How I Learned To Stop Worrying And Love The Electro-Magnetic Pulse Effect

Frequent commenter Revere Rides Again has asked about EMP (electro-magnetic pulse) detonation twice, so I decided it's time to put up a post on the subject. So, I figured it is time to answer her.

An EMP occurs when a nuclear weapon is detonated at high-altitude, sending a "pulse" of energy downward and outward. This "pulse" has tremendous destructive power capable of taking out electronics systems across a large land mass.

An EMP attack upon a nation would be a great way to soften them up for an attack upon the country as a whole, because it would render their ordinary computer-run defense systems useless.

The possibility exists, if I am not mistaken, that one of our enemies could choose to hit us with an EMP attack coming in the guise of a diplomatic mission. For instance, Mr. Ahmadinejad could say he intends to visit the U.S. in order to speak at the United Nations. He could then, theoretically, send an airliner over to America which did not contain his person, but instead contained a nuclear weapon, to be set off at high-altitude.

One would imagine that our Defense Department has gamed the possibility and has some sort of way of detecting whether airliners arriving from Axis of Evil countries contain nuclear materials.

Yes, one would imagine, right? Hey, how you doing there, Mr. Atta? Have a nice flight.

Anyway, here's an article to answer Revere Rides Again's question. I'm sure she isn't the only person who would be interested in the subject. Never let it be said we aren't responsive here at IBA. This is from the Federation of American Scientists:


A high-altitude nuclear detonation produces an immediate flux of gamma rays from the nuclear reactions within the device. These photons in turn produce high energy free electrons by Compton scattering at altitudes between (roughly) 20 and 40 km. These electrons are then trapped in the Earth’s magnetic field, giving rise to an oscillating electric current. This current is asymmetric in general and gives rise to a rapidly rising radiated electromagnetic field called an electromagnetic pulse (EMP). Because the electrons are trapped essentially simultaneously, a very large electromagnetic source radiates coherently.

The pulse can easily span continent-sized areas, and this radiation can affect systems on land, sea, and air. The first recorded EMP incident accompanied a high-altitude nuclear test over the South Pacific and resulted in power system failures as far away as Hawaii. A large device detonated at 400–500 km over Kansas would affect all of CONUS. The signal from such an event extends to the visual horizon as seen from the burst point.

Military systems must survive all aspects of the EMP, from the rapid spike of the early time events to the longer duration heave signal. One of the principal problems in assuring such survival is the lack of test data from actual high-altitude nuclear explosions. Only a few such experiments were carried out before the LTBT took effect, and at that time the theoretical understanding of the phenomenon of HEMP was relatively poor. No high-altitude tests have been conducted by the United States since 1963. In addition to the more familiar high-yield tests mentioned above, three small devices were exploded in the Van Allen belts as part of Project Argus. That experiment was intended to explore the methods by which electrons were trapped and traveled along magnetic field lines.

The “acid test” of the response of modern military systems to EMP is their performance in simulators, particularly where a large number of components are involved. So many cables, pins, connectors, and devices are to be found in real hardware that computation of the progress of the EMP signal cannot be predicted, even conceptually, after the field enters a real system. System failures or upsets will depend upon the most intricate details of current paths and interior electrical connections, and one cannot analyze these beforehand. Threat-level field illumination from simulators combined with pulsed-current injection are used to evaluate the survivability of a real system against an HEMP threat.

The technology to build simulators with risetimes on the order of 10 ns is well known. This risetime is, however, longer than that of a real HEMP signal. Since 1986 the United States has used a new EMP standard which requires waveforms at threat levels having risetimes under a few nanoseconds. Threat-level simulators provide the best technique for establishing the hardness of systems against early-time HEMP. They are, however, limited to finite volumes (aircraft, tanks, communications nodes) and cannot encompass an extended system. For these systems current injection must be used.

HEMP can pose a serious threat to military systems when even a single high-altitude nuclear explosion occurs. In principle, even a new nuclear proliferator could execute such a strike. In practice, however, it seems unlikely that such a state would use one of its scarce warheads to inflict damage which must be considered secondary to the primary effects of blast, shock, and thermal pulse.

Furthermore, a HEMP attack must use a relatively large warhead to be effective (perhaps on the order of one mega-ton), and new proliferators are unlikely to be able to construct such a device, much less make it small enough to be lofted to high altitude by a ballistic missile or space launcher.


That's a scientific explanation and exploration of the possibilities of the EMP effect. Here is a doomsday article on the subject from World Net Daily:


WASHINGTON -- Iran is not only covertly developing nuclear weapons, it is already testing ballistic missiles specifically designed to destroy America's technical infrastructure, effectively neutralizing the world's lone superpower, say U.S. intelligence sources, top scientists and western missile industry experts.

