Overview

The high-altitude nuclear weapon-generated electromagnetic pulse (EMP) is one of a small number of threats that has the potential to hold American society seriously at risk and might result in defeat of our military forces.

Briefly, an EMP event could render most all electrical devices in the United States useless, including the electrical components in cars and trucks. Specifically, a single nuclear weapon exploded at high altitude above the United States will interact with the Earth's atmosphere, ionosphere, and magnetic field to produce an electromagnetic pulse (EMP) radiating down to the Earth and additionally create electrical currents in the Earth. EMP effects are both direct and indirect. The former are due to electromagnetic "shocking" of electronics and stressing of electrical systems, and the latter arise from the damage that "shocked" - upset, damaged, and destroyed - electronics controls then inflict on the systems in which they are embedded. The indirect effects can be even more severe than the direct effects.

The electromagnetic fields produced by weapons designed and deployed with the intent to produce EMP have a high likelihood of damaging electrical power systems, electronics, and information systems upon which American society depends. Their effects on dependent systems and infrastructures could be sufficient to qualify as catastrophic to the Nation.

Depending on the specific characteristics of the attacks, unprecedented cascading failures of our major infrastructures could result. In that event, a regional or national recovery would be long and difficult and would seriously degrade the safety and overall viability of our Nation. The primary avenues for catastrophic damage to the Nation are through our electric power infrastructure and thence into our telecommunications, energy, and other infrastructures. These, in turn, can seriously impact other important aspects of our Nation's life, including the financial system; means of getting food, water, and medical care to the citizenry; trade; and production of goods and services. The recovery of any one of the key national infrastructures is dependent on the recovery of others. The longer the outage, the more problematic and uncertain the recovery will be. It is possible for the functional outages to become mutually reinforcing until at some point the degradation of infrastructure could have irreversible effects on the country's ability to support its population.

"An electromagnetic pulse (EMP) attack on the American homeland, said one of the distinguished scientists who testified at the hearing, is one of only a few ways that the United States could be defeated by its enemies -- terrorist or otherwise. And it is probably the easiest. A single Scud missile, carrying a single nuclear weapon, detonated at the appropriate altitude, would interact with the Earth's atmosphere, producing an electromagnetic pulse radiating down to the surface at the speed of light. Depending on the location and size of the blast, the effect would be to knock out already stressed power grids and other electrical systems across much or even all of the continental United States, for months if not years.

Few if any people would die right away. But the loss of power would have a cascading effect on all aspects of U.S. society. Communication would be largely impossible. Lack of refrigeration would leave food rotting in warehouses, exacerbated by a lack of transportation as those vehicles still working simply ran out of gas (which is pumped with electricity). The inability to sanitize and distribute water would quickly threaten public health, not to mention the safety of anyone in the path of the inevitable fires, which would rage unchecked. And as we have seen in areas of natural and other disasters, such circumstances often result in a fairly rapid breakdown of social order."
- Congressman Roscoe Bartlett, Nuclear Electromagnetic Pulse Speech, June 9, 2005 (PDF)

a. Electromagnetic pulses can come from nuclear detonations (nondirected EMP), from detonation of conventional explosives coupled with focusing electromechanical devices, or from electrically powered EMP generators on or above the ground.

b. Electromagnetic pulses can damage or destroy sensitive electronic components, such as microchips, coils, and fuses by overloading them with electrical current. Any equipment containing electronic components is subject to damage or destruction from EMP attack. FM radios are susceptible to EMP damage. The amount of damage to equipment depends on its distance from the source of the pulse. EMP can seriously damage electronic devices connected to power sources or antennas. This include communication systems, computers, electrical appliances, and automobile or aircraft ignition systems. The damage could range from a minor interruption to actual burnout of components. Most electronic equipment within 1,000 miles of a high-altitude nuclear detonation could be affected. Battery powered radios with short antennas generally would not be affected.

c. Electromagnetic pulses can be projected into target areas from long ranges. They can enter a targeted device through any opening and attack sensitive components inside even if the device is disconnected or turned off. For example, it can enter a radio set through the louvers over the cooling fans and destroy circuitry inside, making the radio useless. It can also enter through unshielded cables for antennas, power lines, and so on.

d. An EMP attack lasts only for a split second and affects a large area. Protecting equipment from its attack is difficult. The only reliable way to do it is to encase susceptible equipment in some type of heavy gage metal shielding, or to surround it with special metal screening. Burying or covering it with sandbags or other nonmetallic materials does not provide enough protection. Terrain masking is ineffective because EMP follows the curve of the earth.

e. Although EMP is unlikely to harm most people, it could harm those with pacemakers or other implanted electronic devices.