Why Low‐Frequency EMF Safety Would Benefit From Peak‐Based Limits Instead of RMS Values

ABSTRACT

Current low‐frequency EMF exposure limits are based on RMS values. However, the hazard at low frequencies, neural and muscular stimulation is driven by instantaneous peak values. Because action potentials follow an all‐or‐nothing threshold, even a single suprathreshold cycle can trigger excitation, whereas long‐term RMS averages can be arbitrarily reduced by inserting pauses into signals. Pulsed or bursty fields—such as those emitted by certain deactivators used in electronic article surveillance—may comply with RMS‐based limits despite containing peaks capable of exceeding physiological thresholds. Reformulating both basic restrictions and reference levels in terms of peak values would align exposure limits with neurophysiological mechanisms and provide clearer guidance for ensuring safety. As ICNIRP revises its 2010 low‐frequency guidelines, this is an opportune moment to adopt peak‐based limits and better protect workers and the general public.

Summary

• Low‐frequency EMF safety is fundamentally a stimulation issue, and stimulation is triggered by instantaneous peak values—not long‐term RMS averages.

• Reformulating exposure limits in terms of peak values would better align with neurophysiological mechanisms and close safety loopholes created by the RMS‐based methods.

1. Background and Motivation

Low‐frequency electromagnetic field limits (basic restrictions and reference levels) are expressed as root‐mean‐square (RMS) values in the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) (2010) guidelines. That convention made sense historically: the ICNIRP (1998) guidelines aimed for a uniform formulation across the whole frequency spectrum (0–300 GHz) and leaned on RMS as a convenient, power‐related measure. But the dominant biological hazard at low frequencies is not heating; it is unintended neural and muscular stimulation. Action potentials follow an all‐or‐nothing rule with a threshold. When thresholds govern risk, instantaneous peaks matter more than time‐averaged power. Using peak‐based limits aligns the metric with the underlying biology and closes loopholes that RMS averaging can inadvertently create.

2. Biological Foundations of Stimulation Thresholds

Neurons and excitable tissues respond when transmembrane voltage crosses a threshold, opening voltage‐gated channels and initiating an action potential. This is a discontinuous event: subthreshold fields may do nothing, while a slightly stronger field elicits a full response. The relevant metric is therefore the instantaneous induced electric field at the membrane and its time course over microseconds to milliseconds—not the average over long time windows.

Stimulation follows a strength–duration behavior: shorter pulses (corresponding to higher frequencies) require higher peaks, longer pulses require lower peaks, but in either case the critical parameter is the peak value relative to a time‐scale‐dependent threshold. A compact way to capture this is the classical strength–duration relation,

$$I_{\mathrm{th}}\left(t_p\right)=I_r(1+\frac{c}{t_p}),$$

where $I_{\mathrm{th}}$ is the peak current needed for a pulse of width $t_p$, $I_r$ is the rheobase, and $c$ is the chronaxie. Regardless of the exact constants in human tissue, the structure of this curve emphasizes peak amplitude and pulse width, not long‐term averages.

Neurostimulation practice routinely leverages high‐peak, short‐duration waveforms—transcranial magnetic stimulation and peripheral nerve stimulators deliver pulses designed to exceed thresholds briefly, not to raise RMS power. Simulations and electrophysiological experiments show that even a single near‐threshold sinusoidal cycle can elicit an action potential when its peak amplitude and timing align with membrane dynamics. That is exactly the kind of event RMS averaging will hide.

