2.2. Effect and perception thresholds of static electric fields

Project management: RWTH Aachen University
Start: 1 December 2021
End: 30 November 2023

Background

The importance of electric fields is increasing during the course of power grid expansion, particularly in connection with the expansion of direct current lines. This is because, while there is no limit value for static electric fields, the 26th Ordinance Implementing the Federal Immission Control Act (26^th BImSchV) stipulates that irritation is to be prevented. The perception thresholds must therefore be known. In connection with the expansion of hybrid lines (Ultranet), it is also necessary to know the specific effects of a combination of direct and alternating fields and ion currents.

There are considerable gaps in knowledge regarding the perception of electric fields by humans. This matter is only addressed in two, older scientific publications ^{[1, 2]} as well as a study completed at the end of 2019 by RWTH Aachen University, which yielded unexpectedly low perception thresholds, particularly in the event of a combination of direct and alternating fields ^{[3, 4]}. Ion currents and atmospheric humidity also had a modifying influence. This scenario is relevant to hybrid lines. The results are to be verified, and the mechanisms are to be clarified.

Objective

The research project aims to investigate the perception of hybrid fields by humans and in particular the influence of weak DC background fields (DC = direct current; direct fields) on the perception threshold for AC fields (AC = alternating current; alternating fields). In addition, it will investigate the underlying biological mechanisms of perception. There is some evidence that AC fields cause vibrations in the hair on the arms and legs, whereas DC fields are more likely to be perceived via the head area. As these two modes of perception can interact with one another, the mechanisms are to be investigated both separately and in combination.

Implementation

The existing findings ^{[3, 4]} show that constant, weak AC background fields significantly influence and reduce the DC perception threshold. This project will investigate the influence of constant, weak DC background fields on the AC perception threshold. Forty to fifty particularly sensitive test subjects will be selected from the preliminary study and examined at constant temperature (22 °C) and humidity (50 %) with exposure to constant, weak DC background fields (1, 2, 3 and 4 V/m). The AC field strength will be varied within the range of 1–14 V/m, and the lowest perception threshold will be determined in psychophysiological tests. Some subjects will be sham exposed for control purposes, and the study will be double-blinded – i.e. neither the subjects nor the researchers will know when an electric field is present or not.

In addition, the project will seek to clarify the mechanisms of action that lead to the low perception thresholds. In particular, it will investigate the roles of body hair and atmospheric humidity. To this end, 30 healthy test subjects aged 18–35 will be recruited (15 women and 15 men). In terms of their individual head and body hair, the subjects’ characteristics are to be as different as possible. The air temperature will remain constant at 22 °C, and the humidity will be varied between 30 % and 70 %. Tests will be carried out with AC fields at 8–30 kV/m, DC fields at 14–38 kV/m, and hybrid fields. The physical properties of the hair (moisture content, thickness, length) will be ascertained, and the movements of the hair will be recorded on video. Further investigations will be carried out after the hair has been shaved off. The results will allow conclusions to be drawn regarding the causes of the low thresholds observed for hybrid fields.

References

[1] Blondin JP et al. (1996). Human perception of electric fields and ion currents associated with high-voltage DC transmission lines. Bioelectromagnetics 17: 230 - 241.
[2] Chapman CE et al. (2005). Perception of local DC and AC electric fields in humans. Bioelectromagnetics 26: 357-366.
[3] Jankowiak et al. (2021) Identification of Environmental and Experimental Factors Influencing Human Perception of DC and AC Electric Fields. Bioelectromagnetics 42: 341 - 356
[4] Kursawe et al. (2021) Human detection thresholds of DC, AC, and hybrid electric fields: a double‑blind study. Environ Health 20:92