What are Electromagnetic Pulse (EMP), High Altitude Electromagnetic Pulse (HEMP), and Nuclear Electromagnetic Pulse (NEMP)?


Voltage and current transients and impulses come in a wide variety of forms, and energies, from the benign to the catastrophic. Electrostatic discharge (ESD) is responsible for the damage of semiconductor components, but the total energy from ESD is very small. Lightning can obtain voltage over 1 MV and 100,000 amps during a strike, but the frequency range of these pulses tend to be under 1 MHz. Among the most catastrophic and least understood are the transients associated with an electromagnetic pulse, or EMP. But what is EMP, and how is it created? And why should we be concerned about EMP?

Acronyms Used

BES Bulk Electrical System – the main feeder power grid, which is interconnected across a large region, but does not include local distribution grids
BPS Bulk Power System – see BES
CME Coronal Mass Ejection also called Coronal Mass Discharge (CMD) – can generate Geomagnetic Disturbance
DHS Department of Homeland Security
EMC Electromagnetic Compatibility
EMI Electromagnetic Interference
EMP Electromagnetic Pulse
ESD Electrostatic Discharge
GMD Geomagnetic Disturbance
HEMP High Altitude Electromagnetic Pulse – A high intensity and wide-spread event generated by a nuclear explosion above the atmosphere
HIRF High Intensity Radiated Field
IEMI Intentional Electromagnetic Interference
MCS Mission Critical System
MHz MegaHertz
MOV Metal Oxide Varistor
MV MegaVolts (1,000,000 Volts)
NASA National Aeronautics and Space Administration
NEMP Nuclear generated Electromagnetic Pulse – in this document, used interchangeably with Electromagnetic Pulse
PCI Pulsed Current Injection
POE Point of Entry
SREMP Source Region Electromagnetic Pulse
TVS Transient Voltage Suppression
μS Microsecond

The History of EMP

Electromagnetic Pulse or EMP is the effect generated in the electromagnetic spectrum by the detonation of a nuclear device, although aspects can occur naturally as well. The first concerns for EMP nuclear effects were brought up by the physicist Enrico Fermi during the first atomic bomb detonation. His concerns seemed well founded. For this reason, much of the electrical equipment and cables were doubly shielded to help protect them from radio frequency energy. Despite these precautions, the test equipment was still affected by the detonation. This effect was observed several times in later testing and was called “radio-flash” mainly by the British.

With the advent of the space era and missile development came the concept for space testing of nuclear devices. USA and Soviet testing which occurred from 1961 to 1963 created a few unexpected and surprising results. Soviet testing over present day Kazakhstan caused significant damage to the power grid and several fires in various locations. A 600-mile underground power line was shut down in one test, and a fire at the power plant it was tied to also occurred.1 There is speculation that damage may have occurred to electronics at the Baikonur Cosmodrome, since there was an unusually long gap between manned launches after the K-184 Test on October 22, 1962. In addition, a number of failures of unmanned space craft occurred soon afterward.

The field produced by the Soviet K-184 test is estimated to be about three times larger than the field produced by a geomagnetic storm on March 13, 1989, which collapsed the power grid in Quebec Canada and caused over 200 power grid problems across the United States.2

In addition, the United States performed their own testing under the name STARFISH Prime. In this test, the military detonated a 1.4-megaton thermonuclear bomb about 250 miles above Johnston Atoll in the in the Pacific. Although there were comparatively few satellites in orbit in the early 1960’s, satellites of the US, including TRAAC, Transit 4B, and the first communication satellite Telstar, Brittan’s Ariel 1, and from the USSR all suffered damage. It was reported that 800 miles away in Hawaii, burglar alarms sounded, streetlights blinked out, and phones, radios, and televisions went dead. The resulting effects were much greater than expected, driving measurement instruments into overload, and limiting the quality of the measurements obtained. It is thought that EMP, along with other events at the time, each had a part to play in the signing of the Nuclear Test Ban Treaty in August 1963.

What are EMP, HEMP, and NEMP?

Research into nuclear generated EMP (Nuclear EMP, or NEMP) produced at higher amplitudes (High Altitude EMP, or HEMP). The generation of this aspect of the field is based on gamma ray radiation from the detonation as it interacts with the upper atmosphere of the Earth. The atmosphere becomes ionized by the gamma radiation produced, producing large number of free electrons. The electrons are then captured by the Earth’s magnetic field, causing them to spin around the Earth’s magnetic field lines. This action produces a high intensity, high frequency energy. The duration is very short for the highest amplitude fields, but the ongoing effect can create other issues.

Scientists have established three components of the effect, defined as E1, E2, and E3. These components are based on the time after detonation. E1 is the “Early Time” component, the immediate field created less than 1 µS after detonation. This can be thought of as frequencies from 1 MHz and higher. It is the most intense in terms of field strength and is considered to be responsible for the disruption and damage of semiconductor-based systems, communication, data transmissions, and the like. Although the field will generate currents on power lines and other long data communication lines, the ability of these currents to travel significant distances is attenuated by the cable impedances. It is the fields induced directly into equipment and cables connected to that equipment which are most vulnerable to these fields.

For this reason, shielding of the equipment becomes important. This is either done by using a conductive enclosure for the electronics, or by placing the system in a shielded enclosure of its own. In addition, fast acting filtration and transient protection (TVS) is required to clamp the voltage and current induced on the equipment.

The next component of HEMP is designated as E2 and is the intermediate time component. For this component the energy induced is from 1 μS to 1 second. Due to the roll-off of the field strength and the fact that lightning and voltage surge events are found in the same timeframe, this portion of the composite waveform is of less concern. Protection used for the E1 component, as well as for lightning events, can provide adequate protection for E2. However, it should be noted that most commercially available surge and lightning protection typically use metal oxide varistors (MOV), These MOV’s are able to work with voltage of AC power lines and respond fast enough for lightning and surge impulses. However, MOV’s are considered too slow for the E1 portion of the waveform since they can take over 50 nS to respond to an impulse.

