Small bomb, big noise
"EMP is the most asymmetric threat there is in terms of a single weapon taking out large categories of infrastructure," Dr George Baker, former leader of the Defense Nuclear Agency's EMP program, told The Register. "It's a lot easier to achieve, since you don't need reentry capabilities."
Baker said that a low-yield device such as that thought to be owned by North Korea, detonated at optimum height, would generate EMP over an area with a diameter of around 1,000 miles. He understandably declined to specify the optimum height, but it's thought to be around 50 to 80 miles up.
If such a device were to be detonated over the most densely populated part of the US, namely the North East, the consequences for power grids, computing centers and telecommunications systems could be catastrophic, he explained. Baker and others have formed the Foundation for Resilient Societies to advise Congress on this and other critical infrastructure issues.
His colleague at the foundation, retired Air Force captain Thomas Popik, is principal investigator for the group. Popik told The Register that by far the most vulnerable infrastructure is the power grid. E3 pulses are amplified by the length of the conductive cable they encounter, and the power grid has some very long cables indeed.
"A North Korean EMP attack is extremely credible," he said. "No reentry is required and a low-yield weapon could produce a significant impact on the electrical grid. The grid is designed to be resilient to single failures but not multiple simultaneous failures."
The problem is amplified by the nature of the grid. A series of failures can cause a catastrophic knock-on effect on the rest of the grid as power surges and troughs play merry hell with the network.
Most vulnerable would be the handful of massive transformers needed to keep power regulated through the grid. These enormously costly and complex pieces of equipment currently take around 22 months to build and deliver, so the power companies don't keep many in reserve.
To complicate matters the US has outsourced about 80 per cent of the production of these transformers to countries like China and Germany. They also require a specialized kind of high-tensile coated steel, but as US companies don't make a lot of the transformers, American steel producers have stopped making the necessary materials.
Power plants are going to take a hit, Popik warned, but there was some good news on that front. Many power stations are dual-fuel systems, capable of running on gas and fuel oil. The problem is that many stations don't keep the reserve oil tanks topped up for emergencies.
There's also a surprising number of power stations that don't rely on digital controls. A lot of the hydroelectric stations built in the 1930s and 40s in the West of America, including Hoover Dam, can operate perfectly well using analogue controls and so might well survive an EMP attack.
The telecommunications cables that make up the communications backbone of the US, and the world, would also be extremely vulnerable. Signal amplifiers, switching stations and routers could all be burned out by a strong EMP pulse, and that would have a massive knock-on effect on the computing infrastructure of the nation.
Some more alarmist scenarios depict an EMP pulse destroying all electronics completely, with modern cars, all electronics with chips, and anything with a current getting taken out. That's unlikely, but we don't really know because so little testing has been done on the matter.
In 2004, the EMP Commission tested 37 vehicles by exposing them to steadily more powerful electromagnetic stimuli. The initial results looked promising – none of the cars stopped working permanently, a few did need to be restarted, and there was a minor amount of electrical damage to several of them.
There are some important caveats, however. The cars were deliberately not tested to destruction because they had to be returned to the US Department of Defense, so the minute an effect was noticed the testing was stopped on that vehicle. In addition, none of the cars were built after 2002; it would be interesting to see how a Tesla, let alone any other modern car packed with electronics, measures up.