Introduction

Detonation of a nuclear weapon in the upper atmosphere or in near-Earth space may generate a series of electromagnetic pulses—known collectively as high-altitude electromagnetic pulse (HEMP)—that damage the electric grid and other critical infrastructure on the earth's surface.¹ HEMP may directly radiate and damage sensitive electronics used to operate the grid, or couple with transmission lines and other conductors attached to essential equipment. This report focuses on HEMP-related risk to the electric grid, given its centrality to the operation of many other critical networked systems, such as water, transport, and communications. Other deliberate electromagnetic threats, such as battlefield electromagnetic pulse (EMP) weapons or improvised devices powered by conventional explosives, are outside the scope of this report. Likewise, this report does not provide an assessment of intent or capabilities of potential adversaries, or the likelihood of a HEMP attack.²

While there is broad consensus in the electricity industry, the research community, and among policymakers that high-altitude electromagnetic pulse attacks may pose risk to electricity infrastructure, there is disagreement regarding specific HEMP hazard characteristics, the level of risk, and the need for—or feasibility of—expansive HEMP-hardening initiatives.³

Congress has enacted a variety of mandates—primarily via national defense authorization acts—to spur basic research, applied research, and technology development, as well as risk management activities, risk assessments, adoption of voluntary standards and best practices, and the expansion of public-private partnerships for coordination and information sharing with industry. A congressionally chartered expert commission provided congressional testimony, reports, and recommendations between 2004 and 2017.

Most federal legislation has focused on the electricity sector, reflecting the broad consensus and priorities of government, industry, and the research community. Implementation of previous congressional mandates is ongoing, even as the 117^th Congress has appropriated funds for new infrastructure investments through the Infrastructure Investment and Jobs Act (IIJA; P.L. 117-58), the Inflation Reduction Act (IRA; P.L. 117-169), and other legislation. Prospective upgrades and buildout of electricity infrastructure may affect the sector's overall resilience to HEMP hazards, either by design or by chance. Congress may exercise oversight of related programs and activities to ensure that HEMP resilience is incorporated into electricity infrastructure at desired levels.

This report provides information on (1) the basic physics of HEMP; (2) existing risk management approaches and related legislation, policies, and directives; (3) the current state of scientific knowledge and related research programs; and (4) emerging science and technology policy issues. A concluding section summarizes potential issues for Congress.

High-Altitude Electromagnetic Pulse (HEMP) and Hazards to Electricity Infrastructure

U.S. and Soviet high-altitude weapons tests in the upper atmosphere in the late 1950s and early 1960s suggested that the electromagnetic effects of nuclear bombs detonated at high altitude (above 30 km) were potentially damaging to electrical grids, communications infrastructure, and other vital electronics-based systems many hundreds of miles away from the blast epicenter. Therefore, HEMP became a phenomenon of concern to military and civil defense planners.

The Partial Test Ban Treaty of 1963, signed by the United States, the United Kingdom, and the Soviet Union, precluded further scientific observations of HEMP effects on infrastructure in situ.⁴ However, military and civilian scientists have continued theoretical work and laboratory testing on grid components and other electronics. In addition, naturally occurring space weather produces geomagnetic disturbances (GMD)—comparable in some aspects to the late-time (E3) magnetohydrodynamic pulse produced during HEMP events—that inform empirical research on large-scale electromagnetic hazards to infrastructure in natural settings.⁵

The HEMP Waveform

In general, scientists believe HEMP is generated by the interaction of the radiation and blast effects of an exploding nuclear device with the earth's upper atmosphere, magnetic field, and conductive geologic formations. HEMP has three main time components, usually labeled E1, E2, and E3, which occur in rapid sequence and create distinct and potentially hazardous effects over a broad geographic area.

Figure 1. Representation of HEMP Electric Field

Source: Edward Savage, James Gilbert, and William Radasky, The Early-Time (E1) High-Altitude Electromagnetic Pulse (HEMP) and Its Impact on the U.S. Power Grid, Metatech, Meta-R-320, Goleta, CA, January 2010, p. 2-2. Notes: E(t) (V/m) = electric field in Volts per meter. s = seconds. E1 is seen in the upper left quadrant of the graph as a rapid rise in electromagnetic energy. E2 is seen in a less pronounced peak in the middle of the graph. E3 is seen at the far right as two lower amplitude pulses. The graph is illustrative and provides only a generic representation of HEMP electric fields and timescales.

E1: Early Time Pulse

The fission component of a modern nuclear weapon (typically used to trigger a more powerful fusion reaction) releases an intense burst of gamma radiation within the first microsecond of detonation. When detonations occur at high altitude, the radiation ionizes air molecules in the gamma absorption layer roughly 30 kilometers (km) above the earth's surface. Electrons freed by this process scatter and interact with the earth's upper atmosphere and magnetic field before losing their energy and being reabsorbed a short time later. The brief, but high energy, movement of free electrons along the lines of the earth's ambient magnetic field generates a secondary electromagnetic pulse. Dependent on a number of conditions, part of this pulse may radiate downward towards Earth's surface as a high-amplitude radio signal.⁶

Although this E1 pulse may reach continental scale, the maximum strength of the electric field it generates—measured in kilovolts per meter (kV/m)—is concentrated within a smaller crescent-shaped area equatorward (i.e., southward in the Northern hemisphere) of the blast epicenter (see Figure 2) due to the influence of the Earth's magnetic field. The E1 pulse may damage electrical systems and electronic devices in two ways: (1) direct radiation of internal components, or (2) coupling with conductors, such as power transmission lines, power control lines, and certain communications lines, which act as antennae and may conduct damaging voltage surges into connected devices.