The final component of HEMP is the E3 portion. E3 is a widespread, long duration field, lasting from a few seconds to several minutes. For the E1 portion, field strengths are about 50,000 V/m or higher, whereas for E3 they are measured to be 0.001-0.1 V/m (1 to 100 V/km). Although this seems to be a low level, the large area covered by these fields produce voltage along power transmission lines, creating a DC current through transformers at either end of the line. The resulting current through the transformer can cause saturation of the transformer core, which results in distortion of the voltage waveform. In severe cases, the transformer can burn out, needing extensive repair or replacement. If this occurs across a power grid, significant time may be required by the utilities to perform the repairs to reestablish power to a region. The concern is that if power is lost to the plants who provide the materials needed for the repairs, the problems cascade and can extend the time needed to bring power back online. Beyond this, other public utilities will be affected by the power loss, as well as all manner of industry, business, banking, food distribution, and all aspects of public infrastructure. Estimates as high as 40% of public power in the US could become compromised.

In the event of a coronal mass ejection (CME), a great quantity of plasma is expelled by the sun’s atmosphere (the corona). These plasma ejections come with induced magnetic fields or flow along “flux ropes”, helical shaped magnetic fields created by the flow of spinning and moving electrons. Although these ejections can be in any direction, on occasion, the Earth is in the path. When they strike the Earth, they can create a geomagnetic disturbance (GMD) or storm. When they are large enough, they can compress the Earth’s magnetosphere on the sun side of the Earth, and strongly distort it on the leeward side. These events can release huge amounts of energy, and to cause occur events such as the Quebec power grid failure.

GMD have many of the same effects as EMP E3 components, however, it is likely that the EMP effects will be much more intense, although for a much shorter time than GMD (1-2 minutes verses hours for GMD). With modern space observations and equipment, NASA has established the Space Weather Prediction Center3, which should provide us with a forewarning of future CME and possible GMD events a day or more in advance of their occurrence.

Why Worry About EMP?

According to the Department of Homeland Security, EMP is considered a cyberweapon, and their occurrence is not likely to be predicted or planned. The entire field of intentional electromagnetic interference (IEMI) and electronic weapons (eBombs) is becoming a significant concern. For many countries, this is called the Sixth Generation Warfare, or Non-Contact Warfare. A military textbook written by Russian General Vladimir Slipchenko discusses this concept in detail.4 In another report, it is stated, “American forces may be vulnerable to electronic warfare attacks, in particular, an electromagnetic pulse that is a brief powerful electromagnetic field capable of overloading or destroying numerous electronic systems and high-tech microcircuits that are very sensitive to the electromagnetic field, even if transmitted from a distance.”5

In the Cold War era, there was greater concern of EMP than in the 20 years afterward. However, with increasing threats from numerous countries capable of missile launches and nuclear attack, the threat of EMP has significantly increased. Numerous publications created by government agencies, researchers, and the like culminated in Executive Order 13865: Coordinating National Resilience to Electromagnetic Pulses.6 The intent of the order is to increase awareness of human-made (directed energy weapons that can fit in a pickup truck or landscape trailer) and naturally occurring EMP, the potential to disrupt, degrade, and damage technology and critical infrastructure systems, and to “foster sustainable, efficient, and cost-effective approaches to improving the Nation’s resilience to the effects of EMPs”.

To assist federal, state, and local governing officials, as well as owners of critical infrastructure and telecommunication equipment, data storage and centers, and all aspects of information technology, the National Coordinating Center for Communications developed a protection and resilience guideline in the event of EMP.7 In the document, four levels of EMP protection are defined:

  • Level 1 – Lowest cost; longer mission outages permitted. These are the lowest cost and best practices to protect the most important infrastructure. This also includes supplies for personnel (water, food, battery operated radio and equipment), in the event of a disruption lasting weeks or more.
  • Level 2 – Only hours of mission outages are permitted. This requires EMP E1 and E2 capable filters with TVS and/or surge suppression on all electrical lines (power, signal, antenna cable).
  • Level 3 – Only minutes of mission outages are permitted. Starting with Level 2 protection, additional shielding is required of at least 30 dB to protect critical computers, data centers, phone switches, industrial equipment, and substation controls, and other electronics. Additional filtering for E3 component of the EMP event.
  • Level 4 – Only seconds of mission outages are permitted. Requires highest level of shielding and filtering, with over 80 dB of shielding needed. Double door entry into shielded enclosures should be used. MIL-STD-188-125-1 hardening required.

From a wide range of sources, both governmental and private, the threat of disruption or damage due to electromagnetic impulse and geomagnetic disturbances, whether man made or natural, are real, serious, and likely to occur. It is imperative that mitigation techniques are utilized, and careful planning is made soon.


  1. http://www.futurescience.com/emp/test184.html
  2. https://www.nasa.gov/topics/earth/features/sun_darkness.html
  3. https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections
  4. General Vladimir Slipchenko, Non-Contact Wars (Moscow: January 1, 2000)
  5. Colonel A.V. Kopylov, Weak Points of the U.S. Concept of Network-Centric Warfare – Military Thought, Volume 3, 2011
  6. https://www.federalregister.gov/documents/2019/03/29/2019-06325/coordinating-national-resilience-to-electromagnetic-pulses
  7. Electromagnetic Pulse (EMP) Protection and Resilience Guidelines for Critical Infrastructure and Equipment, February 5, 2019, National Cybersecurity and Communications Integration Center, Arlington, Virginia

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