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High-Altitude Electromagnetic Pulse (HEMP): A Threat to Our Way of Life

By William A. Radasky, Ph.D., P.E.

A nuclear burst detonated in space over the United States would create a high-altitude electromagnetic pulse (HEMP) that could cause the functional collapse of the electrical power grid. As a result, major infrastructures such as communications, transportation, financial services, emergency services, energy distribution, food and water could also be disrupted or extremely impaired.

The United States Congress formed a Commission in 2003 to examine the impact of nuclear weapon generated electromagnetic pulse (EMP) on the United States. The work performed by the EMP Commission has been groundbreaking in terms of studying the impact of HEMP on the civil infrastructure of the United States. They initiated a comprehensive research program and clearly identified the threat and general mitigation strategies. In 2007 they are meeting again to check on the progress of government and industry bodies with regard to their recommendations. Unfortunately, it is not clear whether action will be taken by those responsible to deal with this problem. In addition, the proposed legislation to reestablish the EMP Commission for a period of four years, until the year 2010, long enough for the Commission to help implement its 3-5 year plan for neutralizing the catastrophic EMP threat, has not yet been approved. We should remember that while the threat may be of low probability, the impact on the United States could be devastating. In fact the Commission makes the point that by doing nothing, we may be inviting attack.

For those who are interested in this subject, it is important to read the EMP Commission Report and to evaluate for yourselves whether actions could be taken in areas of your expertise to remedy the current situation. It is also critical that those in Congress understand the importance of protecting our infrastructure from this serious threat.

This article reviews the public information available concerning HEMP and its likely effects on commercial systems. Much of the technical information described in this article is found in the EMP Commission Report [1] and in the standardization work of Subcommittee 77C of the International Electrotechnical Commission (IEC) [2].


The high-altitude electromagnetic pulse (HEMP) is defined as a series of electromagnetic waveforms that are generated from a nuclear detonation at altitudes above 30 km and propagate to the Earth’s surface. While the existence of HEMP has been known since the early 1960s, improvements in the understanding of the HEMP and increases in the susceptibility of electronics to HEMP over the years has raised new issues for commercial equipment and systems that are part of the civil infrastructure. In addition, an important new study by the Congressional EMP Commission published in 2004 [1], clearly indicates that the U.S. infrastructure is vulnerable to the possibility of even a single high-altitude nuclear burst. With the end of the Cold War, the possibility of a massive nuclear exchange has diminished, while the possibility of a limited attack by a terrorist group has increased. This means that the future target of HEMP may well be the civil infrastructure of the United States as opposed to military systems, which have considered the HEMP threat for many years.

The U.S. Congressional EMP Commission

The United States Congress formed a Commission in 2003 to examine the impact of nuclear weapon generated electromagnetic pulse (EMP) on the United States. The term EMP was understood for the purposes of the study to cover the electromagnetic fields generated from a high-altitude burst, which is more narrowly defined as HEMP. The Commission is chaired by Dr. William R. Graham and consists of nine members with broad experience in areas of military and commercial systems and electronics. It was chartered to:

  1. Assess the EMP threat to the United States including the nature and magnitude of EMP threats within the next 15 years from all potentially hostile states or non-state actors.

  2. Evaluate the vulnerability of U.S. military and especially civilian systems.

  3. Determine the capability of the U.S. to repair and recover from damage to military and civilian systems.

  4. Examine the feasibility and cost of EMP hardening select military and civilian systems.

  5. Recommend protection steps the U.S. should take.

In order to begin their study, the Commission examined the HEMP research performed in the past (mainly for military purposes) and paid particular attention to the results of several high-altitude nuclear tests performed by the United States and the Soviet Union in 1962. In addition the Commission directed new research to evaluate the possible impact of the HEMP waveform on present-day commercial equipment and systems that are part of the infrastructure. With these new research findings, the Commission drew conclusions concerning the seriousness of the threat and recommended broad mitigation measures for the future. Some important results from their study are summarized in this article.

