Electromagnetic radiation consists of waves.

A depiction of electric and magnetic energy moving together through space at the speed of light is shown in Figure 1.

All frequencies (or wavelengths) of electromagnetic energy are referred to as the electromagnetic spectrum, shown in Figure 2.

Figure 2. Electromagnetic Spectrum (Additional chart detailing military and civilian uses of RF and other spectra can be found at http://www.disa.mil/jsc/speccht.html).

Radio waves and microwaves emitted by transmitting antennas, illustrated in Figure 3, are one form of electromagnetic energy. They are collectively referred to as "radiofrequency" radiation (RFR). RF energy includes frequencies ranging from 0 to 3000 GHz.

Microwaves, very short waves of electromagnetic energy, include frequencies ranging from around 300 megahertz (MHz) to 300 gigahertz (GHz). Microwaves are often referred to as "high frequency (HF) radio waves." High frequency radio waves are used to transmit information from one place to another, because microwave energy can penetrate haze, light rain and snow, clouds, and smoke. Remote sensing is a common application of microwaves. There are two types of microwave remote sensing; 1) active and 2) passive.

Exposure to RF energy of sufficient intensity at frequencies between 3 kilohertz (kHz) and 300 GHz can adversely affect personnel, ordnance, and fuel. Potential exposures of this magnitude aboard ships are primarily associated with the operation of various radars and communication systems as illustrated in the photo below.

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Biological effects that result from heating of tissue by RF energy are often referred to as "thermal" effects. Exposure to very high levels of RF radiation can be harmful due to the ability of RF energy to heat biological tissue. In a healthy human body, the thermo-regulatory system will cope with the absorbed heat until it reaches the point at which it cannot maintain a stable body core temperature. Beyond this point the body may experience hyperthermia (heat exhaustion) and/or irreversible damage to human tissue if the cell temperature reaches about 43 degrees Celsius. There is a higher risk of heat damage for organs that have poor temperature control, such as the lens of the eye and the testes. The amount of absorbed energy to produce thermal stress is affected by the health of the individual (some medical conditions and medications may affect thermoregulation), environmental conditions (higher ambient temperature and relative humidity make it harder for the body to release heat), and physical activity (strenuous work can raise rectal temperature by itself).

Radiated energy can also result in high levels of induced and contact current through the body when in close proximity to high-power RF transmitting antennas. The biological hazards associated with electromagnetic radiation, established by the Institute of Electrical and Electronics Engineers (IEEE) C95.1 Standards Committee and adopted by the Tri-Service Electromagnetic Radiation Panel, is in DODINST 6055.11, Protection of DoD Personnel from Exposure to Radiofrequency Radiation and Military Exempt Lasers.

In addition to personnel concerns, RF fields may generate induced currents or voltages that could cause premature activation of electro-explosive devices in ordnance, equipment interference or sparks, and arcs that may ignite flammable materials and fuels.

NAVSEA OP 3565/NAVAIR 16-1-529/NAVELEX 0967-LP-624-6010/Volume I, Electromagnetic Radiation Hazards (U) (Hazards To Personnel, Fuel And Other Flammable Material) (U) [Distribution authorized to U.S. Government agencies and their contractors; administrative/operational use; 1 February 2003. Other requests for this document must be referred to the Naval Sea Systems Command (NAVSEA) (SEA 05).], and Volume II, Technical Manual, Electromagnetic Radiation Hazards (Hazards to Ordnance) [Note: certificate required], contain RF hazard (RADHAZ) guidance regarding hazards of RF exposure to personnel, fuels, and ordnance. It should be noted that the current industrial specifications for RADHAZ are contained in ANSI/IEEE C95.1-1992, which was used as a reference to create the combined Navy regulation NAVSEA OP3565 /NAVAIR 16-1-529.

