The DEFCON Warning System

Ongoing Geointel and Analysis in the theater of nuclear war. Established 1984

EMP Effects: Facts, Myths, and the Unknown

EMP Effects

Facts, Myths, and the Unknown

A lot has been said during the past year about EMP – ElectroMagnetic Pulse – usually in conversations involving North Korea, officially called the Democratic People’s Republic of Korea, or DPRK.  Statements range from one extreme: EMP will destroy everything electronic around the globe, sending the planet back to the Stone Age, to the other extreme: EMP effects are greatly exaggerated and nothing will happen other than a few blown fuses.  As is frequently the case, both extreme viewpoints are incorrect, and the truth lies between them.

 This article will delve into the details of EMP, using layman’s terms as much as possible, to separate fact from fiction.  At the end of the article, there will be a hypothetical scenario, describing an EMP event from the viewpoint of an average American family.

First, a basic definition and introduction to EMP:  An Electromagnetic Pulse is a large burst of energy,  usually associated with the detonation of a nuclear weapon, that is capable of affecting electronic circuits and devices within range of the detonation.  EMP effects were observed during the testing of early atomic and thermonuclear weapons by both Soviet and American scientists.  A lot of this information was naturally classified by both sides, but has recently been declassified and made available to the public.  When countries stopped conducting atmospheric tests of nuclear weapons, research into EMP continued through laboratory testing and computer simulations.

FACT:  An Electromagnetic Pulse consists of three distinct components, defined by factors such as arrival time, duration, wavelength, and amplitude.  These components are designated by the labels of E1, E2, and E3.

 To understand how EMP affects electronic circuits, a very basic understanding of these elements is required.  The easiest way to do that is to begin with the simplest component: E2.  The E2 component is best compared to a bolt of lightning.  It is similar in duration, amplitude, and wavelength to lightning bolts that strike the planet thousands of times each day.  E2 is the least destructive of the three components simply because most modern surge suppressors and voltage regulators, having been designed to protect sensitive electronics from lightning, can compensate for its effects.

The E1 component arrives milliseconds before E2, and can best be described as a bolt of lightning on steroids.  It is much more intense than E2, with a faster, shorter waveform.  Some higher-end protective equipment is advanced enough to handle this burst of energy.  Less expensive, consumer grade surge suppressors are not designed to compensate quickly enough, however, which can result in both the protective systems and the sensitive electronics connected to them being damaged.  This component can affect televisions, computers, and other standard household items connected to typical electrical wiring.

The E3 component is the last to arrive, and can last several seconds to several minutes.  E3’s waveform is the longest, and is therefore easily conducted through long wires, such as telephone lines and high tension power lines.  The E3 component would impact utility companies, power substations, and other portions of the local, state, or national power infrastructure, depending on severity.  Vehicles, houses, cell phones, and other electronics would not be susceptible to the E3 pulse due to the length of conductors required.  Therefore, E1 and E2 would affect mostly residential and consumer grade electronics, while E3 is going to affect industrial electrical equipment.

So, in the event of a high altitude EMP (HEMP) event, the timing and effects of the pulse would occur in the following manner:

The E1 component arrives almost instantly, traveling at 90% the speed of light.  Any electronic devices not specifically shielded against EMP or not protected by expensive surge suppression equipment will be susceptible to damage similar in nature to a powerful lightning strike.  This does not mean they will be damaged, but they can be.

Several milliseconds later, the E2 component arrives.  Any protective equipment in place that survived the E1 component might now be susceptible to the E2 component, so electronic devices that were not damaged by E1 might possibly be damaged by E2.

A full second later, E3 arrives, lasting several minutes, travelling through long phone lines and high tension power lines that cross the country for hundreds of miles.  While E1 and E2 damage has been restricted primarily to devices with integrated circuits (ICs), E3 is capable of overloading, damaging, or destroying large transformers and other power delivery equipment that is part of the national power grid.  Power outages can almost be guaranteed.

 FACT:  Repairing damage to the national power grid caused by an EMP event would take years to complete.

 Large transformers – 345 kilovolts or higher – are extremely large and expensive to manufacture and ship.  Spare units are few and far between, certainly not abundant enough to replace on a national scale.