High-altitude Nuclear Tests Performed in 1962

On the evening of July 9, 1962 [1] the United States performed a high-altitude nuclear test known as Starfish; it was publicized in advance and was observed by the public in Honolulu, Hawaii. The U.S. government indicated that the device had a yield of 1.4 MT and was detonated at an altitude of 400 km; this was at a distance of 800 nautical miles (~1400 km) from Hawaii. The EMP Commission Report contains one of the photographs that were taken at the time [1]. While there were no noticeable direct impacts to individuals on the ground (no blast, shock, radiation, etc.) some electrical systems were still affected by the electromagnetic fields. Reports included the facts that some streetlights were extinguished, microwave communications were disrupted, and burglar alarms had sounded. While these system effects were not very dramatic in 1962, it is clear that the level of technology used in electronic equipment has changed significantly over the years: from analog to digital, with operating frequencies increasing from megahertz to gigahertz, and with the operating voltages of chips reaching ever lower levels. These changes have increased the probability of malfunction of 2007 commercial equipment to the HEMP threat.

Figure 1. Photograph of the Starfish explosion from Honolulu on the evening of July 9, 1962 [1].

Later in October 1962, the Soviet Union performed a series of three high-altitude nuclear tests over what is now Kazakhstan. In these tests many more impacts were noted in electrical systems including physical damage to power line insulators, outages of long communications lines (both buried and above-ground), damage to diesel power systems, and impacts on radar systems [3]. Clearly the fact that the Soviet tests were performed over land provided a greater opportunity for electrical systems to be exposed. Russian scientists indicated that in nearly all situations, the observed system impacts were due to the interaction of the HEMP fields with long metallic lines (on the order of 100 meters or longer), which then conducted disabling transient voltages and currents into the affected systems. Later work by Russian scientists examining the specific outages of two communication lines [4] provided a clear indication that these specific outages were due to the late-time HEMP, which lasts for tens of seconds after the detonation.

The HEMP Time Waveform

At this point it is important for the reader to understand that HEMP is not described as a single pulse, but rather as a series of waveforms covering times from nanoseconds to hundreds of seconds. After years of research it has been determined that three main waveforms are generated due to different nuclear generation and atmospheric mechanisms. The description of the mechanisms is beyond the scope of this article, but readers with an interest are referred to other papers [5, 6]. Figure 2 illustrates the three main waveforms of interest as defined by the IEC [7]. The early-time waveform is referred to in the figure as E1, the intermediate-time waveform is referred to as E2 and the late-time waveform is known as E3. The reader should note that the pulse widths of these three waveforms are ~100 ns, 1 ms, and 10s of seconds, respectively. The peak values shown in Figure 2 are 50 kV/m, 100 V, and 40 V/km, respectively. An important feature of this waveform is that it can expose a very large area of the Earth (on the order of several million square kilometers) simultaneously (it propagates at the speed of light), and this creates a special hazard for large area networks such as the electric power network which are designed to withstand a series of single point failures as long as each failure is recognized in turn. For example, a single high-altitude burst over the U.S. could expose the entire electrical grid east of the Mississippi River to a severe HEMP transient within one power cycle (16.6 ms).

Figure 2. Three portions of the HEMP electric field waveform in volts/meter from IEC 61000-2-9 [7].

While the overall electromagnetic field waveform is a direct threat to some electronic systems, it is clear that the E2 and E3 waveforms are only of concern for systems connected to very long lines (hundreds of meters to hundreds of kilometers) due to the HEMP wavelengths involved. The early-time E1 waveform is somewhat different in that it can directly penetrate through apertures in the external case of equipment, such as a computer, and induce significant currents and voltages at the circuit board level. These voltages can create malfunctions in the operation of the equipment and may cause damage depending on the shielding effectiveness of the equipment case. The early-time HEMP waveform also couples efficiently to short lines (1-10 meters) connected to equipment (power, signal lines, etc.) and can induce large voltages and currents that can be conducted to the inside of the equipment. Laboratory E1 HEMP experiments for unhardened (to HEMP) commercial equipment indicate that the coupling to these short lines is the major threat to most commercial equipment.

