What Is an EMP? A Plain-English Guide to Electromagnetic Pulses

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What is an EMP? An electromagnetic pulse is a sudden burst of electromagnetic energy strong enough to damage power lines, communications and electronic equipment. The Department of Homeland Security describes the man-made version as a burst produced by a nuclear explosion in the atmosphere. Nature makes a cousin of it too: severe solar storms that disturb Earth’s magnetic field.

EMP shows up in a lot of movies and a lot of scary posts online. If you’ve ever typed “what is an EMP” into a search bar after a frightening headline, this plain-English explainer is for you. It sticks to what government sources actually say: the types of EMP, what one could affect, and how realistic the risk is. If you are ready for protection steps, we link to our detailed guides along the way.

What is an EMP, in plain English?

The simplest answer to what is an EMP: think of it as a giant, extremely fast power surge that arrives through the air instead of through the wall outlet. Long wires such as power lines act like antennas and pick up the energy, then carry it into whatever is connected to them. Sensitive electronics can also be hit directly.

DHS says EMP and its natural counterpart, geomagnetic disturbance, “can be caused by man or nature” and can “disrupt and permanently damage electrical components and entire systems” in most critical infrastructure sectors.

Nuclear EMP vs. natural EMP

Nuclear EMP (HEMP)

When people ask what is an EMP attack, they usually mean the version officials worry about most: a high-altitude electromagnetic pulse, or HEMP. It comes from a nuclear weapon detonated high in the atmosphere or in near-Earth space. According to the Congressional Research Service, U.S. and Soviet high-altitude tests in the late 1950s and early 1960s suggested these effects could damage electrical grids, communications and electronics many hundreds of miles from the blast. The 1963 Partial Test Ban Treaty ended those tests.

A HEMP arrives in three parts, labeled E1, E2 and E3:

• E1 (fastest): may directly hit sensitive electronics or travel into equipment through control cables and other conductors.
• E2 (middle): similar to lightning. Many scientists believe existing lightning protection is enough for it, though some warn E1 may damage that protection first.
• E3 (slowest): may push currents through long-distance transmission lines that can damage or disrupt large power transformers.

Natural EMP: solar storms

The sun throws off huge clouds of charged particles called coronal mass ejections. When one hits Earth, it can cause a geomagnetic disturbance, which CRS says is comparable in some ways to the slow E3 part of a nuclear EMP.

• 1859, the Carrington Event: the strongest geomagnetic storm on record. The National Weather Service says excess currents on telegraph lines shocked technicians and sometimes set equipment on fire.
• 1989, Quebec: a solar storm left six million people without power for nine hours, according to NOAA.

The difference that matters for families: a solar storm is a natural event that will happen again at some point, and NOAA’s Space Weather Prediction Center issues watches and warnings for them. A nuclear EMP attack would require a nuclear weapon and the intent to use it.

Smaller, non-nuclear devices

CRS also notes other deliberate electromagnetic threats, such as battlefield EMP weapons and improvised devices powered by conventional explosives. CRS treats these separately, and CISA calls the high-altitude nuclear version the most concerning type because it could damage large sections of the grid.

What would an EMP attack affect?

CISA says EMP and severe solar storm events could damage the electrical grid, communications equipment, water and wastewater systems and transportation, with effects spreading to other sectors and regions.

The grid is the core concern because almost everything else runs on it. The National Weather Service warns that a major outage can cascade into:

• Water and wastewater systems
• Perishable food and medicine
• Heating, cooling and lighting
• Phones, computers, GPS and satellite networks
• Public transportation and fuel distribution

Large power transformers are a special worry. CRS notes they require long lead times to manufacture and customize, so replacing damaged ones would not be quick.

What about cars, phones and other small electronics? Honest answer: the specifics are debated. CRS says that while there is broad agreement HEMP poses a risk to the grid, there is disagreement over specific hazard characteristics and the level of risk. Our guides on EMP protection for electronics and EMP protection for your car cover the practical side.

How realistic is the EMP risk?

Here is the calm version. CISA calls extreme EMP and solar storm events “low probability/high consequence scenarios.” That means they are unlikely in any given year, but serious enough that the government plans for them. Executive Order 13865, signed March 26, 2019, put DHS in charge of coordinating national resilience to electromagnetic pulses.

CRS also points out real scientific uncertainty. The basic theories behind HEMP are well established, but many of the complex physical effects are not fully understood, and experts disagree about how much hardening is needed.

So what is an EMP risk worth to a family? Not panic, and not a bunker. The practical takeaway is that an EMP, a huge solar storm, a cyber attack and a bad ice storm all end the same way at home: a long power outage. Preparing for that covers most of the risk.

How to prepare without overthinking it

Once you have the answer to “what is an EMP,” the prep list looks a lot like any long-outage plan.

1. Water first. Ready.gov recommends one gallon per person per day for several days. Add a filter that works without power, such as the gravity-fed Alexapure Pro Water Filtration System.
2. Food that needs no fridge. The 1-Week Food Supply Ammo Can provides 14,860 calories in a grab-and-go ammo can, with a listed shelf life of up to 25 years when stored properly.
3. Light and communication. Flashlights, spare batteries and a battery or hand-crank radio.
4. Protect a few key electronics. Many preppers store a spare radio, flashlight or small device in a Faraday container. See our EMP protection guide for how.
5. Backup power. Some solar generators now market EMP features. The Grid Doctor 3300 Solar Generator includes what its maker calls EMP Intercept Technology, which the maker says is designed to help protect connected electronics from surges, lightning events and electromagnetic disturbances. We have not seen independent test data, so treat it as the maker’s claim.

For the full outage checklist, see our power outage emergency kit guide.

Worried about a longer, wider outage? Our power grid failure guide explains the causes and how to prepare in layers.

Why are planners talking about 90 days? Our FORTRESS America explained guide separates what the Pentagon confirmed from what was only reported.

For more on this, see our guide: Faraday Bag Guide.

Frequently asked questions

Can an EMP happen naturally?

Yes, in a sense. Severe solar storms cause geomagnetic disturbances that can damage power systems. The 1989 Quebec blackout is the best-known example.

Has an EMP ever happened?

Nuclear EMP effects were observed during high-altitude weapons tests in the late 1950s and early 1960s, before the 1963 Partial Test Ban Treaty. Natural geomagnetic storms happen regularly, though extreme ones are rare.

Is an EMP attack dangerous to people directly?

The government sources cited here focus on damage to equipment and infrastructure, not on direct harm to people. The bigger human risk comes from losing power, water, heat and communications over a long period.

What is an EMP’s biggest threat to my family?

A long power outage and everything that comes with it. That is why water, shelf-stable food, light and safe heat are the best first steps.

The bottom line

What is an EMP? A powerful burst of electromagnetic energy, either man-made from a high-altitude nuclear blast or natural from a severe solar storm, that can damage the grid and electronics. It is a low-probability, high-consequence risk. Prepare for a long outage, protect a few key electronics, and you have covered most of what an EMP could throw at you.

Sources: DHS Science and Technology: EMP/GMD, CISA: Electromagnetic Pulse and Geomagnetic Disturbance, Congressional Research Service R47339, National Weather Service: Space Weather, NOAA NESDIS, NOAA: Space Weather, Ready.gov. Product details are from My Patriot Supply product pages as of October 27, 2026.