An electromagnetic pulse (EMP) or severe geomagnetic storm caused by a solar coronal mass ejection (CME) represents one of the most potentially severe — and most misunderstood — emergency scenarios. The 1859 Carrington Event, the largest solar storm in recorded history, caused widespread telegraph system failures, fires in telegraph offices, and auroras visible in the tropics. A Carrington-class event today would impact power grid infrastructure that did not exist in 1859 and would be catastrophically difficult to repair. This guide covers what is known about EMP effects, what is not known, and what preparation is rational given the uncertainty.
Two Different Threats: Nuclear EMP vs. Solar CME
| Threat | Cause | Affected area | Effect on electronics | Warning time |
|---|---|---|---|---|
| Nuclear EMP (HEMP) | High-altitude nuclear detonation (30–300 miles) | Line-of-sight from detonation (up to continental scale) | Three components (E1, E2, E3) — E1 destroys semiconductors in nanoseconds | None |
| Solar CME (geomagnetic storm) | Coronal mass ejection from sun | Hemisphere-scale (Earth’s sun-facing side) | Primarily E3-like induced currents in long conductors (power lines, pipelines); less effect on electronics not connected to grid | 18–72 hours from observation |
| Carrington-class CME | Extreme solar event (~once per 100–200 years) | Global | Transformer damage across grid; severity uncertain for modern electronics | 18–72 hours |
Critical distinction: A nuclear EMP is optimized to damage electronic circuits (the E1 component produces a very fast pulse that destroys semiconductors). A solar CME primarily induces currents in long conductors, which destroys transformers and transmission equipment — but may have less direct effect on electronics not connected to the grid at the time of impact. The extreme severity predictions often cited for EMP scenarios apply primarily to the nuclear EMP threat, not the solar event.
The Carrington Event (September 1–2, 1859)
The Carrington Event remains the benchmark for extreme geomagnetic storms. What actually happened:
- The storm hit Earth approximately 17.6 hours after the initial CME observation — unusually fast transit time
- Telegraph systems worldwide failed. Some telegraph operators reported receiving shocks from their equipment. Some systems operated without batteries (powered by the induced current from the storm)
- Auroras were visible as far south as Cuba, Hawaii, and Colombia
- A smaller but still severe event in July 2012 narrowly missed Earth — had it hit, the Oak Ridge National Laboratory estimated $2.6 trillion in damages to the US alone
The probability of a Carrington-class event reaching Earth in any given decade is estimated at approximately 10–12% (National Academy of Sciences, 2008 report on space weather). It is a low-probability, high-consequence event.
What Survives: Electronics Vulnerability Assessment
The empirical data on EMP effects on modern electronics is limited — nuclear testing that would produce relevant data has not been conducted since the 1960s. However, the following is generally accepted:
- Grid-connected electronics are most vulnerable: Transformers, surge protectors, and anything connected to power lines during a severe CME. The grid infrastructure itself is the primary casualty of a solar event.
- Disconnected electronics have uncertain survival probability: For solar CME, portable electronics that are not plugged into the grid at the time of impact have a better survival probability than connected devices. For nuclear EMP, the E1 component can damage electronics even when unplugged.
- Vehicles: Modern vehicles with sophisticated electronic control modules are more vulnerable than older (pre-1980) carbureted, mechanically timed vehicles. However, real-world EMP tests on vehicles have shown varying results — many vehicles with damage modes that could be reset, not permanently destroyed. The 2004 EMP Commission found most vehicles kept driving during simulated E1 pulses, though some stalled and required restart.
- Older electronic equipment: Vacuum tube equipment, older transistor radios, and equipment from the 1950s–60s era with larger component geometries is generally more resistant to EMP than modern nanoscale semiconductors.
Faraday Cages: What They Do and How to Build One
A Faraday cage is a conductive enclosure that blocks external electromagnetic fields. For EMP protection, it needs to be fully enclosed, conductive, and grounded (for static discharge). Practical options:
- Metal garbage can with tight-fitting metal lid ($20–40): A galvanized steel can with a gasketed lid provides meaningful attenuation. Line the interior with cardboard, foam, or paper to prevent electronics from touching the metal walls (direct contact can allow current transfer during discharge). This is the most cited practical Faraday cage for civilians.
- Ammo cans (military surplus $15–30): Excellent seal, compact, stackable. 50-caliber or .30-caliber ammo cans work well for small electronics.
- Mylar emergency blanket + aluminum foil wrap: Multiple layers of heavy-duty aluminum foil wrapped tightly around electronics with no gaps provides partial protection. Not as effective as a metal box. Use for items that won’t fit in a box.
What to protect in a Faraday cage:
- Backup radio (NOAA weather radio, AM/FM)
- Backup phone (old smartphone with downloaded maps, contacts, medical info)
- Solar charge controller (for solar panel system restoration)
- Battery-powered inverter or small power station
- Shortwave or ham radio receiver
- LED flashlights and spare rechargeable batteries
Grid Recovery Timeline After Major Solar Event
The most significant uncertainty in solar EMP preparedness is how long power grid restoration would take after a Carrington-class event:
- Optimistic scenario (transformers mostly survive, control systems recoverable): Weeks to months for most areas
- Moderate damage scenario (significant transformer damage): 6–18 months for primary restoration; transformer manufacturing backlogs are 1–2 years under normal demand
- Extreme scenario (widespread extra-high-voltage transformer loss): Multi-year restoration; the US manufactures fewer than 20 extra-high-voltage transformers per year
This is why a Carrington-class event represents a qualitatively different scenario from weather emergencies — the grid can be repaired after an ice storm in days; replacing transformers can take years.
Practical EMP/CME Preparation Priority List
- Build 1–2 Faraday cages (metal trash can + ammo can) with backup communication and power equipment protected inside
- 6-month food and water supply (grid-down recovery after a severe CME takes months to years)
- Solar panel system with protected charge controller and battery bank (provides power independent of grid)
- Non-electronic backup skills and equipment: manual tools, mechanical watches, paper maps, analog gauges
- Community connections (a network of people with complementary skills is far more valuable than any electronics cache)
Where to Go Next
Extended power outage preparation for the grid-down aftermath — generator and battery bank sizing — is in extended power outage: grid-down preparedness for 14-day blackout. Emergency power systems and solar panel setup are in emergency power: generators, solar panels, and battery banks.