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RF hazards aboard ships can be broken down into three main categories:

1. Hazards of Electromagnetic Radiation to Personnel (HERP):

Radar and communication systems, which use high-power RF transmitters and high-gain antennas represent a biological hazard to personnel working on, or in the vicinity of, these systems. The detrimental effects of overexposure to RFR are associated with an increase in overall body temperature or a temperature rise in specific organs of the body. High-level electromagnetic energy can also induce electrical currents or voltages that may cause shocks and burns. An RF burn is the result of RF current flow through that portion of the body in direct contact with a conductive object (in which an RF voltage has been induced) or at the site of a spark discharge (no direct contact with a conductive object).

The use of HF transmitters (1 kilowatt and up) and the complicated structure and rigging aboard ship, especially cargo ships, has increased the probability of voltages being induced on various objects. The handling of metallic cargo lines while shipboard HF transmitters are radiating can be hazardous to ship’s personnel. On numerous occasions, RF voltages have been encountered on items such as crane hooks, running rigging, booms, missile launchers, and parked aircraft. These voltages, which may be sufficient to cause injury, are induced on the metallic items by radiation from nearby transmitting antennas.

In addition to electromagnetic radiation hazards, there are other physical hazards to Navy personnel working aloft on shipboard radar antennas. Working aloft presents a fall hazard. In addition, rotating antennas might accidentally be energized causing an injury from contact or a fall. [See Acquisition Safety Fall Protection for fall hazards onboard Navy ships.]

2. Hazards of Electromagnetic Radiation to Ordnance (HERO): The high intensity RFR fields produced by modern radio and radar transmitting equipment can cause sensitiveelectrically initiated devices (EIDs),classically known as electro-explosive devices (EEDs),contained in ordnance systems to actuate prematurely. RFR energy may enter an ordnance item through a hole or crack in its skin or through firing leads, wires, and so on. In general, electrically initiated ordnance systems are most susceptible during assembly, disassembly, loading, unloading, and handling in RFR electromagnetic fields. The potential dangers to ordnance and fuels are obvious because there could be an explosive chain reaction.

3. Hazards of Electromagnetic Radiation to Fuel (HERF): Fuel vapors can be ignited by RF induced arcs during fuel handling operations close to high powered radar and radio transmitting antennas. For example, many ships carry at least one helicopter or have the ability to refuel a helicopter and, therefore, carry fuel to support helo operations. [Note: All of these operations are inherently dangerous by themselves and require the utmost attention and alertness.]

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Hazards of Electromagnetic Radiation to Personnel (HERP)

OPNAVINST 5100.23 Series, Navy Safety & Occupational Health (SOH) Program Manual, requires activities performing research, development, testing and evaluation (RDT&E) and acquisition of RF systems, including non-developmental items and commercial off-the-shelf items, to identify RF control requirements by incorporating adequate protection measures or identifying appropriate operational restrictions to maintain personnel exposures within the exposure limit.

•  Engineering Controls: Engineering controls that should be kept in mind by the designer include:

•  Properly design and install shielding material on RF energy sources. MIL-STD-1310, Standard Practice For Shipboard Bonding, Grounding, And Other Techniques For Electromagnetic Compatibility And Safety provides requirements for shipboard bonding, grounding, shielding, and the use of nonmetallic materials to reduce Electromagnetic Interference and to protect personnel from electrical shock.
•  Design devices which produce high levels of stray RF radiation so that they can be operated remotely.
•  Use nonmetallic materials where RF burn-hazards are a problem.
•  Electrically ground and/or insulate metallic structures producing contact shocks.
•  Rotate antennas to make it less likely that sufficient energy will be transmitted to cause an adverse effect to personnel, ordnance, and fuel because the rotation reduces the time of exposure to any single location. Place the antenna at a greater height, pointing it at a greater elevation angle, and blank the signal while the energy may be directed in the path of a ship structure to further reduce the potential for adverse effects.
•  Install safety disconnect switches for all rotatable antennas (except submarine and ECM antennas) to disable antenna rotation and equipment radiation prior to personnel entering the antenna swing circle. Lockout devices for disconnect switches will prevent inadvertent activation and save manhours used to perform maintenance procedures.
•  Coordinate with other system designers and installers to avoid undesired interaction between ship systems.
•  See the Acquisition Safety Fall Protection section for Fall Protection design recommendations.

