Energy Guide

EMF & RF Safety Levels - A Comparative Guide ScanTech
www.scantech7.com 214.912.4691
tropic Radiated Power) for 802.11b (2.4GHz) devices
A study conducted in the Unites States found that, in large cities , the average background RF levels were about 50 μ
W/m 2 . About 1% of people living in large cities are exposed to RF fields exceeding 10 mW/m 2 . Higher RF field levels
can occur in areas located close to transmitter sites or radar systems.
The average GSM mobile handset has a power output of around 600 milliwatts
Compare this with microwave ovens, which can emit 500 to 700 Watts
RF fields between 10 MHz and 10 GHz penetrate exposed tissues and produce heating due to energy absorption in
these tissues. The depth of penetration of the RF field into the tissue depends on the frequency of the field and is greater
for lower frequencies.
SAR is the basic dosimetric quantity for RF fields between about 1 MHz and 10 GHz. A SAR of at least 4 W/kg is
needed to produce adverse health effects in people exposed to RF fields in this frequency range. Such energies are
found tens of meters away from powerful FM antennas at the top of high towers, which makes these areas inaccessible.
RF fields above 10 GHz are absorbed at the skin surface, with very little of the energy penetrating into the underlying
tissues.
For adverse health effects, such as eye cataracts and skin burns, to occur from exposure to RF fields above 10 GHz,
power densities above 1000 W/m 2 are needed. Such densities are not found in everyday life. They do exist in very
close proximity to powerful radars. Current exposure standards preclude human presence in this areas.
RADIATION LEVELS & SAFETY
Rem ( R oentgen E quivalent M an) is the unit of Dose (actually absorbed taking biological effects into account)
Rad (Roentgen Absorbed Dose) is simply the actual amount of radiation absorbed
Rem = Rads x Quality Factor (QF)
where the Quality Factor depends on the type of radiation. Heavy particles as alphas have a QF of 20, neutrons have a
QF of 3-10 depending on the energy of the neutrons. Betas and gammas have a QF of 1.
The amount of ionising radiation, or 'dose', received by a person is measured in terms of the energy absorbed in the
body tissue, and is expressed in gray . One gray (Gy) is one joule deposited per kilogram of mass.
Equal exposure to different types of radiation expressed as gray do not however necessarily produce equal biological
effects. One gray of alpha radiation, for example, will have a greater effect than one gray of beta radiation. When we talk
about radiation effects, we therefore express the radiation as effective dose, in a unit called the sievert (Sv).
1 Rem = .01 Sieverts
A former unit of (radio)activity is the Curie - 1 Bq is 27 x 10 -12 curies.
Title 10 Code of Federal Regulations Part 20
(10CFR20) is the NRC regulation governing radiation protection at a nu-
clear power plant. This regulation imposes requirements on such important items as annual allowed radiation exposure,
radiation protection methods, radioactive releases, and records.
Adult workers may receive a whole body dose 5 Rem per year; minors are restricted to 0.5 Rem per year; pregnant
women are restricted to 0.5 Rem during the term of the pregnancy (for protection of the embryo). For comparison, actual
physical effects (minor blood changes) from radiation exposure are not expected until a person receives 25 Rem in a
short period of time. Higher eye and extremity doses are allowed because these have less effect than on that part of the