FOREWORD
This order establishes criteria, standards, procedures, and guidelines
for the recognition, evaluation, and control of radiation health
hazards in FAA workplaces. It is a part of the agency's continuing
effort to manage or control losses due to occupational accidents,
injuries, illnesses, and management deficiencies, and to provide
safe and healthful working conditions for all employees as prescribed
by the Occupational Safety and Health Act (PL 91596) and as directed
by Executive Order 12196. The provisions contained in this order
are consistent with the requirements of FAA Order 3900.19A, Occupational
Safety and Health.
H. L. Reighard, M.D.
Federal Air Surgeon, AAM1
TABLE OF CONTENTS
Page No.
CHAPTER 1. GENERAL
1. Purpose 1
2. Distribution 1
3. Cancellation 1
4. Explanation of Changes 1
5. Definitions 1
6. Responsibilities 3
719. Reserved 5
Figure 1.1. Electromagnetic Spectrum 6
CHAPTER 2. IONIZING RADIATION
SECTION 1. GENERAL
20. Effects ant Hazards 9
21. Sources of Exposure 10
22. Permissible Exposure Limits (PEL's) 11
Figure 21 Ionizing Radiation PEL's 11
23. Evaluation of Hazards 12
24. Control of Hazards 14
Figure 22. XRadiation Warning Sign 16
SECTION 2. XRADIATION
25. Radar Systems 17
26. VORTAC's and TACAN's 18
SECTION 3. RADIONUCLIDES
27. Radioactive Electron Tubes 20
28. Aircraft Instrument Dials 21
29. Radioactive Control Knobs on Radar Equipment 22
CHAPTER 3. NONIONIZING RADIATION
SECTION 1. RADIOFREQUENCY/MICROWAVE RADIATION
30. General 23
31. Effects and Hazards 23
32. Sources of Exposure 24
33. Permissible Exposure Limits (PEL's) 25
Figure 31. RF/Microwave PEL's 25
34. Evaluation of Hazards 26
35. Control of Hazards 27
Figure 32. RF Radiation Warning Sign 28
36. Radar Systems 28
Figure 33. Radars Capable of Producing Power
Densities in excess of the PEL 29
Figure 34. Attenuation of RF Radiation
Provided by Various Types of Shielding 30
37. VORTAC's and TACAN's 31
38. Communication Systems 32
39. Microwave Landing Systems 32
40. Microwave Ovens 33
41. Medical Diathermy 33
42. Cathode Ray Tubes 34
CHAPTER 1. GENERAL
1. PURPOSE. This order establishes criteria, standards,
procedures, and guidelines for the recognition, evaluation, and
control of radiation health hazards in FAA workplaces.
2. DISTRIBUTION. This order is distributed to director
level in Washington, except in Air Traffic, Systems Engineering,
and Program Engineering and Maintenance Service, and Aviation
Medicine. It is distributed to branch level in Air Traffic, Systems
Engineering, Program Engineering and Maintenance Service, and
to division level in Aviation Medicine. Distribution is to division
level in Regions and Centers, with limited distribution to all
Air Traffic and Airway Facilities Field Offices
3. CANCELLATION. Order 3910.3, Radiation Health Hazards
and Protection, dated February 12, 1970, is canceled.
4. EXPLANATION OF CHANGES
a. This order restructures agency radiation protection responsibilities
to better utilize available expertise. Specific responsibilities
are assigned to the Office of Aviation Medicine (AAM), the Office
of Personnel ant Training (APT), the Systems Engineering Service
(AES), and the Program Engineering and Maintenance Service (APM).
b. Information pertaining to the identification, evaluation,
and control of radiation health hazards in FAA workplaces is expanded
and updated.
c. A new health protection standard for RF/microwave radiation
is established and interpreted with respect to all sources of
RF/microwave radiation in FAA facilities and operations.
5. DEFINITIONS.
a. Alpha Particle. A particle emitted spontaneously from the
nuclei of some radioactive elements. It is identical with a helium
nucleus and consists of two protons and two neutrons; it has an
electric charge of two positive units.
b. Beta Particle. A charged particle emitted from the
nucleus of an atom. It has the same mass and negative electric
charge as an electron.
c. Controlled Area. An area which requires control of
access, occupancy, and working conditions for radiation protection
Purposes.
d. Dose. The amount of radiation delivered to a specified
area or volume or to the whole body.
e. Dose Rate. Radiation dose delivered per unit time.
f. Electric (E) Field. One of two mutually supporting
vectors of an electromagnetic wave the intensity of which is expressed
in volts per meter (V/m). An electric field exists in a region
if charged objects in the region experience a force.
g. Electromagnetic Spectrum. A graphical representation
of radiant energy in an orderly arrangement according to its wave
length or frequency (Figure 11).
h. Gamma Radiation. Short wavelength electromagnetic radiations
of high energy originating in atomic nuclei.
i. Ion. Atomic particle, atom, or chemical radical bearing
an electrical charge, either negative or positive.
j. Ionizing Radiation. Electromagnetic radiation (gamma
rays or xrays) or particulate radiation (alpha particles, beta
particles, neutrons, etc.) capable of producing ions, directly
or indirectly, in its passage through matter.
k. Magnetic (H) Field. One of two mutually supporting
vectors of an electromagnetic wave the intensity of which is expressed
in amperes per meter (A/m). A magnetic field exists in a region
if magnetic objects in the region experience a force.
l. Microwave Radiation. Electromagnetic radiation ranging
in frequency from 300 megahertz (MHz) to 300 gigahertz (GHz) with
corresponding wavelengths ranging from 1.0 meter (m) to 0.1 centimeter
(cm).
m. Neutron. An electrically neutral particle of approximately
unit mass, present in all atomic nuclei, except those of ordinary
hydrogen.
n. Nonionizing Radiation. The less energetic forms of
electromagnetic radiation, such as near ultraviolet, visible light,
infrared, microwave, radio, and electric power.
o. Nonoccupational Exposure. Exposure that occurs outside
a controlled area or to a visitor to a controlled area.
p.Occupational Exposure. Exposure to ionizing radiation
which occurs to a worker assigned to a controlled area.
q. Photon. A unit (quantum) of electromagnetic
energy.
r. Power Density. The intensity of microwave/radiofrequency
radiation at a given point. Power density is the average power
per unit area expressed as milliwatts per square centimeter (mW/cm2).
s. Rad. The unit of absorbed dose of ionizing radiation
which is 0.01 Joules/kilogram or 100 ergs/gram in any medium.
t. Radiofrequency (RF) Radiation. Electromagnetic radiation
ranging in frequency from 300 kilohertz (kHz) to 300 GHz with
corresponding wavelengths ranging from 103m to 0.1cm. The microwave
region is included in the RE range.
u. Rem. The rem is the unit of radiation dose. It is the
measure of the dose of any ionizing radiation to body tissue in
terms of its estimated biological effect relative to a dose of
1 rad of 250 kilovolt (kv) xrays. The relation of the rem to other
dose units depends upon the biological effect under consideration
and upon the conditions of irradiation. For the purpose of this
order, any of the following is considered to be equivalent to
a dose of one rem:
(1) A does of 1 R due to x or gamma radiation.
(2) A does of 1 rad due to x, gamma or beta radiation.
(3) A does of 0.1 rad due to neutrons.