“There are about 2,000 transformers rated at or above 345 kV in the United States with about 1 percent per year being replaced due to failure or by the addition of new ones. Worldwide production capacity is less than 100 units per year and serves a world market, one that is growing at a rapid rate in such countries as China and India. Delivery of a new large transformer ordered today is nearly 3 years, including both manufacturing and transportation. An event damaging several of these transformers at once means it may extend the delivery times to well beyond current time frames as production is taxed. The resulting impact on timing for restoration can be devastating. Lack of high voltage equipment manufacturing capacity represents a glaring weakness in our survival and recovery to the extent these transformers are vulnerable.”

Page 27 – Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack, CRITICAL NATIONAL INFRASTRUCTURES, April 2008

“EMP effects are the type of damage which is seen with transformers in the core of geomagnetic storms. The geomagnetic storm, in turn, is a very tepid, weak flavor of the so-called slow component of EMP. So when those transformers are subjected to the slow component of the EMP, they basically burn, not due to the EMP itself but due to the interaction of the EMP and normal power system operation. Transformers burn, and when they burn, sir, they go and they are not repairable, and they get replaced, as you very aptly pointed out, from only foreign sources. The United States, as part of its comparative advantage, no longer makes big power transformers anywhere at all. They are all sourced from abroad. And when you want a new one, you order it and it is delivered – it is, first of all, manufactured. They don’t stockpile them. There is no inventory. It is manufactured, it is shipped, and then it is delivered by very complex and tedious means within the U.S. because they are very large and very massive objects. They come in slowly and painfully. Typical sort of delays from the time that you order until the time that you have a transformer in service are one to 2 years, and that is with everything working great. If the United States was already out of power and it suddenly needed a few hundred new transformers because of burnout, you could understand why we found not that it would take a year or two to recover, it might take decades, because you burn down the national plant, you have no way of fixing it and really no way of reconstituting it other than waiting for slow-moving foreign manufacturers to very slowly reconstitute an entire continent’s worth of burned down power plant.”

Testimony of Dr. Lowell Wood, Senate Hearings 109-30, March 8, 2005

MYTH:  Larger yields on nuclear weapons are required to produce more powerful, more damaging EMPs.

The yield of a nuclear weapon has much less to do with the strength of the resulting EMP than most people realize.  It is, in fact, very possible for a device in the kiloton range to produce a much stronger EMP field than a device in the megaton range, depending on its design and where it is detonated.

Thus, low yield bombs at somewhat lower altitudes than 400 km can produce peak EMP fields that exceed those from the 1962 high altitude thermonuclear tests, while still affecting vast areas. Single stage (fission) weapons in some cases produce a larger EMP than high-yield two-stage thermonuclear weapons, mentioned above. Weapon designs that use a minimal tamper, a minimal shell of TNT for implosion, or a linear implosion system, and a minimal outer casing, can maximise the fraction of the prompt gamma rays which escape from the weapon, enhancing the EMP.

Declassified Effects of Nuclear Weapons and Other Threats: Minimizing Weapons Effects on Civilians: EMP Radiation from Nuclear Space Bursts in 1962
March 23, 2014

While yield is definitely a factor in determining EMP strength, other factors such as weapon design, strength and orientation of the Earth’s geomagnetic field at the exact moment of detonation, as well as the altitude and latitude of detonation, play a significant role in the strength of an EMP, and therefore the amount of damage it is capable of causing.

The American 1.4 megaton Starfish test at 400 km (altitude), on 9 July 1962, induced large EMP currents in the overhead wires of 30 strings of Oahu streetlights, each string having 10 lights (300 streetlights in all). The induced current was sufficient to blow the fuses. EMP currents in the power lines set off ‘hundreds’ of household burglar alarms and opened many power line circuit breakers. On the island of Kauai, EMP closed down telephone calls to the other islands despite the 1962 sturdy relay (electromechanical) telephone technology, by damaging the microwave diode in the electronic microwave link used to connect the telephone systems between different Hawaiian islands (because of the depth of the ocean between the islands, the use of undersea cables was impractical). If the Starfish Prime warhead had been detonated over the northern continental United States, the magnitude of the EMP would have been about 2.4 times larger because of the stronger magnetic field over the USA which deflects Compton electrons to produce EMP, while the much longer power lines over the USA would pick up a lot more EMP energy than the short power lines in Hawaiian islands, and finally the 1962 commonplace electronic ‘vacuum tubes’ or ‘triode valves’ (used before transistors and microchips became common) which could survive 1-2 Joules of EMP, have now been completely replaced by modern semiconductor microchips which are millions of times times more sensitive to EMP (burning out at typically 1 microJoule of EMP energy or less), simply because they pack millions of times more components into the same space, so the over-heating problem is far worse for a very sudden EMP power surge (rising within a microsecond). Heat can’t be dissipated fast enough so the microchip literally melts or burns up under EMP exposure, while older electronics can take a lot more punishment. So new electronics are a million times more vulnerable than in 1962.