Figure 2. Potential HEMP E1 Effects of 1,000 Kiloton Weapon at 200 km Altitude over Central United States

Source: Los Alamos National Laboratory, in Electric Power Research Institute (EPRI), High-Altitude Electromagnetic Pulse and the Bulk Power System: Potential Impacts and Mitigation Strategies (the EPRI study), Palo Alto, CA, April 2019, p. 2-3, https://www.roxtec.com/globalassets/03.-files/campaign-pages/emc/2019-epri-report.pdf.

The strength of the E1 pulse is only weakly correlated with increased weapon yield, because the same process that generates the radio signal described above also creates a powerful return current that builds throughout the E1 phase of the HEMP event. The return current partially attenuates the primary signal.⁷ Height of burst also affects the strength of HEMP E1 hazard fields measured on the earth's surface. E1 effects are limited to line of sight from the epicenter to the earth's surface, so that detonations at higher altitudes affect a wider geographic area. As with any source of radiation, the intensity of illumination decreases with distance from the source. Any given weapon yield has an "optimal" height of burst wherein the strength of the hazard field created by the E1 pulse is maximized as shown in Table 1.

The geographic area of maximum E1 electric field strength does not necessarily overlap with the geographic areas where infrastructure assets are most vulnerable to E1 hazards, according to a 2019 study by the Electric Power Research Institute (EPRI), an industry group. The report states that "maximum coupling generally occurs in areas to the east and west of ground zero and not south of ground zero where the area of maximum electric field amplitude is located."⁸

Peak field strength is therefore only one of several factors affecting overall risk to exposed electricity infrastructure. Other factors listed in the EPRI study include polarization of the E1 field, incidence angle between burst location and location of the asset on the ground, and azimuthal angle—the angle between the wave of electromagnetic energy and a wire or other conductor on or near the Earth's surface.⁹

E2: Intermediate Time Pulse

The E2 pulse (between 1 microsecond and 1 tenth of a second after detonation) is also generated by the fission component of a nuclear weapon.¹⁰ The E2 pulse creates an electric discharge similar to lightning in its basic physics, but occurring over a much wider geographic area. Many scientists believe protective equipment that is already installed to prevent damage to the electric grid from lighting strikes is sufficient to mitigate E2 effects. However, some have cautioned that the earlier E1 pulse may damage this protective equipment, leaving grid infrastructure exposed to hazardous effects of the E2 pulse.¹¹ Despite this uncertainty, most EMP research focuses on the E1 and E3 pulses and their effects.

E3: Late Time Pulse

E3 is generated by the fusion component of a nuclear device. The physics and time scale of the E3 pulse differ from those of E1 and E2, because E3 is produced by the explosive effects of the device, not the initial release of gamma radiation from the fission reaction described above (see the "E1: Early Time Pulse" section). According to the LANL study, "The primary physical effect at work in the E3 phase involves the motion of plasma, ionized weapon debris, and ionized atmosphere within the Earth's magnetic field."¹² In general, E1 and E3 effects cannot be maximized simultaneously with a single weapon, because parameters such as optimal weapon yield and optimal detonation altitude are different for E1 and E3. Even so, significant E1 and E3 effects on the earth's surface may overlap in some cases.¹³

The two primary components of the E3 pulse are the "blast" component (E3A) and the "heave" component (E3B). The E3A component is caused by the expansion of a large superheated conductive plasma ball produced by the detonation. The plasma ball pushes the earth's ambient geomagnetic field lines outwards as it expands and rises through the upper atmosphere. Much of the E3A component is attenuated by the effects of atmospheric absorption of the weapon's x-ray emissions below the blast epicenter, and so presents a lesser risk to infrastructure.

The E3B pulse is produced later as the plasma ball and associated effects dissipate, and the "ionized remnants of bomb debris and shock-heated atmospheric ions" settle in the upper atmosphere below the blast epicenter. This creates a conductive "hot ion patch," which heats and expands. This heated conductive patch becomes buoyant and rises through the upper atmosphere, producing an artificial geomagnetic disturbance as it pulls the geomagnetic field lines inwards.¹⁴ According to a LANL model of an E3B environment, location of peak voltages changes over the course of the event.¹⁵ Figure 3 depicts the geoelectric hazard field 40 seconds after the blast.

Figure 3. Notional Geoelectric Field of "Heave" E3B Pulse at 40 Seconds 10,000 Kiloton Yield at 200 km (Magnitude in V/km)

Source: LANL diagram in EPRI Study. Notes: The graphic does not depict predicted effects of a specific weapon.

As with E1, weapon yield and height of burst affect the strength of the resulting E3B hazard field. However, the magnitude of the E3B pulse does not increase much after weapon yield exceeds 10 kilotons—a yield typical of a small tactical warhead. However, the surface area of the hot ion patch increases with weapon yield and may disrupt Earth's magnetic field over a larger area.¹⁶ A larger patch presents greater risk to electricity infrastructure, because the resulting E3B pulse causes geomagnetic induced currents (GIC) that build cumulatively as they flow through long conductors, such as long-distance transmission lines.¹⁷

GIC may saturate the magnetic cores of large power transformers (LPTs) that enable transmission and local distribution of alternating current at useable voltages. According to a Department of Energy (DOE) study on naturally-occurring geomagnetic disturbances, saturation of the magnetic cores of LPTs by GIC can cause several damaging effects:¹⁸

• harmonic currents that can cause relays to trip equipment;
• fringing magnetic fields (i.e., flux outside the core) that can create heating in the transformer, which, if sufficiently high and of long duration, can lead to overheating and reduction of a transformer's life;
• increased reactive power consumption that can cause the system to collapse due to voltage instability;¹⁹ and
• damage and upset of customer equipment due to power quality disturbances.