(4) A does of 0.05 rad due to alpha radiation (internal exposure).
v. Roentgen (R). A unit of exposure dose. It is that quantity
of x or gamma radiation which produces one electrostatic unit
of positive or negative electricity per cubic centimeter of air
at standard temperature and pressure or 2.083 x 109 ion pairs
per cubic centimeter of dry air.
w. SAR. The specific absorption rate, expressed in watts
per kilogram (W/kg), is the rate at which RF energy is absorbed
in irradiated tissue.
x. XRadiation. Penetrating electromagnetic radiations
which have wave lengths shorter than those of visible light and
which are usually produced by bombarding a metallic target with
fast electrons in a high
vacuum.
6. RESPONSIBILITIES.
a. The Industrial Hygiene Program Manager
(located within AAM) shall serve as the FAA Radiation Protection
Officer and shall:
(1) Provide guidance and consultation on matters pertaining
to the health effects of ionizing and nonionizing radiation in
FAA operations.
(2) Investigate reports of radiation health hazards in FAA and
jointuse military facilities under the responsibility of the FAA.
(3) Coordinate with the Industrial Hygiene Investigations Program
Manager (located within the Civil Aeromedical Institute), AES/Regional
Frequency Management Engineers, the Occupational Safety Program
Manager, and Safety and Health Managers in performing radiation
health hazards evaluations and in recommending corrective action
where needed.
(4) Represent the FAA in liaison with Governmental and private
organizations on matters related to radiation health hazards and
protection.
b. The Industrial Hygiene Investigations Program Manager
shall:
(1) Coordinate and consult with the Industrial Hygiene Program
Manager in providing advice and information on matters pertaining
to radiation health hazards in FAA operations.
(2) Coordinate with the Industrial Hygiene Program Manager,
AES/Regional Frequency Management Engineers, and Safety and Health
Managers in responding promptly to reports of radiation health
hazards.
(3) Perform radiation health hazards evaluations on new and
modified facilities that house equipment, systems, or substances
capable of producing external ionizing or nonionizing radiation
fields.
c. AES/Regional Frequency Management Engineers shall:
(1) Coordinate and consult with the Industrial Hygiene Program
Manager in providing advice and information on matters pertaining
to radiation health hazards in FAA operations.
(2) Coordinate with the Industrial Hygiene Program Manager,
the Industrial Hygiene Investigations Program Manager, and Safety
and Health Managers in responding promptly to reports of radiation
health hazards.
(3) Perform radiation health hazards surveys on new and modified
facilities that house equipment, systems, or substances capable
of producing external ionizing or nonionizing radiation fields.
(4) Perform other radiation health hazards surveys as required.
d. Safety and Health Managers shall:
(1) Receive and review all employee reports of radiation health
hazards and coordinate a response according to procedures established
in Order 3900.19A, Occupational Safety and Health.
(2) Coordinate and consult with the Industrial Hygiene Program
Manager, the Industrial Hygiene Investigations Program Manager,
or AES/Regional Frequency Management Engineers in responding to
reports of radiation health hazards.
(3) Perform routine radiation health hazards evaluations during
periodic safety and health inspections authorized by Order 3900.19A,
Occupational Safety and Health.
(4) Coordinate and consult with Regional Flight Surgeons regarding
the health effects of radiation in the workplace.
e. Regional Flight Surgeons shall provide consultation
and advice on matters relating to the health effects of radiation
in the workplace.
f. The Program Engineering and Maintenance Service shall
require manufacturers, as a part of equipment specifications,
to make complete safety evaluations and provide written reports
on prototypes of radiation producing systems prior to their use
by FAA personnel. The evaluations shall include complete assessments
of external ionizing and/or nonionizing radiation fields, safety
interlocks, and safe operating procedures.
g. Facility Managers/Supervisors shall:
(1) Ensure that all personnel working with radiation producing
devices or substances are familiar with the contents of
this order.
(2) Request a health hazard evaluation when in their judgment
one is warranted.
h. FAA Depot Managers/Supervisors shall ensure that all personnel
working in the Depot shops and storage areas with radiation producing
devices or substances are familiar with the contents of this order.
719. RESERVED
FIGURE 11. ELECTROMAGNETIC SPECTRUM
CHAPTER 2. IONIZING RADIATION
SECTION 1. GENERAL
20. EFFECTS AND HAZARDS. Living cells are vulnerable to
ionizing radiations, the nature and extent of their response depending
upon the amount of exposure. The degree of injury to an individual
is a function of the dose of ionizing radiation and will vary
from person to person. An individual can tolerate much larger
doses to a small part of the body than to the entire body. Exposures
involving a small part of the body affect mainly the tissues in
the radiation beam whereas whole body exposures are more likely
to result in generalized response. There is some recovery but
this becomes less significant as the total accumulated dose becomes
greater.
There are two general types of ionizing radiation health effects;
i.e., somatic and genetic:
a. Somatic Effect. Ionizing radiation injuries to body
tissues are called somatic effects. Those that occur within a
few days or weeks after the beginning of exposure are called "immediate"
somatic effects and those that appear thereafter are called "late"
somatic effects. Both are usually the result of relatively high
radiation doses (> 50 rads and are most often due to gross
negligence. They are rarely seen in the workplace.
Immediate somatic effects can range from barely discernible chromosomal
alterations to profound and dramatic radiation sickness. Late
somatic effects include various forms of cancer, reductions in
life span and fertility, growth retardation, and cataracts, all
known to occur in humans in the absence of significant radiation
exposure. Because of the latter and the many other complicating
factors involved (e.g., age, tissue and cell radiosensitivity,
tissue and organ recovery and repair, exposure time factors, etc.),
it is virtually impossible to demonstrate late somatic effects
conclusively in individual cases. Their relationship to radiation
exposure can only be deduced in carefully designed epidemiologic
studies.
b. Genetic Effect. Ionizing radiation injury to hereditary
material is called genetic effect. Although not apparent in the
exposed individual, it may become evident in the transmission
of hereditary defects to descendants. Genetic effects can occur
only if the gonads of an individual are exposed to radiation.
Resultant damage is to the chromosomes of the reproductive cells.
Genes contained in the chromosomes determine the characteristics
and general health of the individual. Mutation (alteration) in
the genes cannot be identified by examination. Only a comparison
of the individual's characteristics with those of descendants
can reveal such changes. Ionizing radiation is only one of several
agents that produce mutations. They can be caused by certain chemicals
and high body temperatures and they can occur spontaneously. Consequently,
when an individual exhibits a genetic defect it is extremely difficult
to attribute it to parental irradiation.
21. SOURCES OF EXPOSURE.
a. Cosmic and Earth Radiations. Everyone is continuously
exposed to cosmic rays and radiations from radioactive materials
in the atmosphere-earth, rocks, building materials, etc. Even
the human body contains radioactive substances; these include
radioisotopes of potassium, cesium, radium, carbon, hydrogen,
polonium, bismuth, radon, uranium, etc. Both cosmic and earth
radiations vary from place to place. Mankind has always lived
with this "background" radiation. In the United States
the outdoor exposure to background radiation ranges from about
15 to 140 millirems per year.
b. Medical exposures to ionizing radiation have increased
in frequency and magnitude of dose in recent years, especially
in therapeutic applications which involve external irradiation
with beta, gamma or xradiation and internal irradiation from ingested,
injected, or implanted radionuclides. Exposure to radiation in
diagnostic xray procedures is particularly widespread; it is the
largest and most significant exposure for the general population.
It is estimated that medical xray procedures contribute about
77 percent of the average absorbeddose rate for the bone marrow
of the adult U. S. population and that fluoroscopic and dental
examinations contribute 20 percent and 3 percent respectively.
Examples of bone marrow average absorbeddose per examination for
various procedures include:
(1) Chest xray 10 millirads (mrads).
(2) Upper gastrointestinal series 535 mrads.
