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Our dependence on electricity has made the entire world vulnerable to an existential threat. That threat is what might occur should there be a prolonged cutoff of electrical power to cities and even countries.

At least two kinds of events might cause a widespread loss of electrical power: a major coronal mass ejection (CME) from the sun directed toward Earth and the electromagnetic pulse (EMP) from the detonation of a nuclear explosion above the atmosphere. These events have the potential to shut down regional or even international electrical grids for days, months, or even years if high-voltage transformers at power plants and substations are destroyed by the huge electrical currents that a CME or EMP event can induce in high-voltage transmission lines.

The EMP from a nuclear explosion includes a secondary threat, for its nanosecond rise-time has the potential of damaging many kinds of electronic devices not connected to the grid.

Solar Flares

On September 1, 1859, British astronomer Richard Carrington was sketching a cluster of sunspots viewed through his solar telescope when he saw what he described as “two patches of intensely bright and white light.” Fellow astronomer Richard Hodgson also observed the phenomenon.

Figure A: Medium-class solar flare (bright flash) and accompanying CME on October 2, 2014.

They had observed a massive solar flare accompanied by a CME that propelled an immensely powerful burst of energy directly toward Earth (Figure A). Less than a day later, the CME arrived and triggered brilliant, worldwide auroras. Telegraph operators reported large sparks in their equipment, and some received electrical shocks.

This historic phenomenon, which was named the Carrington Event, was the first known visual observation of a solar flare. The telegraph disruptions occurred because the wires strung from poles across the countryside served as antennas that received the oncoming energy and transmitted it as an electrical current.

What might occur today if a Carrington-scale solar storm occurred? A hint occurred on March 13, 1989, when a much smaller CME created a geomagnetic disturbance (GMD) that disrupted satellites, caused a 9-hour power failure across Quebec, Canada, and destroyed a multi-million-dollar transformer at New Jersey’s Salem Nuclear Power Plant. A Carrington-scale CME has the potential of shutting down electrical grids around the world, and that almost happened on July 23, 2012, when the most powerful CME ever monitored passed close to Earth.

Should a potentially damaging CME event occur, the National Oceanic and Atmospheric Administration (NOAA) will post advisories on its Space Weather Prediction Center website (swpc.noaa.gov) half a day or so before it arrives.

Nuclear EMP

A nuclear explosion generates a powerful electromagnetic pulse having an electric field of thousands of volts per meter (the potential difference between two points 1 meter apart). I’ve measured 2,000 volts/meter directly under high-voltage transmission lines. A nuclear EMP would create a much higher voltage in an ultra-fast pulse over many thousands of square miles.

Figure B: Excerpt from Atomic Energy Commission film of Starfish Prime nuclear explosion.

On July 9, 1962, the Starfish Prime nuclear bomb was detonated 250 miles over Johnston Atoll, 826 miles from Honolulu. Figure B is a frame from an Atomic Energy Commission film of the event, provided by atomcentral.com; you can watch it at youtube.com/watch?v=XoXtUkcFmG4. An EMP of about 5,600 volts/meter from the blast disabled at least six satellites and a few hundred streetlights in Hawaii.

In his report “Soviet Test 184: The 1962 Soviet Nuclear EMP Tests over Kazakhstan,” Jerry Emanuelson describes the damages caused by the estimated 10,000 volts/meter EMP from a Soviet nuclear test 180 miles over Kazakhstan on October 22, 1962. Facilities damaged included a power plant, diesel generators, a radar system, and lengthy buried and above-ground cables.

Figure C: Estimated EMP in volts/meter, from a nuclear weapon detonated high above the United States.

Much more powerful EMP bombs have been developed by China, Russia, and the United States. North Korea has claimed it could shut down the U.S. power grid with an EMP bomb. James Stavridis, a retired U.S. Navy admiral and former NATO commander, is deeply concerned that North Korea might someday attempt an EMP attack against the United States. Figure C shows the estimated EMP in volts/meter from a bomb detonated high over the central U.S.