In addition, GIC may cause harmonic damage to generator rotors and thermal damage to static VAR compensators that provide reactive power to the grid, according to industry sources.²⁰

The CISR Framework and HEMP

The technical summary presented above is a simplification of complex phenomena that are the subjects of continuing scientific research programs across numerous disciplines and sub-disciplines. The degree (and policy relevance) of scientific uncertainty is itself a significant source of disagreement among stakeholders in the national critical infrastructure security and resilience (CISR) enterprise. Industry stakeholders generally wish to avoid what some see as costly mandates to invest in unproven technologies based on limited scientific research, while some policymakers and advocacy groups believe the existing knowledge and technological bases are sufficient to justify an expansive hardening program across vulnerable critical infrastructure sectors.²¹

Industry adoption of EMP-hardened equipment in the electricity sector is market-driven in the United States. Equipment manufacturers may choose from among available hardening standards or specify their own proprietary testing criteria if they wish to make EMP resilience part of their product marketing.²² In some cases, manufacturers have also advertised the successful use of their equipment in testing by federal agencies or federally-sanctioned industry reliability organizations.²³ Companies may self-certify or seek third-party certification from an accredited body to indicate compliance with specific standards. Electricity producers may then decide whether the cost premium for hardened equipment is justified, given their specific risk profiles and tolerances.

Because much of the nation's critical infrastructure is owned and operated by the private sector on a for-profit basis, implementation of federal initiatives to counter known threats to infrastructure, including HEMP, often depends on industry engagement in public-private partnerships for resilience. Such engagement may involve sharing potentially sensitive information with government and nongovernment stakeholders, investing in research, and making relevant resilience investments based on available risk assessments and protection standards. These investments may involve significant up-front business costs that must be absorbed or passed to customers.

Federal initiatives to increase infrastructure resilience to HEMP hazards—often in response to congressional mandates or executive branch directives—have generally assumed the voluntary public-private partnership model as the basis for programs and activities. There is no federal regulatory requirement for hardening of critical infrastructure against HEMP.²⁴ Likewise, there is no relevant reporting requirement or centralized database containing information about industry adoption of hardening measures. However, the Department of Homeland Security (DHS) administers voluntary protected disclosure programs.²⁵ According to some observers, private-sector investment in HEMP resilience has generally been uneven and limited.²⁶

Under the current regulatory framework, the federal government oversees reliability for the generation and transmission systems of the electric power sector. These components comprise the bulk power system. The Energy Policy Act of 2005 (EPACT05; P.L. 109-58) authorized the Federal Energy Regulatory Commission (FERC) and its certified electric reliability organization, the North American Electric Reliability Corporation (NERC), to develop and enforce mandatory reliability standards for the bulk power system.²⁷

In most cases, state and local authorities regulate local distribution systems and retail sales to customers, and may also mandate relevant reliability standards or specific risk mitigation activities. Federal or state regulatory authorities may allow for cost-recovery—i.e., passing costs of regulatory compliance on to customers. Alternatively, Congress or state legislatures may provide grants or otherwise direct relevant regulatory agencies to force utilities to absorb these costs.

Strategies, Plans, Policies, and Legislation

A variety of strategies, plans, policies, and legislation have guided federal efforts to understand and manage HEMP-related risks in recent decades.

Agency Strategies and Action Plans

In 2015, the Secretary of Energy directed DOE to develop an EMP resilience strategy (the DOE Joint Strategy) in coordination with the electric power industry through EPRI. DOE described the Joint Strategy, released in 2016, as "a public-private collaborative effort, designed to establish a common framework with consistent goals and objectives that will guide both government and industry efforts to increase grid resilience to EMP threats."²⁸

The DOE Joint Strategy identified five goals:

• 1. improve and share understanding of EMP threat, effects, and impacts;
• 2. identify priority infrastructure;
• 3. test and promote mitigation and protection approaches;
• 4. enhance response and recovery capabilities to an EMP attack; and
• 5. share best practices across government and industry, nationally and internationally. An action plan based on the strategy was released in 2017.²⁹

In 2018, DHS released an EMP/GMD strategy (the DHS strategy) in fulfilment of a congressional mandate enacted by Section 1913 of the National Defense Authorization Act for 2017 (FY2017 NDAA; P.L. 114-328).³⁰ The strategy identified three main goals:

• 1. improve risk awareness of electromagnetic threats and hazards;
• 2. enhance capabilities to protect critical infrastructure from the impact of an electromagnetic incident; and
• 3. promote effective electromagnetic-incident response and recovery efforts. DHS indicated that the strategy will remain in effect until 2026 and be updated every two years thereafter.³¹

The EMP Commission

Congress first established the Commission to Assess the Threat to the United States from Electromagnetic Pulse Attack (EMP Commission) under Title XIV of the Floyd D. Spence National Defense Authorization Act (NDAA) for Fiscal Year 2001 (P.L. 106-398). It was reestablished under Section 1052 of FY2006 NDAA (P.L. 109-163). Section 1075 of the FY2008 NDAA (P.L. 110-181) modified the EMP Commission's authorities, extending the deadline for previous reporting requirements among other provisions. The EMP Commission was reestablished for a second time under Section 1089 of the FY2016 NDAA (P.L. 114-92). Section 1691 of the FY2018 NDAA (P.L. 115-91) established a new EMP Commission to complete another assessment and report due April 1, 2019, but the provision was subsequently repealed by Section 1695 of the FY2020 NDAA (P.L. 116-92).