A Quick Look at the Technical Results of Starfish Prime, 1962, pages A1-27

MYTH:  An EMP burst will short out computer systems on all late-model vehicles with modern electronics, rendering them incapable of being started.

EMP is capable of damaging electrical systems in modern vehicles. but not all vehicles will be affected, and those that are will not all be affected in the same way.  In laboratory testing, most vehicles were affected in one way or another, but were still capable of being started and driven.

“We tested a sample of 37 cars in an EMP simulation laboratory, with automobile vintages ranging from 1986 through 2002.  The most serious effect observed on running automobiles was that the motors in three cars stopped at field strengths of approximately 30 kV/m or above. In an actual EMP exposure, these vehicles would glide to a stop and require the driver to restart them. Electronics in the dashboard of one automobile were damaged and required repair. Based on these test results, we expect few automobile effects at EMP field levels below 25 kV/m. Approximately 10 percent or more of the automobiles exposed to higher field levels may experience serious EMP effects, including engine stall, that require driver intervention to correct.”

“Five of the 18 trucks tested did not exhibit any anomalous response up to field strengths of approximately 50 kV/m. Based on these test results, we expect few truck effects at EMP field levels below approximately 12 kV/m. At higher field levels, 70 percent or more of the trucks on the road will manifest some anomalous response following EMP exposure. Approximately 15 percent or more of the trucks will experience engine stall, sometimes with permanent damage that the driver cannot correct.”

Pages 115 – 166 – Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack, CRITICAL NATIONAL INFRASTRUCTURES, April 2008

These tests confirm that while severe damage to a vehicle by an EMP is possible, it is certainly not the doomsday scenario that has been portrayed in popular fiction.  In the event of an EMP event, most vehicles will probably stall, requiring nothing more than being restarted by the driver.  Some vehicles may sustain damage to non-critical systems, such as digital dashboard displays or radio systems, but they can still be started and driven normally.  Some vehicles might require minor repairs to start, possibly as simple as disconnecting the battery for several minutes and reconnecting it.  And a few vehicles will probably sustain damage severe enough to render them inoperable, at least for the short term.

Essentially, there is no way of knowing which vehicles will be affected in what manner, but statistically, the odds of any one specific vehicle being damaged beyond repair are relatively low.

MYTH:  All cell phones and portable radios will be destroyed by EMP.

Portable electronic devices that are not plugged into the power grid at the instant of an EMP will most likely survive it.  The electrical pulses require a conductor through which to travel, such as an antenna, power line, phone line, or any other physical conductive material, and those conductors need to be of certain length to pick up on the wavelength of each pulse.  Devices such as cell phones, MP3 players, tablets, and other small, portable electronics have antennae built into them but they are insufficient length to pick up on the electrical energy emitted by an EMP burst.  Therefore, most of them will remain functional after an EMP, although they will be incapable of communicating with cell towers, which most certainly will be damaged.  The only exception will be devices that are plugged into a power source while charging.  Those devices will be subject to damage by pulses coming through the electrical wiring of the building.

In the 1958 Teak test the 3.8 Mt bomb exploded 77 km directly over Johnston Island, producing a massive EMP, but again no portable radios were destroyed. In the 1962 Starfish test, and also three Russian tests, lots of things were damaged but only if they were connected to long wires. Portable radios working off batteries were okay. Although modern microchips are up to a million times more sensitive than valve/vacuum tube radios, the aerial size in a UHF cellular phone is really tiny compared to the long aerials of old HF valve/vacuum tube radios, so things balance out. I agree that anything you can fit in your pocket is not likely to be damaged by EMP, unless it is being recharged from the mains when the bomb exploded.  Batteries could only be damaged if they were being recharged at the time. However, a safe, working cellular radio wouldn’t be any use to you if the network (running from mains electricity) was zapped by EMP!