(3) Gall bladder series 168 mrads.
(4) Dental xray 9.4 mrads.
c. Other sources include effluents from nuclear and other
facilities processing or using radionuclides; luminous clocks
or watches and signs; and electronic devices utilizing high accelerating
voltages and beam currents.
22. PERMISSIBLE EXPOSURE LIMITS (PEL's). The permissible
exposure limits for external exposure to ionizing radiation shown
in Figure 21 shall apply to all occupants of controlled areas.
The PEL's were adopted from the Occupational Safety and Health
Administration (OSHA) standard for ionizing radiation, 29 CFR
1910.96 (b).
Figure 21. Ionizing Radiation PEL's
PEL (Dose) Per
Calendar Quarter
Type of Exposure (rems)
Occupational
Whole body, head and trunk,
active bloodforming organs,
lens of eye, or gonads 1 1/4
Hands and forearms, feet,
and ankles 18 3/4
Skin of whole body 7 1/2
Nonoccupational
Whole body, head and trunk,
active bloodforming organs,
or lens of eye 1/8
NOTE: Based upon a 5day week, 8hour day, 1 1/4 rems/quarter translates
approximately to the following: 100/millirems per week (mrems/week),
20 mrems/day, and 2.5 mrems/hour. The hourly value is applicable
to hazards evaluations using survey rate meters, but discretion
must be exercised in interpreting exposure rates with respect
to the PEL's. Only when the duration of exposure is known or determinable,
can a reasonable estimate of accumulated dose be deduced from
exposure rate measurements.
a. Quarterly Limit. During any calendar quarter, a maximum
occupational whole body dose of 3 rems may be permitted provided,
however, that such dose when added to the accumulated whole body
dose shall not exceed 5 (N18) rems where "N" equals
an individual's age in years at his last birthday.
b. No employee under 18 years of age shall be occupationally
exposed to ionizing radiation.
c. Accumulated Limit. The accumulated occupational exposure
of an individual at any age shall not exceed 5 rems multiplied
by the number of years beyond age 18. When any person is accepted
for employment in a controlled area it shall be assumed that he
had up to that time received the maximum permissible accumulated
dose unless proven otherwise.
23. EVALUATION OF HAZARDS.
a. Equipment. There is no single survey instrument that
will measure or even detect all types of ionizing radiation. Portable
instruments with ionization chambers or GeigerMueller (GM) tubes
are used to monitor beta and gamma radiation. With proper shields
over the detecting elements it is possible to discriminate gamma
from the less penetrating beta radiation.
(1) The CDV700 is a GM survey meter that is suitable
to measure low dose rate gamma and detect the presence of beta
radiation. Three ranges provide fullscale indication in steps
of 0.5, 5.0, and 50 mR/hour. Earphones, when connected to the
instrument, will provide an audible signal in the presence of
radiation. Though intended for Defense Readiness radiological
monitoring, this instrument may be used for detection of gamma,
beta, and xradiation from many sources provided that certain factors
are considered:
(a) The CDV700 survey meter is not shielded against
RF radiation and should not be used to measure xradiation in the
presence of RF energy. Xradiation measurements made with this
instrument near RF generators may be inaccurate and imprecise;
they can be affected by the orientation of the meter and its probe
and by variations in the RF field. The extent of the instrument's
sensitivity to RF energy has not been determined.
(b) GM counters, when exposed to high levels of radiation,
may fall back after a fullscale deflection of the indicator.
(2) RF shielded ionization chamber survey meters shall be used
for measurements of xradiation in the presence of both pulsed
and steady state RF energy.
(3) Personnel Dosimetry. Film badges, pocket dosimeters,
and thermoluminescent dosimeters record the dose of radiation
received over a period of time.
(a) Film badges are worn on the outer clothing and detect
x or gamma radiation and highenergy beta radiation. Xray films
of varying sensitivities are laminated with suitable shielding
and filtering material and placed inside a Jacket of metal or
plastic. After the film badge is worn for an interval, the film
is developed and "read" for determination of beta and
xor gamma radiation exposure.
(b) Pocket dosimeters are also worn on the clothing
and provide an integrated record of exposure. The dosimeter is
an ionization chamber containing a quartz fiber electrometer and
a graduated scale across which the shadow of the fiber moves to
indicate the applied dose. An electric charge impressed on the
electrometer and the chamber wall leaks off when ionizing radiation
enters the chamber. This discharge causes a deflection of the
fiber across the graduated scale providing a measure of the total
dose in mR or R. Dosimeters should be read and the dose recorded
daily.
(c) Thermoluminescent dosimeters (TLD's) are replacing
film badges and pocket dosimeters in many applications. The TLD
consists of a small crystalline detector; e.g., lithium fluoride,
lithium borate, calcium fluoride, or calcium sulfate which, when
exposed to radiation, absorbs energy quantitatively in traps.
Subsequently, when heated, the crystalline material's stored energy
is quantitatively released in the form of light to provide a good
estimate of radiation exposure. The TLD is sensitive, accurate
and its reproducibility is excellent.
(d) Thermoluminescent dosimeter service is available
to FAA facilities that utilize ionizing radiation producing devices
or substances. It is provided by the United States Air Force (USAF)
Logistics Command. Use of the service shall be at the direction
of the Regional Flight Surgeon or other cognizant medical officer
when radiation surveys have shown that its use would be beneficial.
To obtain the TLD service requests should be directed to:
USAF Occupational and Environmental Health Laboratory
OEHL/CC
Brooks AFB, Texas 78235
b. Procedures. The following procedures are intended as
guidelines; they may be modified or supplemented to meet survey
requirements. Survey equipment manuals should be consulted for
complete operating instructions.
(1) Accurate or precise radiation measurements can only be made
with properly calibrated meters. All survey meters should be factory
calibrated annually or as recommended by the manufacturer. If
a check source is available, meters should be field calibrated
before and after each use.
(2) To avoid unnecessary personnel exposure, a radiation source
should be approached from a known safe distance with the survey
meter range selection initially set to the lowest (most sensitive)
position.
(3) In the event that an excessive radiation level is found
to persist in a location accessible to personnel it is important
that the best estimate of potential exposure duration be determined.
This can be obtained by consulting employees and supervisors,
worklogs and records, or by direct observation of work processes.
(4) For survey purposes, a measured exposure rate of 2.5 mR/hour
should be regarded as an action level in a controlled area; i.e.,
some corrective measures should be initiated to prevent extended
personnel exposure at this level (survey meters read out in mR/hr;
in the measurement of x or gamma radiation exposure rates, mR/hr
and mrems/hr are equivalent) However, it should not be regarded
as a fine line between a safe and unsafe condition. It should
be viewed with concern, not alarm. Refer to paragraph 22 for the
derivation of the 2.5 mR/hour value.
(5) When surveying xradiation sources, every accessible surface
of the source should be slowly scanned in a systematic pattern
so that all possible leaks are detected.
24. CONTROL OF HAZARDS.
a. Exposure Control Methods. There are three basic methods
of controlling exposure to ionizing radiation:
(1) Limit Exposure Time. For a source of given strength
the absorbed dose is proportional to the duration of the exposure;
limiting the time limits the exposure. Relatively high intensities
of radiation can be tolerated for short periods of time if the
need arises.
(2) Increase Distance. The effect of distance on radiation
is quite startling. The exposure rate varies inversely with the
square of the distance from the source of radiation to the measurement
location; i.e.
I1 d22
=
I2 d12
where I1 and I2 are the exposure rates (intensities) at distances
d1 and d2 from the source.