In terms of understanding the response of electronic equipment to the HEMP threat, it is useful to recognize that there are natural electromagnetic equivalents to the three HEMP waveforms. For the E1 waveform, its electromagnetic field is very similar to the field generated close to an electrostatic discharge (ESD) [8]. The ESD field can reach ~10 kV/m at a distance of 10 cm from an arc. It also has a rise time of 0.7 ns and a pulse width of 30 ns. For conducted transients that are naturally observed, most electronic equipment is exposed to the electrical fast transient (EFT) waveform [9] that is generated in electrical substations and propagates to factories and homes through the power network. These EFT waveforms typically reach peak levels of ~4 kV and have a 5 ns rise time and a 50 ns decay time at the locations of electronic equipment.

To compare to the E2 waveform, the electromagnetic field produced by a lightning ground return stroke is similar in waveshape and can reach levels of 100 kV/m very close (~50 meters) to the stroke, but these fields decrease rapidly with distance from the stroke. The pulse widths of these fields extend from 100 microseconds to as long as 1 millisecond for positive lightning strokes. The E2 fields from HEMP are much lower, but do not vary significantly with distance. It is possible that the E2 fields could be a problem for very long power or communication lines.

To compare to the E3 HEMP waveform, the fields created by a geomagnetic (solar) storm last from a few to hundreds of seconds [10]. It is known that a large geomagnetic storm can produce electric fields on the order of 1 V/km, and levels such as these have caused a regional power grid blackout as experienced by the Hydro-Quebec Power Company on March 13, 1989.

Given that the three HEMP waveforms have natural disturbance equivalents, it appears that the E1 and E3 HEMP waveform peak values are likely to be significantly larger in magnitude than the natural exposure levels. This is a concern, because it is known from high-frequency EMC standardized testing that electronic equipment usually requires some protection to survive the ESD and EFT threats. These EMC test levels are, however, much lower than the levels produced by E1 HEMP. For the E3 HEMP, it is clear that power grids can collapse due to the threat of a severe geomagnetic storm, which produces electric fields with similar waveshapes and area coverage; however, the E3 HEMP is again likely to have a much higher peak field level. The protection against severe geomagnetic storms is difficult and has not been fully implemented by any power grid operator at this time.

The EMP Commission and the Power Grid

While the EMP Commission examined the impacts of HEMP on all portions of the critical infrastructure, they determined that the power system was the most critical due to its direct support of the other major infrastructures such as communications, transportation, financial services, emergency services, energy distribution, water/food, etc. Their conclusions regarding the power system were [11]:

  1. HEMP-induced functional collapse of the electrical power grid risks the continued existence of U.S. civil society

  2. Early-time HEMP (E1) transients are likely to exceed the capabilities of protective safety relays

  3. Late-time HEMP (E3) could induce currents that create significant damage throughout the grid

  4. The national electrical grid is not designed to withstand near simultaneous functional collapse

  5. Procedures do not exist to perform a “black start” after an EMP attack, as restart would depend on telecom and energy transport, which depend on power

  6. Restoration of the national power grid could take months to years

  7. HEMP-induced destruction of power grid components could substantially delay recovery

The EMP Commission’s overall power system conclusion was: “Widespread functional collapse of the electric power system in the area affected by EMP is likely.”

While the Commission felt that there were approaches available to deal with many of the problems raised above, it is not clear who should lead the effort to mitigate the threat of HEMP on the power grid. Of course, even if we knew the “who,” there would still be the question of “what”? One option in the opinion of this writer is to develop protective methods, operational responses, and restoration approaches for the power system. The best approach to deliver this information to manufacturers and operators would be to develop standards that deal with the problem.

IEC SC 77C (EMC: High Power Transient Phenomena)

During the cold war, several European countries were concerned about the possibility of a high-altitude nuclear detonation over Europe that could produce high levels of HEMP and potentially damage their civil infrastructure. These countries turned to the International Electrotechnical Commission (IEC) to write standards for protection of electronic systems from HEMP.

Since 1989, the International Electrotechnical Commission (IEC) headquartered in Geneva, Switzerland has been publishing standards and reports dealing with the HEMP threat and methods to protect civilian systems from these threats under Subcommittee 77C (High Power Transient Phenomena). As these are electromagnetic threats, it was decided from the beginning that this work would be closely integrated with the electromagnetic compatibility (EMC) work being performed by the IEC. This author has had the privilege of being elected as the Chairman of IEC Subcommittee 77C and of serving as Chairman since the subcommittee’s inception.