3. Why RMS Can Underestimate Risk in Pulsed Low‐Frequency Fields

RMS averages power over a chosen window, inherently rewarding signals with pauses. By definition,

$$x_{\mathrm{rms}}=\sqrt{\frac{1}{T}{\int }_0^T{x}^2\left(t\right)\mathit{dt}}.$$

For a continuous sinusoid, RMS and peak values are linked by a factor of $\sqrt{2}$. But many real‐world low‐frequency exposures are bursty: brief sinusoids or pulses separated by gaps. For a sinusoidal burst train with duty cycle $D$ (on‐time fraction), the RMS scales as

$$x_{\mathrm{rms}}\approx \frac{x_{\mathrm{peak}}}{\sqrt{2}}\sqrt{D}.$$

As $D$ shrinks, RMS plummets even if $x_{\mathrm{peak}}$ stays fixed. Therefore, high peaks can be masked behind low RMS values.

Note that a single suprathreshold cycle or short pulse can trigger an action potential. RMS, by construction, can be made arbitrarily small by inserting pauses, while the biological effect of the peaks remains unchanged. When averaging times are long (e.g., 1 s as specified in standards for RMS measurements), even sparse bursts of millisecond‐scale peaks can fall “compliant” by RMS while still exceeding stimulation thresholds at the tissue level.

4. Example of Electronic Article Surveillance

A concrete safety concern arises at certain deactivators used in electronic article surveillance systems. These deactivators often emit short sinusoidal magnetic pulses on the order of a few milliseconds. Over a 1‐s window their RMS can be well within current limits because the duty cycle is small. Yet the instantaneous peaks can be high enough to exceed stimulation thresholds in nearby tissue. If one looks only at RMS, these exposures appear benign, but if one evaluates peak values the risk profile changes. This issue is well known. For example, it has already been mentioned by Jokela (2000).

Manufacturers can argue that the fields are “sinusoidal” and therefore adequately represented by RMS values. Within each millisecond burst, the waveform may indeed be close to a sinusoid, but biology does not integrate over the off‐time to forgive the on‐time peaks. Compliance can be demonstrated based on current RMS limits. However, it is questionable if exposed people are adequately protected from possible stimulation effects.

5. Implications for Standards and Measurement

Current low‐frequency frameworks (ICNIRP 2010 or IEEE C95.1, The Institute of Electrical and Electronics Engineers Inc. 2019) set “basic restrictions/dosimetric reference limits” (induced electric field in tissue) and “reference levels/exposure reference levels” (external field surrogates) in terms of RMS values. That leaves room for compliance by duty‐cycle engineering: inserting pauses into the signal lowers the RMS value but keeps the peak values. It also creates ambiguity for measuring the fields: changing the RMS averaging window can change the compliance verdict. IEEE C95.1 specifies an averaging time of 200 ms, but most measurement devices do not allow to change the averaging time and use a standard value of 1000 ms.

Both ICNIRP guidelines and IEEE standards include special methods for non‐sinusoidal or pulsed fields (e.g., the weighted peak method in ICNIRP 2003). However, in our experience these methods are often ignored in practice. It is argued that the pulsed fields are sinusoidal and that therefore the RMS limits for a given frequency can be applied. This results in lengthy discussions about methodological issues and is not helpful for providing safe exposure conditions.

Shifting to peak‐based limits would resolve these issues and better match the hazard mechanism. Measuring peak values for short pulses might be more technically challenging and require more expertise for some exposure scenarios than measuring RMS values. Therefore, it would be desirable to have guidelines providing precise reference measurement methods to address these challenges. In our opinion, peak‐based limits would be advantageous for EMF safety and since ICNIRP is currently revising its 2010 low‐frequency guidelines, this might be a good time to consider such a shift to peak‐based limits.

6. Conclusion

Low‐frequency EMF safety is fundamentally a stimulation problem, and stimulation is governed by instantaneous thresholds, not long‐term averages. RMS limits reward pauses, and EMF can certify as “safe” exposures that contain brief but biologically potent peaks. By reformulating both basic restrictions and reference levels in peak terms, guidelines and standards would align with neurophysiology, eliminate averaging‐time ambiguity, provide clearer methodological guidance and result in better exposure evaluation along with higher safety for workers and the general public.

Funding

The authors received no specific funding for this work.

Conflicts of Interest

The authors declare no conflicts of interest.