Electromagnetic Radiation

Electromagnetic Radiation

Introduction

Electromagnetic Radiation (EMR) is energy emitted and absorbed by charged particles that exhibit wave-like behavior as they travel through space. EMR is a specific form of the more general electromagnetic field, which is produced by moving charges. EMR is produced when charged particles are accelerated by forces acting on them. Electrons are responsible for the emission of most EMR because they have low mass and are therefore easily accelerated. EMR exhibits wave properties and particle characteristics at the same time. EMR carries energy through space, continuously away from the source. Most EMR sources of concern are man-made and propagate from electronic equipment, such as radar, microwaves, computer terminals, and radio/television transmitters. EMR waves come in a variety of lengths and are categorized along the electromagnetic spectrum. The electromagnetic spectrum is comprised of two divisions: ionizing and non-ionizing radiation. Figure 1 illustrates the types of radiation in the electromagnetic spectrum.

Figure 1. Types of Radiation in the Electromagnetic Spectrum

Ionizing radiation is any electromagnetic or particulate radiation with sufficient energy to strip away electrons from atoms in the media which it passes through. Ionizing radiation includes:

• alpha particles
• beta particles
• neutrons
• ultraviolet light
• X-rays
• gamma rays

Non-ionizing radiation is less energetic radiation not capable of stripping electrons, but can still cause changes in vibrational and rotational energies of molecules usually dissipated in the form of heat. Non-ionizing radiation includes:

• microwaves
• radio waves
• infrared light
• visible light

EMR hazards, sometimes referred to as RADHAZ, exist whenever there is an electromagnetic field of sufficient intensity to cause personnel injury, ignition of explosives/fuels/material, or disruption of electronics. In some cases, such as large ground-based radar or radio transmitter systems, EMR may pose a hazard to wildlife. Some of the most common hazard effects from exposure to EMR are identified in Table 1. 

Ionizing radiation is any electromagnetic or particulate radiation with sufficient energy to strip away electrons from atoms in the media which it passes through. Ionizing radiation includes:

• alpha particles
• beta particles
• neutrons
• ultraviolet light
• X-rays
• gamma rays

Non-ionizing radiation is less energetic radiation not capable of stripping electrons, but can still cause changes in vibrational and rotational energies of molecules usually dissipated in the form of heat. Non-ionizing radiation includes:

• microwaves
• radio waves
• infrared light
• visible light

EMR hazards, sometimes referred to as RADHAZ, exist whenever there is an electromagnetic field of sufficient intensity to cause personnel injury, ignition of explosives/fuels/material, or disruption of electronics. In some cases, such as large ground-based radar or radio transmitter systems, EMR may pose a hazard to wildlife. Some of the most common hazard effects from exposure to EMR are identified in Table 1.

Figure 2. Hazardous Effects of EMR

DoD Electromagnetic Environmental Effects (E3) Program

Electromagnetic Environmental Effects (E3) is the term used by DoD to describe the impact of the existing natural and man-made electromagnetic environment (EME) on the operational capability of military forces, equipment, systems, and platforms. It encompasses all electromagnetic disciplines, including electromagnetic compatibility (EMC) and EMI; electromagnetic vulnerability; electromagnetic pulse; electro-static discharge; hazards of EMR to personnel, ordnance, and volatile materials; and natural phenomena effects of lightning and precipitation static. The DoD E3 Program is established by DoDD 3222.3, DoD Electromagnetic Environmental Effects (E3) Program, to “ensure mutual electromagnetic compatibility (EMC) and effective E3 control among ground, air, sea, and space-based electronic and electrical systems, subsystems, and equipment, and with the existing natural and man-made electromagnetic environment (EME). Operational EMC and effective E3 control is achieved when systems, subsystems, and equipment operate in their intended EME without suffering unacceptable performance degradation from E3 or causing unintentional performance degradation to other systems.” DoDD 3222.3 requires that hazards of electromagnetic radiation to ordnance (HERO), hazards of electromagnetic radiation to personnel (HERP), and hazards of electromagnetic radiation to volatile materials (such as fuels [HERF]) must be mitigated prior to the conduct of all military exercises, operations, and activities.