For example: The intensity at 2 feet from the source is 1/4 the
intensity at 1 foot. At 10 feet the intensity is only 1/100 of
what it is at 1 foot. This method is used in establishing controlled
areas for minimizing exposure of personnel to ionizing radiation.
The boundaries of controlled areas shall be determined by the
Safety and Health Manager in consultation with the Radiation Protection
Officer.
(3) Provide Shielding. Any substance may serve to attenuate
radiation to acceptable levels provided that sufficient thickness
is used. Certain materials, however, are more effective in shielding
certain types of radiation.
(a) Alpha particles are stopped by an ordinary sheet
of paper or a few inches of air.
(b) Beta particles are slowed by the interaction with
material. Thus, the denser the material, the more effective it
will be in stopping beta particles. Clothing affords little protection
against any but low energy beta radiation. The air between the
radiation source and the worker may provide some degree of shielding.
Beta particles have a negative charge and are repelled by the
electrons in the atoms of the air. This causes their paths to
deviate, slowing them. The range of beta particles in the air
is a function of their energy.
(c) Gamma rays and xrays of a single energy are attenuated
exponentially. Therefore, theoretically, it is not possible to
attenuate the radiation completely although the exposure rate
can be reduced to any desired level by use of halfvalue layers
of materials. The halfvalue layer is the thickness of an absorber
that reduces the radiation dose to onehalf the initial amount.
A thickness of three such halfvalue layers will reduce the dose
to oneeighth (i.e., 1/2 x 1/2 x 1/2) the initial amount.
b. Shielding materials of high atomic number such as lead
and iron are generally the most effective absorbers or shields
for x and gamma rays. However, concrete, brick, or other materials
of lower atomic number can provide the same degree of protection
if used in appropriately greater thicknesses.
c. Placement of Shielding Material. In providing shielding
for any type radiation the shield material should be placed as
near as possible to the source of radiation. The required thickness
of the shield is not reduced by this procedure, but its area is
decreased, thus reducing its total volume and weight.
d. Warning Signs. The presence of ionizing radiation in
an area shall be indicated by posting conspicuous signs or labels
which bear appropriate wording (i.e., Caution XRays, Danger
Radiation, Caution Radioactive Material, etc.). All such radiation
warning signs and labels shall bear the standard symbol as shown
in Figure 22. Examples of xray warning sign locations are as follows:
(1) On the klystron housing of all ARSR3 and military (AN/FPS)
radars.
(2) On the inner panels of cabinets containing the amplitrons,
magnetrons, and thyratrons of all ARSR1 and 2 radars, and
(3) On the inner panels or doors of cabinets containing the
klystrons, magnetrons, and thyratrons of ASR radars.
These signs are commercially available in pressure sensitive paper,
vinyl, or tape form.
FIGURE 22 XRADIATION WARNING SIGN
SECTION 2. XRADIATION
25. RADAR SYSTEMS.
a. Hazards. Many of the high power electronic tubes used
in the production of RF/microwave energy are capable of generating
xradiation as an unwanted byproduct. These include collectoranode
klystrons and magnetrons, travelingwave tubes, and highvoltage
thyratrons. The intensity of the xrays that they produce is directly
proportional to the tube current, the accelerating voltage, and
the atomic number of the target element (anode). Tube age can
also be a factor; the intensity of xrays from older tubes can
increase with aging and gradual deterioration.
The xradiation produced by these tubes is relatively "soft;"
i.e., it has low photon energy, long wave length, and most important,
low penetrating power, even in air. It decreases rapidly with
distance and is easily attenuated with high density material such
as lead, steel, or Aluminum. The choice depends upon the energy
of the radiation produced.
A radiation hazard exists in the transmitter cabinets of unshielded
energized highpower output tubes in the following equipment: FPS6/90,
FPS20, FPS24, FPS27, FPS35, FPS60, ARSR, and ASR series radars.
Under certain operating conditions, xradiation hazards may be
encountered in other radars not listed above. For example; malfunctions
such as highpower output arcing, oscillation, and sputtering may
be accompanied by increased voltages sufficient to produce hazardous
xradiation.
b. Engineering Controls. Tubes with high accelerating
potentials are usually shielded with lead to such an extent that
they do not produce external radiation fields. The steel and/or
aluminum cabinet and chamber walls confining magnetrons and thyratrons
are generally adequate to contain any xradiation that these tubes
emit, or to limit transmitted radiation to acceptable levels.
During routine maintenance or normal operating procedures, the
integrity of tube shielding must be preserved to avoid exposure
of personnel. Major maintenance operations, necessitating removal
of manufacturer's shielding, should be conducted only by experienced
personnel who are aware of the hazards involved.
c. Procedural Controls.
(1) To the fullest extent possible, all highpower output tube
cabinet doors shall be kept closed while high voltage is applied.
(2) Interlocks shall not be bypassed without special permission
of supervisory personnel and only when it is absolutely necessary.
In the event that corrective work requires bypassing of interlock(s)
while high voltage is applied, the maximum distance from the tube
and the briefest exposure to it shall be maintained.
(3) Should any one or a combination of the malfunctions described
in paragraph 25.a. occur, personnel should avoid standing near
the transmitter cabinet housing the highpower output tube. Standing
in front of the power supply cabinet is safe. Should external
adjustments such as are available at the control panel in front
of the power supply cabinet fail to correct the difficulty, any
corrective work in the vicinity of the highpower output tube cabinet
shall be done with the high voltage off.
(4) Radar equipment capable of producing external xradiation
under any operating conditions should be surveyed routinely and
also whenever it is suspected that maintenance or operational
changes have altered the radiation hazard potential.
26. VORTAC's AND TACAN's.
a. Hazards. Individual TACAN's and the TACAN units of
VORTAC's are equipped with high power electronic tubes that are
capable of producing xradiation, but only certain types of klystron
and high voltage rectifier tubes of the RTB2 TACAN's have been
found to emit this radiation beyond the tubes' envelopes. External
xradiation has not been detected around similar tubes in the GRN9
TACAN's. Characteristics of the xradiation produced by these tubes
and the parameters that determine its intensity are discussed
in paragraph 25.a.
b. Engineering Controls. The steel and/or aluminum cabinet
and compartment walls and doors confining the klystron and rectifier
tubes are usually adequate to contain any xradiation emitted or
to limit transmitted radiation to acceptable levels. Further shielding
should not be employed unless the xradiation cannot be controlled
at the source by the Procedures described below.
c. Procedural Controls for Klystrons.
(1) Tests have shown that lowering the applied high voltage
is effective in reducing, if not eliminating, external xradiation
from the klystrons. The 5 kilowatt (kW) beacon power output specified
in Order 6780.3A, Maintenance of TACAN/DME Equipment, can be maintained
at klystron anode potentials of 1820 kv by properly adjusting
the beam current pulse shape.
(2) If the procedure described in paragraph 26.c.(1) does not
adequately reduce or eliminate the xradiation, the problem may
be that the klystron is faulty and should be replaced.
d. Procedural Controls for High Voltage Rectifier Tubes.
(1) Xradiation emitted by 8020 rectifiers can be completely
eliminated by replacing them with ED 9840 solid state rectifiers
and by reducing the high voltage to 1820 kv.
(2) In the event that the solid state rectifiers are not available,
xradiation produced by 8020 rectifier tubes can be controlled
to acceptable levels by the procedure described in paragraph 26.c.(1).
e. Procedural Controls Applicable to Klystrons and High Voltage
Rectifiers. Until the controls described in paragraph 26.c.
and 26.d. have been adopted, personnel exposure to xradiation
shall be minimized by strict observance of the following procedures:
(1) To the fullest extent possible, keep TACAN receiver/transmitter
and highvoltage power supply cabinet doors closed while the equipment
is energized.
