Skip to Content Skip to Search Skip to Left Navigation U.S. Department of Transportation (US DOT) Logo Research and Innovative Technology Administration (RITA) Logo National Transportation Library
  ABOUT RITA | CONTACT US | PRESS ROOM | CAREERS | SITE MAP
 


Radiation Health Hazard and Protection - FAA Order 3910.3a



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.

(3910-3a.html)
Jump To Top