•  Administrative Controls: Administrative controls are related to procedures, which the designer is responsible for establishing and must also be linked to Human Systems Integration (see the Human Factors Engineering section of this website).

•  Use physical barriers (such as fences, warning signs, lights, or alarms) that identify the radiation-control area at its perimeters and access routes to preclude individuals from RF radiation exposure.
•  Keep radar beams pointed away from personnel working areas. Aircraft using high-power radars will be parked (or the antennas oriented) so that beams are directed away from work areas.
•  Maximize the distance between the worker and the source of RF energy emission.
•  Tune the equipment electronically to minimize the stray power emitted.
•  Operate transmitters at reduced power.
•  Restrict simultaneous use of certain combinations of antennas, frequencies, and cargo handling equipment.
•  Develop standard operating procedures (SOPs) to inform those who use the system about RF control procedures.
•  Provide RF safety and health training to ensure that all ship personnel understand the RF hazards to which they may be exposed and the means by which the hazards are controlled.
•  Ensure that radiation hazard (RADHAZ) warning signs are properly posted and boundary lines are established in accordance with the ship's current RADHAZ certification.
•  Ensure that required tags are installed properly and observed when working on radar antennas.
•  Working aloft, especially near shipboard antennas, presents special considerations and procedures for safety. See the Fall Protection section of the Acquisition Safety web pages for a full discussion.

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•  Personal Protection: When exposures cannot be reduced by engineering and administrative control methods, RFR protective suits, including head and eye protection, can be used. Suits should be tested to ensure that they reduce worker exposure to levels below the occupational exposure limits and that they do not pose any safety hazards (e.g., overheating, shocks, or fire). It should be noted that the Navy does not authorize RF-shielded protective clothing for routine use as a means of protecting personnel. However, this does not preclude use of other protective equipment, such as electrically insulated gloves and shoes for protection against electrical shock or RF burn, or for insulation from the ground plane.

Hazards of Electromagnetic Radiation to Ordnance (HERO)

For most ordnance, a HERO problem is inevitable unless the designer recognizes the possible hazards and organizes all phases of the ship’s development so that the hazard is precluded in the initial design. Retrofitting after a HERO problem is discovered at some later stage of development is, at best, expensive and time consuming and often detracts from the tactical reliability of the ordnance. Impacts on war-fighting performance and acquisition program cost and schedule can be significant.

NAVSEA OD 30393, Design Principles And Practices For Controlling Hazards Of Electromagnetic Radiation To Ordnance (Hero Design Guide) provides HERO preventive techniques to be applied to the design and construction of weapons and subsystems. This design guide is intended primarily to assist the ordnance system developer to solve the problem of premature actuation or degradation of EIDs.

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•  Engineering Controls: There are four basic approaches to solving the HERO problem:

1. Continuous RF Shield: This approach consists of enclosing all EID’s and their firing circuits (including all power sources, transmission lines, and switching and arming devices) within a continuous electromagnetic interference (EMI) shield or “conductive box.” Use of a conductive box requires that proposed design techniques and fabrication methods will ensure that the electromagnetic environments (EME) cannot penetrate into the shielded area. This concept is illustrated in Figure 4 and requires that the integrity of the RF shield be designed and maintained throughout the life cycle of the system.

2. Shielded Compartments and Interconnections: Another method to exclude RF energy from coupling into ordnance is to compartmentalize the system into shielded subsystems connected with RF-shielded or protected interconnects as shown in Figure 5. This technique requires that the RF shielding integrity of each subsystem and of each interconnection be designed so that the EME cannot couple into the system at any point.

3. EMI Filtering: Most ordnance requires breaking electrical connections when the parts of the system are physically separated. Thus, it is often impossible or impractical to keep all conductors within one continuous shield. Therefore, EM energy must be excluded by some other method. It can be excluded from a shielded enclosure at a connector by means of an EMI filter (a low-pass filter). The proper use of a filter is illustrated in Figure 6.

