Value chain · CLM-1334
In plain terms
In 1978 the US environment agency calculated that the American safety limit of the time could, at some radio frequencies, heat parts of the body far more than normal metabolism does. It found that a cautious heat-based limit would land close to the much stricter Soviet limit.
The claim as recorded
A 1978 US EPA technical note took 1 W/kg, about the resting metabolic rate averaged over the body, as a reference thermal load and worked out the exposure fields that produce it across frequency. It finds a body resonance range of about 10 to 1000 MHz in which exposure at the then US guide of 10 mW/cm2 could give whole-body loads several times the metabolic rate. For an adult at about 70 MHz, a far-field equivalent of 4.2 mW/cm2 doubles the body's heat load, while uneven absorption could give local rates up to 30 W/kg. In some frequency regions above 10 MHz the 10 mW/cm2 guide could put energy into some tissues at 100 times the resting whole-body metabolic rate. The note says limiting any tissue to an extra 10 per cent of the metabolic load gives exposures equal to the Soviet occupational standard, and speculates that Soviet limits may relate to very slight tissue heating labelled non-thermal. It concludes that applying the US guide to the whole population raises serious reservations, and that whole-body limits from 10 to 1000 MHz could be two orders of magnitude lower if conservative tissue-level thermal protection is wanted.
Evidence behind this: T3, a reviewed and approved US EPA technical note with a named author and a stated method; it permits "the EPA note calculates Y". The absorption data are taken from published models and measurements by others; the note does not measure absorption itself.
Scope and limits
Thermal analysis only; the note states it does not treat non-thermal or pulsed-field effects. The tissue intensification factors are stated as possible values, not measured. The Soviet comparison is the note's speculation; it gives no Soviet limit value on these pages. The note's resonance range (10-1000 MHz) lies below the 2.45 and 5.8 GHz bands used in power-beaming designs, so its headline figures do not transfer to those frequencies without its frequency curves (Figure 9, not read here). The US guide it tests (ANSI C95.1-1974) has since been replaced.
What it assumes
Plane-wave far-field exposure; adult (70 kg, 1.75 m) and infant-proxy absorption models from the cited literature; field intensification factors of 30 (free space) and 10 (grounded) from whole body to selectively heated tissue (Table 1 notes, printed p.26).
Where it comes from
PDF p.6 / printed iv: resonance range 10 to 1000 MHz with "whole body thermal loads several times the whole body basal metabolic rate" at the US standard. PDF p.37 / printed 27: above 10 MHz "there are regions wherein" the 10 mW/cm2 level "could introduce power deposition in selective tissues of the body 100 times greater than the resting whole body BMR". PDF p.39 / printed 29: limiting tissue deposition to "an additional 10 percent of the inherent BMR" gives exposures "equal to the present Soviet occupational exposure standard". PDF p.42 / printed 32: at about 70 MHz, "a far-field equivalent of 4.2 mW/cm2" doubles the BMR heat load; local rates "as high as 30 W/kg" (PDF p.43 / printed 33). PDF p.43 / printed 33: "serious reservations" about applying the ANSI standard to the population. PDF p.14 / printed 4: whole-body limits "could be two orders of magnitude below the presently accepted safe limit".
Basis: mW/cm2 incident; W/kg absorbed; J/m3 field energy density
Related records
- Answers question
- QST-001 not published in this release
Cite this
energyaperture.com/c/clm-1334
CLM-1334, Energy Aperture, as of 1978-04.
Connected records
Other published records linked to this one. A list, not a judgement.