A nuclear electromagnetic pulse (NEMP) is a sudden burst of energy caused by a nuclear explosion. This energy creates fast-changing electric and magnetic fields that can interact with electrical and electronic systems, leading to strong electrical currents and voltage spikes that harm these systems. The details of a nuclear EMP event depend on several factors, with the most important being the height at which the nuclear explosion occurs.
The term "electromagnetic pulse" usually does not include light (such as infrared, visible, and ultraviolet) or ionizing radiation (like X-rays and gamma rays). In military terms, a nuclear weapon exploded tens to hundreds of miles above Earth’s surface is called a high-altitude electromagnetic pulse (HEMP) device. The effects of a HEMP device depend on factors such as the height of the explosion, the energy released, the amount of gamma rays produced, how these rays interact with Earth’s magnetic field, and how well the targets are protected from electromagnetic interference.
History
Scientists knew early on that a nuclear explosion creates an electromagnetic pulse (EMP). However, the strength of the EMP and the effects it could cause were not fully understood at first.
During the first U.S. nuclear test on July 16, 1945, electronic equipment was protected because Enrico Fermi believed an EMP would occur. The official report from that test said, "All signal lines were completely shielded, in many cases shielded twice. Despite this, many records were lost because of unwanted signals that stopped the recording equipment from working." During British nuclear tests in 1952–53, problems with instruments were blamed on "radioflash," which was their name for EMP.
The first public report about the special effects of high-altitude EMP happened during the Yucca test on April 28, 1958, part of the Hardtack I series. The test used a 1.7 kiloton weapon lifted by a helium balloon. The electric field measured during the explosion was much stronger than the instruments could handle, estimated to be about five times the limit of the oscilloscopes. The Yucca EMP was positive at first, while low-altitude EMPs were negative. Also, the Yucca EMP had horizontal polarization, while low-altitude EMPs had vertical polarization. Despite these differences, scientists at the time thought the results might be due to a wave movement error.
High-altitude nuclear tests in 1962 confirmed the unique EMP effects seen in the Yucca test and made more scientists aware of the problem. A series of articles published in 1981 by William J. Broad in Science helped the larger scientific community understand the importance of EMP.
On July 1962, the U.S. tested Starfish Prime, exploding a 1.44 megaton bomb 400 kilometers above the Pacific Ocean. This showed that high-altitude nuclear explosions had much larger effects than previously thought. The EMP from Starfish Prime caused electrical damage in Hawaii, about 1,445 kilometers away, including disabling 300 streetlights, triggering burglar alarms, and damaging a microwave link.
Starfish Prime was the first test in the 1962 U.S. high-altitude nuclear tests called Operation Fishbowl. Later tests in the same operation collected more data about high-altitude EMP.
Tests called Bluegill Triple Prime and Kingfish in October and November 1962 gave clear evidence that helped scientists understand the physical causes of EMP.
The damage from Starfish Prime in Hawaii was repaired quickly because the EMP there was weak compared to what a stronger pulse could cause. Also, Hawaii's electrical systems in 1962 were more durable than modern systems. The small size of the EMP in Hawaii (about 5.6 kilovolts/meter) and limited damage (such as 1% to 3% of streetlights failing) led some scientists to think EMP might not be a major issue. Later calculations showed that if the Starfish Prime bomb had been exploded over the northern U.S., the EMP would have been much stronger (22 to 30 kilovolts/meter) due to the Earth's magnetic field and location. These findings, along with growing use of electronics sensitive to EMP, increased concern about EMP as a serious problem.
In 1962, the Soviet Union tested three EMP-producing nuclear weapons in space over Kazakhstan, the last part of the "Soviet Project K" tests. Though these weapons were smaller (300 kilotons) than Starfish Prime, they were over a populated area and where the Earth's magnetic field was stronger. The EMP damage was reportedly worse than in Starfish Prime. A geomagnetic storm-like E3 pulse from one test caused a current surge in an underground power line, starting a fire in a power plant in Karaganda.
After the Soviet Union dissolved, details about this damage were shared informally with U.S. scientists. For a few years, U.S. and Russian scientists worked together on the HEMP phenomenon. Funding allowed Russian scientists to publish some Soviet EMP results in international journals. As a result, some information about EMP damage in Kazakhstan is now documented, though it remains limited in public scientific sources.
