The Realistic EMP Assessment
EMP preparedness exists in a space between legitimate concern and significant popular mythology. The popular narrative (every vehicle stopped, complete civilization collapse, instant return to the stone age) does not match the technical literature or the 2008 Congressional EMP Commission's actual findings.
The legitimate concern: a high-altitude nuclear detonation designed for maximum EMP effect over the continental United States would damage a significant percentage of grid infrastructure, disable some electronics, and create a major national emergency. The Congressional EMP Commission estimated that 90% of the US population could die within a year of such an event — not from the initial pulse, but from the cascading failures of infrastructure and the inability to restore it without the electronic manufacturing base needed to rebuild.
That is a serious threat worth preparing for. It is not the complete-instantaneous-collapse of popular fiction.
What EMP Actually Does
An EMP attack generates three distinct pulse components:
E1: Ultra-fast pulse (nanoseconds duration). Couples into short conductors and antennas. Most damaging to electronics directly. Can penetrate most shielding that is not properly grounded.
E2: Similar to lightning (microseconds duration). Standard lightning protection equipment handles this effectively. The main threat: E2 arrives immediately after E1 before surge protectors have recovered.
E3: Slow pulse (seconds to minutes). Caused by the distortion of the Earth's magnetic field. Induces large currents in long conductors — power transmission lines, pipelines. Equivalent to a severe geomagnetic storm. Damages transformers.
The E3 component is the most serious for grid infrastructure because large power transformers are difficult to manufacture, expensive (multi-million dollar units), and not stockpiled. Recovering from large-scale transformer damage could take years.
What Is Actually Vulnerable
Grid Infrastructure (High Vulnerability)
- High-voltage transformers and substations
- Long transmission lines (act as antennas for E3)
- SCADA systems controlling the grid
This is the actual catastrophic concern. Not stopped vehicles — a damaged grid that takes years to restore.
Consumer Electronics (Variable Vulnerability)
- High vulnerability: Devices connected to grid power or long antenna-like conductors
- Moderate vulnerability: Battery-operated devices with microelectronics
- Lower vulnerability: Simple devices, older tube-type equipment, mechanical systems
Most battery-operated devices that are not connected to external conductors at the moment of the pulse have a reasonable chance of survival from an E1 pulse.
Vehicles (Lower Vulnerability Than Portrayed)
The EMP Commission's testing showed that most modern vehicles continue operating after EMP exposure. Some experienced temporary disruptions that self-cleared. A small percentage experienced failures requiring repair. Complete vehicle stoppage was not the universal outcome.
Older (pre-1970s) vehicles with no electronic ignition are the most resistant. Modern vehicles with electronic engine management are more vulnerable but far more resistant than popular culture suggests.
What to Protect: Faraday Cage Priorities
Given limited preparation time and resources, protect in this order:
Priority 1: Communications Equipment
- Battery-operated AM/FM/shortwave radio (NOAA weather radio)
- Ham radio transceiver (Baofeng UV-5R is inexpensive and worth protecting)
- Satellite messenger (Garmin inReach or similar)
Information is the highest-leverage early asset in a grid-down event. Knowing what is happening, what areas are affected, and when infrastructure is being restored is critical for decision-making.
Priority 2: Medical Electronics
- Pulse oximeter
- Blood glucose monitor and supplies
- Hearing aids (if applicable)
- Any life-critical medical devices
Priority 3: Practical Electronics
- Portable solar charge controllers
- LED flashlights and headlamps
- Battery-operated tools
What Does NOT Need Protection
- Mechanical watches (not electronic)
- Hand tools
- Firearms
- Vehicles (lower vulnerability than assumed; spare ignition modules are a reasonable hedge)
Building a Faraday Cage
Option 1: Metal Ammo Can (Best Practical Option)
A metal military surplus ammunition can with a tight-fitting metal lid provides good shielding.
Preparation:
- Clean the can — no rust at the lid gasket point
- Line the inside with 1/2-inch foam or cardboard (prevents items from contacting the metal sides and creating a ground path through the item)
- Place electronics inside, not touching the metal walls
- Close the lid tightly
- Verify seal: place a small radio inside tuned to a station, close the lid — if you can still hear the radio, the seal is inadequate
Limitations: Standard ammo can gaskets are rubber, which can degrade over time. The shielding effectiveness varies with the quality of the lid seal.
Option 2: Galvanized Metal Trash Can
A 20-30 gallon galvanized metal trash can with a tight metal lid provides reasonable shielding for larger items.
Preparation: Same as ammo can: line interior with non-conducting material, ensure lid seats tightly against the can body. The rim of the trash can and the interior of the lid should make solid metal-to-metal contact.
Option 3: Commercial EMP Bags
Multiple manufacturers produce Faraday bags for electronics. Less robust than metal enclosures but practical for individual devices and easier to use in daily carry (phone, radio, etc.).
Recovery Planning
If a major EMP event occurs and significant grid infrastructure is damaged:
Short term (days 1-30): This looks identical to a major grid-down scenario. See 30-day-grid-down.mdx. Your immediate preparation is the same.
Medium term (months 1-12): If grid infrastructure cannot be restored, this becomes a year-long SHTF scenario. See 1-year-shtf.mdx.
Long term: Recovery depends on the extent of infrastructure damage. The specific concern with a severe EMP is that the electronics needed to manufacture replacement power transformers are themselves damaged — creating a recovery delay of years rather than months.
The preparation for EMP long-term recovery is identical to preparation for an extended grid-down scenario of any cause: food production, water independence, community organization, and skills.
Sources
Frequently Asked Questions
Would a high-altitude EMP actually stop all vehicles?
The 2008 Congressional EMP Commission tested over 50 vehicles. No vehicles stopped completely. Most continued operating. Some experienced temporary failures that cleared when the ignition was cycled. Modern vehicles with electronic engine management are vulnerable to damage, but complete vehicle stoppage across an entire fleet is not the universal outcome the popular narrative suggests.
How do Faraday cages work?
A Faraday cage is a conductive enclosure that distributes electromagnetic charge around its outer surface, shielding the interior from electromagnetic fields. Common implementations: metal ammunition cans with conductive foam lining, galvanized metal trash cans with metal lids, commercial EMP bags, and improvised solutions using multiple layers of aluminum foil.
What electronics are most vulnerable to EMP?
Solid-state electronics (microprocessors, transistors, integrated circuits) are the most vulnerable. Older electronics with tubes or relays are more resistant. Modern vehicles with electronic engine control modules are more vulnerable than older carbureted vehicles. Battery-operated devices not connected to the grid are less vulnerable than grid-connected devices.