The EMP Commission released several reports under these authorizations, with the final report being published in July 2017. EMP Commission members have generally presented HEMP risk to critical infrastructure as posing an existential threat to the United States—a position that appears to have informed policy in some instances. According to a former senior Commission staff member, the EMP Commission informed development of Executive Order (E.O.) 13865, "Coordinating National Resilience to Electromagnetic Pulses," which—he claimed—sought to implement the EMP Commission's core recommendations "on an accelerated basis."³²

Executive Order (E.O.) 13865 and the FY2020 NDAA

Table 2 summarizes EMP resilience provisions in Section 1740 of the National Defense Authorization Act for Fiscal Year 2020 (FY2020 NDAA; P.L. 116-92) derived from E.O. 13865, and the current status of mandated programs and activities.³³ In 2020, DHS published an update on steps taken to comply with E.O. 13865, and indicated it would conduct additional vulnerability testing of "prioritized critical infrastructure components" and validation testing of mitigation options "as funding becomes available."³⁴

Not included in the FY2020 NDAA is the E.O. 13865 requirement for DHS and other federal agencies to "identify regulatory and non-regulatory mechanisms, including cost recovery measures" for private sector entities to address EMP risk.³⁵

HEMP and Infrastructure Legislation in the 117^th Congress

The IIJA contains several infrastructure resilience provisions that either explicitly include addressing HEMP as a program consideration or implicitly allow addressing HEMP as part of an all-hazards risk management approach. Other provisions confine funding to extreme weather, wildfire, and natural disasters, but nevertheless may still affect HEMP resilience incidentally. For general information on IIJA grid resilience provisions, see CRS Report R47034, Energy and Minerals Provisions in the Infrastructure Investment and Jobs Act (P.L. 117-58), coordinated by Brent D. Yacobucci.

IRA does not contain HEMP-specific provisions. However, changes in grid technology and topology envisioned under the law—such as increased use of renewable energy sources—may affect HEMP resilience incidentally. For general information on relevant IRA programs, see CRS Report R47262, Inflation Reduction Act of 2022 (IRA): Provisions Related to Climate Change, coordinated by Jane A. Leggett and Jonathan L. Ramseur.

HEMP-Specific Provisions in the IIJA

Section 40125(d), "Modeling and Assessing Energy Infrastructure Risk," authorized $50 million over five years for creation of an "advanced energy security program" within DOE to support modeling of risks to energy networks posed by natural and human-made threats and hazards, "including electromagnetic pulse and geomagnetic disturbance."³⁶ EMP and GMD are the only hazards specifically named under this provision. Examples of eligible activities include development of new capacities to identify vulnerable grid components, research on grid hardening solutions, research mitigation and recovery solutions, grid resilience exercises and assessments, and "technical assistance to States and other entities for standards and risk analysis."

Section 40103(d), "Energy Infrastructure Resilience Framework," directs the Secretary of Energy, in collaboration with the Secretary of Homeland Security, FERC, NERC, and "interested energy infrastructure stakeholders," to research options for building and stockpiling portable replacement LPTs. In 2017, DOE published a plan in compliance with a similar congressional mandate enacted under Section 61004 of the Fixing America's Transportation Act (P.L. 114-94) to establish a strategic transformer reserve in partnership with industry stakeholders.³⁷

Section 40321, under Subtitle C, "Nuclear Energy Infrastructure," requires DOE to submit a report to Congress on micro and small nuclear reactors. The mandated report must describe how the department could enhance energy resilience of DOE facilities and remote communities using micro-reactors and small modular reactors, and include an assessment of how such installations might address the "need for protection against cyber threats and electromagnetic pulses," among other threats and hazards.

IIJA appropriated $157.5 million under the "Science and Technology Directorate, Research and Development" heading, available until September 30, 2026, to the DHS Science and Technology Directorate (S&T) for CISR-related "research, development, test, and evaluation." EMP and GMD resilience capabilities were one of five named eligible categories for use of funds.³⁸

Other Potentially Relevant IIJA Grid Resilience Provisions

Section 40101, "Preventing Outages and Enhancing the Resilience of the Electric Grid," authorized $5 billion in grant programs for electricity infrastructure owners and operators to protect the grid against "disruptive events"—defined as extreme weather, wildfire, or natural disaster occurrences that result in preventive or accidental outages, or hazardous safety conditions. Eligible activities include construction of microgrids and battery storage equipment, installation of adaptive protection technologies, replacement of power lines and underground cables, and hardening of power lines, facilities, substations, and other systems.

Section 40102, "Hazard Mitigation Using Disaster Assistance," amended the Robert T. Stafford Disaster Relief and Emergency Assistance Act (Stafford Act; 42 U.S.C. 5170c (f)(12)) to make installation of fire-resistant wires and undergrounding of wires eligible for Stafford Act funding. (Undergrounding wires may provide some attenuation of HEMP hazards; see the "Undergrounding Electrical Equipment and Power Lines" section.)