For reference purposes, Figure 3 illustrates the entire list of publications completed by IEC SC 77C, and they are numbered according to the numbering scheme developed for all EMC publications in the IEC. Of these documents displayed in Figure 3, those shown in orange deal with high power EM aspects, including intentional electromagnetic interference (IEMI). The others deal mainly with HEMP, although some of the publications dealing with mitigation and protection are general to many different types of EM transients.

Figure 3. Seventeen publications prepared by IEC SC 77C dealing
with HEMP, HPEM and general EM protection methods.

It should be noted that the standards developed thus far by SC 77C for HEMP describe the effects of HEMP on systems (IEC 61000-1-3), the different types of radiated and conducted HEMP environments that may be produced (IEC 61000-2-9, -10, -11), the different test methods for checking the HEMP immunity (or susceptibility) of equipment or systems (IEC 61000-4-23, -24, -25, -32), the general protection methods for intense electromagnetic fields (IEC 61000-5-3, 4, 5, 6), and a generic HEMP standard for protecting electronic equipment inside of different types of buildings (IEC 61000-6-6). Additional work is currently underway to standardize the method to protect distributed infrastructure systems to HEMP (61000-5-8) and to assess the HEMP hardness of a civil system (61000-5-9).

What Can We Do?

The situation created by the HEMP threat is clear. Many portions of our critical infrastructure are at risk, including the power grid itself. While there are options available for dealing with HEMP, the most important question is whether we can expect commercial business to deal with this problem alone. The EMP Commission has discussed this point in their deliberations, and while commercial businesses could choose to enhance their protection levels above those needed for other electromagnetic threats, the distributed infrastructure cannot be protected with a piecemeal local approach. Government will have to take a role, either by coordinating the work to be done and/or by providing incentives to accomplish the job over time. While the military has experience in dealing with its systems and the threat of HEMP, it is not well positioned to deal with the commercial infrastructure. It seems that this is a role for the newly formed Department of Homeland Security. Unfortunately the DHS plate is very full with short-term threats such as terrorism, hurricanes, etc. HEMP is a low probability but high impact threat that requires a combination of protection, operational procedures and rebuilding after an attack.

From a protection point of view, standardization bodies such as the IEC have already initiated standards dealing with protecting equipment and systems from HEMP. In addition the IEEE has several standards dealing with electromagnetic compatibility of equipment in the IEEE EMC Society and the Power Engineering Society. These standards could be strengthened to deal with the threat of HEMP.

From an operational point of view, studies should be performed for each of the infrastructures to determine whether an alert would allow them to be placed in a less vulnerable state. For example, Metatech Corporation has provided a power grid operator 30 minutes notice of an impending geomagnetic storm that could cause a regional power system collapse. In addition, operational actions were predetermined in order to allow quick reaction to the impending storm. With pre-planning, power companies would be prepared to avoid a potentially severe power grid voltage collapse caused by a HEMP burst in their region of operation.

In terms of rebuilding after an attack, another option is to anticipate the types of damage that could occur and to preposition replacement equipment where it is likely to be needed. This could reduce the problem of shortages of equipment that seldom fail under normal operations but would have a much higher failure rate during a HEMP attack.

It should be understood that these three building blocks are not mutually exclusive, and in fact cost-benefit analyses would be effective in determining the optimum balance between protection, operational responses and rebuilding. In the end, however, it is still critical that DHS or another government agency take the responsibility to plan and oversee the protection of the critical infrastructure from this HEMP threat. In the meantime, the EMP Commission needs to continue its work to ensure that progress is made in dealing with this threat.


[1] “Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack,” Vol. I: Executive Report, 7 April 2004 . http://www.globalsecurity.org/wmd/library/congress/2004_r/04-07-22emp.pdf

[2] IEC Subcommittee 77C: “EMC: High Power Transient Phenomena,” International Electrotechnical Commission, Geneva, Switzerland: www.iec.ch

[3] V.M. Loborev, “Up to Date State of the NEMP Problems and Topical Research Directions,” Electromagnetic Environments and Consequences: Proceedings of the EUROEM 94 International Symposium, Bordeaux, France, 30 May – 3 June 2004, pp. 15-21.

