Electromagnetic pulse (EMP)

On March 13, 1989, a solar storm hit Earth. Within 90 seconds, the entire Hydro-Québec power grid collapsed. Nine million people lost electricity for nine hours. Transformers overheated, circuit breakers tripped in cascade, and the damage extended across the northeastern United States.

That was a moderate solar event — a geomagnetic storm rated roughly one-third the intensity of the 1859 Carrington Event, which remains the most powerful on record. If the Carrington-class solar eruption that narrowly missed Earth on July 23, 2012 had arrived a week earlier, it would have intersected the planet's orbit directly.

Electromagnetic pulse is the sudden burst of electromagnetic energy that disrupts or destroys electronic and electrical equipment. Two sources create threats relevant to preparation: natural solar events (geomagnetic storms) and nuclear detonations above the atmosphere. Their effects differ in important ways, and so does the preparation.

Solar EMP (geomagnetic storms)

The sun periodically ejects massive clouds of magnetized plasma called coronal mass ejections (CMEs). When a powerful CME strikes Earth's magnetic field, the interaction induces electrical currents in long conductors — power lines, pipelines, railroad tracks — and overloads the transformers that regulate the grid.

The 1989 Quebec storm demonstrates the vulnerability: a nine-hour outage for nine million people, damaged transformers across the northeastern U.S., and disrupted satellite operations. A Carrington-class event would be orders of magnitude larger. Modern power grids, which have far longer transmission lines than 1989 systems, are more vulnerable, not less.

Critical damage in a major solar EMP comes from geomagnetically induced currents (GICs) in the grid infrastructure. High-voltage transformers — the massive units that step voltage up and down at substations — are the primary failure point. These transformers are custom-built, weigh up to 400 tons (360 metric tons), and have lead times of 12 to 18 months for replacement. A storm that damages hundreds of them simultaneously would extend the recovery timeline from days to years.

Your personal electronics — phones, laptops, radios — are less vulnerable to a geomagnetic storm than they are to a nuclear EMP. The primary threat from solar events is grid failure and the cascade of downstream systems that depend on it.

Nuclear EMP (high-altitude detonation)

A nuclear weapon detonated at high altitude — roughly 25 to 250 miles (40 to 400 km) above the Earth's surface — produces a very different kind of EMP. Instead of slow-moving geomagnetically induced currents, a nuclear EMP produces three distinct pulses:

E1 is an extremely fast, high-voltage spike occurring within nanoseconds of detonation. It travels at the speed of light and damages solid-state electronics — the microprocessors and transistors in modern devices. Surge protectors designed for lightning cannot respond fast enough to intercept E1.

E2 arrives within a millisecond and resembles a lightning strike in character. Most systems with standard surge protection can handle E2, though E1 damage may have already compromised protection components.

E3 is a slow, long-duration pulse similar to a powerful geomagnetic storm. It damages power grid infrastructure through the same GIC mechanism as a solar event.

The combined effect of E1+E2+E3 from a high-altitude nuclear detonation would be substantially more damaging to electronics than a solar storm. The geographic coverage depends on detonation altitude — a 250-mile (400 km) detonation can affect electronics across a continental-scale area.

Vehicles and older electronics

Testing conducted for the U.S. Congressional EMP Commission found that most vehicles continued to operate after EMP exposure, though some with heavy electronic control systems stopped and required restarting. Older vehicles with fewer microprocessors and no engine control units are more resilient. Equipment without microchips — older mechanical radios, non-electronic hand tools, gravity-fed water systems — is essentially immune to E1 effects.

What survives without protection

Understanding what is and isn't vulnerable helps prioritize preparation effort.

Likely to survive a nuclear EMP without protection: purely mechanical devices (hand tools, manual typewriters, non-electric vehicles, clockwork mechanisms), older vehicles with simple electrical systems, incandescent light bulbs, non-digital battery-powered devices without microprocessors, and underground electrical infrastructure (protected by the ground).

Likely to be damaged or destroyed: modern smartphones, laptops, tablets, solar charge controllers, inverters with digital controls, vehicles with engine control units, grid-tied solar systems, anything connected to the power grid at the moment of an E3 event, and any electronics with antenna connections (which act as collection points for E1 energy).

