High-Altitude Electromagetic Pulse and How to Protect Against It

Description of High-Altitude Electromagnetic Pulse
HEMP is produced when a nuclear weapon is detonated high above the Earth’s surface, creating gamma-radiation that interacts with the atmosphere to create an instantaneous intense electromagnetic energy field that is harmless to people as it radiates outward, but which can overload computer circuitry with effects similar to, but causing damage much more swiftly than a lightning strike.

The effects of HEMP became fully known to the United States in 1962 during a high-altitude nuclear test (code named “Starfish Prime”) over the Pacific Ocean, when radio stations and electronic equipment were disrupted 800 miles away through parts of Hawaii. The HEMP effect can span thousands of miles, depending on the altitude and the design and power of the nuclear burst (a single device detonated at an appropriate altitude over Kansas reportedly could affect all of the continental United States) and can be picked up by metallic conductors such as wires or power cables, acting as antennas to conduct the energy shockwave into the electronic systems of cars, airplanes, and communications equipment.

Disruptive Capabilities of HEMP and HPM Weapons
Studies related to the effects of electromagnetic weapons have been published infrequently, or remain classified. Nevertheless, it is known that a powerful HEMP field as it radiates outward can interfere with radio frequency links and instantly produce damaging voltage and currents in electronic devices thousands of miles from the nuclear explosion. Effectiveness is increased if the electronic devices are connected to any metal that could also act as an antenna. Because infrastructure computer systems are interconnected, a widespread HEMP effect could lead to possible long-term disruption of power, fuel distribution, transportation systems, food and water supplies, hospitals, and law enforcement communications, as well as military communications systems which utilize the civilian infrastructure. The disruptive effects of both HEMP and HPM reportedly diminish with distance, and electronic equipment that is turned off is less likely to be damaged.

A high altitude nuclear explosion (that creates HEMP) produces three major energy components that arrive in sequence, and which have measurably different effects that can be cumulatively damaging to electronic equipment. The first energy component is the initial energy shockwave which lasts about one microsecond, and is similar to extremely intense static electricity that can overload circuitry for every electronic device that is within line of sight of the burst. A secondary energy component then arrives, which has characteristics that are similar to a lightning strike. By itself, this second energy component might not be an issue for some critical infrastructure equipment, if anti-lightning protective measures are already in place. However, the rise time of the first component is so rapid and intense that it can destroy many protective measures, allowing the second component to further disrupt the electronic equipment. The third energy component is a longer-lasting magnetic signal, from about one microsecond to one full second in duration. This geomagnetic signal causes an effect that is damaging primarily to long-lines electronic equipment. A localized magnetic effect builds up throughout the length of the transmission lines and then quickly collapses, producing a magnetohydrodynamic (MHD) “heave,” or “late-time,” power surge that overloads equipment connected to the power and telecommunications infrastructure. This latetime effect adds to the initial HEMP effect, and systems connected to long-lines power and communications systems may be further disrupted by the combined effects. Smaller isolated systems do not collect so much of this third energy component, and are usually disrupted only by the first energy component of HEMP.

HEMP or HPM energy fields, as they instantly spread outward, may also affect nearby hospital equipment or personal medical devices, such as pacemakers, and may damage critical electronic systems throughout other parts of the surrounding civilian infrastructure.

Many commercial communications satellites, particularly those in low earth orbit, reportedly may degrade or cease to function shortly after a high altitude nuclear explosion.

Hardening Against HEMP and HPM Weapons
Electronic equipment may be hardened by surrounding it with protective metallic shielding which routes damaging electromagnetic fields away from highly sensitive electrical components. This method, known as Faraday cage protection, is traditionally used to protect electronic equipment from a lightning strike. However, power surges HEMP or HPM weapons could possibly involve peak currents of tens of millions of amps which can pass through a protective Faraday cage. (If the cage is near the blast) Additionally, equipment placed within a Faraday cage may also be made vulnerable by any wires running into to the cage which can conduct the electromagnetic shockwave into the equipment. Depending on the power level involved, points of entry into the shielded cages can sometimes be protected from electromagnetic pulse by using specially designed surge protectors, or other types of specially-designed electrical filters.