• HERO - the danger of accidental actuation of electro-explosive devices or otherwise electrically activating ordnance because of radio frequency electromagnetic fields
• HERP - the potential hazard that exists when personnel are exposed to an electromagnetic field of sufficient intensity to heat the human body
• HERF - the potential hazard that is created when volatile combustibles, such as fuel, are exposed to electromagnetic fields of sufficient energy to cause ignition

Radio Frequency (RF) Radiation

Modern communication and radar transmitters used as part of weapon systems can produce High-Intensity RF (HIRF) radiation environments that are potentially hazardous to operating and maintenance personnel, ordnance and fuel, and associated equipment.

HIRF radiation is also referred to as high intensity radiated fields (HIRF). HIRF refers to RF energy of strength sufficient to pose a hazard to living organisms or affect the performance of electrical and electronic systems when they are exposed to it. HIRF poses a significant threat to the operation of system electrical and electronics systems, particularly when those systems control mission critical functions (such as flight control, navigation, or fuzing of ordnance). HIRF may cause premature activation of electrically initiated devices (EIDs) and arcs that may ignite flammable materials. EIDs include items such as exploding foil initiators, burn wires, fusible links, hot bridge wires, carbon bridges, and conductive compositions.

The type of biological effect, also called thermal effect, on people from RF radiation depends on the frequency of the electromagnetic wave. The severity of the biological effect depends on the intensity (strength) of the RF radiation. Exposure to very high levels of RF radiation can be harmful due to the ability of RF energy to heat biological tissue. Excessive levels of exposure to RF radiation can result in adverse acute effects on people, such as:

• involuntary muscle contractions
• electrical shocks/burns
• excessive heating of tissue
• blindness, sterility, and other serious health problems in extreme cases of RF induced heating

Electromagnetic Interference (EMI)

EMI is any electromagnetic disturbance (intentional or unintentional) that interrupts, obstructs, degrades, or limits the effective performance of electronics and electrical equipment. EMI disturbance of electronic devices can occur due to inadequate evaluation and control of the system or component operating. EMI can result in hazardous situations with consequences ranging from a degradation of data to total loss of data. All electronic technologies can suffer from degraded functionality when exposed to EMI hazards.

EMR Safety Considerations

ESOH practitioners working on acquisition programs need to consider hazards associated with EMR, both ionizing and non-ionizing, as part of ESOH risk management. EMR issues associated with the system in its intended EME should be identified and assessed prior to entering the Engineering and Manufacturing Development and Production and Deployment phases. EMR issues should also be discussed at the Preliminary Design Review and Critical Design Review. The Test and Evaluation Master Plan should include the requirement to demonstrate the effective EMR control of systems, subsystems, and equipment as critical operational issues and sub-issues. Each EMR hazard should be assessed in accordance with the MIL-STD-882E, DoD Standard Practice for System Safety, methodology. Hazard assessments should include mitigations to ensure that personnel, fuels, and ordnance are not exposed to levels of EMR that exceed established safe criteria levels. Mitigations may include:

• establishing safety zones, warnings, and cautions to ensure safety of operators and maintainers in vicinity of equipment emitting EMR
• ensuring safety critical electronic subsystems are not adversely affected by EMI

• ensuring design redundancy cannot be failed or disrupted by a common cause EMI source
• ensuring system electronics meet the RF radiation emissions requirements

ESOH practitioners should maintain an awareness of current DoD and Component requirements relating to EMR and coordinate with appropriate weapon safety and laser safety review boards. Any required permits or authorizations for use of EMR sources (such as radioactive materials and lasers) need to be obtained as well prior to test and evaluation, fielding, operation, and maintenance of the system.