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Biological Effects of Radiofrequency and Microwave Radiation:
Application, Hazards, and Safeguards. by Wolfgang W. Scherer ( 25. March 1994 )
mW = milli-Watt = 1/thousandth Watt = 10-3 Watt
µW = micro-Watt = 1/Millionth Watt = 10-6 Watt
nW = nano-Watt = 1/Billionth Watt = 10-9 Watt
pW = pico -Watt = 1/Trillionth Watt = 10-12 Watt
...... the simple fact that these scientists assume what is experienced
on an animal can be transferred to humans by multiplying the results with
a ratio number obtained by measuring the length and weight of the object
seems highly naive. Emphasizing the "resonant frequency", only
being the one doing apparently the most damage, conceals the fact that
the whole frequency range is just as hazardous. The effects only peak at
this particular frequency.This simplified approach to such a complex problem
is unacceptable today, but our Code standards are based on such methods!
This also means that only one dimension of the complex three-dimensional shape of a human body is considered in this calculations, the other two dimensions for 'thickness' and 'width' would give at least two more resonant frequency ranges which are totally neglected. This is unsatisfactory and needs immediate consideration! The linear extrapolation for the dosage based on the relative weight from animal to human is also not convincing. The fact that the thermoregulatory mechanisms of fur bearing animals differ widely from those in humans with their different body shape, their exposed skin, and their ability to sweat makes direct use of data that result from animal experiments even more difficult. A better scientific approach and a more acceptable method to determine those important benchmarks is needed. .....
... Thermal effects can be measured long before temperature changes
are observed. The blood vessels are dilating and the blood flow increases
substantially as the thermoregulatory mechanism is activated in order to
keep the body temperature constant. With rising body temperature the metabolic
rate rises also, what may lead to Stress-Adaptation-Fatigue Syndrome. This
may be the thermal explanation for late and cumulative effects of radio-frequency
radiation, that other researchers try to explain through non thermal effects
of radiation exposure.  ( It does not really make a difference
how to explain the effect, since all agree it is caused by this radiation
What distinguishes radiofrequency introduced heating from other means of heating is the rapidity of heating, the depth of penetration, and the existence of internal hot-spots, that can result in tissue damage long before the overall body temperature increases dramatically. The brain is particularly susceptible to the occurrence of these hot-spots. Depending on the size of the head and the frequency of the radiation , regions of relatively high absorption can occur at or near the center of the brain . These effects are especially uncontrollable in the near-field during the use of mobile communication devices like cordless and cellular phones and very unpredictable due to the variable shape ,size, and thickness of skulls.
However, the main objectively measurable hazard of microwave radiation is injury to the eyes, especially damaging at frequencies above 800 MHz. Since the lens of the eye does not have an adequate vascular system for the exchange of heat, even a slight rise in temperature can cause protein coagulation, and opacities in the lens may form. This may already be defined as a cataract, however in clinical practice the term cataract is normally not used unless the opacity has progressed so much as to interfere with visual acuity. Experimentally cataracts in animals develop after exposure to power densities above 100 mW/cm². Missing was exact information on duration. It is safe to assume a short pulse was sufficient , since most researchers feel strongly that repeated exposure of the lens to lower doses of radiation can result in accumulation of injury. .......................
...... A special role is played by the electrophonic effect of microwave hearing. Humans can perceive a buzzing or clicking sound in the back of their heads at exposure to power densities as low as 0.1 mW/cm² of pulsed microwave radiation (200-3000 MHz) , depending on the pulse repetition frequency and the peak power density (around 300 mW/cm²). The absorbed energy produces a thermoelastic expansion of the brain tissue causing an acoustic pressure wave which is detected in the cochlea by the hair cells of the organ of Corti. The energy needed to produce this effect is so small that it does not actually increase the mean temperature of the brain, yet the acoustic sensation is strong enough to be clearly perceived in an ambient noise level of circa 65 dB. Due to this fact microwave hearing does not cause an apparent physical reaction within the head, but it is well known that humans suffer general stress reactions when they are exposed to higher levels of sound. Noise cannot only be an annoyance, but when it consists of pulsed sounds it affects heart beat and metabolic rates.  The subliminal aspects of noise levels are here not even considered despite the recognized physiological effects of acoustic noise. It would be a very interesting field for research to probe the subliminal acoustic effects of such exposure to low radio frequency radiation. A possible link between such radiation and noise related reactions , effects, or damages would be an aspect worth of further investigation......
....... We face another problem in evaluating standards : the different
time periods used to express the values. The listed field intensities of
recommended exposure levels must be compared carefully since they refer
to different exposure times . As stated above the significant factor is
the accumulated exposure over a relative short length of time, but the
codes do not give any value for a total accumulation like in X-ray exposure
Limits as given in the Canadian Safety Code 6 (1991)  for occupational exposure to radio wave energy are 1 mW/cm² averaged over one hour period and 25 mW/cm² averaged over one minute period. They allow much higher pulse levels than the Swedish Standard  which even differentiates for the frequency range and has especially lower limits for the more damaging microwave range 5 mW/cm² 10-300 MHz averaged over 0.1h (=6 min.) 1 mW/cm² 0.3-300 GHz averaged over 0.1h (=6 min.) 25 mW/cm² 10 MHz-300 Ghz averaged over 1 sec !
