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Two Letters Re: The EMP Threat May Be Worse Than We Had Thought

Hi Jim:
I understand about an EMP attack and it's possibilities to wreak havoc. But I can't help but wonder when I hear about a possible future EMP attack if we are trying to convince the terrorists through disinformation to detonate their nuclear weapons at a safe altitude instead of over the capitol during the state of the union speech.
I am thinking that for an EMP attack to be effective they would need at least 4 or 5 high yield nuclear weapons of at least 1 megaton each . These would have to be evenly spread over the US relative to population density. Russia could pull it off, and I am sure they would begin a nuclear attack an EMP. But I think the EMP effects of one 15 kiloton range weapon a terrorist would have would be isolated.
I could be wrong, but I can't help but wonder. - David

Jim:
That EMP report is good news.It shows that an EMP attack would cause significant but not catastrophic disruptions in our critical national infrastructure, and only scattered failures of cars, computers, and other electronic devices. These facts are even more favorable than I wrote in my e-mail to you in March of 2007. As I suspected, but couldn't prove at the time, the anti-ESD structures in modern semiconductors are very effective against EMP.

The report shows, for example, that there is no longer any strong reason to avoid modern cars. Of 37 modern cars tested in the report, only three were temporarily stopped when exposed to EMP while running, and all could be restarted. Only one car experienced permanent damage, but that was to some unidentified electronics in the dashboard apparently not affecting drivability.
From my experience in the electronics industry, I believe that the most modern, most expensive cars-- the ones intended to last a long time-- are the most survivable because they are more likely to incorporate better-designed, better-protected and thus more-expensive electronics.

As another hard data point, modern radios are basically immune to EMP. The report states "none of the radios tested showed any damage with EMP fields up to 50 kV/m." The same circuits that protect radios from ESD to antennas and controls protect them from EMP.

The report is quite definite: EMP is a serious threat to anything with long wires, but not so much to anything small, portable, or mobile.

An EMP attack from a fission weapon would be harmful, especially to our power and telecommunications systems, but the effect would be local and temporary-- not really very different from that of a hurricane or powerful earthquake. You owe it to your readers to set the record straight on this topic - PNG

JWR Replies: Yes, that report is good news for automobiles and mobile, battery-operated electronic devices with short antennas. However, the huge, almost incalculable problem is that railroad networks, power grids, and to a lesser extent telephone systems serve as enormous antennas for EMP that can carry EMP for very long distances. In the event of a high altitude megaton-range hydrogen bomb blast, this linear coupling will carry EMP for hundreds of miles beyond line of sight (BLOS). Within that extended footprint it could potentially fry the microcircuits of any device that is plugged in to a utility power wall socket. There could be hundreds of billions of dollars worth of short term damage and a multiple of that in long term damage (loss of productivity) and along with it the risk of a societal collapse and an enormous die-off due to dislocation, exposure, and disrupted chains of supply.

Linear coupling of EMP is one of the reasons that I discourage people from installing "grid-tied" photovoltaic power systems. Sure, it is great fun watching a power meter run backwards and getting a check in the mail from your utility instead of a bill for eight months of each year. But the EMP risk outweighs the benefits. If you go solar, then make it a stand-alone system! Linear coupling is also the reason that I advocate keeping all of your spare radios and computers disconnected and stored in Faraday-shielded containers whenever they are not being used.

What I took away from the report is confirmation of what I had concluded years ago: That for next 10 to 30 years, the EMP threat posed by terrorists will be localized, since they will most likely have access to low-yield fission bombs and will be most likely to employ them in ground bursts with small "footprints". In ground bursts or in low-altitude air bursts, the line of sight is limited, minimizing the EMP effect. But in any case the linear coupling through the power grid could magnify the EMP damage.

I concur with the report's finding that there is a the possibility of a massive population loss in the event of a well-coordinated EMP attack by a major power such as Russia or China. That scenario is a "time on target" attack with multiple simultaneous high altitude air bursts of multi-megaton hydrogen bombs. Such an attack would blanket the entire continental United States with high field strength EMP. The word "devastating" doesn't begin to convey the long term effects. We'd find ourselves back to both 19th Century technology and 19th Century population levels. And, BTW, much of the most heavily populated portions of Canada and Mexico would receive extensive collateral EMP damage.

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