View Full Version : Electromagnetic Pulse: Duration of?

11-16-2009, 10:48 PM

I've had to shelve my last project becuae I just couldn't get the first chapter to work. I'll retunr to it one day when I'm ready to tell it, but in the meantime, I'm writing a story that's based on a dream my wife had.

It's partly post-apocalyptic which I'm wroking up to, but in the build up to the big "Boom" I'm having a series of other events occur to add to the confusion and disorientation fo the characters and the world around them.

Part of this, I'm hoping, will involve the loss of normal day to day functions. I figured the best way to knock out the UK's infrastructure would be to fry the whole lot with a big-ass EMP.

Whether or not I continue with the EMP route thought depends largely on what kind of duration it has.

Woud any of you kind people be ableto offer me any answeres on this? Is there a possibility that the explosion could be sufficient enough to permanantly take down the power grids but still be high enough altitude to not kill everyone... Or whatever combination works for this scenario.

Having surviviors is important to the story, at least to begin with. If I'm barking up the wrong tree, please let me know and if possible give me some pointers on other avenue I could explore.

Any and all help is greatly appreciated.

Thanks in advance,


Mike Martyn
11-17-2009, 03:03 AM
During the cold war there was a lot of public speculation concerning EMP as the opening salvo in a full scale nuclear exchage. If you explode a 10 or 20 megaton bomb at very high altitude (100,000 ft ?) you generate and emp without destroying the real estate or exposing the population to serious doses of radiation. Anyway, that was the idea although I don't believe either side has ever publicly acknowleged this.

Would it be permanent? No but you'd have to do a lot of repairs to power distribution grids. Also semiconductors that are integral to computer systems are very sensative to EMP and so kiss your computer goodby unless it was sheilded to mil spec rating. For what it's worth, certain key circuitry used old style vacuum tubes since they weren't as sensitive to EMP.

11-17-2009, 03:16 AM
Read Lucifers Hammer, by Jerry Pournell. It's already been done ...

11-17-2009, 01:55 PM
rom what I remember the duration of the pulse itself is instantaneous (unless you get into quantum stuff). Electrical/electronic equipment 'knocked out' by an EMP would be either permanently damaged or require extensive repair.

The effect wouldn't be even either, the further away from the point of origin and the better shielded a piece of equipmen was the less damage done to it.

It's not a silver bullet - which is probably why no one ever tried using one in the cold war

11-17-2009, 04:50 PM

Thanks for the advice.

I think with something like this that is probably a little implausible and mostly guesswork, it should leave things open enough for me to apply a little artistic license.

If I take the route of the majority of the power grid being too damaged to work properly without repairs, that gives me a bit of time to activate the next plot device to make it impossible to complete the repairs.

I just need power to be out for long enough that the country goes into panic mode and for all hell to break lose.

I'll look up 'Lucifers Hammer', the chances are that I'll have to continue writing while I try and lay my hands on a copy of it, but if it can help me, I can always go back and change bits later on.

Thanks again for all the advice.


11-27-2009, 05:08 PM
Another question regarding EMP's, but this time on its effects...

My only knowledge of EMP's comes from website's I don;t really understand, Wikipedia (which I don't trust) and Hollywood movies (Which I definitely don't trust).

Lets say a sufficiently powerful EMP was set off at high altitude and the national grid has been knocked out. That much I'm fine with, because as already mentioned, unless extensive repairs are made, it won;t be coming back on anytime soon.

But to make my characters experience the level of disorientation and confusion required for the setting I'm creating, I need them to be completely cut-off.

That means I can't have any easy and convenient means of transport. While it hurts me to do so, I'm trying to kill the car.

Would it be within the realms of plausible deniability to have all the cars electronic systems totally fail/overload/whatever? If so, I'm guessing the only ones that survive would be the ones with the battery disconnected.

Or is it a case of it would be fine so long as it was switched off at the time? If this is the case, are there any other ways to kill almost all the cars. I say 'almost all' because it might come in handy to have one or two later in the story.

Any input on this would be really appreciated.

Thanks in advance,


Mike Martyn
11-27-2009, 10:26 PM
Emp or "electromagnetic pulse" induces a current in any conducting substance such as copper wiring. Microelectronics are low voltage devices (5 to 9 volts) and hence very susceptiple to the voltage spike induced by EMP.

What that means is that all a modern cars electronics including the clever little bits that run the fuel injectors are zapped along with the radio, cd player etc, not to mention your computer. Having it turned off or with the battery disconnected won't neccesarily save it depending on the strength of the pulse.

However, older vehicles wouldn't have any microelectronics. Even the old car radios had vacuum tubes (200 volts plus) so your protag should be able to cruise around in his 1961 Dodge Dart or granpa's old pickup just fine while listening to the latest post apocolypse updates on his car radio, the one with the big chrome push buttons.http://absolutewrite.com/forums/images/icons/icon7.gif

11-27-2009, 11:30 PM

That's really, REALLY, REALLY useful!

While in my neck of the woods we'd have a bit of trouble picking up a classic Dodge Dart, I'll research into some older cars and see if I can find a couple of examples I like that we may have had over here.