Declassified Effects of Nuclear Weapons and Other Threats: Minimizing Weapons Effects on Civilians: EMP Radiation from Nuclear Space Bursts in 1962
March 23, 2014

 MYTH:  Airplanes will fall from the skies after an EMP detonation.

This is one of the classic myths perpetuated by science fiction movies, usually involving airliners crashing to the earth in a flat spin after an EMP event of some kind.  This is not to say airborne planes won’t be affected or there won’t be some rough landings and potential crashes.  An EMP event will certainly damage any planes not specifically shielded against EMP, such as Air Force One and other military aircraft.  However, some of the planes will still be able to be controlled by the pilots even if the computer controls are destroyed.  Even if the engines completely stall and are unable to be restarted, most commercial airliners have a decent glide ratio, and the pilots will be able to control the plane through a slow descent, hopefully to a soft belly landing in a field somewhere.  There will certainly not be thousands of planes spinning out of control and plummeting to the ground as has been popularized in modern fiction.


A high-altitude nuclear detonation above the central United States will certainly not go unnoticed. There will be power outages; electrical devices will be damaged; cars might behave strangely; and any planes airborne at the time had better have some pretty experienced pilots at the controls. However, it will not be a complete return to the Stone Age for the entire country.  Below is a timeline of a hypothetical EMP event over the United States as witnessed by an average American family in Iowa.  For the purposes of this timeline, the EMP event is singular, and will not precede a nuclear attack, although this is certainly a possibility in reality.  However, since the purpose of this article is to dispel myths about EMP specifically, the specter of nuclear war is being removed from the story.

Home of John and Mary Williams

February 19, 2020

Lake City, Iowa

08:00:00.00   Unknown hostiles launch a missile carrying a stolen 80 kiloton warhead from a cargo container aboard a ship in the Gulf of Mexico.  It follows a ballistic trajectory due North.

08:15:00.00   The warhead detonates 300 miles above Nebraska, creating an Electromagnetic pulse that blankets most of the Continental United States.

08:15:00.10   The E1 Pulse arrives. Some electronics in John and Mary’s house are damaged, but not all.  John’s cell phone was already unplugged from its charger and is still working, but Mary’s was charging at the time of the detonation and is now inoperable.  Several devices, such as their microwave oven, clock radios, and other relatively inexpensive electronics are damaged and no longer working.  However, all the components of their new entertainment system, which was protected by an expensive surge suppressor, are still functional.  There is still electrical power supplied to the house and the neighborhood.  For the moment.

08:15:00.25   The E2 pulse arrives, largely unnoticed.  The surge suppressor protecting the home entertainment system is unable to withstand this second surge so quickly after the first one, and is irreparably damaged.  The devices plugged into it, however, still work.

08:15:30.00   The E3 Pulse arrives, having traveled through miles of power lines, blowing up transformers and damaging substations across the entire state. Power for the neighborhood goes out. However, backup generators kick in, providing temporary power to hospitals and other critical services. Some places still have power from the grid, at least temporarily.

08:18:00.00   The E3 Pulse ends.  More transformers explode across the country.  250 million Americans are without electrical power.  There are cities and towns with partial power on the outside fringes of the country where the EMP field was weakest, but the grid is severely damaged.

08:19:00.00   Emergency dispatch centers are overwhelmed with 911 calls, but only from people with old style landline phones.  Cellular service and VOIP phones have no connection.  John discovers his cell phone works, but he has no signal to place calls or send text messages.

08:20:00.00   Some structure fires have broken out throughout the city, mostly due to the E2 pulse hitting buildings with improperly grounded electrical wiring. Firefighting services are stretched thin and dispatching capabilities are limited.

08:25:00.00   John has started up a portable generator and is able to provide temporary electrical power to undamaged devices in the house.  John turns on the television, but his cable service is dead.  He switches the television to antenna mode and picks up a very low-power broadcast from a TV station in Des Moines.  The Emergency Alert System has been activated, and John learns that the entire country has been affected by the EMP burst.

08:30:00.00   John discovers that his 2016 SUV starts up, but the digital dashboard display is dead, as is the radio.  Mary’s 2018 sedan doesn’t start right away, but finally starts after John disconnects the battery for a few minutes and reconnects it.  Other than that, her car appears undamaged.

08:35:00.00   John drives to the gas station a few blocks away, but without power, the gas cannot be pumped from the underground storage tanks.  A huge line has formed inside with people purchasing whatever items they can with cash.  Most ATMs and credit card machines do not work, and those that do cannot connect to anything.  Digital currency transactions are dead.