However the accumulative exposure is not addressed . Those above limits only make sense in an environment where one is exposed to peaks or pulses of radiation especially in radar sites or to radiation during the operation of microwave equipment (ovens or heaters), which are switched on and off. These values do not regulate how long one may be exposed to such electromagnetic fields not even the maximum levels one is exposed to.
With a pulse train, that has a 1:20 on/off ratio, one could be exposed to pulse energies proven to be highly dangerous - e.g. 500 mW/cm²- without violation of the Code. Also one could be exposed for a full second to 1.5 W/cm²over a one minute periode. Recall from above: 7% of this value causes eye damage!
To be useful the Code has to give a peak limit and a dosage limit. Power we get from our utility is measured in Kilo-Watt-Hour, a unit used to measure accumulated power consumption over a time period . A unit for accumulated exposure to radiofrequency radiation should be established in the same manner, for example mWh/cm². If we use the exposure rates allowed by Safety Code 6 we get as an accumulated dose 1 mWh/cm²for one hour but 0.4 mWh/cm² for a minute Allowed by the Swedish Code are for the 10-300 MHz range 5m Wh/cm² for the 300 MHz- 300 GHz range the same as the Canadian Code. Only the maximal dose for one second which calculates to 7 µWh/cm² may enforce lower peak values of exposure. But in both codes no values for accumulated doses are given and science has yet to come up with a dose that can be endured without damage , setting a radiation level that can be considered safe for permanent exposure.
Missing is such an accumulative exposure limit probably for the reason, that with it the necessary (mandatory) required - exposure free - recovery time has to be stated - like for X-ray exposure - a difficult problem in our current "radio" environment!
From the allowable occupational exposure it could be calculated that
by multiplying this numbers with 8 hours of a work shift , an allowable
dose of 8 mWh/cm² per day could be established. But this would then
only be valid for a 8 hour work shift with a 16 hour recovery period and
would establish an occupational exposure level only.
A further linear reduction to 0.3 mW/cm² as a permanent exposure rate causing the same dose over a 24 hour period is merely a mathematical exercise and does not address accumulation with no recovery period. More problematic if that exposure is not occupational but involuntary.
The controversy in adequate assessment of the hazards of radiofrequency radiation stems from the lack of explicit data. Unfortunately there is still no specific long term exposure research to establish data as we know it from X-ray exposure, where after a given exposure a rest or recovery period is mandatory. If we consider a similar accumulation in the area of microwave exposure and accept for involuntary permanent exposure a rate at 1% of this 0.3 mW/cm² resulting in a value of 3µW/cm², we are likely at a level which may already been exceeded in some areas. ( Recall from above - 1970 in the USA- 1µW/cm² in cities).
A different calculation derived from the electrophonic effect -described above - leads to much lower values. If we use the before mentioned values of 0.1 mW/cm² and 65 dB noise level and that the clicking sound has to be about 3 dB above that ambient noise to be clearly perceived, it allows us to assume that 0.1 mW/cm² cause an equal effect as a 68 dB sound level.If we compare this to a 8 dB sound level which is considered "quiet" the difference of 60 dB calculates to a value that is one Million times smaller. This means that for an equivalent energy level to be perceived as quiet the radio frequency density level would have to be about 0.1 nW/cm² = 100 pW/cm².
( the 0 db level or - perceptive threshold - would then be equivalent to 15.8 picoW/cm². - 19.02 1999 - W.W.S )
If we consider this value, an ambient radiation level of 1µW/cm²
(as measured for 1970) is already 10 000 times higher. All our universities
and research facilities are most likely exposed to such levels, so it seems
puzzling that there research could been done to establish a safe threshold
level that may have been exceeded decades ago!
Nobody has ever established what level of radio frequency radiation is safe or unsafe for permanent accumulative exposure with no recovery period. A situation that has concerned people already demanding a moratorium on any further expansion of wireless communications.
 NATO Advanced Study Institute on Advances in Biological Effects and Dosimetry of Low Energy Electromagnetic Fields. (1981: Erice, Italy) . Biological effects and dosimetry of non-ionizing radiation: radiofrequency and microwave energies. New York. Plenus Press, 1983.
 Baranski, Stanislaw. Biological effects of microwaves. Stroudsburg, Pa. Dowden, Hutchinson and Ross, 1976.
 Canada. Environmental Health Directorate. Limits of exposure to radiofrequency fields at frequencies from 10 KHz - 300 GHz. Safety Code 6. 1991.
 International Labour Office. Protection of workers against radiofrequency and microwave radiation. A technical review . Geneva , 1986.
 Cleary, Stephen F. et al. Effects and health implications of microwave radiation. Medical College of Virginia. U.S.Department of Health, Education and Welfare, 1969.
 Osepchuk, John M. et al. Biological effects of electromagnetic radiation. IEEE, 1986.
 Michaelson, Solomon M. et al. Fundamental and applied aspects of non-ionizing radiation. Rochester International Conference on Environmental Toxicity, 1974. New York, Plenum Press, 1975.
 Welch, Bruce L. & Annemarie S. et al. Physiological effects of noise. New York, Plenum Press, 1970.
copyright ©1994 -1997 by Wolfgang W. Schererfor comments or questions e-mail the author Wolfgang W. Scherer