I Smell Sensationalism

[daqq]

Sensationalism, inflating or inventing facts and outright lies?!?!? In the media no less!? Well, I'm shocked and outraged!

[Kremmen]

Apparently the main threat from an EMP is not from the radiation from the actual detonation, but from electrons and positrons emitted by the explosion which then cause secondary wideband radiation. At low altitude the atmosphere will stop these particles within a few tens of miles, and therefore the effect is relatively short-ranged. However at stratospheric altitudes the combination of thinner air and the strength of the earth's magnetic field can carry the particles over an extremely wide area, allowing for heavy EMP over a wide geographical area. Bombs can also be optimized to output more beta/electron radiation to worsen the EMP effect.

The shape of the magnetic field over North America makes EMP especially threatening, in that a powerful EMP-optimized bomb detonated over the Dakotas could knock out the electrical grid and computing resources of almost the entire central US. The coasts would probably be mostly ok, however.

There is no mechanism by which nuclear fission in a U or Pu bomb would produce electrons and positrons (which strictly speaking are antimatter) as its main products, but rather neutrons and gamma rays - well a lot of EM radiation at different frequencies. But it is the gamma giving rise to an avalance phenomenon in the electron shells of atmospheric gas atoms.
So i think you got it a bit backwards - it is the radiation causing electron avalanche which in turn causes high electric fields causing sparkovers and general mayhem in circuits and structures.
A reasonably lucid explanation of EMP can be found e.g. here: http://www.thespacereview.com/article/1549/1

[FJV]

The real danger is that you aren't always able to tell if an attack is going to be an EMP or nuclear.

When you detect the missiles flying towards you, there's no way of knowing that the payload is non-nuclear.
And you may decide to fire nukes back before they will be destroyed, rather than wait and see.

All adversaries with ICBM's know this and are not stupid enough to take the risk.

[G7PSK]

The real danger is that you aren't always able to tell if an attack is going to be an EMP or nuclear.

When you detect the missiles flying towards you, there's no way of knowing that the payload is non-nuclear.
And you may decide to fire nukes back before they will be destroyed, rather than wait and see.

All adversaries with ICBM's know this and are not stupid enough to take the risk.

MAD. Mutual assured destruction.

[Tinkerer]

I have to dispute the claim that this is pure sensationalism.

An EMP doesnt have to be produced by a nuclear weapon, it can be produced by something called an explosively pumped flux compression generator. Anyone with a few hundred $$ can put one of these things together and hit a city with it, more if they can launch it high enough into the air. The likelyhood of this is small though since not too many people apparently know about it.

As for damage caused, depends on the height of detonation and the yeild and of course distance from the detonation. There is a max theoretical strength though I think is estimated between 35-50kV per sq m? This limits the distance to something like 500 miles I believe.(no I am not 100% on this, but it should give an idea)
Vehicles in general arnt going to die instantly upon being hit with any EMP, in fact it would take a sizable one to fry everything.(above 15-20kV is a good estimate) As more electronics get added, we will probably become more vulnerable there. There would still be some damage, but at least on a smaller EMP many would still be able to run. Hit with a proper sized blast though, and you will have everything fried and not just on vehicles. The power grid is currently vulnerable as of course people have indicated in links prior this post.
Heres the big thing many people forget, we rely a massive amount on refridgeration and food getting to where it needs to go just in time to be sold. Not to mention the water pumping systems that people need for drinking water. Energy pumped into the grid with fry all the refridgeration systems hooked to it that are within range as well as the water pumping systems. Any major disruptions of this and you will have chaos as people start starving unless an alternate source of food and water arrives within a week; gas pumps wouldnt work too well either meaning people better have a full tank and hope they dont get mobbed.
I am not so worried about immediate deaths(well planes falling out the sky could ruin a person's day; or maybe you were touching something metal and got shocked) so much as what I noted above, the removal of food and water transport systems.
Eitherway, any well place EMP could take out a chunk of the US infrastructure and I have yet to mention those giant transformers they use that are the size of a small(very small) building. They dont keep those things laying around ya know, imagine a few of them blowing. Average time for building a new one is 2 years.(which suprised me when I looked it up)

This also says not a thing about solar flares. We have been incredably lucky(we as in major population centers) not to have gotten hit by a large flare like the one that hit Canada a few years back and fried alot of stuff.

Sensationalism is the title, yes, but dont just dismiss something like this offhand because this danger is incredibly real.

[T3sl4co1l]

There is no mechanism by which nuclear fission in a U or Pu bomb would produce electrons and positrons (which strictly speaking are antimatter) as its main products, but rather neutrons and gamma rays - well a lot of EM radiation at different frequencies.