08:45:00.00   John returns home and he and Mary continue to watch the television and listen to the radio for any information they can find.  A few neighbors arrive at their house trying to obtain information as well.

10:00:00.00   John and Mary, as well as most of their neighborhood, now know that a nuclear weapon detonated in space above the United States is responsible for the ongoing situation, and they are beginning to realize the extent of the damage and the long-term impacts.  John has enough fuel in storage cans and the two vehicles to keep his generator running for about a week.  The weather is cold, so they are using their fireplace for heat.  Fortunately, John keeps a decent supply of firewood on hand.

12:00:00.00   The residents of John and Mary’s neighborhood have a meeting to discuss options. They all agree to share resources.  John and Mary trade food, water, and firewood to other residents who have fuel, but no generators, extending the use of their generator by another two weeks if they do not use it continuously.  They allow neighbors to tap into their generator when they run it.

EMP + 30 Days        Power is still out in Lake City.  Spring has arrived, allowing the residents of John and Mary’s neighborhood to spend more time outside.  Hunting and fishing, as well as scavenging for supplies in surrounding towns has become routine, and residents sent to scout surrounding communities with what little fuel the community has left return with some badly needed supplies.

 EMP + 90 Days        Power is still out in Lake City, but the situation has become less dangerous with the arrival of warmer weather.  Residents learn that Sioux City and Des Moines have limited power in some sections of each city.

EMP + 180 Days     Power is still out in Lake City.  Regular supply runs to surrounding communities, Sioux City and Des Moines have allowed the neighborhood to begin to stockpile for the upcoming winter.

EMP + 1 Year           Power is still out in Lake City.  Some residents of John and Mary’s neighborhood have left to search for better conditions, leaving some houses empty.  Bigger cities are experiencing problems with crime and most people decide it is safer to remain in a smaller town.

EMP + 2 Years         Capitol cities across the country begin to receive replacement parts for power plants and other portions of the power grid.  These parts had to be manufactured overseas and shipped to the United States.  Progress is slow due to the lack of power across 85% of the country.

EMP + 3 Years         Power is still out in Lake City, but power has been restored to 67% of Des Moines.  Crime starts to decline and supply runs from Lake City to Des Moines become safer and more productive.

EMP + 4 Years         A large generator has been obtained for Lake City from the government in Des Moines, allowing the gas stations to pump gas on a limited basis.  Fuel tankers begin to arrive to fill the underground tanks that have been empty for almost 4 years.

EMP + 5 Years         Power has been restored to most sections of major cities.  Semi trucks and tankers are making regular deliveries to Lake City.

EMP + 10 Years      The United States has fully recovered and is back to pre-EMP status.  The country’s population has fallen to under 150 million due to deaths from exposure, hunger, crime, and disease.  The new power grid has been rebuilt to withstand EMP, as well as hardened against cyberattacks.


The preceding hypothetical situation is probably a reasonable scenario in the event of an EMP event affecting the continental United States, based on currently available information on EMP and its effects.  Obviously, events could potentially be better or worse, depending on variables too numerous to detail here.  What can be said for sure is that an EMP event as described above will not send the country – or the planet – back to the Stone Age for generations.  Nor will it be a non-event where nothing happens and daily life continues as before with no damage.  Reality, as usual, lies somewhere in the uncertain murky middle ground between these two extremes.  Unfortunately, we won’t know what that reality actually is until it happens.  Those who are informed and prepared will be best situated to navigate the hazards of that unknown reality.

The DEFCON Warning System is a private intelligence organization which has monitored and assessed nuclear threats against the United States by national entities since 1984. It is not affiliated with any government agency and does not represent the alert status of any military branch. The public should make their own evaluations and not rely on the DEFCON Warning System for any strategic planning. At all times, citizens are urged to learn what steps to take in the event of a nuclear attack.

Ongoing Geointel and Analysis in the theater of nuclear war.

© 2023 The DEFCON Warning System. Established 1984.

The DEFCON Warning System is a private intelligence organization which has monitored and assessed nuclear threats by national entities since 1984. It is not affiliated with any government agency and does not represent the alert status of any military branch. The public should make their own evaluations and not rely on the DEFCON Warning System for any strategic planning. At all times, citizens are urged to learn what steps to take in the event of a nuclear attack.