The grid itself: Whether from a solar event or nuclear EMP, the grid infrastructure — particularly high-voltage transformers — is the most consequential failure. Everything that depends on grid power fails with it.

Faraday protection

A Faraday cage is a conductive enclosure that redistributes electromagnetic energy around its exterior, shielding the interior. For E1 protection (the nuclear EMP concern), the cage needs to be a continuous conductive surface without gaps — a mesh screen with openings larger than the wavelength of concern is inadequate.

Simple DIY option: A galvanized steel trash can with a tight-fitting lid, lined inside with cardboard or foam to prevent electronics from touching the metal. Seal the lid seam with aluminum foil tape. Cost: inexpensive. Effectiveness: adequate for solar events and likely adequate for nuclear E1, though not laboratory-certified.

Better option: Nested protection. Place electronics in a sealed ziplock bag, then inside a steel container, then inside a larger steel container. Each layer adds attenuation. Critical items (backup radio, spare charge controller, medications that require powered devices) warrant this extra step.

What to protect: - A backup handheld radio (HAM or General Mobile Radio Service (GMRS)) for communications - Spare solar charge controller (modern units with digital displays are vulnerable) - USB power banks (small, easily stored) - Backup hard drives with offline maps, medical references, and critical documents - Hearing aids, blood glucose monitors, and other medical electronics

Field note

The most commonly overlooked item in EMP preparation is the spare solar charge controller. Panels themselves are largely unaffected by EMP — they are passive devices — but the charge controller that converts panel output to battery-compatible voltage uses microprocessors and is vulnerable. A stored spare in a Faraday container costs the price of a mid-range unit and keeps your entire solar system functional after an event.

Hardening priority sequence

Not everything can be Faraday-protected before an event. Prioritize protection in this order, which reflects both criticality and replacement difficulty:

  1. Communications first. A battery or hand-crank AM/FM/shortwave radio and a handheld GMRS or HAM radio are your link to emergency broadcasts and local coordination. Without communications you cannot assess the situation or coordinate with others. These are small, inexpensive, and easy to store. Disconnect the antenna and store it inside the same container.

  2. Medical devices second. Hearing aids, blood glucose monitors, insulin pumps, CPAP machines, and cardiac devices cannot be improvised from analog alternatives. If a household member depends on one, it goes into Faraday storage before anything else. Keep a spare where possible; for complex devices (insulin pumps, implanted monitors), consult your physician about spare device programs.

  3. Lighting third. A Faraday-stored LED headlamp and a spare set of batteries per person costs almost nothing and solves an immediate post-event problem. Modern LEDs use microprocessors for their drivers and are technically vulnerable; the risk is lower than for charge controllers but worth protecting given the negligible size.

  4. Power generation support last. The solar panels themselves — passive silicon cells — are essentially immune to E1. The charge controller is not. A spare charge controller in Faraday storage restores your entire energy system after the event. This is a moderate investment for the storage container and controller, and it has no downside — you were planning to buy a backup anyway.

Faraday cage construction: practical specs

A purpose-built Faraday cage does not need to be laboratory-grade to provide meaningful protection against a solar event and likely protection against nuclear E1. Two practical builds:

Galvanized steel trash can (budget option): Use a standard 20–32 gallon (76–121 L) galvanized steel trash can with a tight-fitting lid. The can must be seamless steel — no plastic inserts. Line the entire inside with cardboard (minimum 1/4 inch (6 mm) thickness) so no electronics contact the metal wall directly. If electronics touch the cage wall, the induced current transfers directly to the device. Seal the lid-to-can seam completely with aluminum foil tape or copper tape, pressing firmly into the seam channel. The seal is the most critical step — a continuous conductive path around the lid prevents gap leakage. Place electronics in sealed plastic bags before inserting, as condensation can accumulate.

Nested steel boxes (better option): Place the device in a ziplock bag, then in a smaller steel container (a surplus military ammo can works well — the rubber gasket helps seal the lid), then in the larger steel trash can. Each conductive layer adds attenuation of the signal. For items you depend on absolutely (medical devices, primary radio), nested protection is worth the added bulk.