Section 40103 authorized $5 billion to support a new DOE program, "Upgrading Our Electric Grid and Ensuring Reliability and Resilience," which would offer competitive grants for states, tribes, local governments, and public utility commissions. Grants would fund technology demonstration projects related to resilience and reliability of the electric grid. The provision does not name specific threats or hazards. As of this writing, DOE has issued a request for information seeking information from stakeholders and a draft funding opportunity announcement.³⁹

Section 40106, "Transmission Facilitation Program," authorized programs to increase transmission capacity, connect isolated microgrids to infrastructure, and support adoption of advanced technologies to increase "capacity, efficiency, resiliency, or reliability of an electric power transmission system."

Section 40107, "Deployment of Technologies to Enhance Grid Flexibility" authorized $3 billion in funds for the DOE Smart Grid Investment Matching Grant Program. Authorized activities include buildout of fiber and wireless broadband communication networks, and advanced transmission technologies and sensors, to enable better coordination of grid operations and enhance grid flexibility. (This includes the ability to island sections of the grid to isolate against cascading grid failures in case of extreme weather and nature disasters.) Grid flexibility is a power system's capacity to dynamically balance power supply with demand across a wide area using networked systems of electricity generation, transmission, and distribution.

Section 40108, "State Energy Security Plans" amends the Energy Policy and Conservation Act of 1975 (P.L. 94-163; EPCA) to modify requirements for state energy security plans. Plans must address all energy sources and providers, include a state energy profile, address cyber and physical vulnerabilities, provide a risk assessment, and provide a risk mitigation approach, among other requirements, in order to receive federal financial assistance under Part D of EPCA. The program provides grants to support implementation of state energy plans.⁴⁰ Congress appropriated $500 million for formula grants to be awarded under the State Energy Program between FY2022 and FY2026.⁴¹

Section 40125, "Enhanced Grid Security," authorizes $250 million over five years for cybersecurity-related projects, and to support all-hazards based risk assessments of communications, control systems, and power systems architectures used to operate the grid. Additionally, it supports pilot projects with energy sector stakeholders to gain experience using relevant emerging technologies.

Section 11105, "National Highway Performance Program," allows for undergrounding "public utility infrastructure" in conjunction with otherwise eligible transportation projects authorized under the National Highway Performance Program (23 U.S.C. 119).

Research Issues

Issues of scientific theory, method, and analysis continue to be debated within the broader research community in response to emerging HEMP research and related policy initiatives. To date, research programs—each with its own objectives, assumptions, resources, and limitations—have generally produced inconsistent or incomplete estimates of HEMP-related risks to infrastructure. As such, existing research has failed to elicit broad industry consensus on the methods, scale, and scope of any broad-based hazard mitigation program.

HEMP Environments and Benchmarks

Non-defense research generally relies upon a limited number of unclassified models of electromagnetic hazard fields generated by HEMP—usually referred to as HEMP environments—to assess the potential effects of high-altitude nuclear detonations. Unclassified HEMP environments, such as the one represented graphically in Figure 2, provide the predicted peak strength of hazard fields in a given location in relation to the blast epicenter based on a generic waveform, but do not provide the fidelity needed to inform comprehensive and authoritative risk assessments, according to researchers.

For example, the EPRI study states, "several unclassified E1 EMP environments exist, but in general, these environments have limited usability because they are comprised of a single waveform or ... provide a generic representation of the peak electric field on the ground," and do not include other important parameters, such as polarization of the electric field and angle of incidence.⁴² Researchers must then make educated assumptions about these parameters in order to predict effects on exposed infrastructure systems. (See the "Obstacles to Improved Risk Management" section.) Detailed findings and data from classified EMP research are generally not available outside the defense research community. In its final report, the EMP Commission criticized Department of Defense (DOD) data classification policies and the "absence of technology transfer and other support" to other agencies and critical infrastructure stakeholders.⁴³

In a January 2021 memorandum, the Secretary of Energy released benchmark waveforms to inform testing and predictive modeling by industry and government entities in fulfillment of E.O. 13865.⁴⁴ The memorandum did not provide specific hardening standards or "specify the level of risk critical infrastructure faces from HEMP."⁴⁵ As such, the Secretary presented it as "a first step in a long conversation with civilian stakeholders to begin to understand the threat, consequence, and risk associated with EMPs and how to address the risks."⁴⁶

The benchmark waveforms published in the memorandum were based on available unclassified research from the International Electrotechnical Commission (IEC), Oak Ridge National Laboratory (ORNL), and the EMP Commission. The provided peak field strengths for E1 and E3 electric fields were as follows:

• E1: 50 kV/m (Source: IEC)
• E3A: 80 V/km (Source: EMP Commission)
• E3B: 50 V/km (Source: IEC)

The DOE memorandum indicated that the benchmark values it provides were provisional, and that testing against these benchmarks may "exceed DOE's currently assessed threat levels by a factor of 2 due to predictive modeling uncertainties and potential excursions in HEMP environment levels." Further, "The recommended E1, E2, and E3 HEMP environment benchmark waveforms will be updated as necessary, based on further developments in our understanding of HEMP generation and modeling and simulation phenomenology."⁴⁷

Modeling and Simulation of Infrastructure Resilience

Modeling and simulation are used to estimate risk levels to infrastructure in a given HEMP environment. Although straightforward in principle, the integration of modeling, simulation, and experimental testing of system components to identify and measure relevant risk factors is complex in practice.