(2) If maintenance or operating activities require access to
energized equipment (e.g., tuning the klystron), the time spent
at the tuning position should be kept to a minimum.
(3) TACAN equipment capable of producing external xradiation
under any operating conditions should be surveyed routinely and
also whenever it is suspected that maintenance or operational
changes have altered the radiation hazard potential.
SECTION 3. RADIONUCLIDES
27. RADIOACTIVE ELECTRON TUBES.
a. Hazards. Certain types of electron tubes that contain
radioactive materials as activators are used at FAA and jointuse
(USAF/FAA) sites. The quantity of radioactive material in the
tubes is so small that no external radiation hazard exists when
the tubes are handled singly or in small numbers. Extremely large
quantities of radioactive tubes such as the distribution inventory
at the FAA Depot may, however, present an external hazard. Breakage
of more than one of the tubes can present a potential internal
hazard to personnel working in the area where the breakage occurs
as the radioactive materials may be inhaled or ingested. Since
the inventory of radioactive tubes used by the FAA is extensive
and subject to frequent change, a list is not included in this
order. Tubes containing radioactive material are labeled as such.
b. Controls.
(1) Handling. There is no external radiation hazard due
to normal handling of radioactive electron tubes.
(2) Storage. Exercise judgment and caution to avoid large
quantity storage and possible breakage. Under no condition shall
random storage in boxes or bins be permitted. All storage areas
for large quantities of radioactive tubes, such as the FAA Depot,
shall be clearly marked with radiation warning signs as described
in paragraph 24.d.
(3) Decontamination. In the event of breakage, decontamination
shall proceed as follows:
(a) Dust. Avoid agitation of dust in order to minimize
dispersion of the radioactive material. Internal exposure by ingestion
and/or inhalation should be avoided. Should either or both occur,
contact the cognizant Aviation Medicine Office.
(b) Tube Fragments. Retrieve tube fragments with forceps
or pliers and dispose of them as normal waste. Clean instruments
with a dampened cloth. If forceps or pliers are not available,
use gloves and dispose of them immediately after use. Do not handle
tube fragments with bare hands.
(c) Use of Cloths. Using a cloth dampened with water,
wipe across the contaminated area making each swipe in the same
direction. Do not work the radioactive material into the surface
by rubbing back and forth. Fold the cloth in half after each swipe.
Dispose of all wipe cloths as normal waste.
(d) Hands. Wash hands thoroughly. Do not smoke or eat
in the area where breakage occurred.
(e) Area Survey. The area shall be surveyed after decontamination
to ensure that the residual radiation exposure level does not
exceed 0.5 mR/hour and that no significant removable radioactivity
remains. The CDV700 surrey meter is suitable for this purpose.
(4) Disposal.
(a) Sanitary Fill Disposal. Since radioactive tubes
contain very little radioactive material, unserviceable tubes,
tube fragments and decontamination wastes may be added to or treated
as normal waste and disposed of in a normal fashion provided that
it is certain that the waste will be buried in a sanitary fill
and that this procedure is in compliance with requirements of
the state health agency concerned.
(b) Incinerator or Dump Area. If the normal waste is
destined for an incinerator or dump area, the radioactive material
should be withheld to prevent atmospheric contamination by combustion
and possible injury to inquisitive persons removing tubes from
dump sites.
(c) Other Disposal. Where sanitary fill is not available,
it is recommended that the radioactive wastes be conveyed to a
licensed radioactive waste disposal firm. The names of such firms
can be obtained from the state health agency concerned.
28 RADIOACTIVE AIRCRAFT INSTRUMENT DIALS.
a. Hazards. Many older flight instruments have radiumactivated
luminous markings. Although the external radiation hazard due
to normal handling of these instruments is negligible, repair
of them presents a potential health problem. The selfluminous
material, generally found on dial faces and pointers and adjacent
to or on switches, tends to flake with age. When an instrument
is damaged or dismantled, particles of the radium paint can be
ingested, inhaled, or absorbed through a break in the skin. Ingestion
can occur following accumulation of radioactive material on the
hands, cigarettes, and food. Benefits derived from use of radiumactivated
luminous dials rarely warrant the health hazards involved in reconditioning
the dial faces. Though many of the dials have long since lost
their lightemitting property, the radium is still present.
b. Controls.
(1) Replacement. It is recommended that all radiumpainted
surfaces of flight instruments undergoing repair be replaced with
surfaces that do not contain radioactive materials.
(2) Storage. Aircraft instruments containing radium dials
should be segregated from those that do not. This can be done
simply with a betagamma survey meter; the CDV700 meter is suitable
for this test. Large quantity storage and loose storage in boxes
or bins shall be avoided.
(3) Decontamination. In the event of breakage of dial
faces, decontamination shall proceed as in paragraph 27.b.(3).
(4) Disposal. Unserviceable radioactive dials and pointers
shall be disposed of. It is recommended that arrangements for
the disposal of the radioactive waste be made with a licensed
radioactive waste disposal firm (see subparagraph 27.b.(4)(c)).
29. RADIOACTIVE CONTROL KNOBS ON RADAR EQUIPMENT.
a. Hazards. Control knobs and dials on obsolescent CPN18
Radar Indicator and FPN16 Precision Approach Control consoles
contain radiumactivated luminous paint. The maximum life of the
luminous material is usually 10 years and the average is 5 years.
Although the knobs no longer "glow," the radium is still
present in the paint and is measurable with a betagamma survey
meter. The external radiation exposure is not a hazard and the
potential for internal exposure is minimal so long as good personal
hygiene is practiced. In 1966 the USAF Radiological Health Laboratory
investigated radiation hazards associated with the CPN18 and FPN16
control knobs. Whole body counting tests on air traffic controllers
who had worked with this equipment 814 years revealed that not
one had accumulated any detectable body burden of radium. In January
1968 whole body counts were performed on FAA air traffic controllers
who had worked with the same type of equipment in a temporary
installation with inadequate sanitary facilities; these also produced
negative results.
b. Controls. The risks involved in this radiation hazard
are extremely small but are not justifiable due to the lack of
any derived benefits. Although the CPN18 and FPN16 consoles are
obsolescent and are being phased out, some may remain in service.
While they do, certain precautions are recommended in order of
preference as follows:
(1) Replacement. Where practicable, all items containing
luminescent markings with radium shall be replaced. Where replacement
of consoles is imminent (within one year), this recommendation
need not be followed. Radioactive items shall be disposed of as
in subparagraph 27.b.(4)(c).
(2) Interim Measure. As an interim measure, the markings
may be covered with transparent tape provided that the tape is
maintained in good condition.
CHAPTER 3. NONIONIZING RADIATION
SECTION 1. RADIOFREQUENCY/MICROWAVE RADIATION
30. GENERAL. The widespread and growing use of highpower
output radar, navigational aids, and communications systems has
increased the potential for personnel exposure to radiofrequency
(RF)/microwave radiation. Therefore, it is important that operating
personnel become familiar with the nature of the biological effects
of exposure to this form of energy and that certain exaggerations
and misconceptions be dispelled. Activities around high power
electronics equipment are completely safe provided that the guidance
contained in this section is followed.
For the purposes of this order, RF radiation shall refer to all
electromagnetic radiation ranging in frequency from 300 kHz to
300 GHz and shall include the microwave radiation region ranging
in frequency from 300 MHz to 300 GHz. The entire RF portion of
the electromagnetic spectrum (Figure 11) is far removed from the
xray and gammaray region and is classified as nonionizing radiation.
