture in the skin and the distribution of substances inside the body. The body resistance decreases with increasing voltage, but there is no linear relationship between the applied voltage and the resulting body current. Because of this, measurements and conclusions based on body resistance are fraught with great uncertainties and errors. Measurements on dry skin lead - depending on the parameters used - to relatively high resistance values of up to over 1 MΩ ; these relatively high resistance values result from the fact that the upper skin layer acts as an insulator and thus causes a high resistance value. In specialist literature, the body resistance is given as around 500 Ω to 1.3 kΩ. In the event of contact with higher voltages above 100 V, the upper skin layer is broken down and no longer offers any resistance.

Furthermore, the body resistance depends largely on the entry and exit points on the body, as this results in current paths of different lengths through the body. In addition, the body resistance also differs from person to person under identical external conditions and, as a rule, only statistical statements and information on mean values are possible. Various organizations such as the Employers' Liability Insurance Association for Energy, Textile, and Electrical Media Products regularly carry out statistical studies on this topic and publish them.

If you look at the equivalent circuit diagram, you can see a series connection of capacitance (upper skin layer) followed by an ohmic resistance (inside of the body), which in turn is followed by a capacitance (upper skin layer). Body resistance is then referred to as body impedance, a form of AC resistance . Bioelectrical impedance analysis ( body fat scales ) and impedance cardiography are examples of medical applications of impedance measurement.

The International Electrotechnical Commission , as a standards organization, publishes IEC 60479-1 as a guide on this topic.

history

First measurements to determine the body resistance for the purpose of accident prevention go back to Heinrich Freiberger . In 1933 and 1934 he published the results of systematically carried out measurements at different voltages on living test persons up to 50 V and on corpses with and without skin at voltages up to 5 kV. It turned out that the body resistance of corpses differed significantly from the body resistance of living people.

This gave rise to the problem that the modeling for many decades was not based on reliable data and that limit values were conservatively set downwards. The first reliable data on determined body impedances can be found in IEC report 60479-1 in the 1990s.

Numerical values

Extensive tables and numerical values for the amount of body impedance under different conditions can be found in IEC specification 60479-1 and in Biegelmeier.

For illustration, numerical values taken from, for the total body impedance, current path between fingertip-fingertip from one arm to the other, with a contact pressure of 22 N, a contact area of approx. 250 mm ² , dry skin, flow duration 20 ms with an alternating voltage of 50 Hz and at the point of switch-on in the voltage zero crossing, the following absolute values of the body impedance are determined as a function of the effective alternating voltage:

Voltage in V	Body impedance in kΩ
25th	67.3
50	44.9
75	24.8
100	10.9
125	8th
150	5.2
175	4.3
200	3.8

Literature sources

Gottfried Biegelmeier, Dieter Kieback, Gerhard Kiefer, Karl-Heinz Krefter: Protection in electrical systems, Volume 1 .: Dangers from electrical current . 2nd Edition. VDE Verlag GmbH, 2003, ISBN 3-8007-2603-3 .

Individual evidence

↑ Josef Eichmeier: Medical Electronics: An Introduction for Students of Engineering, Physics, Medicine and Biology . Springer-Verlag, 2013, ISBN 978-3-662-08623-0 , pp. 86.87 ( limited preview in Google Book Search [accessed February 14, 2017]).
^ Norbert Leitgeb: Safety of medical devices: Law - Risk - Opportunities . Springer-Verlag, 2015, ISBN 978-3-662-44657-7 , pp. 176 ( limited preview in Google Book Search [accessed February 14, 2017]).
↑ Bernd Diekmann, Eberhard Rosenthal: Energy: Physical principles of their generation, conversion and use . Springer-Verlag, 2013, ISBN 978-3-658-00501-6 , pp. 299 ( limited preview in Google Book Search [accessed February 14, 2017]).
↑ Jürgen Kupfer, Michael Rock .: Effects of step and touch tension on the human body. Association of German Lightning Protection Companies, accessed on October 27, 2019 .
↑ Statistical evaluations of key data on electrical accidents and their lethality to assess the marginal risk for the occurrence of ventricular fibrillation in humans. Employer's Liability Insurance Association for Energy, Textile, and Electrical Media Products, accessed on October 25, 2019 .
↑ DIN IEC / TS 60479-1 VDE V 0140-479-1 - Effects of electrical current on people and livestock. In: VDE Association of Electrical Engineering Electronics Information Technology e. V. Retrieved October 27, 2019 .
↑ Heinrich Freiberger: The electrical resistance of the human body to technical direct and alternating current . Springer, Berlin 1934 (Ed. With the support of the Association of the German Employers' Liability Insurance Association, Employers Liability Insurance Association for Precision Mechanics and Electrical Engineering, Berliner Städtische Elektrizitätswerke AG).
↑ ^a ^b IEC TS 60479-1: 2005 + AMD1: 2016 CSV: Effects of current on human beings and livestock - Part 1: General aspects . 4.1 Edition. IEC, Geneva 2016.
↑ ^a ^b Gottfried Biegelmeier, Dieter Kieback, Gerhard Kiefer, Karl-Heinz Krefter: Protection in electrical systems, Volume 1: Dangers from electrical current . 2nd Edition. VDE Verlag GmbH, 2003, ISBN 3-8007-2603-3 .

[1] Josef Eichmeier: Medical Electronics: An Introduction for Students of Engineering, Physics, Medicine and Biology . Springer-Verlag, 2013, ISBN 978-3-662-08623-0 , pp. 86.87 ( limited preview in Google Book Search [accessed February 14, 2017]).

[2] Norbert Leitgeb: Safety of medical devices: Law - Risk - Opportunities . Springer-Verlag, 2015, ISBN 978-3-662-44657-7 , pp. 176 ( limited preview in Google Book Search [accessed February 14, 2017]).

[3] Bernd Diekmann, Eberhard Rosenthal: Energy: Physical principles of their generation, conversion and use . Springer-Verlag, 2013, ISBN 978-3-658-00501-6 , pp. 299 ( limited preview in Google Book Search [accessed February 14, 2017]).

[4] Jürgen Kupfer, Michael Rock .: Effects of step and touch tension on the human body. Association of German Lightning Protection Companies, accessed on October 27, 2019 .

[5] Statistical evaluations of key data on electrical accidents and their lethality to assess the marginal risk for the occurrence of ventricular fibrillation in humans. Employer's Liability Insurance Association for Energy, Textile, and Electrical Media Products, accessed on October 25, 2019 .

[6] DIN IEC / TS 60479-1 VDE V 0140-479-1 - Effects of electrical current on people and livestock. In: VDE Association of Electrical Engineering Electronics Information Technology e. V. Retrieved October 27, 2019 .

[freiberger-7] Heinrich Freiberger: The electrical resistance of the human body to technical direct and alternating current . Springer, Berlin 1934 (Ed. With the support of the Association of the German Employers' Liability Insurance Association, Employers Liability Insurance Association for Precision Mechanics and Electrical Engineering, Berliner Städtische Elektrizitätswerke AG).

[iec_60479-1-8] IEC TS 60479-1: 2005 + AMD1: 2016 CSV: Effects of current on human beings and livestock - Part 1: General aspects . 4.1 Edition. IEC, Geneva 2016.

[biegelmeier-9] Gottfried Biegelmeier, Dieter Kieback, Gerhard Kiefer, Karl-Heinz Krefter: Protection in electrical systems, Volume 1: Dangers from electrical current . 2nd Edition. VDE Verlag GmbH, 2003, ISBN 3-8007-2603-3 .