Modeling and simulation studies must account for one or more of the following:

• interaction of radiation and blast effects of the weapon with the natural environment to produce HEMP hazard fields,
• interaction of HEMP hazard fields with exposed infrastructure systems and assets, and
• secondary or cascading effects of such interactions on critical infrastructure functions.

Researchers have used modeling and simulation to create and test synthetic electrical grids against notional HEMP events, but—absent data on specific system topologies and other sources of uncertainty—such tests can produce only general insights on grid behavior and failure modes.⁴⁸ According to EPRI, "Interconnection scale modeling requires a high-fidelity E1 EMP environment (not publicly available) and ability to perform coupling calculations on 1000's of substations simultaneously."⁴⁹

Studies using a variety of research designs and methods have produced scientific advancement and limited consensus in some areas. However, widely divergent results and assessments of HEMP risk to critical infrastructure has highlighted a need for further research and methodological advancement.

Summary of HEMP Research Results

Despite significant gaps, existing HEMP research has identified several issues of concern that E1 radiative and conductive threats both present hazards to unprotected DPR, DCS, and supervisory control and data acquisition (SCADA) systems in control houses or generation facilities, according to some studies.⁵⁰ (Older electromechanical relays, which have largely been supplanted by DPRs, have been found to be highly resistant to electromagnetic pulses.)⁵¹ However, conductive threats generally present higher risk. Relatively simple (and inexpensive) mitigations, such as use of shielding, grounding, and insulation of control lines, as well as modification of control house design and materials, appear to significantly reduce—but not eliminate—vulnerability to E1 hazards.⁵²

LPTs may suffer physical damage from both E1 and E3 hazards, although estimates of likely damage vary. The EMP Commission warned of LPT hotspot heating caused by E3 induced core saturation and system harmonics on sufficient scale to render major grid interconnections inoperable for months or longer. More recent studies by EPRI and ORNL predicted that such losses would occur on a lesser scale and would likely not present a systemic hazard to grid operations—assuming that control and communications systems remained operable, and other grid equipment was undamaged.⁵³

Several studies identify voltage collapse caused by E3B as being of generally greater concern than heat damage to a large number of transformers.⁵⁴ Experts predict that in the case of an interconnection-scale voltage collapse, restoration would be a complex and lengthy process. Lack of availability of utility-scale power adjacent to affected areas and functioning communications between geographically dispersed system operators might pose significant challenges.⁵⁵

The vulnerability of generation facilities to HEMP threats is a topic of concern. Preliminary field testing of a working generation facility by EIS found that E1 threats "will likely disrupt or damage typical power plants."⁵⁶ The EPRI report stated, "Additional research is needed to evaluate the potential impacts of HEMP on generation facilities themselves," and suggested extending the existing mitigation framework for the transmission system to develop hardening and mitigation options for generation facilities.⁵⁷ Additionally, the increasing prevalence of renewables may offer both additional resilience and potential vulnerabilities. These technologies are rapidly evolving, and research on potential HEMP vulnerabilities is in its preliminary stages (see the "Inverter-Based Resources" section).

The Foundation for Resilient Societies, a critical infrastructure resilience research and advocacy organization, published a report in 2020 that highlighted vulnerabilities of communications technologies used to control electricity generation, transmission, and distribution.⁵⁸ For example, non-conductive fiber optic lines used for communications between electricity grid substations rely upon amplifier points—placed at roughly 80 mile intervals—and fiber transceivers at substations and control rooms. Fiber optic amplifiers and transceivers are vulnerable to HEMP, according to the report.⁵⁹ Similar risk exists where grid operators use wireless communications to control grid assets—often in inaccessible areas where fiber optic technology is cost-prohibitive. Wireless communications assets, such as cell towers, are protected against routine electromagnetic interference, but may be vulnerable to HEMP.⁶⁰

Appendix A provides a summary of selected research products.

Emerging Science and Technology Policy Issues

Major infrastructure legislation enacted during the 117^th Congress funds buildout of infrastructure capacity, research and planning activities, risk management activities, and expanded use of emerging renewable energy technologies in the electricity sector. As of this writing, implementation of authorized programs is in its early stages, and any eventual impact on HEMP resilience is unknown. The following sections highlight certain technologies supported via congressional authorizations and appropriations enacted under IIJA and IRA (see "HEMP and Infrastructure Legislation in the 117th Congress" section) that may have implications for HEMP resilience depending upon implementation policies.