31. EFFECTS AND HAZARDS. In contrast to the cumulative
biological effects associated with exposure to ionizing radiation,
the only confirmed harmful effects from exposure to RF/microwave
radiation are thermal in nature. It is to protect against the
heating effect and its consequent influence upon workers that
the permissible exposure limits are set.
a. Thermal Effects. The depth of human tissue heating
caused by exposure to RF/microwave radiation depends upon the
frequency of the incident energy. Above 10 GHz (3 cm wavelength)
heating occurs mainly in the superficial tissues (outer skin surface).
From 10 GHz to 3 GHz (3 cm to 10 cm) the penetration and heating
is deeper, and from 1.2 GHz to 150 MHz (25 cm to 200 cm) penetration
and absorption are sufficient to cause heating of internal body
tissues. The body attempts to regulate temperature increases through:
(1) Perspiration and
(2) Heat exchange via blood circulation
Those organs which have a limited circulatory system are considered
vulnerable to RF/microwave radiation exposure. Two structures
in the human body are more susceptible to high radiation intensities
than the remainder of the body:
(a) The testes are vulnerable due to their sensitivity to temperature
change. Intense microwave radiation exposure to the testes of
experimental animals has been shown to impart temporary and reversible
sterility.
(b) The lens of the eye cannot dissipate heat as readily as
the rest of the body and can suffer damage from microwave radiation.
This has been demonstrated experimentally with small animals.
b. Nonthermal Effects. Nonthermal effect refers to an
observable or measurable biological change produced by exposure
to RF/microwave radiation without a detectable temperature rise
in a test system. Recent research has suggested that nonthermal
effects do occur. The phenomenon of RF "hearing" has
been reported and verified. Alterations in animal behavior patterns
following RF/microwave radiation exposure have been observed.
Effects on the immune response system and upon the central nervous
system are receiving considerable attention. Efforts continue
to determine if these subtle and usually reversible changes have
any public health significance.
32. SOURCES OF EXPOSURE. Many potential exposure sources
lie within the RF range of the electromagnetic spectrum. Among
them in ascending frequency order are AM and FM radio, television,
VHF and UHF communications, radar, diathermy, microwave cooking,
and materials drying. Natural sources of RF and microwave energy
also exist, as in the case of measurable ground level electric
fields produced by the movement of cold fronts.
The most attention by far has been directed toward the microwave
region. It is in this range that a great number of commercial
applications have developed and it is in this range that biological
effects have been studied the most. However, with this writing,
attention is shifting to some of the lower frequencies; i.e.,<
1,000 MHz, and to the potential effects of exposure to sources
that lie within this range.
VHF and UHF radio and television broadcasts are the main source
of ambient RE exposure in the United States. Of these the FM radio
broadcast band is the greatest contributor. On January 1, 1980,
there were 9,756 broadcasting stations in operation including
1,008 television stations, 4,554 AM radio stations, and 4,194
FM stations.
Within the FAA, the sources of RF radiation include the ASR and
ARSR radars, ASDE and airborne radars, microwave landing systems,
VORTAC's and TACAN's, communication systems (VHF, UHF, RMLs, etc.),
diathermy machines, and microwave ovens. The sources of greatest
concern are those that are capable of generating and emitting
strong RF field intensities; i.e., the radars.
33. PERMISSIBLE EXPOSURE LIMITS (PEL's). The permissible
exposure limits for RF/microwave radiation shown in Figure 31
shall apply to all occupants of controlled areas. There is no
distinction between occupational and nonoccupational exposure
in their application.
NOTE: The PEL's were adopted from the American National Standards
Institute, ANSI C95.11982 Standard. This standard is comprised
of a series of radiofrequency protection guides which are defined
as "the radiofrequency field strength or equivalent plane
wave power density which should not be exceeded without (1) careful
consideration of the reasons for doing so, (2) careful estimation
of the increased energy deposition in the human body, and (3)
careful consideration of the increased risk of unwanted biological
effects."
FIGURE 31. RF/MICROWAVE PEL's
Mean Squared Mean Squared Equivalent
Frequency Electric Field Magnetic Field Plane Wave
Range Strength (E2) Strength (H2) Power Density (PD)
(MHz ) (v2/m2 ) (A2/m2 ) (mW/cm2 )
0.3 3 400,000 2.5 100
3 30 4,000 (900/f2)** 0.025 (900/f2) 900/f2
30 300 4,000 0.025 1.0
300 1,500 4,000 (f/300) 0.025 (f/300) f/300
1,500 100,000 20,000 0.125 5.0
a. For near field exposures where power density (PD) cannot be
measured accurately, the only applicable PEL's are the mean squared
electric (E) and magnetic (H) field strengths. Equivalent plane
wave PD can be calculated from field strength measurements as
follows:
PD in mW/cm2 = E2/3770 (where E2 is in V2/m2)
PD in mW/cm2 = 37.7 H2 (where H2 is in A2/m2)
b. For pulsed and continuous wave (CW) fields, the PD and the
squares of the field strengths (E2 and H2) are averaged over any
6minute period.
c. For fields consisting of multiple frequencies, the fraction
of the PEL incurred within each frequency range should be determined
and the sum of all fractions should not exceed unity.
**f=frequency (MHz)
34. EVALUATION OF HAZARDS.
a. Equipment. There are two general types of instruments
available for RF radiation evaluations; those that measure power
density and those that measure field intensity (or field strength).
Power density meters are more commonly used in health hazards
evaluations largely because of their portability and direct reading
capability. Field intensity meters, although less portable, are
particularly valuable in the detection and measurement of low
levels of RF radiation.
(1) Power Density Devices currently in use are broadband
isotropic systems consisting of a meter and probe(s) that provide
near and far field power density measurements regardless of polarization
and direction of the incident RF energy. They integrate pulsed
or CW signals into an average power density reading in mW/cm2.
Probes are available to provide a dynamic range of 0.02 to 100
mW/cm2 across frequencies ranging from 500 KHz to 18 GHz. These
instruments are lightweight, easy to use, and reasonably accurate.
They have two distinct limitations; (1) they cannot be calibrated
in the field and must be returned for factory calibration, and
(2) their probes are subject to peak power burnout even when the
instrument is turned off.
(2) Field Intensity Devices, which usually consist of
an assortment of calibrated antennas coupled to an interference
analyzer, are extremely accurate and sensitive over a wide dynamic
range. They have certain disadvantages that limit their use in
routine health hazards evaluations. They are bulky, nonportable,
and require special training for proper use. Their antennas are
highly directional and field intensity measurements made with
these systems may not be completely representative of the exposure
potential that exists at the point of measurement. Nonetheless,
they remain the best devices for evaluation of far field low level
RE energy, particularly in the low frequencies; e.g.,< 500
KHz.
b. Procedures. The following procedures are intended as
guidelines; conditions at the survey site may suggest or require
modifying them. Survey equipment manuals should be consulted for
complete operating instructions.
(1) RF measurements are no better than the calibration of the
survey equipment used to make the measurements. As a minimum,
survey meters must be calibrated annually. The power density meters
currently in use must be returned to the manufacturer for calibration.
(2) An RF source should be approached from a known safe distance
with the detector initially set on its maximum range. This is
to avoid unnecessary personnel exposure and, in the case of power
density meters, to avoid peak power burnout of the probe.
(3) All RF measurements should be made in close coordination
with operating personnel so that the exact conditions under which
measurements are made are know to allconcerned
(4) When surveying radar antenna systems, the area between the
feedhorn and the reflector should always be considered hazardous
and carefully avoided.