For one of the K Project tests, Soviet scientists monitored a 570-kilometer section of a telephone line they expected the EMP to affect. The line was divided into shorter sections, separated by repeaters. Each section had fuses and gas-filled protectors. The EMP from the K-3 test (Test 184) destroyed all fuses and protectors. Reports, including a 1998 IEEE article, said ceramic insulators on power lines had serious problems during the tests. A 2010 report from Oak Ridge National Laboratory stated, "Power line insulators were damaged, causing short circuits and some lines to fall from poles to the ground."
Characteristics
Nuclear EMP is a complex event with multiple pulses. The International Electrotechnical Commission (IEC) describes it in three parts: E1, E2, and E3. These parts are categorized based on how long each pulse lasts and when it occurs.
E1 is the fastest pulse, often called the "early time" EMP. The term "EMP" usually refers to this E1 component. It is a brief but strong electromagnetic field that can cause high voltages in electrical conductors. E1 damages equipment by exceeding the voltage limits of electrical systems. It can harm computers and communication devices and moves too quickly for ordinary surge protectors to stop it. Special surge protectors, such as those using TVS diodes, can block E1.
E1 is created when gamma radiation from a nuclear explosion strips electrons from atoms in the upper atmosphere. This process is called the Compton effect, and the resulting current is called the "Compton current." Electrons move downward at very high speeds. The Earth's magnetic field causes these electrons to curve, creating a type of radiation called synchrotron radiation. This radiation combines to form a strong, short pulse.
In 1963, physicist Conrad Longmire identified the mechanism behind E1. He studied a typical E1 pulse from a second-generation nuclear weapon, such as those used in Operation Fishbowl. These weapons release gamma rays with about 2 MeV of energy. Half of this energy is transferred to electrons, giving them about 1 MeV. In a vacuum, these electrons would create a current of tens of amperes per square meter. However, the Earth's magnetic field causes electrons to spiral, and they eventually stop after colliding with air molecules. This interaction produces an electromagnetic pulse that peaks in about five nanoseconds and lasts up to 1,000 nanoseconds.
At mid-latitudes, electrons spiral around magnetic field lines with a radius of about 85 meters. They stop after traveling about 170 meters due to collisions with air molecules. This process creates an E1 pulse with a peak strength of about 50,000 volts per meter near ground level. The ionization process in the mid-stratosphere makes this region conductive, limiting the pulse's strength. The E1 pulse's intensity depends on the number and energy of gamma rays and the speed of the gamma-ray burst.
Some sources mention "super-EMP" weapons that may produce stronger pulses than 50,000 volts per meter. However, details about these weapons are classified and not confirmed in scientific literature.
E2 is an "intermediate time" pulse, lasting from one microsecond to one second. It is caused by scattered gamma rays and neutrons. E2 is similar to lightning but generally weaker than lightning-induced pulses. Lightning protection systems are often used to defend against E2. However, the United States EMP Commission warns that E2 can damage protective systems if they were already harmed by the earlier E1 pulse.
E3 is a much slower pulse, lasting tens to hundreds of seconds. It is caused by the temporary distortion of the Earth's magnetic field from a nuclear explosion. E3 is similar to a geomagnetic storm and can create currents in long electrical conductors, such as power lines, damaging transformers. Because of this similarity, solar-induced geomagnetic storms are sometimes called "Solar EMP." However, "Solar EMP" does not include E1 or E2 components.
Generation
Factors that affect how well a weapon works include altitude, the weapon's power (yield), how it is built, how far the target is, natural features like mountains or hills, and the strength of Earth's magnetic field in the area.
According to a guide published by the Federation of American Scientists, for equipment to be affected by a weapon, the weapon must be above the visual horizon.
The altitude required for this is higher than that of the International Space Station and many satellites that orbit close to Earth. Large weapons could greatly harm satellite operations and communications, as happened during Operation Fishbowl. Damage to orbiting satellites is usually caused by factors other than EMP. In the Starfish Prime nuclear test, most damage was to the satellites' solar panels as they passed through radiation belts created by the explosion.