Inverter-Based Resources

Wind, solar, fuel cells, and batteries make up an increasing share of power generation and supply capacity. These power sources use inverters to convert the direct current electricity they produce to alternating current electricity used by most electricity consumers. Wind resources are usually implemented on utility-scale. Solar and battery resources may be implemented at utility-scale to provide power for the grid, or may be used for rooftop and residential applications as distributed energy resources (DERs). Hybrid approaches use digital control systems to combine DERs operating as virtual power plants with grid-scale generation assets. Development and deployment of such systems is in its early stages, as of this writing.⁶¹

The comparative advantages or disadvantages of distributed or hybrid generation using inverter-based resources to provide energy and grid services during a HEMP event have not yet been extensively researched.⁶²

A 2022 National Renewable Energy Laboratory (NREL) study on hybrid power plants and grid resilience suggested that "hybridizing or spatially distributing renewable energy generation assets, the complementarity of the distinct resources can be leveraged to provide energy and grid services more reliably than any of the assets can on their own."⁶³ However, it did not examine potential effects of HEMP on inverter-based resources or associated electronic control systems necessary to administer and provide operational control of hybrid power plants. The 2019 EPRI report states that resilience of inverter-based generation against E1 hazards is unknown. Other preliminary research indicates that photovoltaic panels are highly resistant to E1, but more testing of connected inverters and associated electronic control systems is necessary.⁶⁴

Inverter-based resources can provide ancillary services to the electricity grid such as voltage support to help maintain stability if designed and configured appropriately.⁶⁵ Electric vehicles—essentially batteries on wheels—equipped with vehicle-to-grid (V2G) technology may provide the same grid services, but the relevant technologies to automatically aggregate and coordinate charging and power dispatch are still in the development and planning stages.⁶⁶ Existing research and development largely focuses on the routine application of battery storage and V2G technologies for maintaining grid stability. The utility of these technologies in a HEMP scenario is largely unknown.

Microgrids

Microgrids may operate independently of the bulk electricity system if they are configured with the appropriate hardware and software.⁶⁷ Microgrids may be powered by a variety of power sources and may offer some resilience to connected homes, businesses, and essential facilities against large-scale outages caused by HEMP. However, microgrids—especially those intended for civilian use—are not necessarily designed to withstand E1 pulses that may affect power control systems and other sensitive electronics.⁶⁸

Nonetheless, hardening microgrids against HEMP through the use of protective enclosures and other measures may be more practical and less costly than for conventional grid assets.⁶⁹

By definition, microgrids do not use long transmission lines and LPTs that form the backbone of the electric grid, and so they do not have direct vulnerability to GMD caused by E3 when operated independently of the grid. Some connected microgrids have the capability to disconnect from major distribution networks and operate in "island" mode during an emergency in order to avoid cascading effects of large-scale grid failures.

Transmission Facilitation and Grid Flexibility

For economic reasons, the existing electricity system operates with minimal redundancy and spare capacity—a condition enabled by increased adoption of (potentially vulnerable) electronic controls and other digital technologies in recent decades.⁷⁰ Power grids are more vulnerable to disruption when they operate with little spare capacity, according to experts.⁷¹ Increased transmission capacity provides greater margins for grid operators to manage disruptions and provide additional reactive power to maintain system voltages if necessary. A 2019 study by the National Renewable Energy Laboratory predicted that considerable growth in electricity demand due to anticipated electrification of residential heating and transportation (electric vehicles) would "likely require grid capacity expansion and make grid operations and planning more challenging."⁷²

Infrastructure programs to support increased transmission capacity and grid flexibility may remediate these deficiencies to some degree. However, IIJA and IRA infrastructure programs to facilitate integration of inverter-based resources and microgrids into the existing bulk electric system focus on environmental performance—i.e., lower carbon dioxide emissions—and resilience to extreme weather, wildfires, and natural disasters.

Improvements in grid flexibility may enhance the power system's capacity to dynamically balance power supply with demand across a wide area using networked systems of electricity generation, transmission, and distribution during a HEMP event, if only incidentally. However, potential operational benefits and resilience of such prospective systems to HEMP—many of which are still in the research and development phase—are largely unknown.⁷⁴ Loss of grid flexibility during a HEMP event may complicate efforts to manage disruptions and maintain functioning power supply. Existing HEMP research has largely focused on hazards to conventional grid operations, rather than inverter-based resources, microgrids, and advanced transmission technologies (see the section "Modeling and Simulation of Infrastructure Resilience").

Undergrounding Electrical Equipment and Power Lines

IIJA funds for undergrounding electrical equipment and power lines are restricted to protection against extreme weather, wildfires, and natural disasters (see "Other Potentially Relevant IIJA Grid Resilience Provisions"). However, undergrounding certain assets to protect against these hazards may incidentally affect HEMP resilience. EPRI research showed that undergrounding control cables at substations connected to DPRs provided significant equipment protection against simulated E1 pulses.⁷⁵ In the case of buried long-distance transmission lines, conductive earth may attenuate early-time E1 pulses—lessening any coupling hazards to the grid. However, undergrounding long-distance transmission lines would not prevent GIC caused by E3 magnetohydrodynamic effects, which propagate through conductive geologic formations underground and enter the grid through transformer groundings.

Issues for Congress

As of this writing, DHS and other relevant federal agencies continue to implement legislative mandates contained in the FY2020 NDAA, which legislate many of the directives contained in E.O. 13865 (see the "Executive Order (E.O.) 13865 and the FY2020 NDAA" section). Major outstanding items include DHS risk models for critical infrastructure and associated risk assessments, engineering approaches for risk mitigation, and identification of emerging EMP protection technologies. Many mandated deadlines have already passed. Documents submitted by other agencies in compliance with E.O. 13865, such as the DOE memorandum on HEMP waveforms (see the "HEMP Environments and Benchmarks" section) present data from existing sources that are more than a decade old in some cases, and contain caveats indicating uncertainty.

