Biological Effects - RF/Microwave Interaction with Biological Tissues - page 130

sible long-term effects.” Health epidemiologists have to evaluate if the safety
factor is large enough.
One may compare a temperature elevation of “less than 1°C” by microwave
heating with a temperature elevation of less than 1°C due to physical efforts.
In an experimental study, 59 healthy young men have been submitted to a
maximal exercise test on a treadmill (stress test) for 18 min, during which the
limits of the cardiorespiratory physiology are reached. During the last minute
of the test, the energetic expense of the adult (20 kcal) is 20 times higher than
that of the same adult at rest. Considering that approximately 22.5% of the
calories generated during work in aerobiose are transformed into useful exter-
nal work, the mean energy density was found 102 W min kg -1 . The temperature
elevations were measured, yielding an average temperature elevation of
0.736°C. On the other hand, the total energy density due to 30 min microwave
exposure with an SAR of 4 W kg -1 is equal to 120 W min kg -1 . The comparison
of the two values shows that, if the two temperature elevations are propor-
tional, the temperature due to this microwave exposure would produce a tem-
perature elevation equal to 0.866°C. It is interesting to observe that this
external microwave heating and the maximal exercise testing produce about
the same temperature elevation [115].
As can be seen, establishing standards is not an easy thing to do. As an
example, it is worth considering the values used in Europe for the standard
related to European GSM mobile telephony, at 900 MHz, for the general
public, expressed in volts per meter: (1) The WHO, ICNIRP, and European
Union recommend not to exceed 41.2 V m -1 ; (2) several European
governments have adopted lower values, such as Belgium (20.6 V m -1 ), Italy
(20 V m -1 ,6Vm -1 for an exposure of 4 h or more), Switzerland (4 or 6 V m -1 ),
and Luxembourg (3 V m -1 ); (3) effects on BBB permeability have been
observed at 0.016 W kg -1 , that is, 18 V m -1 ; (4) considering the possibility of
isothermal or microthermal effects implies an extra factor of about 100 in
power, yielding 4 V m -1 ; (5) two epidemiology studies out of four on TV/FM
exposure evidenced a twofold increase of leukemia under 2 to 4 V m -1 expo-
sures; (6) the Belgian High Council for Health has recommended an extra
safetyfactor of 100-200, yielding 4 to 3 V m -1 ; and (7) in February 2003, the
City of Paris, France, obtained from the operators not to exceed a value
between 1 and 2 V m -1 , depending on the power transmitted at 1800 MHz.
Hence, the picture is complex because a number of arguments can be used
which do not lead to the same conclusions.

3.11.2 Tissue Phantoms and SAR Measurements

The increase in public concern about possible health risks from microwave
energy has stimulated a number of investigations in vivo and in vitro. A step
necessary for assessing the potential risks is to analyze and quantify the EM
energy induced in the human body, in particular the human head, by external
sources, such as cellular telephones and the associated base stations.