I wouldn't say none.  I don't think fission directly produces anything (i.e., within femtoseconds; maybe a rare pair-production from sheer quantum vacuum voodoo?), but the products should make plenty of nasties.  Sr90 is a good example of beta-bearing waste; much more will be made in odd nuclear ratios (neutron rich/heavy) which result in relatively quick (microseconds to seconds) weak decays, resulting in both types of 'trons.

The impact from these sources is probably tiny though (would the betas even leave the fireball in time to make a difference in the plasma wave?).

A reasonably lucid explanation of EMP can be found e.g. here: http://www.thespacereview.com/article/1549/1

Good article, thanks.

Tim

[Kremmen]

There is no mechanism by which nuclear fission in a U or Pu bomb would produce electrons and positrons (which strictly speaking are antimatter) as its main products, but rather neutrons and gamma rays - well a lot of EM radiation at different frequencies.

I wouldn't say none.  I don't think fission directly produces anything (i.e., within femtoseconds; maybe a rare pair-production from sheer quantum vacuum voodoo?), but the products should make plenty of nasties.  Sr90 is a good example of beta-bearing waste; much more will be made in odd nuclear ratios (neutron rich/heavy) which result in relatively quick (microseconds to seconds) weak decays, resulting in both types of 'trons.

That is why i hedged my bets by saying "main products". I'm sure you are correct but my own thinking was/is that as far as EMP is concerned the relevant production mechanism is the one originating from the gamma burst. As noted in the article and elsewhere, the source of EMP does not even have to be nuclear - any mechanism able to rip electrons off atoms can in principle cause an EMP. The burst of radio static caused by a lightning flash is an example. So a secondary effect based on something else than gamma is certainly possible. I just suspect that for a nuke, anything other than the primary mechanism will disappear in the background noise. But i have no proof of this of course.

[G7PSK]

Just rapid thermal heating of the atmosphere will produce a plasma, a hydrogen bomb makes a lot of heat. That's a lot of plasma without taking into account the effects of radiation on the surrounding atmosphere.The temperature produced by a hydrogen bomb is several times that of the surface of the sun.

[richard.cs]

EMP effects are unlikely to cause permanant damage to modern cars, which are fairly well protected (due to the electrically awful nature of car electrics they need to be), are enclosed in a metal cage, and are electrically short. Tests where cars have been struck by lighting typically shows no effect or them stalling and needing to be restarted. Despite claims to the contary older Kettering ignition systems will be fine too unless you happen to have a mile of wire trailing out of your car. Of course thousands of cars stopping on a busy road can still be damaging - even if they can be restarted it doesn't stop people driving into each other.

Most aircraft controls should be fine too, but navigation and communication could easily fail so I'd expect some collisions when attempting to land, particularly in poor visibility.

The things that really get hit hard are those with long cables (power grids, telephone lines) or which are sensative by design such as radio receivers. Expect to loose the power grid for some weeks or months. And whilst backup generators are likely to start ok there are likely to be enormous problems with fuel distribution, and also with damage to switchgear on large installations such as hospitals. The main questions I would ask to decide if the 500,000 is sensationalist are:
1) How many deaths could be expected from car crashes resulting from unexpected engine failure and
2) How many Americans (in hospitals or otherwise) rely on electricity for life support in a way that 30 minutes matter.

Of course this is only relevent if the EMP is caused by a solar flare, if it was nuclear then MAD dictates many more deaths from the resulting war.

[SolarSunrise]

EMP effects are unlikely to cause permanant damage to modern cars, which are fairly well protected (due to the electrically awful nature of car electrics they need to be), are enclosed in a metal cage, and are electrically short. Tests where cars have been struck by lighting typically shows no effect or them stalling and needing to be restarted. Despite claims to the contary older Kettering ignition systems will be fine too unless you happen to have a mile of wire trailing out of your car. Of course thousands of cars stopping on a busy road can still be damaging - even if they can be restarted it doesn't stop people driving into each other.

Most aircraft controls should be fine too, but navigation and communication could easily fail so I'd expect some collisions when attempting to land, particularly in poor visibility.

The things that really get hit hard are those with long cables (power grids, telephone lines) or which are sensative by design such as radio receivers. Expect to loose the power grid for some weeks or months. And whilst backup generators are likely to start ok there are likely to be enormous problems with fuel distribution, and also with damage to switchgear on large installations such as hospitals. The main questions I would ask to decide if the 500,000 is sensationalist are:
1) How many deaths could be expected from car crashes resulting from unexpected engine failure and
2) How many Americans (in hospitals or otherwise) rely on electricity for life support in a way that 30 minutes matter.

Of course this is only relevent if the EMP is caused by a solar flare, if it was nuclear then MAD dictates many more deaths from the resulting war.