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4. RF Arcing Protection: The design of circuits associated with systems that have electrical connections exposed to the EME is very important. RF arcs can occur when connectors are mated and unmated, especially for ordnance that may be attached to very large structures or host platforms that are exposed to high-frequency environments. These arcs can generate EM energy throughout the RF spectrum, including low-frequency components that are in the same band as the firing signal, and will even pass through a filter if one is installed. A break in the firing circuit between the arc point and the EID until after the connection is made will circumvent this problem because a direct current path is necessary for an arc to occur. This technique is illustrated in Figure 7.

•  Administrative Controls: HERO reduction techniques vary depending on susceptibility of the ordnance involved and frequencies and power density of radiation involved. Ship's personnel can cope with HERO restrictions by:

•  Reducing power output of the transmitting antenna,
•  Increasing the distance between ordnance and the transmitting antenna,
•  Performing tasks in shielded areas.

To ensure the HERO safety and HERO reliability of ordnance systems, the Naval Sea Systems Command sponsors an extensive ordnance testing/ship survey program to determine ordnance susceptibilities to RFR energy and to characterize the operational EME and provide HERO Emission Control (EMCON) bills that detail the precautions needed to mitigate HERO. HERO requirements and precautions are provided in NAVSEA OP 3565/NAVAIR 16-1-529/NAVELEX 0967-LP-624-6010/Volume II, Electromagnetic Radiation Hazards (U)(Hazards to Ordnance)(U). [Note: certificate required]

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Hazards of Electromagnetic Radiation to Fuel (HERF)

RF induced arcs can ignite fuel vapors during fuel handling operations close to high-powered radar and radio transmitting antennas. Personnel handling fuels afloat should be aware of this potential hazard. The probability of ignition during normal fueling procedures is reduced by the following methods:

•  Using less volatile fuels. As the RFR energy radiated from high-powered communications and radar equipment installed on ships increased in recent years, the Navy has shifted to less volatile fuels such as JP-5. The vapor pressure of JP-5 and DFM (diesel fuel marine or F-76) is low enough that, under normal temperatures, there is virtually no chance of accidental fires from RF arcs.
•  Introducing pressurized fueling systems on aircraft.
•  Locating transmitting antennas away from fueling stations and vents. Electromagnetic Radiation Hazards (U) (Hazards to Personnel, Fuel and Other Flammable Material) (U), NAVSEA OP 3565/NAVAIR16-1-529/NAVELEX 0967-LP-624- 6010/Volume I specifies the safe distances from radiating sources at which fueling operations may be conducted.
•  Securing all transmitting antennas located within the quadrant of the ship in which fueling is being conducted.
•  Ensuring RADHAZ cutouts for microwave radiators are not overridden during fueling, which could result in the illumination of fueling areas.
•  Avoiding energizing any transmitter (radar or communications) on the aircraft or motor vehicle being fueled or on adjacent aircraft or motor vehicles.

Avoiding making or breaking any electrical, static ground wire, tie-down connection, or any other metallic connection to the aircraft or motor vehicle while it is being fueled; making the connections before fueling commences; and breaking them afterwards.

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Radio Frequency Radiation can be potentially hazardous to 1) operating and maintenance personnel, 2) ordnance and fuels, and 3) associated equipment. Radio Frequency radiation hazards can be reduced by properly designing and installing shielding material on RF energy sources. Radar and communication systems aboard ships should be designed and installed for safe operation and maintenance to avoid shock, RF burn, and fall hazards.

Ship and weapon designers should recognize the possible electromagnetic radiation hazards to ship personnel, ordnance, and fuels and organize all phases of the development so that these hazards are precluded or minimized in the initial ship design.

Incorporating electromagnetic radiation hazard protection during the planning and design phases of any new ship acquisition decreases operation and maintenance costs compared to the cost of retrofitting an already built system. The Acquisition Program Manager’s participation in system safety working groups and other Integrated Process Teams (IPTs) supports efficient communication on all system safety issues. Early and continued coordination with other system designers and installers is essential to avoiding undesired interaction between systems and to developing common control and display and operational processes.

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•  DoD/Navy Instructions and Design Criteria
•  Other RFR References

DOD & Navy Instructions and Design Criteria

DODINST 6055.11, Protecting Personnel from Electromagnetic Fields of 19 Aug 09
This Instruction updates policy, responsibilities, and procedures for protecting personnel from exposure to electromagnetic fields (EMFs) from 0 to 300 gigahertz (GHz). 