[4] Greetsai, V.N., A.H. Kozlovsky, M. M. Kuvshinnikov, V.M. Loborev, Yu. V. Parfenov, O.A. Tarasov, L.N. Zdoukhov, “Response of Long Lines to Nuclear High-Altitude Electromagnetic Pulse (HEMP),” IEEE Transactions on EMC, Vol. 40, No. 4, November 1998, pp. 348-354.

[5] Radasky, W. A., “High-altitude EMP (HEMP) Environments and Effects,” NBC Report, Spring/Summer 2002, pp. 24-29.

[6] Radasky, W. A., J. Kappenman and R. Pfeffer, “Nuclear and Space Weather Effects on the Electric Power Infrastructure,” NBC Report, Fall/Winter 2001, pp. 37-42.

[7] IEC 61000-2-9, “Electromagnetic Compatibility (EMC) – Part 2: Environment – Section 9: Description of HEMP Environment – Radiated Disturbance,” International Electrotechnical Commission, Geneva, Switzerland, February 1996.

[8] IEC 61000-4-2, “Electromagnetic Compatibility (EMC) – Part 4: Testing and Measurement Techniques – Section 2: Electrostatic Discharge Immunity Test,” International Electrotechnical Commission, Geneva, Switzerland, April 2001.

[9] IEC 61000-4-4, “Electromagnetic Compatibility (EMC) – Part 4-4: Testing and Measurement Techniques – Electrical Fast Transient/Burst Immunity Test,” International Electrotechnical Commission, Geneva, Switzerland, April 2007.

[10] J. G. Kappenman, W. A. Radasky, J. L. Gilbert, I. A. Erinmez, “Advanced Geomagnetic Storm Forecasting: A Risk Management Tool for Electric Power Operations,” IEEE Plasma Society Special Issue on Space Plasmas, December 2000, Vol. 28, No. 6, pp. 2114-2121.

[1]] W. R. Graham, “Commission to Assess the Threat from High Altitude Electromagnetic Pulse (EMP): Overview,” Briefing to the U. S. House of Representatives, Committee on Armed Services, 22 July 2004.




Dr. William A. Radasky received the B.S. degree with a double major in Electrical Engineering and Engineering Science from the U.S. Air Force Academy in 1968. He also received the M.S. and Ph.D. degrees in Electrical Engineering from the University of New Mexico in 1971 and the University of California, Santa Barbara in 1981, respectively. He became a student member of the IEEE in 1967 while studying at the Air Force Academy and is currently a Senior Member of the IEEE.

He started his career as a research engineer at the Air Force Weapons Laboratory in Albuquerque, New Mexico working on the theory of the electromagnetic pulse (EMP). In 1984 he founded Metatech Corporation in Goleta, California where he is currently President and Managing Engineer. During his 39-year career, he has published over 350 technical papers and reports dealing with electromagnetic interference (EMI) and protection.

Dr. Radasky’s current interests include a new effort to provide cost-efficient protection to commercial facilities from the threats of HEMP and Intentional EMI (IEMI). He is Chairman of IEC Subcommittee 77C, which is developing high-power electromagnetic protection and test standards for civil systems. He is also the Chairman of TC-5 (High Power EM) for the IEEE EMC Society. Other activities include his role as Associate Editor for the IEEE EMC Transactions special issue on IEMI and HPEM in 2004 and as chair of the IEEE Standards Working Group 1642 to provide protection guidelines for publicly accessible computers from the threat of IEMI. In addition he is the Chairman of the IEC Advisory Committee on EMC (ACEC), which is tasked to coordinate all EMC standardization work for the IEC. He is an EMP fellow and a member of the Eta Kappa Nu and Tau Beta Pi honor societies. In October 2004 he was presented the Lord Kelvin Medal in Seoul, South Korea by the International Electrotechnical Commission for exceptional contributions to international standardization.

Comments may be submitted to todaysengineer@ieee.org. Opinions expressed are the author's.

Copyright © 2008 IEEE

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