So that bit in 'Broken Arrow' where Travolta switches off is humvee and sets off the nuke a few feet underground, only to restart it and drive off a few minutes later, is either another example why the film should never have been made in the first place or is saying that the military humvee is just old and full of antiquated technology.

Thanks ever-so!

I can keep writing. Yay!


11-27-2009, 11:43 PM
Hey Stargazer, I'm already writing this book. ALREADY WRITING IT, I say! Let's see who finishes first, shall we? ;)

Mike Martyn
11-27-2009, 11:51 PM
My granny had a 1956 Morris Minor that had these cute little arms that popped out of the side when she signaled a turn, not that she ever signaled, having a sense of entitlement to the entire road which seems to be the special province of elderly Scottish women.http://absolutewrite.com/forums/images/icons/icon7.gif

I bet the '56 Morris Minor would survive an EMP just fine.

11-27-2009, 11:54 PM
Well... My one was inspired bt a crazy messed up dream that my wife had. Try beating that for inspiration!

And my stories don't tend to work out well for most of my characters. Happy endings are wasted on me. If my audience don't finish with true ambivalence about the tone of my endings, I feel as though I've failed.

I have no idea how you work/write, but I'm confident we'll travel very different paths into the apocalyptic future and come out the other end with very different perspectives.

But since you seem like the competitive type... I'll have to get cracking. Preface, Five Chapters and a short sub-section in, and I'm at just over 24000 words.


EDIT: Just saw your reply Mike. The old Morris Minors... Wow. One of my friends from school got one of those as her first car. It was absolutely invincible. I also read about a truck tipping over onto someone elses Morris and the driver survived untouched because the body was so thick, it absorbed the weight of the truck, unlike modern cars that just crumple up. Amazing old things!

11-28-2009, 12:03 AM
I have a head start on you. But no, not terribly competitive, just a bit angsty whenever I see someone working on stuff similar to mine. But it won't stop me from wishing you good luck. So, good luck!

11-28-2009, 12:11 AM
...just a bit angsty whenever I see someone working on stuff similar to mine.

I understand. But look at this this way. The chances are very good that we write very differently. The ideas you have that cause the apocalypse are probably slightly different to mine, and while we may share a delivery method, the characters, the things that happen to them and the places they go are likely going to be so far from what we each have, it needn't be worth worrying about.

Besides, someone somewhere is likely to say to me at some point that everything I write looks like it was put together by a five-year-old and therefore I'm unpublishable.

Thanks for the 'Good Luck' and I wish you the same. And if it really does end up that we both wrote the same thing, look on the bright side... you got to it first before I did.


11-28-2009, 01:11 AM
I know. Still, it helps hearing it.

11-28-2009, 01:34 AM
There's a book, One Second After, that came out last spring that deals with the aftermath of an EMP. The characters are in the mountains of North Carolina and have very little news of what has happened to the rest of the world. It was one of those books that I figured probably had some logic holes, but I couldn't stop reading it.

11-30-2009, 12:42 PM
So that bit in 'Broken Arrow' where Travolta switches off is humvee and sets off the nuke a few feet underground, only to restart it and drive off a few minutes later, is either another example why the film should never have been made in the first place or is saying that the military humvee is just old and full of antiquated technology.

Technically a Humvee, beeing a military vehicle, is probably shielded against EMP, also AFAIK underground nuclear detonations don't generate much (if any) EMP.

It's still Hollywood though - get a military engineer to answer the question.

going out on a limb here: fuses in almost all cars might be blown by an EMP, that's what they're designed for after all. So cars that are pre microelectronics might get away with just needing the fuses replaced. Anything up to the late seventies/early eighties could be salvaged. I doubt any vehicle from the nineties or beyond, unless it was 'old-tech', would survive.

Mac H.
11-30-2009, 01:15 PM
So that bit in 'Broken Arrow' where Travolta switches off is humvee and sets off the nuke a few feet underground, only to restart it and drive off a few minutes later, is either another example why the film should never have been made in the first place or is saying that the military humvee is just old and full of antiquated technology.Not necessarily. It might be plausible.

Remember that an EMP won't cause much in the way of blown fuses in a small vehicle .. even though it can do a lot more damage in an electricity grid.

That's because it's actually the size of the enclosed area that's the problem. A wire loop containing 10 square miles (eg: A small town) is going to have 26 million times the current flowing due to the EMP compared to a small vehicle. (Since 1 square mile is about 26 million times 1 square metre)

So if a small vehicle gets 1 amp flowing at the wrong time - it probably won't even blow a fuse. But the same EMP could cause a 26 million amps to flow in the electricity grid .. and could certainly do some major damage.

The other problem is that the ultra fast transients would cause microelectronics to suffer 'latch up'. This can really only be corrected by power cycling the device.

So the electronics stability & control system on the helicopter in 'Broken Arrow' would fail. It might not be permanently damaged - but it would crash before they could power cycle everything. (And they might not be able to power cycle things in the air, because the generator from the rotor blades might be keeping things latched up ?)

So the scene where they just restart the car yet the helicopter crashes might be plausible.

*MIGHT* be.


