Analysis of ICNIRP 2020 Basic Restrictions for Localized Radiofrequency Exposure in the Frequency Range Above 6 GHz

2020 · Mixed · Low evidence

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MixedLow evidencePaper 792

Study snapshot

Publicationmanual · 2020

Study typeengineering

Reported directionMixed

Evidence ratingLow

Abstract

Analysis of ICNIRP 2020 Basic Restrictions for Localized Radiofrequency Exposure in the Frequency Range Above 6 GHz Eric Lemay, Gregory B Gajda, Gregory W McGarr, Mykola Zhuk, Jonathan Paradis. Analysis of ICNIRP 2020 Basic Restrictions for Localized Radiofrequency Exposure in the Frequency Range Above 6 GHz. Health Phys. 2022 May 21. doi: 10.1097/HP.0000000000001581. Abstract ICNIRP 2020 guidelines have defined a practical temperature elevation threshold for human health effects, namely the operational adverse health effect threshold that forms the basis of the absorbed power and energy density basic restrictions. These basic restrictions for localized exposures at frequencies above 6 GHz were evaluated by comparing numerically computed temperature rise against the target temperature rise of 2.5 oC, which is the operational adverse health effect threshold divided by the occupational safety factor of 2. The numerical model employs the maximum absorbed power and energy density levels allowed by the occupational basic restriction for both pulsed and continuous wave exposures. These analyses were performed considering 3- and 4-tissue layer models and a variety of beam diameters, frequencies, and exposure durations. The smallest beam diameters were based on a study of theoretically achievable beam widths from half-wave resonant dipoles and show the impact of the averaging area on the computed temperature elevation. The results demonstrated that ICNIRP's assumed occupational safety factors in the frequency range above 6 GHz were not sufficiently maintained for all exposure scenarios and particularly for short pulse exposures at frequencies of 30 GHz or higher with small beam diameters. Worst-case tissue temperature elevations were estimated to be as much as 3.6 times higher than ICNIRP's target temperature increases. Consequently, the authors suggest a small modification in the application of the ICNIRP 2020 localized basic restrictions, thereby limiting the worst-case tissue temperature increases to 1.4 times the target value. Conclusion Numerical computations of the SAR distribution and resulting temperature rise in models of superficial tissue at levels allowed by the ICNIRP (2020) BRs for frequencies above 6 GHz were carried out to investigate the safety factors from the assumed OAHET thermal thresholds inherent in the BRs. The results showed that for a range of beam sizes, pulse durations, and carrier frequencies, the safety factors are reduced from their assumed values of 2 times below an OAHET temperature rise of 5 oC for the occupationally exposed. The lowest safety factors (the worst case was 0.56, resulting in a temperature rise of 1.8 times the OAHET) occurred for single pulses with the smallest assumed spot size of FWHM = 0.005 m (or an assumed unperturbed power density beam diameter of 0.0063 m) for short durations (td < 1 s) at 200 GHz. Examinations of SAR distributions from half-wave resonant dipoles (Appendix) led to the decision to set a lower value of FWHM = 0.005 m for frequencies of 30 GHz and beyond. While it may be argued that current mobile applications may not deliver such small SAR distributions, there exists the theoretical possibility that even smaller spots sizes can be generated at the higher millimeter-wave frequencies covered in the ICNIRP (2020) guideline. Safety factors for CW exposures (td > 360 s) were generally higher than for a single pulse, with the worst-case (a safety factor of 1.46 as opposed to the assumed value of 2) again occurring for the smallest spot size. Despite the low worst-case safety factors and high resulting temperature rises, CEM43 calculations suggest that even minor damage to the skin is unlikely at the current BR levels in ICNIRP (2020). The small beam diameters at which the lowest safety factors occur would suggest that maintaining the beam on the skin for a length of time necessary to induce even minor damage would be practically impossible, especially given that under such conditions, exposed individuals would likely remove the affected tissue away from the RF heat source in response to the sensation of warmth and/or heat pain before tissue damage could occur. Mitigation of the low safety factors that occurred for the smallest beam diameters can be accomplished by changing the 1 cm2 spatial averaging 0 cm2 (essentially the spatial peak of the beam). If this modification to the local BRs is applied, the associated maximum (worst-case) tissue temperature rise is ≈ 3.5 oC for exposures at the occupational BR (≈ 0.7 oC for general public BR). This modification to the BR rules is easy to implement and would allow use of the ICNIRP (2020) AED formulae and APD limits for localized exposures above 6 GHz to 300 GHz to remain unchanged. Open access paper: journals.lww.com physics/Fulltext/9900/Analysis_of_ICNIRP_2020_Basic_Restrictions_for.15.aspx