MIL-HDBK-240, Hazards of Electromagnetic Radiation to Ordnance (HERO) Test Guide
This handbook is concerned with Hazards of Electromagnetic Radiation to Ordnance (HERO) testing for all Air Force, Army, Navy, and Marine Corps ordnance items and support equipment, for all mission areas. Although this handbook is intended primarily for use by DoD HERO test activities, it also provides a consolidation of corporate knowledge about the subject that should be of interest to procurement authorities and system developers.

MIL-STD-464A, Electromagnetic Environmental Effects Requirements for Systems
This standard establishes electromagnetic environmental effects (E3) interface requirements and verification criteria for airborne, sea, space, and ground systems, including associated ordnance and is applicable for complete systems, both new and modified.

MIL-STD-1310, Standard Practice For Shipboard Bonding, Grounding, and Other Techniques for Electromagnetic Compatibility and Safety
Provides for shipboard EM compatibility (EMC) and safe operation, requirements and guidance for EMI prevention and safe operation in the EM environmental effects (E ) areas, including the ship's common ground plane, hull-generated EMI control, hull-penetration EMI, cable and case penetration/radiation EMI, superstructure blockage/reflections, EM signature reduction, equipment-generated EMI prevention, and electrical safety ground.

NAVSEA INSTRUCTION 9700.2, INTEGRATED Topside Safety and Certification Program for Surface Ships

NAVSEA OD 30393, Design Principles and Practices For Controlling Hazards of Electromagnetic Radiation to Ordnance (HERO Design Guide)
Design Guide intended primarily to help the weapon developer solve the problem of premature actuation of electroexplosive devices; however, it should be of some help in solving problems experienced with damage or trigger solid state circuits, damage or cause erratic readings in test sets, cause possible biological injury to personnel, or produce sparks that can ignite flammable fuel-air mixtures.

Naval Shore Electronics Criteria Handbook, NSWSG 0101, 106
Electromagnetic Radiation Hazards for guidance on Hazards of Electromagnetic Radiation to Personnel (HERP), Ordnance (HERO), or Fuel (HERF) shielding.

OPNAVINST 5100.19 Series
Navy Safety and Occupational Health (SOH) Program Manual for Forces Afloat, Chapter B9.

OPNAVINST 5100.23 Series
Navy Safety & Occupational Health (SOH) Program Manual, CH 22.

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Other RFR References

American Council of Government Industrial Hygienists
Search for Threshold Limit Values and Biological Exposure Indices. [Search requires user name & password]

Ellis, F. P., et al., The upper limits of tolerance of environmental stress pp. 158-179. In Physiological Responses to Hot Environments. Special report, Series go-. 298, Medical Research Council, London, 1964.

Interim Guidelines on Limits of Exposure to 50/60 Hz Electric and Magnetic Fields
International Radiation Protection Association, International Non-Ionizing Radiation Committee.

International Radiation Protection Association
Search on "Non-Ionizing Radiation."

Kitchen, Ronald, RF and Microwave Radiation Safety, 2nd Ed., ISBN 0 7506 43552, 2001, Elsevier Science & Technology Books 2001.

OSHA Radiofrequency and Microwave Radiation Hazard Locations and Solutions
Occupational Safety and Health Administration (OSHA) page on RFR resources for hazard locations and solutions.

Recommended Practice for Measurement of Potentially Hazardous Electromagnetic Fields, RF and Microwave
Institute of Electrical and Electronics Engineers (IEEE) Standard, IEEE C95.3-2002.

Safety Levels with Respect to Human Exposure to Electromagnetic Fields 0-3 kHz
Institute of Electrical and Electronics Engineers (IEEE) Standard, IEEE C95.6, 2002.

Safety Levels with Respect to Human Exposure to Radiofrequency Electromagnetic Fields 3kHz to 3GHz
Institute of Electrical and Electronics Engineers (IEEE) Standard, IEEE Std.C95.1, 1999 Edition.

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