Lightning is a natural form of EMP, and engineers have developed many ways to protect transformers from lightning strikes. While the duration of the secondary phases of a nuclear EMP resembles lightning, there is concern that older transformers are at serious risk. Then there’s the initial phase of the pulse, which has a rise time measured in nanoseconds with maximum power between 100kHz and 1GHz. This pulse can be fatal to semiconductor components such as CMOS integrated circuits not connected to the grid.

EMP vs. Personal Electronics

A solar CME and a nuclear EMP both pose a potential threat to most electronic systems connected to the grid. Personal electronics not connected to the grid or cables will probably be unaffected by a CME but might be damaged or even fried by an EMP. Small devices like electronic watches, calculators, radios, and phones might be safe, but no one knows.

A Faraday shield that blocks electromagnetic radiation is the best way to reduce the effect of a nuclear EMP on personal electronics. The ideal Faraday shield is a fully enclosed metal enclosure with no unshielded external wires or cables that would function as antennas and thereby couple EMP into the enclosure.

Many kinds of DIY Faraday shields for protecting personal electronics can be found online. Among the best sites is disasterpreparer.com by Arthur Bradley, a former NASA engineer who has a doctorate in electrical engineering.

Bradley knows his stuff. For example, many sites claim a Faraday shield must be grounded. Bradley denies this, and he’s right. Bradley has used sophisticated instrumentation to test the most common Faraday cages described online. He has given the results in YouTube videos accessible on his website and in Disaster Preparedness for EMP Attacks and Solar Storms, a book available in print or as a Kindle ebook
from Amazon.

The effectiveness of Faraday cages in reducing an EMP is given in the following chart in decibels.

Bradley recommends providing shielding with at least 50dB attenuation. His YouTube videos include tests of the EMP reduction provided by a simple Faraday cage made by wrapping a cardboard box with aluminum foil. If the foil provides a tight shield when the box is closed, his tests shows that it will provide a shielding of >50dB across most of the EMP spectrum. Sealing the foil-lined lid with aluminum tape helps. His YouTube tests include Faraday shields made from conductive fabric, static bags, ammo boxes, and trash cans.

Shielded static bags are among the simplest and easiest to use Faraday shields. Bradley’s tests show that SCS Dri-Shield 3400 moisture barrier bags are the best. You can buy these from disasterpreparer.com and digikey.com.

Figure D: A DIY Faraday bag — an antistatic bag with an inner conductive fabric lining — can provide up to 50dB protection for small electronics.

Figure E

Figure F

Figures D through F show an EMP shield for a tablet that I quickly made from a DIY conductive fabric pouch inserted inside an SCS 3400 bag with Velcro closures I added. Conductive fabric is available from many sources, including Bradley’s site. I used Mission Darkness fabric sealed with their tough TitanRF Faraday Tape (mosequipment.com). This simple Faraday cage provides excellent shielding and can be used for laptops, radios, phones, and other small devices potentially vulnerable to an EMP.

Figure G: Mission Darkness Faraday shield testing app.

Mission Darkness has a free app that provides an estimate of the EMP blocking capability of Faraday shields by using Wi-Fi and phone signals as surrogates for EMP (Figure G). Activate the app on a phone, insert the phone in the enclosure for 30 seconds, and then remove it to see the results.

Learning More

You can find considerable information online about the hazards presented by a major CME and an EMP attack. A good brief summary is “Report to the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack: Risk-Based National Infrastructure Protection Priorities for EMP and Solar Storms” by George H. Baker (July 2017).

Finally, if an EMP or GMD event shuts down power to law enforcement, water and sewer systems, gas stations, grocery stores, and hospitals, the least of your concerns might be protecting personal electronics. So be sure to check out the survival recommendations at redcross.org and private sites.

Congressional EMP commission reports: firstempcommission.org.