Value chain · CLM-1323
In plain terms
By 1970 most western countries used a limit of 10 milliwatts per square centimetre, first chosen in 1957 for lack of better data. The Soviet Union and Poland allowed a thousand times less, because they accepted evidence of effects that do not come from heating.
The claim as recorded
A 1970 journal review of microwave exposure criteria states that the first US limit, 10 mW/cm2 for all frequencies, came from a 1957 military conference that judged the data too thin to set levels by frequency, and the US Air Force adopted it in 1958. A 1960 industry guide held levels under 1 mW/cm2 safe for indefinitely prolonged exposure and 1 to 10 mW/cm2 safe only for occasional exposure. The 1966 US standard set 10 mW/cm2 averaged over any 0.1 hour. The review lists Soviet limits above 300 MHz of 10 uW/cm2 for a working day, 100 uW/cm2 for 2 hours a day and 1000 uW/cm2 for 15 minutes a day; Poland set the same 10 uW/cm2 with no time limit in 1961. A 1968 Czechoslovak proposal set daily doses for the general population equal to a 24-hour average of 2.5 uW/cm2 for continuous and 1 uW/cm2 for pulsed sources. The review concludes that western countries generally accepted 10 mW/cm2, that the USSR and Poland were lower by a factor of 1000, and that the differences arise in general from accepting data showing non-thermal functional changes in animals and people.
Evidence behind this: T2, a peer-reviewed journal review of national criteria; it permits "the review states Y". The national instruments it quotes were not checked.
Scope and limits
The Czechoslovak figures were a 1968 proposal, not an adopted limit. The review says the basis of the differences "was not discussed in this paper", so its one-line cause is a general remark. The bundled 1969 oven-repair paper in the same file gives the Soviet short-exposure limit as 1.0 mW/cm2 for up to 20 minutes with goggles (PDF p.14 / printed 138), not 15 minutes; the two papers disagree on the time and the source behind each was not read. The "uW" in the text layer reads as "p,W" or "mu W" and was taken as micro by context and by the stated 1000-fold ratio.
What it assumes
The criteria in force or proposed up to late 1969 (the paper was received in November 1969).
Where it comes from
PDF p.2 / printed 624: "a level of 10 mW/cm2 was selected for all frequencies"; Air Force adoption May 1958; Bell 1960: "Power levels under 1 mW/cm2 are safe for indefinitely prolonged exposure". PDF p.3 / printed 625: USASI 1966 "10 mW/cm2, as averaged over any possible 0.1-hour period". PDF p.4 / printed 626: Poland 1961 "Intensity 10 uW/cm2-no limitation for time of work"; USSR "10 uW/cm2 for a working day", "100 uW/cm2 for 2 hours daily", "1000 uW/cm2 for 15 minutes daily". PDF p.5 / printed 627: general population, continuous, "twenty-four hours exposure time corresponds to an average energy flow of 2.5 uW/cm2"; pulsed, "1 uW/cm2". PDF p.6 / printed 628 (inferred): "lower by a factor of 1000 at 10 uW/cm2"; differences "arise by the acceptance of data showing nonthermal functional changes".
Basis: mW/cm2 and uW/cm2 by exposure time
Related records
- Answers question
- QST-001 not published in this release
Cite this
energyaperture.com/c/clm-1323
CLM-1323, Energy Aperture, as of 1970-09.