strength of the field presents a biological hazard to
personnel located at the point where the measurements
were taken. PEL readings are the basis for determining
RADHAZ safety boundaries.
Permissible Exposure Time (PET)—This is the
maximum time of exposure to a specific power density
for which the PEL will not be exceeded when the
exposure is averaged over any 6-minute period. Table
3-1 shows the PET for a variety of radars operated at
their normal power levels.
If you suspect that you or someone else has been
overexposed to EMR, follow the flow chart in figure
3-2. If you confirm your suspicions, the exposure is
considered an incident and must be reported as
required by Protection of DOD Personnel from
Exposure to Radio Frequency Radiation, DOD
Instruction 6055.11.
RFR HAZARDS TO THE SKIN.—The energy
impinging on a person in an electromagnetic field may
be scattered, transmitted, or absorbed. The energy
absorbed into the body depends upon the dimensions
of the body, the electrical properties of the tissues, and
the wavelength of the RFR. Thus, the wavelength of
the energy and its relationship to a person’s
dimensions are important factors bearing on the
biological effects produced by RFR.
Significant energy absorption will occur only
when a personal dimension is equivalent to at least
one-tenth of a wavelength. As the frequency of
radiation increases, the wavelength decreases and the
person’s height represents an increasingly greater
number of electrical wavelengths, increasing the
danger from RFR exposure. As the frequency is
decreased, the wavelength increases and the person
becomes a less significant object in the radiation field.
Thus, the likelihood of biological damage increases
with an increase in radiation frequency. Also, as the
radiation frequency increases and the wavelength
becomes progressively shorter, the dimensions of parts
and appendages of the body become increasingly
significant in terms of the number of equivalent
electrical wavelengths.
When a person stands erect in a RFR field, the
body is comparable to a broadband receiving antenna.
3-5
Figure 3-2.—Personnel RFR exposure decision chart.