What not to use: Aluminum foil wrapping alone provides some shielding but is difficult to seal reliably at the seams. A microwave oven is often cited as a Faraday cage — it is not designed for EMP protection and its waveguide opening defeats it for E1 frequencies. Mesh cages with gaps larger than 1/4 inch (6 mm) are inadequate for the wavelengths generated by a nuclear E1 pulse.

Pre-EMP preparedness checklist

  • Identify the two or three devices whose loss would most constrain your household response and Faraday-protect those first
  • Build or acquire a galvanized steel container with a tight lid; line with cardboard; seal lid seam with aluminum foil tape
  • Store backup GMRS or HAM handheld with antenna disconnected and batteries separated
  • Store a spare solar charge controller if you have a solar system
  • Store medical electronics spares (hearing aid batteries, glucose meter, CPAP power adapter) in Faraday protection
  • Test your Faraday container: place a phone inside, seal it, and call the number — if it rings, the cage has gaps; reseal and retest
  • Keep offline copies of critical documents, maps, and medical references on a USB drive inside the container

Layered preparation

EMP preparation is most productive when it is layered on a baseline of general grid-down capability rather than treated as a standalone specialization.

Layer 1 — Grid failure resilience: Everything in the grid-down page applies to EMP scenarios. If you can function without grid power for two weeks using stored fuel, food, and water, you have addressed most of the immediate survival period regardless of the outage cause.

Layer 2 — Communications: A battery-powered AM/FM/SW radio in a Faraday container maintains access to emergency broadcasts. A stored GMRS or HAM handheld maintains local communication capability. The antenna should be disconnected and stored inside the cage — antennas connected to electronics at the moment of an E1 event concentrate the pulse and increase damage.

Layer 3 — Protected critical electronics: Identify the devices whose loss would most constrain your response: charge controllers, medical devices, navigation equipment, backup drives. These go into Faraday protection.

Layer 4 — Non-electronic alternatives: For every critical function dependent on electronics, identify a non-electronic fallback. Paper maps replace GPS. A solar oven or rocket stove replaces an electric range. A hand pump or gravity system replaces an electric well pump.

Do not disconnect from the grid preemptively

There is no reliable advance warning for nuclear EMP, and solar storm warnings average 15 to 60 minutes between detection and arrival — not enough time for most protective actions unless systems are already in place. Focus on pre-positioned protection (stored spares in Faraday containers, non-electronic fallbacks ready to use) rather than hoping to respond in real time.

Probability and perspective

Carrington-class solar storms occur roughly every 100 to 200 years based on historical record; the last one was in 1859. A near-miss occurred in 2012. The probability of one occurring in any given decade is meaningful, not negligible.

High-altitude nuclear EMP is a lower-probability but higher-consequence scenario. The preparation for it is largely the same as for a major solar event, and both overlap substantially with general grid-down preparation. The investment in Faraday-protected spares is modest; the investment in grid-independent systems is substantial but independently useful.

Preparation checklist

  • Place a backup handheld radio (HAM or GMRS) in a sealed metal container with the antenna disconnected
  • Store a spare solar charge controller in Faraday protection if you have a solar system
  • Keep a USB power bank in a Faraday container for initial device charging
  • Build or buy a galvanized steel container with a lid; line with cardboard; seal seams with aluminum tape
  • Identify and store non-electronic fallbacks for critical functions: paper maps, manual water pump, non-electric cooking
  • Review the grid-down page — all extended outage preparation applies here
  • Keep a full 14-day supply of critical medications; refill on the earliest allowed date
  • Back up essential documents (medical records, IDs, maps, reference guides) to an offline drive in Faraday storage

An EMP — solar or nuclear — produces an extended grid-down scenario. The physical preparation is the same: water, food, heat, and communications independent of the grid. The grid-down page builds that baseline; EMP-specific Faraday protection and non-electronic fallbacks extend it.

For the household planning framework that ties this scenario to insurance, drills, and the likelihood × severity matrix, see threat planning.