Electric Shock and Safety Evaluation for Electrostatic Discharge from Human

Abstract

In 2010, the international commission on non-ionizing radiation protection (ICNIRP) guidelines provided the reference levels of contact currents in the frequency range from 1 Hz to 10 MHz. These restrictions are based on the threshold levels of electric shocks of human volunteers in response to sinusoidal contact current stimuli except transient currents due to electrostatic discharges (ESDs), despite the fact that such transient currents should also cause the electric shock. In this study, concerning the contact currents causing electric shocks, we compared the charge amounts from an electrostatically charged human and from an induction charging conductor exposed to a power-frequency electric field, which were measured in volunteers' experiments by our group and by Reilly, respectively. The results showed that both the charge thresholds have almost the same level. We then conducted a human safety evaluation of a 2-kV discharge current for ESD immunity testing prescribed in the standard of the international electrotechnical commission (IEC), integrating the ratio η of the frequency spectrum of the current to the ICNIRP reference level (named conformity index), in view of the conformity criterion of simultaneous exposure to multiple frequency fields. As a result, we found that the integrated ratio or conformity index η is significantly greater than 1. This means that the 2-kV discharge current exceeds the ICNIRP reference level of contact currents. It was also found that charge voltages to provide the transient currents not exceeding the reference level from η < 1, are 30 V and 70 V for general public exposure and occupational environment, respectively, which match the safety limit of electric shock from direct-current voltages with a short time interval.