I concur that anyone with a megaton-range weapon would probably not use it on EMP, but I think that someone with one or a few 10-kiloton range weapons would be strongly tempted to try an EMP shot. What I do not know is the effective radius of such a weapon, or rather, how the affected radii scale with yield. If they scale the way blast effects do, with the cube root of yield, then a 10-kT nuke would have fully 1/10 the EMP radius of a 10-MT one. If it’s the square root, then the radius would be only about 1/30.

This could be surprisingly important. Actual recovery from such an attack would be via a sort of dry-land Dunkirk. If the vehicles used in evacuation could get in and out of the affected area on a single tank of gas, such an operation becomes much easier to carry out.

Enough EMP. If I managed to say anything important in this post, it was probably the notion that Baghdad is the place to watch for a bioterror incident.

A substantial percentage of the energy of the bomb is converted into the pulse.

The numbers I’ve seen are under 1/2% of the bomb’s energy. That’s hardly “a substantial percentage” Shannon.

The speed of the pulse (zero to zenith to zero) is several hundred times faster than that of lightening which is what most surge suppressors are designed to handle.

The rise time of the surge is only important if you’re depending on heating to melt fuses or mechanical circuit breakers to trip. Diodes don’t care about rise times. When the exceed voltage is reached, the diode becomes a path to ground.

There’s also a lot mythology surrounding EMP. The exoatmospheric tests in the above the Pacific in the 50’s (Starfish?) supposedly caused lots of power outages in Hawaii. Turns out, not true! There were minor effects, a few street lights went out, a few burgular alarms, etc.

New solid state suppressors are supposed to be able to stop the pulses but the vast majority of civilian systems won’t have them.

Diodes and transzorbs ARE solid state suppressors. There’s nothing new about them. They’re ubiquitous, even in consumer grade electronics, which are typically made to the lowest reliability classification.

Worse, the pulse can evoke destructive currents inside chips themselves.

That would depend on the intensity of the pulse.

Consider this: your average PC is subjected to electromagnetic radiation all the time, from radio waves to cell phones to EMI of various frequencies being emitted by motors, heaters, mechanical switches, etc. Does everyone’s PC die every day? Do all the internet servers die when there’s a thunder storm somewhere? No.

Consider this: once upon a time solar flares wreaked havoc on early telecom satellites. Not any longer. We’ve learned to deal with it effectively. To this day though, whenever there’s a solar flare announced, you’ll read predictions that we should expect “major” disruptions in the world’s telecom systems and power grids. Rarely is there a even problem.

Consider this: power companies routinely deal with surges on their sytems in excess of 1 million volts from lightning. There have been lightning strikes in excess of 5 million volts that were effectively clamped and caused no damage.

As I said, the idea that EMP is a potential WMD is unconvincing. If someone has a multimegaton thermonuclear weapon, they’re likely to set off over New York, where the blast and heat will kill thousands to millions of people, not 50 miles up over Kansas in hopes of frying our computers.

Interestingly, the record of nerve gas as a terrorist weapon is poor; see the limited effect of the Aum Shinrikyo attacks in Tokyo. The question is, what went “wrong”?

Aum Shinrikyo didn’t invest any effort into their delivery system. They basically used a system of perforated bottles that slowly oozed the sarin into balled up tissue paper. They needed a system that would let the people deploy the weapon get away.

If they had used a simply compressed air aerosol system or suicide attackers, the death toll could have been a couple of orders of magnitude higher. Fortunately, the attack was not well planned having been rushed into place to create a diversion from an expected police raid.

I think your underestimating the impact of an EM pulse originating in space. When detonated above the ionosphere a nuclear bomb interacts with the earth’s magnetic field to turn ionosphere into a giant radio broadcaster saturating the area underneath with the pulse. A substantial percentage of the energy of the bomb is converted into the pulse.

Surge protectors sold for computers and home entertainment systems serve this function. Also, many of the high-end electronics (military, industrial) systems have substantial surge protection built in.

The speed of the pulse (zero to zenith to zero) is several hundred times faster than that of lightening which is what most surge suppressors are designed to handle. The pulse will be there and gone long before the vast majority of suppressors even begin to trip. Worse, the pulse can evoke destructive currents inside chips themselves. An EM pulse can kill electronics setting unplugged on the self.

Hardened systems work by shielding the entire system, including the power supply, from the pulse. New solid state suppressors are supposed to be able to stop the pulses but the vast majority of civilian systems won’t have them.

Unfortunately, simple to fix.

Interestingly, the record of nerve gas as a terrorist weapon is poor; see the limited effect of the Aum Shinrikyo attacks in Tokyo. The question is, what went “wrong”?

When an electromagnetic wave passes across a conductor (or the conductor moves through the wave) a voltage is induced in the conductor. If there is a complete circuit, the voltage will force a current to flow through the conductor. That’s the basic principle that makes an electric motor work. But there are quite a few high hurdles to overcome to make EMP a weapon:

1. Voltage does not equal current. Voltage is potential energy, not kinetic, and is analogous to water pressure. You can have pressure in a pipe, but if the valves are closed no water flows. Also, if there are overpressure vents or absorbers in the plumbing system, transient pressure surges are contained or quickly relieved by venting. Diodes and transient voltage suppressors (tranzorbs) serve this function in electrical circuits. They shunt overvoltages directly to ground. Surge protectors sold for computers and home entertainment systems serve this function. Also, many of the high-end electronics (military, industrial) systems have substantial surge protection built in.

2. All noncoherent (meaning non-laser type) radiated energy follows the inverse square rule, approximately stated as Intensity = 1 / Distance Squared. Move away from a radiating source to twice the distance and the intensity drops to 1/4 of what it was, move away 10 times as far and it drops to 1/100th as intense. You would need a very intense source like, say, a 10-20 megaton hydrogen bomb, to create enough initial energy to propagate a wave of energy over enough distance to damage very much. And if you have a 10-20 megaton hydrogen bomb, EMP is just an ancillary effect. I’m more worried about that really damaging sun tan I’m gonna get from it.

I think the big threats come from bioweapons and nerve agents. Nerve gas is incredibly deadly stuff and can be manufactured in any plant that makes pesticides.