It is not clear that existing HEMP research is sufficiently mature for DHS, or any other federal agency, to provide authoritative guidance to policymakers or industry stakeholders on prioritization of critical systems and assets for hardening or other countermeasures in the near future. DHS has indicated more funding would be necessary to support necessary research (see the "Executive Order (E.O.) 13865 and the FY2020 NDAA" section). IIJA appropriations to federal agencies may support further research, depending upon how funds are apportioned to specific research programs by implementing agencies (see the "HEMP-Specific Provisions in the IIJA" section).

In all these potential HEMP-related issues, the appropriate roles for federal agencies, states, and the private sector would be fundamental areas for congressional consideration.

Obstacles to Improved Risk Management

Researchers consistently identify issues with the underlying quality of data used to model HEMP risk to critical infrastructure (see the "HEMP Environments and Benchmarks" section) as an obstacle to providing more authoritative risk assessments to critical infrastructure stakeholders. The EMP Commission and others have suggested that improved access to DOD and DOE/National Nuclear Security Administration data and research on electromagnetic effects of nuclear weapons, and selective declassification of certain data and research, might reduce such obstacles, if only to a degree. Congress may consider legislating parameters and specific objectives of interagency cooperation between DOD, DHS, DOE, and other relevant federal agencies, and provide funding and oversight as appropriate.

Researchers also note the need for more detailed modeling of underground geologic formations that play a role in propagation of E3 related hazards, and more detailed knowledge of specific infrastructure topologies that affect system-level resilience to HEMP (see the "Modeling and Simulation of Infrastructure Resilience" section). The U.S. Geological Survey, an agency of the Department of the Interior, administers a geomagnetism program that supports the National Space Weather Strategy, which focuses on naturally occurring electromagnetic hazards similar to manmade E3. The program received increased funding under the FY2020 appropriations act to continue a national magnetotelluric survey started by other federal agencies.⁷⁶ Congress may consider exercising oversight and other authorities to ensure relevant findings are available to the HEMP research community.

Similarly, Congress may consider exercising oversight of existing DHS administered partnerships with critical infrastructure stakeholders for protected critical infrastructure information disclosure and information sharing, such as the Protected Critical Infrastructure Information program, which may assist DHS in completing HEMP risk management activities mandated by the FY2020 NDAA (see the "The CISR Framework and HEMP" section).

Incentivizing and Facilitating Investment in HEMP Resilience

E.O. 13865 contemplates future introduction of cost-recovery mechanisms (such as increased consumer electricity rates) that certain electricity providers could use to fund HEMP resilience investments. In September 2022, FERC released a Notice of Proposed Rulemaking (NOPR) to provide "incentive-based rate treatment" for utilities that invest in "advanced cybersecurity technology" and participate in cybersecurity threat information sharing programs, pursuant to Congress's instructions in IIJA.⁷⁷ The NOPR suggests certain cost-recovery mechanisms that may be further elaborated during the rulemaking process. Congress may wish to direct FERC to develop a similar rule to incentivize investment in HEMP resilience. Development and implementation of such a rule might depend in part on availability of improved risk models, risk assessments, and mitigation technologies as described above.

Congress may consider exercising oversight of development and implementation of State Energy Security Plans described in Section 40108 of the IIJA (see the "Other Potentially Relevant IIJA Grid Resilience Provisions" section) to ensure that HEMP resilience considerations are included as deemed appropriate. DOE administers the program at the federal level and reviews and approves individual state plans based on compliance with IIJA statutory requirements.⁷⁸

Any congressional action would take place in a rapidly changing technology environment as grid modernization and hardening initiatives authorized under IIJA, IRA, and other legislation proceed, offering both opportunities and risk to policymakers (see the "Emerging Science and Technology Policy Issues" section). Inverter-based energy resources and microgrids may contribute to grid resilience against HEMP threats if they are appropriately configured and located to provide grid services, such as voltage support, and are able to survive the HEMP environment. Congress may consider supporting relevant research and development activities through legislation, oversight, and appropriations.

Relevant (functionally identical) technologies may be more or less resilient to HEMP, depending on what technical standards are applied to their design and manufacture, and their system configuration. Existing legislation primarily contemplates resilience to extreme weather hazards, wildfire, and other natural disasters as design considerations (see the "HEMP and Infrastructure Legislation in the 117th Congress" section). Congress may consider explicit inclusion of HEMP resilience in future infrastructure or related grants legislation. Additionally, Congress may consider directing FERC to oversee development and implementation of infrastructure protection standards specific to HEMP if deemed necessary (see "The CISR Framework and HEMP" section).

Future Technological Advancements

Congress may consider future technological advancements when developing policies relevant to HEMP resilience. For example, LPT stockpiling programs considered in the IIJA and previous legislation assume existing transformer designs as the basis for operational control of electricity transmission and distribution, which require large lead times for manufacture, customization, and transport (see the "HEMP-Specific Provisions in the IIJA" section). Emerging solid state technologies may enable a more rapid and flexible use of standardized systems to support a building-block approach to construction and repair of grid infrastructure that would eliminate the need for vulnerable LPTs. Likewise, such technology might enhance efficiency without increasing risks to grid stability—an improvement over most existing technologies (see "Future Grid Technologies and HEMP" text box, p. 20). Congress may consider balancing the need to manage risks to existing infrastructure against the possibility of eliminating certain risks through adoption of new technologies. Given the long service life of most electricity infrastructure assets, it may be appropriate to encourage investment in next-generation technologies where possible to avoid inefficient use of limited resources to harden obsolescent technologies against HEMP.

Appendix. Appendix A. Selected Studies by Year