An electromagnetic pulse would affect virtually anything that runs on electricity or contains electronic components, from the power grid and vehicles to medical devices and household appliances. The scale of damage depends on the type of EMP, its strength, and how close the affected equipment is to the source. But the short answer is that modern life depends heavily on electronics, and an EMP exploits that dependency across nearly every system simultaneously.
How an EMP Actually Works
An EMP isn’t a single event. A nuclear detonation at high altitude, the scenario most commonly discussed, produces three distinct waves that each threaten different types of equipment.
The first wave, called E1, is the fastest and most damaging to everyday electronics. It reaches peak intensity in about five nanoseconds, far too fast for surge protectors or circuit breakers to react. It works by stripping electrons from atoms in the upper atmosphere, creating a massive burst of electromagnetic energy that radiates downward. This pulse induces voltage spikes in any conductive material it reaches: wiring, circuit boards, antennas, even the traces inside a microchip.
The second wave, E2, lasts from about one microsecond to one second. It behaves similarly to a lightning strike and would normally be manageable, except that the E1 pulse has likely already destroyed the surge protection devices that would have absorbed it.
The third wave, E3, is the slowest, lasting tens to hundreds of seconds. It distorts the Earth’s magnetic field itself, inducing massive currents in very long conductors like power lines, pipelines, and undersea cables. This is the wave that threatens the backbone of the electrical grid.
The Power Grid
The electrical grid is the single most consequential target. High-voltage transformers, the massive units that step power up and down between generation plants and your home, are especially vulnerable to the E3 pulse. The slow, powerful currents it induces can overheat transformer windings and degrade the oil-paper insulation inside them. Testing on distribution transformers has shown that as the pulse amplitude increases, internal damage worsens in a stepwise pattern, with electrical discharges inside the insulation growing more frequent and intense. This kind of insulation breakdown is a primary cause of transformer failure.
The real problem is replacement time. Large high-voltage transformers are custom-built, weigh hundreds of tons, and can take 12 to 18 months to manufacture. The United States has limited domestic production capacity for these units. A widespread EMP event that damages dozens or hundreds of them simultaneously could leave large regions without power for months or longer, cascading into failures across every other system that depends on electricity.
Water and Sewage Systems
Modern water treatment plants and pumping stations rely on electronic control systems called SCADA (supervisory control and data acquisition) to monitor water pressure, chemical treatment levels, and distribution flow. These systems are particularly vulnerable to the fast E1 pulse because their electronic components, including chips, power supplies, and circuit boards, can be damaged or destroyed by the induced voltage spikes. Unlike the transformers threatened by E3, SCADA systems don’t need long cable runs to be affected. Their own internal wiring and connections are enough to pick up the pulse.
Without functioning SCADA systems, water treatment plants can’t automatically adjust chemical dosing or manage distribution. Without grid power to run the pumps, water simply stops flowing to homes and businesses that rely on municipal pressure. Buildings with rooftop tanks might have a few hours of gravity-fed water. Most homes would have none.
Vehicles and Transportation
Modern cars, trucks, and buses depend on electronic control units (ECUs) to manage everything from fuel injection and transmission shifting to braking and steering assist. An EMP can damage or destroy these processors outright, disrupting the internal processor and rendering the vehicle unable to start or run. Research into this problem has focused on developing emergency workarounds for heavy transport vehicles whose ECUs have been destroyed by electromagnetic pulses, which confirms that permanent damage, not just temporary disruption, is a realistic outcome for unshielded vehicles.
The picture for aircraft is more nuanced. Military aircraft are built to specific hardening standards that protect against EMP through shielding and surge protection at critical system interfaces, with protection levels defined across three tiers of increasing resilience. Commercial aircraft are not built to these military standards, though they do undergo electromagnetic compatibility testing for other interference sources. A fly-by-wire airliner that lost its flight computers mid-flight would face an extremely serious situation, though many commercial planes retain some backup mechanical or hydraulic control paths.
Trains, subways, and traffic management systems all run on electronic controls and would be similarly affected. Traffic signals failing across an entire metropolitan area simultaneously would create immediate gridlock and accidents.