For explosions in the atmosphere, the situation is more complex. Within the range of gamma ray effects, simple rules no longer apply because the air becomes charged, and other EMP effects occur, such as electric fields caused by electrons separating from air molecules. For a surface burst, gamma rays absorbed by air would limit the range of gamma-ray effects to about 16 kilometers (10 miles). For explosions at high altitudes, where air is less dense, the range of gamma-ray effects would be much greater.
During the Cold War, planners considered nuclear weapons with power between 1 to 10 megatons (Mt) for EMP attacks. This is roughly 50 to 500 times the size of the bombs used in Hiroshima and Nagasaki. Scientists have stated that weapons with power as low as 10 kilotons (kt) can produce a strong EMP.
The strength of the EMP at a fixed distance from an explosion increases, but not as much as the weapon's power. It increases by the square root of the weapon's power. This means that even though a 10 kt weapon has only 0.7% of the energy of a 1.44 Mt test like Starfish Prime, the EMP would be at least 8% as strong. Since the E1 component of EMP depends on gamma-ray output, which was 0.1% of yield in Starfish Prime but can be 0.5% in smaller fission weapons, a 10 kt bomb could be 40% as powerful as the 1.44 Mt Starfish Prime in creating EMP.
In a fission explosion, 3.5% of the energy is prompt gamma rays. However, in a 10 kt explosion, about 85% of these gamma rays are absorbed by the materials around the bomb, leaving only about 0.5% of the energy as gamma rays. In the thermonuclear Starfish Prime test, the fission part of the weapon produced less than 100% of its energy, and the outer casing absorbed about 95% of the gamma rays. Thermonuclear weapons are less effective at creating EMP because the first stage can make the air conductive, which reduces the EMP effect. Small fission weapons with thin cases are more efficient at creating EMP than large thermonuclear bombs.
This analysis applies only to the fast E1 and E2 components of EMP. The slower E3 component, which is similar to a geomagnetic storm, depends more on the total energy of the weapon.
In all EMP events, the electromagnetic pulse is created outside the weapon.
For high-altitude explosions, much of the EMP is generated far from the detonation, where gamma rays from the explosion interact with the upper atmosphere. The electric field from the EMP is very uniform across the large area affected.
According to a standard reference on nuclear weapons effects published by the U.S. Department of Defense, "The peak electric field at Earth's surface from a high-altitude burst depends on the weapon's power, the height of the explosion, the observer's location, and the direction relative to Earth's magnetic field. Generally, the field strength may reach tens of kilovolts per meter over most areas affected by the EMP."
The text also states, "Over most areas affected by the EMP, the electric field strength on the ground would exceed 0.5 E max. For weapons with power less than a few hundred kilotons, this may not be true because the field strength at Earth's tangent could be much less than 0.5 E max."
(E max refers to the strongest electric field in the affected area.)
In other words, the electric field strength across the entire area affected by the EMP is fairly uniform for weapons with high gamma-ray output. For smaller weapons, the electric field may decrease more quickly with distance.
Super-EMP
A super-electromagnetic pulse, also called an "Enhanced-EMP," is a newer type of warfare that uses nuclear weapons to create a much stronger electromagnetic pulse than regular nuclear weapons. These weapons focus on the E1 pulse part of a nuclear explosion, which involves gamma rays, and can produce an EMP strength of up to 200,000 volts per meter. Many countries, including China and Russia, have studied how to build these weapons for many years.
According to a written statement from the Chinese military, China has developed super-EMPs and has talked about using them to attack Taiwan. Such an attack could disable communication and computer systems in Taiwan, making it easier for China to attack directly with soldiers. The Taiwanese military has confirmed that China has these weapons and that they could damage power grids in Taiwan.
Dr. Peter Pry has also discussed the possible effects of a Chinese attack on the United States using super-EMPs. While the United States has nuclear weapons, it has not developed super-EMPs. This makes the U.S. more vulnerable to future attacks because the country depends heavily on computers to manage its government and economy. For example, U.S. aircraft carriers near an area where a super-EMP is used could lose their missiles and communication systems, making it hard for them to contact other ships or land-based controllers.