(5) When surveying in the main beam of a radar, the beam size,
shape and character, and the limit of the PEL should be determined
prior to the survey. The latter can be calculated or obtained
from Figure 33, paragraph 36.a.
35. CONTROL OF HAZARDS. The three basic methods of controlling
exposure to ionizing radiation are good guidelines to be used
in controlling exposure to virtually all forms of RF radiation.
They include:
a. Limit Exposure Time. Although the effects of exposure
to RF radiation are not considered to be cumulative, as in the
case of ionizing radiation, the duration of exposure is an element
of the PELs. They were selected to limit the specific absorption
rate (SAR) to 0.4 W/kg in any 0.1 hour period implying that SARs
in excess of that limit could cause a disruption in biological
tissue or function.
b. Increase Distance. The inverse square relationship
of intensity to distance described in paragraph 24.a(2) for ionizing
radiation is also applicable for RF emissions in the far field
provided that:
(1) The transmitting antenna (source) is isotropic; i.e., it
transmits energy equally in all directions, and
(2) The transmission is through free space; i.e., the energy
is neither absorbed, reflected, refracted, nor scattered.
Such ideal conditions seldom exist, but the inverse square relationship
is valuable "estimator" for determining approximate
safe distances from RF sources. It should not be used as a substitute
for distances determined by field measurement. Mathematical models
are available for calculating safe distances from directional
emitters such as radars and RML's. The values obtained are theoretical
and should always be substantiated by field measurement if possible.
c Shielding. RF radiation can be reflected, refracted,
scattered, and absorbed. It is these properties that enable it
to be directed, conducted, and attenuated. In many systems, the
very devices that enclose and direct RE energy for operational
purposes also provide the required shielding to protect against
personnel exposure; radar waveguides are an example. In most FAA
systems that generate RF radiation it is properly confined where
necessary and no further shielding is required. In those unusual
instances where special shielding is needed, reference can be
made to the information provided in paragraph 36.b.
d. Warning Signs. The standard RF radiation warning sign
shown in Figure 32 shall be posted at the entry to the antenna
deck of each long range and short range radar. This is a precautionary
measure to remind personnel and warn visitors that the PEL for
RF radiation can be exceeded in the vicinity of the radiating
antenna. It does not mean that entry to the antenna deck will
result in overexposure but that in this area RF energy is not
as confined as it is in other parts of the radar system and that
proper precautions should be observed.
FIGURE 32. RF RADIATION WARNING SIGN
The RF warning sign is available in two sizes; i.e.,
Small, 9905010696246, Unit of Issue Each (EA) and
Large, 9905010692315, Unit of Issue Each (EA)
36. RADAR SYSTEMS.
a. Hazards. All radar systems operated and maintained
by the FAA produce RF/microwave radiation. Under normal operating
conditions, it is virtually isolated from the workplace and its
occupants. Hazardous levels are encountered only in the vicinity
of the antenna; i.e., between the feedhorn and the antenna and
out along the projected beam. The hazardous region terminates
at a point on the beam where the radiation intensity has diminished
to a value that equals the PEL. For each FAA 'radar capable of
producing levels in excess of the PEL, the distance to that point
has been calculated (Figure 33). The distance calculations were
made using typical transmitting parameters and should be considered
estimates. They should be authenticated with actual transmitting
data and by field measurements whenever possible.
The PEL for ASR and AN/FPS6/90 radars, read directly from Figure
31, is 5 mW/cm2 power density (E2 = 20,000 V2/m2; H2 = 0.125A2/m2).
The PEL for ARSR, AN/FPS20, and AN/FPS60 radars is calculated
using the relationships shown in Figure 31. For an ARSR transmitting
at 1315 MHz, the PEL is 4.4mW/cm2 power density (E2 = 17,533 V2/m2;
H2 = 0.110 A2/m2). All radar work areas in which the PEL's are
exceeded shall be considered hazardous.
FIGURE 33. RADARS CAPABLE OF PRODUCING POWER
DENSITIES IN EXCESS OF THE PEL
Calculated Distance
from Antenna to
Point on Main Beam
Average Axis Where Power
Transmitter Power Transmitter Density Equals the
Used for Calculations Frequency PEL PEL
Radar Peak Average
(MW) (W) (MHz) (mW/cm2) (feet)
ASR4,5,6 0.425 403 2800 5.0 40
ASR7 0.5 474.5 2800 5.0 50
ASR8 1.4 (Simplex) 875 2800 5.0 125
1.4 (Diplex) 1750 2800 5.0 235
ARSR1,2 5.0 3595 1315 4.4 295
ARSR3 4.6 (Simplex) 3140 1315 4.4 230
4.6 (Diplex) 6280 1315 4.4 460
AN/FPS6/90 2.8 2040 2800 5.0 360
AN/FPS20 2.0 4319 1300 4.3 315
AN/FPS60 2.0 (Simplex) 4319 1300 4.3 315
2.0 (Diplex) 8638 1300 4.3 630
b. Engineering Controls
(1) That portion of the radar transmitting system lying between
the RF generator and the antenna feed horn is a closed system
and shall remain so while the system is energized. Waveguides,
waveguide switches, and enclosures around RF generators provide
sufficient shielding from RF radiation exposure provided that
the integrity of all joints in the system is maintained.
(2) In the event that further shielding is required for special
purposes, the attenuation factors for various materials shown
in Figure 34 may be used as guidelines.
FIGURE 34. ATTENUATION OF RF RADIATION
PROVIDED BY VARIOUS TYPES OF SHIELDING
From Palmisano, W.A. and D. H. Sliney, "Instrumentation and
Methods Used in Microwave Hazard Analysis, "U.S. Army Environmental
Hygiene Agency, Edgewood, MD. Presented at American Industrial
Hygiene Conference, 1967.
Frequency (GHz)
13 35 57 710
Attenuation (dB)
60 x 60 mesh screening 20 25 22 20
32 x 32 mesh screening 18 22 22 18
16 x 16 window screen 18 20 20 22
1/4" mesh (hardware cloth) 18 15 12 10
Window glass 2 2 3 3.5
3/4" pine sheathing 2 2 2 3.5
8" concrete block 20 22 26 30
c. Procedural Controls.
(1) Personnel shall not work on the antenna, waveguide, or feedhorn
structures of a transmitting radar.
(2) The antenna deck of the radar tower shall be considered
a restricted area. Interlocks on antenna deck access gates shall
not be defeated while the radar is transmitting without permission
and without careful consideration of the purpose. This does not
mean that entry to the antenna deck will result in overexposure
to RE radiation, but that in this area the RF energy is neither
a clearly defined field nor is it confined as it is in other parts
of the system. Consequently, extra precautions are necessary to
minimize exposure.
(3) Where sector blanking is used to prevent transmission in
certain azimuths and/or elevations, and overriding will cause
a RF hazard potential in an adjoining workplace, sufficient warning
shall be provided to personnel in the workplace so that proper
precautions may be initiated.
(4) RF generators, waveguide joints, waveguide switches, rotary
joints, etc., that are potential sources of RF radiation leaks
should be surveyed routinely and also whenever it is suspected
that maintenance or operational changes have altered the radiation
hazard potential.
37. VORTAC's and TACAN's.
a. Hazards. VOR's transmit in the frequency range of 108
to 118 MHz. From Figure 31, the PEL is 1.0 mW/cm2 power density
(E2 = 4,000 v2/m2; H2 = 0.025 A2/m2). In a survey of a VOR transmitting
at 110.2 MHz (TACAN off) and 200 W, a mean squared E field strength
of approximately 4624 V2/m2 was measured at the surface of the
conical tower covering the rotating antenna. At the outer edge
of the building roof the level was only 324V2/m2 so it was concluded
that a potential hazard existed at the surface of the conical
tower only.