When I was 12, a long time ago, we had to write a short story of our liking. So I wrote about an apocalyptic story where a solar flare caused an EMP and destroyed the power grid, telephone lines, medical equipment, etc. I got a C because my English teacher pointed out that the story was not logical. When I wrote in my story that lot of people, who relied on electronic devices to keep their heart going, died from electrical failures, her comment was: "Don't Hospitals have backup generators?" 

[G7PSK]

The 500.000 dead are most likely due to gun shot wounds, because if Hollywood and the general media are to be believed the first thing an American does when the lights go out is pick up a gun and start shooting and rioting.

[richard.cs]

...her comment was: "Don't Hospitals have backup generators?" 

My local hospital has a few MW of natural gas generation with all the waste heat used by the hosptial, normally connected in parallel with the grid. If the grid goes down they just island the hospital (possibly with a bit of a brownout as that plant tries to momentarily hold up the whole city ). *If* it gets islanded ok without damge to anything then it could be expected to last weeks because the gas distribution network is largely self-powered, there would be pressure fluctuations as the system would no longer be actively controlled but the pumps that move the gas are all powered by gas turbines.

They do have diesel gensets as well, but I'd imagine they don't have more than a day worth of fuel on site and like most people with backup generators rely on the trucks starting to arrive pretty soon.

[VK5RC]

I don't know how sensitive most cardiac pacemakers are to EMP but about 10% misbehave (usually not critically) with a standard mobile phone placed directly above the pacemaker wire.
I recall hearing that one of the MIG fighters had a thermionic valve front end to be able to tolerate a bit more EMP up the front end.

[Tinkerer]

EMP effects are unlikely to cause permanant damage to modern cars, which are fairly well protected (due to the electrically awful nature of car electrics they need to be), are enclosed in a metal cage, and are electrically short. Tests where cars have been struck by lighting typically shows no effect or them stalling and needing to be restarted. Despite claims to the contary older Kettering ignition systems will be fine too unless you happen to have a mile of wire trailing out of your car.

No that isnt entirely true. Cars are not a complete cage, they have glass and large holes in them that are not conductive etc. There is a huge difference between lightning and an EMP, with lighting being a pinpoint strike, not a wave washing over everything.(Lightning will simply travel around the body to ground like we all expect) Yes, in many cases the car would at least still start, but you would have to think that the radio would at the very least be fried among other things that are exposed. It also doesnt take a mile of wire to pick up an EMP, a mere 3 feet is enough, lessening of course the shorter the length is.
I will agree that the exact damage to occur is a bit unknown given that the terrain matters, the stuff in the vehicle etc etc, but you cant say that cars would be completely fine given the fact that the 'shielding' they have is not a complete or even close to complete enclosure. At the very least, I would have to say that the radio is likely to be fried every time given its supposed to pick up signals and pumping a massive one in is garunteed to do something. There is also the fact that undernath the car isnt enclosed either, that much of the wiring is not shielded and a few electronic components in the engine are simply encased in plastic.

[denelec]

A big solar storm such as the "Carrington Event" of 1859 is much more probable.
It could probably cause widespread blackouts such as the one that happened in Canada in 1989.
http://en.wikipedia.org/wiki/March_1989_geomagnetic_storm
But I'm not sure it would cause a lot of physical damage.
The 1989 storm caused the Quebec power grid to collapse following the tripping of 735kV power lines.  But there was no real damage and no chaos in the province.

[SArepairman]

can yoou include this in the thread topic, i feel like half the people in this thread are totally clueless and should at least read basic theory about this.
https://www.fas.org/man/crs/RL32544.pdf

this is the important bit that the electrical engineer in you is curious to know:

A high altitude nuclear explosion (tha
t creates HEMP) produces three major
energy components that arrive in seque
nce, and which have measurably different
effects that can be cumulatively damaging to electronic equipment. The first energy
component is the initial energy shockwav
e 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 char
acteristics 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 com
ponent is so rapid and intense that it
can destroy many protective measures, a
llowing the s
econd com
ponent to further
disrupt the electronic equipm
ent. The third energy co
mponent is a longer-lasting
magnetic signal, from about one microsec
ond to one full second in duration. This
geomagnetic signal causes an effect that is damaging primarily to long-lines
electronic equipment. A localized magne
tic 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 late-
time effect adds to the initial HEMP eff
ect, 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.


i BELIEVE that if yoou are near a large metal structure during a HEMP it is possible to get zapped (like being a construction worker on a scaffolding).

[peter.mitchell]

---snip---

Mind adjusting your line breaks, this is hard to read; infact, here, just copy-paste this;

Code: [Select]

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 late- time 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.