Communications and Internet
Cell towers, internet routing equipment, data centers, and satellite ground stations all contain dense concentrations of sensitive electronics. The E1 pulse would damage radio receivers, server hardware, and switching equipment. Even if some equipment survived, the loss of grid power would bring most of it down within hours as backup generators run out of fuel or battery reserves drain.
Cell phone services, landline networks, internet connectivity, and GPS would all degrade or fail. Long-term disruption of these systems has been identified alongside power grid damage as one of the chained effects of a nuclear EMP, where the failure of one system pulls others down with it.
Personal devices like smartphones, laptops, and tablets could also be damaged, particularly if they were plugged into wall outlets or connected to long cables acting as antennas at the time of the pulse. A phone sitting in a pocket with no wired connections has a better chance of surviving, but would be largely useless without cell networks or internet to connect to.
Medical Equipment and Implanted Devices
Hospitals are packed with EMP-vulnerable electronics: ventilators, infusion pumps, monitoring systems, imaging machines, and electronic medical records. Most hospitals have backup generators, but those generators themselves rely on electronic controls to start and regulate their output.
Implanted cardiac devices like pacemakers and defibrillators are a particular concern. These devices already contain protective circuits made of special diodes designed to shunt away excess electrical energy. But those protections have limits. Even controlled medical procedures like cardioversion can occasionally cause device malfunctions, including inadvertent deactivation of implanted defibrillators and “power-on reset” events where the device reverts to a basic backup mode. An EMP delivering energy across a broad spectrum and at high amplitude could overwhelm these protections entirely. For the roughly 3 million Americans with implanted cardiac devices, this represents a direct, life-threatening risk.
Insulin pumps, cochlear implants, and other electronic medical devices would face similar vulnerabilities, though the consequences vary by device type and how dependent the patient is on continuous device function.
Financial Systems and Supply Chains
Banking, payment processing, and stock exchanges run on electronic networks. ATMs, credit card terminals, and online banking would all go offline with the communications and power infrastructure. Physical cash would become the only functioning medium of exchange, and most people carry very little of it.
Supply chains depend on electronic inventory management, GPS-guided shipping, and constant communication between warehouses, trucks, and retail locations. Grocery stores typically carry about three days of inventory. Without electronic resupply systems, restocking would slow to a crawl even in areas where transportation remained partially functional.
What Would Likely Survive
Not everything is equally vulnerable. Simple electrical devices with no microprocessors, like basic hand tools, manual appliances, incandescent light bulbs, and older diesel engines with mechanical fuel injection, would generally be unaffected. The pulse targets semiconductor electronics, so anything without a circuit board has little to fear.
Devices stored inside metal enclosures get some natural protection. A Faraday cage, essentially a sealed metal box, can reduce electromagnetic energy reaching the electronics inside, though the shielding effectiveness varies enormously with construction quality. A purpose-built military enclosure might achieve 60 dB or more of attenuation (reducing the signal to one millionth of its original strength), while a basic welded steel structure might only manage around 18 dB. A metal trash can with a tight-fitting lid provides some protection but far less than dedicated shielding.
Equipment that is unplugged, turned off, and disconnected from any antennas or long cables is also less vulnerable, since there’s no conductive path to channel the induced current into the device’s internals. This is why preparedness guidance often suggests keeping backup electronics in shielded containers with no external connections.
Scale Matters
A single nuclear weapon detonated at high altitude could blanket a continent-sized area. The 1962 Starfish Prime test, a 1.4-megaton warhead detonated 250 miles above the Pacific Ocean, caused electrical disruptions in Hawaii nearly 900 miles away, damaging street lights and triggering burglar alarms. That test used 1960s-era weapon technology against 1960s-era electronics, which were far simpler and more robust than today’s microprocessors. Modern chips, with features measured in nanometers, are significantly more sensitive to voltage spikes.
Smaller, non-nuclear EMP weapons exist as well, but their effective range is measured in hundreds of meters rather than hundreds of miles. These would affect a building or a city block, not an entire region. The catastrophic scenario that drives most EMP concern is the high-altitude nuclear detonation, specifically because of its ability to affect everything within line of sight of the blast point simultaneously.