TACAN's transmit in either of two frequency bands, 962 to 1024
MHz or 1151 to 1213 MHz. The PEL is defined in Figure 31 as f/300
mW/cm2 power density (E2 = 4,000 f/300 V2/m2; H2 = 0.025 f/300
A2/m2). In a survey of a typical TACAN operating at 6.5 kW peak
power (130 W average power) and a frequency of 983 MHz, a mean
squared E field strength of 13,924 V2/m2 was measured at a distance
of 5 cm from the surface of the radome; at 20 cm the level was
11,664 V2/m2. Since the PEL for a 983 MHz source is 13,107 V2/m2,
it was concluded that a potential hazard existed at the surface
of the radome only.
b. Procedural Controls.
(1) Personnel should avoid direct contact with the surface of
the VOR conical tower and, to avoid unnecessary exposure to low
level RF energy, they should limit their occupancy of the counterpoise
while the VOR is transmitting.
(2) To the fullest extent possible personnel should avoid
direct contact with the TACAN radome and limit the duration of
maintenance work in close proximity to the antenna while the TACAN
is transmitting.
38. COMMUNICATION SYSTEMS.
a. Hazards. VHF transmitters operate in the 118 to 136
MHz band at power levels ranging from 10 to 50 W. UHF transmitters
operate in the 225 to 400 MHz band at power levels ranging from
25 to 100 W. For VHF and UHF transmissions below 300 MHz the PEL
is 1.0 mW/cm2 (E2 = 4,000 V2/m2; H2 = 0.025 A2/m2). For UHF transmissions
above 300 MHz, the PEL is defined in Figure 31 as f/300 mW/cm2
power density (E2 = 4,000f/300 V2/m2; H2 = 0.025 f/300 A2/m2).
Only at the surface of antennas transmitting at the higher power
levels is there any evidence of RF in excess of the PEL.
RML's transmit in the 7125 to 8400 MHz frequency band at power
levels ranging from 0.1 to 5 W. TML's transmit at approximately
14 to 15 GHz and 1.0 W. For both RML and TML equipment the PEL
is 5mW/cm2 (E2=20,000 V2m2; H2 = 0.125 A2/m2). Surveys performed
on RML's and TML's have shown RF levels near antennas to be less
than 0.1 mW/cm2 even directly in front of the dish. This was the
lower detectable limit of the survey equipment in use.
b. Procedural Controls.
(1) Other than to avoid direct contact with antennas of VHF
and UHF transmitters operating at high power levels, no special
controls are required.
(2) To avoid unnecessary exposure to low levels of RF energy
in the microwave range it is recommended that work on RML and
TML antennas be conducted only when transmitters are off.
39. MICROWAVE LANDING SYSTEMS.
a. Hazards. Microwave landing systems (MLS's) transmit
in the 5000 to 5250 MHz frequency band. Therefore, the PEL is
5.0 mW/cm2 (E2 = 20,000 V2/m2; H2 = 0.125 A2/m2). Surveys of prototype
MLS's operating in this range have revealed antenna aperture RF/microwave
levels ranging from 0.02 to 0.15 mW/cm2 power density, all far
below the PEL.
b. Procedural Controls
(1) Personnel should avoid direct contact with the antenna apertures
of transmitting MLS equipment.
(2) To avoid unnecessary exposure to low levels of RF/microwave
energy, it is recommended that work on MLS antennas be conducted
only when transmitters are off.
40. MICROWAVE OVENS. A microwave oven is a dielectric heating
unit consisting of a highpowered magnetron or klystron tube which
feeds microwave energy through a waveguide to a cooking chamber.
The tubes operate at either 915 or 2450 MHz at power levels ranging
from 500 to 2000 watts. All units are equipped with interlock
systems which prevent operation with the door open. Microwave
ovens are in widespread use commercially and privately and are
commonly found in FAA lunch rooms, cafeterias, and break areas.
All microwave ovens manufactured in the United States must comply
with Federal limitations.
a. Performance Standard. On October 6, 1970, a "Performance
Standard for Microwave Ovens" was published in the Federal
Register (Subpart C, Part 78, Title 42 CFR). Briefly, it stipulates
that microwave ovens may not emit radiation levels in excess of
1 mW/cm2 power density prior to sales nor in excess of 5 mW/cm2
throughout the useful life of the oven, as measured at 5 cm from
any external surface of the oven. The standard also requires that
ovens be equipped with a minimum of two safety interlocks, one
of which must be concealed.
b. Leak Testing. Testing of ovens for leakage should be
performed at any time that damage has occurred or there is obvious
malfunctioning. Survey instruments and procedures shall conform
to the requirements of the performance standard described in paragraph
40.a.
c. Failure to Comply with Standard. Any oven that is found
to leak microwave radiation in excess of the lifetime performance
standard (5 mW/cm2 at 5 cm), shall be removed from service and
repaired or replaced.
d. Oven Maintenance. Ovens should be maintained clean
and free of food particles, especially around door seals. The
safety interlock system should be observed to shut off the oven
when the door is opened. If it does not, the oven should be removed
from service and repaired or replaced. Periodic servicing to assure
proper operation is encouraged.
41. MEDICAL DIATHERMY. Medical diathermy units utilize
microwave radiation to generate heat intentionally in body tissues
underlying the skin. Most units operate at a frequency of 2450
MHz; the power is variable. These devices are capable of generating
power density levels considerably in excess of 5 mW/cm2. Consequently,
they should be operated only by or under the supervision of trained
medical personnel. Special care should be exercised to confine
the microwave radiation to the target tissues and to avoid unnecessary
exposure of other parts of the body.
42. CATHODE RAY TUBES. Cathode ray tubes (CRT's) are widely
used in the home, office, shop, recreation place, etc. In the
FAA they are found in radar displays, televisions, oscilloscopes,
video display terminals, etc. Much has been written and spoken
about radiation emitted by CRTs, most of it speculative and unsubstantiated;
but two recent investigations by the National Institute for Occupational
Safety and Health (NIOSH) have provided some definitive data on
emissions from the CRTs of radar displays and video display terminals
(VDT).
In July 1980, the Hazards Evaluations and Technical Assistance
Branch of NIOSH conducted a radiation investigation in the Seattle
ARTCC. Among other potential sources they surveyed Plan View Display
(PVD), Radar Bright Display (RBDE), and Plan Position Indicator
(PPI) radar scopes for evidence of ionizing and nonionizing radiation
emissions (i.e., xray, ultraviolet, and RF) and concluded that
all radiation levels were extremely low and insignificant when
compared with existing occupational health standards (NIOSH, TA
80062852).
In January 1980, the same NIOSH organization performed an indepth
investigation of health factors associated with use of VDTs. The
radiation evaluation portion of the study included measurements
of the xray, ultraviolet, visible, and RF portions of the electromagnetic
spectrum on 18 VDTs (5 models). Investigators concluded that VDTs
do not present a radiation hazard to employees working at or near
a terminal. Emissions were well below current occupational exposure
standards, usually below the detection capability of the survey
instruments (NIOSH, 81129).
Additionally, agency Industrial Hygienists and Safety and Health
Managers have surveyed a wide variety of radar scopes over an
810 year period during routine environmental health inspections
required by the Occupational Safety and Health Act (PL 91596)
and have found no evidence of external radiation fields above
background at or near the surfaces of the CRTs.