The radical Shiite regime has conducted successful tests to determine if its Shahab-3 ballistic missiles, capable of carrying a nuclear warhead, can be detonated by a remote-control device while still in high-altitude flight.

Scientists, including President Reagan's top science adviser, William R. Graham, say there is no other explanation for such tests than preparation for the deployment of electromagnetic pulse weapons – even one of which could knock out America's critical electrical and technological infrastructure, effectively sending the continental U.S. back to the 19th century with a recovery time of months or years.

Iran will have that capability – at least theoretically – as soon as it has one nuclear bomb ready to arm such a missile. North Korea, a strategic ally of Iran, already boasts such capability.

Just last month, Congress heard testimony about the use of such weapons and the threat they pose from rogue regimes.

Iran has surprised intelligence analysts by describing the mid-flight detonations of missiles fired from ships on the Caspian Sea as "successful" tests. Even primitive Scud missiles could be used for this purpose. And top U.S. intelligence officials reminded members of Congress that there is a glut of these missiles on the world market. They are currently being bought and sold for about $100,000 apiece.

"A terrorist organization might have trouble putting a nuclear warhead 'on target' with a Scud, but it would be much easier to simply launch and detonate in the atmosphere," wrote Sen. John Kyl, R-Ariz., in the Washington Post a week ago. "No need for the risk and difficulty of trying to smuggle a nuclear weapon over the border or hit a particular city. Just launch a cheap missile from a freighter in international waters – al-Qaida is believed to own about 80 such vessels – and make sure to get it a few miles in the air."

The Iranian missile tests were more sophisticated and capable of detonation at higher elevations – making them more dangerous.

Detonated at a height of 60 to 500 kilometers above the continental U.S., one nuclear warhead could cripple the country – knocking out electrical power and circuit boards and rendering the U.S. domestic communications impotent.

While Iran still insists officially in talks currently underway with the European Union that it is only developing nuclear power for peaceful civilian purposes, the mid-flight detonation missile tests persuade U.S. military planners and intelligence agencies that Tehran can only be planning such an attack, which depends on the availability of at least one nuclear warhead.

Last month, the Senate Judiciary Subcommittee on Terrorism, Technology and Homeland Security chaired by Kyl, held a hearing on the electromagnetic pulse, or EMP, threat.

"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," wrote Kyl "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."

The purpose of an EMP attack, unlike a nuclear attack on land, is not to kill people, but "to kill electrons," as Graham explained. He serves as chairman of the Commission to Assess the Threat to the United States from Electromagnetic Pulse Attack and was director of the White House Office of Science and Technology Policy and science adviser to the president during the Reagan administration.

Graham told WorldNetDaily he could think of no other reason for Iran to be experimenting with mid-air detonation of missiles than for the planning of an EMP-style attack.

"EMP offers a bigger bang for the buck," he said. He also suggested such an attack makes a U.S. nuclear response against a suspected enemy less likely than would the detonation of a nuclear bomb in a major U.S. city.

The commission report went so far as to suggest, in its opening sentence, that an EMP attack "might result in the defeat of our military forces."

The EMP threat is not a new one considered by U.S. defense planners. The Soviet Union had experimented with the idea as a kind of super-weapon against the U.S.

"What is different now is that some potential sources of EMP threats are difficult to deter – they can be terrorist groups that have no state identity, have only one or a few weapons and are motivated to attack the U.S. without regard for their own safety," explains the commission report. "Rogue states, such as North Korea and Iran, may also be developing the capability to pose an EMP threat to the United States and may also be unpredictable and difficult to deter."

Graham describes the potential "cascading effect" of an EMP attack. If electrical power is knocked out and circuit boards fried, telecommunications are disrupted, energy deliveries are impeded, the financial system breaks down, food, water and gasoline become scarce.

As Kyl put it: "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."

"American society has grown so dependent on computer and other electrical systems that we have created our own Achilles' heel of vulnerability, ironically much greater than those of other, less developed nations," the senator wrote. "When deprived of power, we are in many ways helpless, as the New York City blackout made clear. In that case, power was restored quickly because adjacent areas could provide help. But a large-scale burnout caused by a broad EMP attack would create a much more difficult situation. Not only would there be nobody nearby to help, it could take years to replace destroyed equipment."

The commission said hardening key infrastructure systems and procuring vital backup equipment such as transformers is both feasible and – compared with the threat – relatively inexpensive.

"But it will take leadership by the Department of Homeland Security, the Defense Department, and other federal agencies, along with support from Congress, all of which have yet to materialize," wrote Kyl, so far the only elected official blowing the whistle this alarming development.

Kyl concluded in his report: "The Sept. 11 commission report stated that our biggest failure was one of 'imagination.' No one imagined that terrorists would do what they did on Sept. 11. Today few Americans can conceive of the possibility that terrorists could bring our society to its knees by destroying everything we rely on that runs on electricity. But this time we've been warned, and we'd better be prepared to respond."