12-09-2009, 02:19 PM
Everybody let out a deep, frustrated sigh... I have yet another question on this subject.

How would the EMP affect the supply of natural gas? Would people with gas cookers still be able to receive fuel or would the supply be interrupted by all kinds of various electrical systems failing.

And I promise, next time I will write about something that I have a bit of knowledge about.

Feeling a bit daft,


12-09-2009, 04:34 PM
The gas supply still needs pumps and those need control circuitry. The whole pipe network is most likely computer controlled. So I reckon it would all shutdown.

12-09-2009, 11:25 PM
I sense that post apocalyptic Britain is going to see a resurgence in the popularity of corned-beef and spam.

Thanks for the reply Waylander.

12-10-2009, 05:12 AM
Just a brief note. An EMP basically generates tons of electrons that are shooting through the atmosphere, and all metal wires act like an antenna that collect them. The bigger the wire the more they catch. So anything that has a lot of wires would be impacted, but something like a wristwatch for example would probably be fine.

I'm not going to run those numbers because...well that would suck, but it would seem more realistic to me (a guy with a degree in physics) if you did allow for some small electronics to have survived the blast.

Anarchic Q
12-10-2009, 06:45 AM
Well... My one was inspired bt a crazy messed up dream that my wife had. Try beating that for inspiration!
Same thing happened to Stephenie Meyer, which caused her to bring forth Twilight. *Dramatic music!*

12-10-2009, 12:18 PM
I sense that post apocalyptic Britain is going to see a resurgence in the popularity of corned-beef and spam.

Thanks for the reply Waylander.

Spam, lovely Spam, wonderful Spam


As a true Brit I'm now hungry.

12-10-2009, 01:05 PM
Science geek
Loves electronics
Stuff I did in the military

First, you have to decide what sort of effects you want to have happen, then decide the mechanism. For example, I believe you want the power grid affected, but allow smaller electronics to still function. Or maybe you just want the unshielded electronics to fry. Or you want all electronics to fry See below.

Power Grid: The answer to that is a massive solar flare. And itís happened before, too. A large enough solar flare generates an electromagnetic storm, originating from the sun, and impacting the earth. What basically happens is a big bubble of plasma called a coronal mass ejection gets spit out towards Earth. The plasma contains a lot of magnetic field lines. When those interact with the Earthís magnetic field, huge amounts of magnetism sweep through the Earth. When they intersect anything metallic, they set up currents. Same principle used to generate electricity. But if you have a five hundred kilometer gas line, you suddenly have a few thousand amps of current running through the skin of the pipes, just looking for someone to fry. Same thing in power cables. Montreal, Canada, had a day-long blackout from this cause in the late 1980s. Smaller electronics are not affected, since the wires arenít very long. But anything with long lines of metal (power lines, gas/water lines, railroads) will have huge currents induced in them.

Unshielded Electronics. Here is where you want to use EMP. The effect is NOT instantaneous, but is something on the order of seconds, not minutes. A nuke generates a huge cloud of really hot gas. Like millions of degrees. All kinds of radiation gets dumped out. X-Rays, IR, radio, gamma, all up and down the spectrum. The ionizing radiation gets absorbed by the atmosphere, which then re-radiates in other parts of the spectrum, adding to the fun. So, hereís a car radio, wired to receive fairly faint radio waves, amplify them, extract out the music, and play it. Then a big wave of radio noise smashes into the antenna, into the circuitry designed for microvolts Ė totally unprepared for input in the volt range. Zap. Same thing happens with most other electronics. DVD players used to running on house current find themselves faced with a spike of one thousand volts from the house wiring. The on-off switch is no good, because the air gap is too small. Worse, the chips in everything are used to really small voltages, and donít take well to anything large-sized whamming into it.

Everything dies. Here is where you can get really creative. Consider the wavefront of a supernova. And it doesnít have to be very close. Anywhere in the nearest 5000 light years will do. That wavefront is a mixture of the largest thermonuclear explosion in the universe. It has everything in it. Every possible ion, from electrons to naked helium nuclei are cruising through our solar system at about half light speed. When it hits the atmosphere, itís going to do everything from light up the night sky to having neutrons drilling through those chips I talked about above. Everything will go irrevocably dead. People, too, so this requires a bit of fancy footwork to make sure the supernova is far enough away that everyone lives, but still energetic to kill off all electronics. All of them. Like pacemakers, solar cells, and twisty lights. Solar cell calculators will NOT work. The only thing that has a chance is MAYBE something in a mountain bunker, kept in a Faraday cage.

I hope this helps. Feel free to ask me about any of the above. If I donít know, I will tell you.

12-10-2009, 05:07 PM
Same thing happened to Stephenie Meyer, which caused her to bring forth Twilight. *Dramatic music!*

I know... My characters don't sparkle though... I'm hoping that helps to swing things back in my favour.

Spam, lovely Spam, wonderful Spam

Indeed. Perhaps I can add in a small nod to that legendary scene. So much of the story so far has been doom and gloom. It couldn't hurt to add a giggly bit in there.

<<Long but useful poist regarding EMP effects>>

Thank you, thank you, thank you!!!