Since the Cold War, Russia has studied how to design and use EMP bombs. The Soviet Union created a system to send nuclear weapons from low Earth orbit. Russia has also proposed building satellites that could carry EMP capabilities. If used, these satellites could explode up to 100 kilometers (62 miles) above Earth, disrupting electronic systems on U.S. satellites in space. Many of these satellites are important for defense and for warning the United States about possible missile attacks.
Effects
An EMP can cause temporary or permanent damage to electronic devices by creating strong electrical surges. These surges can harm semiconductor components, which are parts of many electronic systems. Damage from an EMP can range from being hard to notice to causing devices to break apart. Even short cables can act like antennas, sending the energy from an EMP to equipment.
Older electronic systems that use vacuum tubes (valves) are usually less likely to be damaged by an EMP compared to newer systems that use solid-state components. Solid-state systems are more vulnerable because they are easily harmed by sudden, strong electrical surges. During the Cold War, Soviet military planes used vacuum tubes for their electronics because solid-state technology was not as advanced, and vacuum tubes were thought to be more reliable during an EMP event.
Vacuum tube systems can still be damaged by an EMP. In 1962, vacuum tube equipment was damaged during EMP testing. A solid-state radio called the PRC-77 survived EMP testing, but an earlier model, the PRC-25, which used a vacuum tube, did not pass the same tests.
Equipment that is turned on during an EMP is more likely to be damaged. A low-energy EMP can still reach the power source, and the entire system can be affected. For example, an EMP might cause a strong electrical path in the power supply, leading to damage. These effects are difficult to predict and require testing to understand risks.
Many nuclear explosions have used aerial bombs. The B-29 planes that dropped nuclear bombs on Hiroshima and Nagasaki did not suffer electrical damage because electrons released by gamma rays stopped quickly in the air below about 10 kilometers (33,000 feet). These electrons were not strongly affected by Earth’s magnetic field.
If the planes had been in the area of intense radiation when the bombs exploded, they might have been damaged by a type of EMP called a radial EMP. This only happens when a bomb explodes at a low altitude, within the severe blast zone.
During Operation Fishbowl, a KC-135 plane flying 300 kilometers (190 miles) from a nuclear explosion experienced EMP disruptions. The plane’s electronics were simpler than modern systems, and it was able to land safely.
Modern planes rely heavily on solid-state electronics, which are very sensitive to EMPs. To protect against EMPs or electromagnetic interference, airline rules now require planes to have high intensity radiated fields (HIRF) standards. This means all parts of the plane must be conductive to block EMP energy. If the plane has no gaps, EMP waves cannot enter the interior. Adding insulation to key computers inside the plane also helps protect against EMPs.
Most cars would likely not be affected by an EMP, even though modern cars use a lot of electronics. This is because car wiring is usually too short to be affected, and the metal frame of a car offers some protection. However, if even a few cars failed due to an EMP, it could cause traffic problems.
Shorter electrical wires are less likely to be damaged by an EMP. Other factors also influence how vulnerable electronics are, so there is no exact length that determines whether a device will survive. Small devices like watches and cell phones are likely to survive an EMP.
After an EMP, electrical charges can build up in wires, but these charges usually do not flow into people or animals. Touching the wires is generally safe.
Very strong EMPs could affect the human body. Possible effects include changes to cells, nerve damage, burns, brain injuries, and temporary memory or thinking problems. These effects would only happen in extreme cases, such as being near the center of a powerful EMP blast and being exposed to large amounts of radiation.
A study found that repeated exposure to EMP pulses caused small leaks in brain blood vessels, which may lead to minor thinking or memory issues. These effects might last up to 12 hours, but they require long exposure times to occur. Since most people would not be exposed for that long, these effects are unlikely. The human body uses chemical signals instead of electrical ones, making it less likely to be affected by EMPs.
In addition to direct harm, a large EMP event could disrupt agriculture. This is because supply chains for farming materials like fertilizers and pesticides might be broken. In areas like Central Europe, this could reduce food production by up to 75%.
Post-Cold War attack scenarios
The United States EMP Commission was formed by the United States Congress in 2001. The commission is officially called the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack.