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typeengineering

Effect directionmixed

PopulationNot supplied

Sample sizeNot supplied

ExposureRF · varied; includes short pulses (td < 1 s) and CW (td > 360 s)

Evidence strengthLowConfidence: 74% · Peer reviewed: yes

Main findings

Using numerical tissue-layer models at the maximum absorbed power/energy density allowed by ICNIRP 2020 occupational basic restrictions above 6 GHz, computed temperature rises exceeded the 2.5 °C target in some scenarios. The lowest safety factors occurred for single short pulses with very small beam diameters at ≥30 GHz (worst case noted at 200 GHz), with worst-case temperature elevations reported up to 3.6× the target; CW exposures generally had higher safety factors. The authors suggest modifying application of the localized basic restrictions (changing spatial averaging) to limit worst-case temperature increases.

Outcomes measured

Numerically computed tissue temperature rise vs ICNIRP target temperature rise (2.5 °C)
Safety factor maintenance relative to operational adverse health effect threshold (OAHET)
SAR distribution in superficial tissue models
CEM43-based assessment of likelihood of minor skin damage

Limitations

Numerical modeling study (no direct human/clinical outcomes reported)
Results depend on assumed tissue-layer models (3- and 4-layer) and assumed beam diameters/spot sizes
Some worst-case spot sizes are described as theoretically possible and may not reflect current mobile applications

View raw extracted JSON

{
  "study_type": "engineering",
  "exposure": {
    "band": "RF",
    "source": "policy/guideline limits (ICNIRP 2020 basic restrictions)",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": "varied; includes short pulses (td < 1 s) and CW (td > 360 s)"
  },
  "population": null,
  "sample_size": null,
  "outcomes": [
    "Numerically computed tissue temperature rise vs ICNIRP target temperature rise (2.5 °C)",
    "Safety factor maintenance relative to operational adverse health effect threshold (OAHET)",
    "SAR distribution in superficial tissue models",
    "CEM43-based assessment of likelihood of minor skin damage"
  ],
  "main_findings": "Using numerical tissue-layer models at the maximum absorbed power/energy density allowed by ICNIRP 2020 occupational basic restrictions above 6 GHz, computed temperature rises exceeded the 2.5 °C target in some scenarios. The lowest safety factors occurred for single short pulses with very small beam diameters at ≥30 GHz (worst case noted at 200 GHz), with worst-case temperature elevations reported up to 3.6× the target; CW exposures generally had higher safety factors. The authors suggest modifying application of the localized basic restrictions (changing spatial averaging) to limit worst-case temperature increases.",
  "effect_direction": "mixed",
  "limitations": [
    "Numerical modeling study (no direct human/clinical outcomes reported)",
    "Results depend on assumed tissue-layer models (3- and 4-layer) and assumed beam diameters/spot sizes",
    "Some worst-case spot sizes are described as theoretically possible and may not reflect current mobile applications"
  ],
  "evidence_strength": "low",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "ICNIRP 2020",
    "basic restrictions",
    "localized exposure",
    "above 6 GHz",
    "millimeter wave",
    "temperature rise",
    "SAR distribution",
    "pulsed exposure",
    "continuous wave",
    "beam diameter",
    "spatial averaging",
    "occupational exposure",
    "CEM43"
  ],
  "suggested_hubs": [
    {
      "slug": "who-icnirp",
      "weight": 0.95,
      "reason": "Direct analysis of ICNIRP 2020 basic restrictions and implied safety factors."
    },
    {
      "slug": "5g-policy",
      "weight": 0.6,
      "reason": "Focus on frequencies above 6 GHz including ≥30 GHz millimeter-wave range relevant to 5G/mmWave policy discussions."
    },
    {
      "slug": "occupational-exposure",
      "weight": 0.75,
      "reason": "Evaluates occupational basic restriction scenarios and occupational safety factor assumptions."
    }
  ]
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1097/hp.0000000000001581
PubMed: Not supplied

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