What Is an EMP Attack? What It Would Do and How to Prepare

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An EMP attack means deliberately using a burst of electromagnetic energy to damage or disrupt electronics and the power grid over a wide area. The usual example is a nuclear weapon exploded high above the earth. According to the federal EMP Commission, the pulse would cover the whole region within line of sight of the explosion, which could mean several states. The effect on the ground would be electrical rather than explosive: damage to power and electronic systems. This page explains what an EMP is, the different kinds, what tests and federal guidance say it would actually affect, and where to go next to prepare a household.

Short version: the main danger from an EMP is a long, wide-area loss of electricity and the services that depend on it, such as water, fuel, communications and refrigeration. It is not instant destruction of every device you own. Preparing for an EMP looks very similar to preparing for a long blackout, with a few extra steps for spare electronics.

What is an EMP?

An electromagnetic pulse is a short, intense burst of electromagnetic energy. Long wires, power lines and antennas pick it up and turn it into surges of current and voltage that can upset or damage the electronics connected to them. Lightning does something similar on a small scale. Federal guidance groups man-made EMP threats into three kinds:

• High-altitude EMP (HEMP): a nuclear detonation high in the atmosphere. The federal EMP Protection and Resilience Guidelines call it the most serious form “due to the potential multi-state to continental extent of impacts.”
• Source-region EMP (SREMP): from a nuclear detonation at or near the ground. Its damage is limited to a city-wide or regional area, but it reaches equipment far beyond the range of the blast itself. Anyone near such an explosion faces blast and fallout first. Our nuclear emergency guide covers what to do.
• Intentional electromagnetic interference (IEMI): non-nuclear radio-frequency weapons aimed at a specific target, such as a data center or grid substation. The effects are local or regional.

E1, E2 and E3: the three parts of a nuclear EMP

A high-altitude nuclear EMP arrives in three overlapping parts, each threatening different things:

• E1 (early): rises in nanoseconds and is over in under a microsecond. It mainly threatens electronics connected to cables and antennas, such as telecommunications, computers, control systems and relays.
• E2 (intermediate): lasts from about a microsecond to a second. It is similar to lightning, and lightning protection helps against it, so federal guidance treats it as the smaller risk.
• E3 (late): lasts from seconds to a couple of minutes. It threatens very long conductors, especially high-voltage transmission lines and the large transformers they connect.

E3 is why the power grid is the central concern. The federal EMP Commission’s 2008 report on critical infrastructure explains the mechanism. E3 drives “minute-long ground-induced currents of hundreds to thousands of amperes” through long transmission lines, enough to damage major grid components. Large transformers are “probably the hardest to replace quickly.” The commission estimated that replacing irreparably damaged large transformers would take one to two years, plus manufacturing and transport backlogs (report pages 33 and 51).

Solar storms: the natural version

A severe geomagnetic storm from the sun produces an effect much like E3, but without E1 or E2. The federal guidelines cite two examples:

• Carrington Event (1859): it electrified telegraph lines.
• March 1989 storm: it collapsed the Hydro-Québec grid “in under two minutes,” leaving more than six million people without power for nine hours. The EMP Commission adds that the same storm damaged a large transformer at a New Jersey nuclear plant beyond repair. A spare happened to be available; otherwise, replacement would normally have taken about a year (report page 42).

There is one practical difference. A geomagnetic storm usually comes with warning: the guidelines list 18 to 72 hours of strategic warning and 20 to 45 minutes of tactical warning. A nuclear EMP may come with none. NOAA’s Space Weather Prediction Center issues geomagnetic storm watches and warnings.

What an EMP would and wouldn’t do

Much EMP writing assumes everything electronic dies instantly. The evidence is more nuanced:

• The grid: this is the real vulnerability. Long lines collect E3, control systems are exposed to E1, and the hardest parts take the longest to replace.
• Water, fuel and refrigeration: these depend on that power. The commission noted that service stations “need electricity to power pumps” and that few have backup generators, and that emergency generators generally hold less than 72 hours of fuel.
• Cars and trucks: in the commission’s tests of 37 cars and 18 trucks, vehicles that were switched off showed no effects. A minority of running vehicles stalled, and most of those restarted. Crashes caused by stalls and failed traffic lights were the main concern. Our guide to the most dangerous places in an EMP covers the numbers and their limits.
• Phones, radios and small devices: the federal guidelines say small electronics without cables are “relatively resilient,” but the networks they rely on are not. A working phone with no signal is a likely outcome.
• Aircraft: not tested. The commission couldn’t confirm flight safety, but said lightning protection may provide it and that aircraft would be directed to land.

How likely is an EMP attack?

No public source gives a credible probability, and we don’t invent one. What exists are government assessments of vulnerability and consequences, such as the EMP Commission reports and the federal guidelines above. The commission calls a high-altitude EMP “one of a small number of threats that can hold our society at risk of catastrophic consequences,” and federal guidance exists to help infrastructure operators harden against it. Neither offers a probability. Claims that a specific percentage of the population would die don’t come from those assessments. For a household, the useful question is not “how likely is an EMP?” but “could we manage two weeks or more without power?” A long outage from storms, grid failure or a solar storm is far more common, and the same preparation covers most of it.

How to prepare a household

In order of value:

1. Prepare for a long power outage. Water first, then food that needs no refrigeration, safe light and heat, and a plan for medicines and medical devices. Our household power-outage planner, emergency water calculator and food supply calculator turn this into numbers for your home.
2. Keep a battery AM/FM/NOAA radio. Federal guidance describes battery radios as “relatively resilient to EMP” and possibly the main way to hear official instructions. Compare models in our hand-crank emergency radio guide, or browse battery and crank NOAA weather radios on Amazon.
3. Unplug spares, then store them properly. Connected cables are the main path for the pulse. Our guide to protecting electronics from an EMP compares foil, Faraday bags and metal containers against federal guidance and published measurements.
4. Make a family plan that doesn’t need phones. Agree on a meeting place and an out-of-area contact, and write them on our printable emergency contact card. Our guide to communications after an EMP covers which radios may help.
5. Know what you would do in the first three days. Our step-by-step plan for the first three days after an EMP sequences these steps hour by hour and day by day.

Why this page changed

Earlier versions of this page leaned on 2005-era news articles. They suggested cake boxes and filing cabinets as Faraday boxes and do-it-yourself circuit hardening with diodes, and claimed most vehicles since the 1960s would be affected. Several of their reference links no longer work. Federal guidance and the EMP Commission’s own tests don’t support those claims, so we rebuilt the page around them.

How we researched this guide

Research method: This is a research-led summary of published government material. It is not personal experience, testing or engineering certification. Definitions, warning times and the solar-storm history come from the CISA-hosted EMP Protection and Resilience Guidelines (version 2.2, February 2019). Grid, transformer, fuel and vehicle findings come from the EMP Commission’s Critical National Infrastructures report (April 2008). Page numbers above are the report’s printed page numbers. We checked both on November 8, 2026. Nobody can predict exactly how a real event would affect a specific device, vehicle or region. We left out casualty and probability estimates because no credible public source supports them.

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