The commission gathered well-known scientists and technologists to create several reports. In 2008, the commission released the "Critical National Infrastructures Report." This report explains the possible effects of a nuclear EMP on public infrastructure. While the report focused on the United States, much of the information is also relevant to other developed countries. The 2008 report followed a more general report the commission issued in 2004.
In a written statement given to the United States Senate in 2005, an EMP Commission staff member explained:
The EMP Commission supported a global study of scientific and military writings from other countries to examine what foreign nations know about EMP attacks and whether they might plan to use them. The study found that knowledge about EMPs and their military use is widely shared in the international community, as shown in official and unofficial documents. Over the past decade, open sources revealed that information about EMPs and EMP attacks is found in writings from at least Britain, France, Germany, Israel, Egypt, Taiwan, Sweden, Cuba, India, Pakistan, Iraq under Saddam Hussein, Iran, North Korea, China, and Russia.
Many foreign analysts—especially in Iran, North Korea, China, and Russia—see the United States as a possible attacker that might use all types of weapons, including nuclear weapons, in an attack. These analysts believe the United States has plans to use nuclear EMP attacks and might carry them out in many situations.
Russian and Chinese military scientists, in public writings, describe the basic design of nuclear weapons made to create a stronger EMP effect, which they call "Super-EMP" weapons. These weapons, according to these writings, could damage even the most protected U.S. military and public electronic systems.
The United States EMP Commission found that protections against EMPs, which have been known for a long time, are almost completely missing in the public infrastructure of the United States. It also found that many parts of the U.S. military were less protected against EMPs than during the Cold War. In public statements, the Commission suggested making electronic equipment and parts resistant to EMPs and keeping spare parts ready for quick repairs. The United States EMP Commission did not examine other countries.
In 2011, the Defense Science Board published a report about efforts to protect important military and public systems from EMPs and other effects of nuclear weapons.
The United States military services created, and in some cases shared, hypothetical scenarios about EMP attacks.
In 2016, the Los Alamos Laboratory began phase 0 of a long-term study (through phase 3) to research EMPs and plan the strategy for the rest of the study.
In 2017, the U.S. Department of Energy released the "DOE Electromagnetic Pulse Resilience Action Plan." Edwin Boston wrote a dissertation on the topic, and the EMP Commission published "Assessing the Threat from Electromagnetic Pulse (EMP)." The EMP Commission was closed in summer 2017. It found that earlier reports had not fully understood the effects of an EMP attack on the national infrastructure, pointed out problems with communication from the Department of Defense because of classified information, and suggested that the Department of Homeland Security should work directly with the more knowledgeable parts of the Department of Energy instead of seeking guidance from the DOE. Several reports are being made public.
Protecting infrastructure
The issue of protecting important buildings and systems from electromagnetic pulse (EMP) has been carefully studied across the European Union, especially by the United Kingdom.
By 2017, several electricity companies in the United States were part of a three-year research project to understand how high-altitude electromagnetic pulse (HEMP) might affect the U.S. power grid. This study was led by a non-profit group called the Electric Power Research Institute (EPRI).
In 2018, the U.S. Department of Homeland Security introduced a plan called the Strategy for Protecting and Preparing the Homeland against Threats from Electromagnetic Pulse (EMP) and Geomagnetic Disturbance (GMD). This was the first plan from the department that used teamwork and long-term strategies to protect important systems and prepare for major electromagnetic events. How much progress has been made is explained in the EMP Program Status Report.
NuScale, a company in Oregon, United States, that makes small nuclear reactors, has designed their reactor to be safe from EMP.
In fiction and popular culture
By 1981, many articles about nuclear electromagnetic pulse (EMP) in magazines and newspapers helped spread information about EMP to the general public. Since then, EMP has appeared in many fictional stories and other parts of popular culture.
Some movies and TV shows often show EMP effects in ways that are not accurate, which can lead to confusion for people, including experts. To address this, the United States Space Command asked science educator Bill Nye to create and present a video titled "Hollywood vs. EMP." The video aimed to help people understand the real effects of EMP and avoid mistakes in how it is shown in fiction. This video is not available to the public.