Capabilities of Other Nations
Reportedly, several potential U.S. adversaries, such as Russia or China, are now capable of launching a crippling HEMP strike against the United States with a nuclear-tipped ballistic missile, and other nations, such as North Korea, and Iran could possibly have the capability by 2015. Other nations that could possibly develop a capability for HEMP operations over the next few years include United Kingdom, France, India, Israel, and Pakistan. According to a 1999 DOD report, China has been actively pursuing the development of electromagnetic pulse weapons, and has devoted significant resources to development of other electronic warfare systems and laser weapons. During 1962, the then Soviet Union conducted a series of atmospheric nuclear tests and observed HEMP effects that included surge protector burnouts, power supply breakdowns, and damage to overhead and underground buried cables at distances of 600 kilometers

A smaller-scale HPM weapon requires a relatively simple design, and can be built using electrical materials and chemical explosives that are easy to obtain. It is estimated that a limited-range suitcase-sized HPM weapon could be constructed for much less than $2,000, and is within the capability of almost any nation, and perhaps many terrorist organizations.

Excerpts from
CRS Report for Congress
High Altitude Electromagnetic Pulse (HEMP) and
High Power Microwave (HPM) Devices:
Threat Assessments Updated March 26, 2008

Faraday Cage

Now that I have your attention, let’s talk about building a Faraday cage.

A Faraday cage can be any size that will fit your needs. First decide what you want to protect from an EMP. Remember that the power grid will be affected. Items like a television, cell phones and the internet aren’t going to work due to the damaged infrastructure.

Things you should consider could be FRS radios, CB radios, Ham equipment, battery operated radio, test equipment like a multimeter, a spare computer controller for your car (expensive), power inverter, Laptop, and even a thumb drives loaded with your vital information. I find that picking up working second had items helps to keep my cost down. Be sure to remove the battery before storing any items. Also remember to store some batteries.

Now that you know what size you could use lets look at building materials. I built my first Faraday cage from an old wooden shelf. I wrapped the shelf with aluminum screen. I was sure to cover 100% even the top and bottom. I then connected this to a ground post with 6 gauge copper wire.

One of the best materials would be copper screening. It will cost more. On any screening material be sure to keep the holes small. This will do a better job. Chicken wire just won’t work.  Solid metal will work. Again copper is best. Aluminum foil would not be a good choice. It is to thin and damages easy.

Some other items you can use could be a metal trash can that the lid is well connected and won’t come off. Don’t forget to ground it. An old microwave can be used. It doesn’t need to be working. We only want to utilize the cage inside. To ground the microwave you can cut off the 2 prongs on the plug BUT REMEMBER to leave the ground prong. Now you can use that to attach it to ground.

Avoid gaps
Doors, panels and other parts need to be connected electrically on all sides. The easiest way to do this is with highly conductive gaskets. I made my gaskets with rolled up aluminum screen material that I placed around my door frame.

You can use the house ground but often this is a very poor ground. Better would be to get an eight foot ground pole from a hardware store and hammer it into the ground. Keep about 2 inches sticking above ground and attach it to your Faraday cage with copper wire. 6 gauge or larger would be best.

When placing your items in your Faraday cage, be careful and don’t let your items touch the metal cage. I found that placing my items in a milk crate or a cardboard box protects my items from touching the metal sides and if the cage ever moves (earthquake or blast) my items won’t touch even when they slide around.

Bottom Line
A Faraday cage should be made of metal. If you use screening be sure the holes are small. Copper is the best material for the cage but cheaper metal will work. The closer you may be to the blast the better the material you should use.  The cage needs to be covered 100% no gaps. Protect the items you will be storing. If they are touching the metal sides of the cage then they will not be protected.

OK that is the basics.

Remember a Faraday cage is no good if you forget to prepare other items like food, water, and medical supplies.

Recommended Reading:

How to build a Faraday Cage

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