An 'Electromagnetic Pulse (EMP) is a (relatively) short burst of energy resulting from an air burst of nuclear weapons or a solar flare that could damage electronics including the power grid.
The likely hood of such a natural disaster or deliberate attack taking out some or all of the power grid is low. According to threat probability assessment and the principle of commonality of disaster preparing for smaller, less catastrophic, more common disasters will lead to being more prepared for a big unlikely disaster such as an EMP attack.
Producing an EMP burst
There are several other means of producing an EMP burst however. Some of these include, Solar Flares which are flares on the Suns surface that produce waves in the Electromagnetic Spectrum. Flux compression generators which were being developed by the US Army, later abandoned and picked up by the Air Force out of Sandia Labs can also accomplish this. Sandia labs reported in late 2000 or early 2001 that they had mounted one in a cruise missile that had a 1000 foot radius.
When a Nuclear Weapon detonates about 40-400km above the surface of the planet, it produces an immediate flux caused by the Nuclear Reactions taking place in the device. These produce Photons which are then trapped in Earth's magnetic field, producing an electric current that would basically fry any electrical device not protected from an Electromagnetic Pulse. The largest part of the EMP is generated by the interaction with the detonation and the upper layers of the atmosphere and not from the nuclear device itself.
The most likely form of a High-altitude Electromagnetic Pulse (HEMP) is a nuclear device detonated 40-400km above the surface of the Earth. This is well within the range of a $100k SCUD missile which could be launched in international waters from a shipping boat. There are many hostile types with these types of boats available to them.
How much damage can an HEMP do?
In 1987 then President Ronald Reagan ordered a study to be conducted on the effects of a HEMP detonation above the center of the United States. This was in response to intel that suggested the Soviet Union was actively trying to develop a HEMP weapons program.
In response to this study, Reagan ordered that the Emergency Broadcast System be shielded in a way to allow for it to survive a HEMP. This system was closed down in 1997, being replaced by the Emergency Alert System which started in 1994. No information has yet been found on the requirements for shielding of the Emergency Alert System, however it is probable that it is shielded as well. This system would allow them to transmit to any device that can still receive.
A more recent US government report indicates that the damage would be less, although this is likely due to a difference in the yield of the devices and construction techniques.
In November 1987 a report on the survivability of fiber optic networks was conducted and recommendations were made to make that more survivable for at least emergency communications (ie military and first responders). The report also states that AT&T and other carriers were getting advice from the Defense Department on what is the most likely safe path to run cables to be the furthest from likely Soviet targets. It is unclear if this communication still exists between the carriers and the government, but it likely does given the governments reliance upon the carriers for communication services.
According to the FEMA Nuclear War Survival Handbook, battery powered radios with antennas of less than 30 inches will survive a HEMP, providing they are not connected to the power grid for charging, or have any other wires protruding. Vehicles may or may not survive, some diesel generators, and other simple internal combustion engine vehicles should survive, although the effects of an HEMP can be amplified by parking the vehicle next to a metal object such as a lamp post or metal shelving in a garage. There is a scientific debate over how many cars would actually be affected. Modern ignition systems would be the most likely things to fail after an HEMP.
How to Protect Your Electronics from an EMP
The only measure you can take to protect electronics from an EMP is to construct what is known as a Faraday Cage.
A Faraday Cage is an enclosed space made of a material (mostly metal) that prevents the entry or escape of a magnetic field. These "cages" would (hopefully) protect any electronics inside from being "fried".
The most common Faraday Cage would probably be metal sheds, to protect electronics it would be best to place all of them inside metal cabinets which are in turn stored in a metal shed. This would be the only real protection the average Joe could really take to protect his electronics from an EMP, without spending a TREMENDOUS amount of money on other means.
EMPs can be generated from several different sources with differing severity.
- Atomic Bomb
- Hydrogen Bomb
- Solar Storms & Solar Flares
- Flux Compression Generator