This might sound very stupid but I am concerned, and this question also extends to my computer. What is in danger in the case of an EMP blast?

I have heard of switches that would cut all power in the case of a charge as big as an EMP. Does this mean it only affects things that are plugged in? I thought EMP blasts meant bye bye car...

I would really appreciate anybody's knowledge on this! Thanks guys.



PS: More about the iPod situation. I love music. I need it. I plan to build a Hand crank Generator that could of course be used to charge an iPod. (and later I plan to build something connected to a bike so I could actually get more than 5 minutes worth of powering anything <img src="/images/graemlins/tongue.gif" alt="" /> )

Oh and also!

If my car's engine is ruined... (I am prrretty sure it doesn't have electric fuel injection <img src="/images/graemlins/blush.gif" alt="" /> )

Is there a way to salvage/fix the engine? (Again assuming that there is gas to be had... watch your tank <img src="/images/graemlins/tongue.gif" alt="" /> )

EMP is induced into wiring to damage equipment, and it doesnt have to be plugged in to receive the power spike.
You can protect the wiring entering a building along similar lines to protecting from Lighning, but if the equipment inside is not sheilded it will still get damaged.
The cost of building a Farraday cage into your house to protect your equipment would be a bit ridiculous. If you realy are conserned I would suggest you read some books on power protection starting with power spikes and lightning protection then work up to EMP after you understand.

Because you can create a non nuclear locallized EMP quite easily, I am surprised that some terrorist cell somewhere hasnt tried this tactic already. I beleive this is a very real threat.

> What is in danger in the case of an EMP blast?

Any good electrical conductor that is very long or very thin. The EMP induces a current which will heat up the conductor. The longer the conductor, the more current. The thinner it is, the less current is needed to melt it. So powerlines which span the country are vulnerable because they are so long. The wires inside integrated circuits are vulnerable because they are so thin. IPods, computers and cars are at risk because they contain circuitry. They are vulnerable even if they are plugged in because the EMP induces the current in them directly.

The good news is that to protect against EMP you just need a Faraday cage, which is just a good conductor (eg metal) box that completely encloses the item you want to protect.. A tin biscuit box (with lid) could do. It doesn't need to be air-tight as long as the holes are small. It doesn't need to be earthed. The device you are protecting should sit inside it without touching the sides.

I suspect the most practical way to be sure you have an iPod is to get 2, and keep one as backup in the metal box. That's what I do with flashlights. Or you could learn to play the flute?

The above is my current understanding. I suspect we won't really know until an EMP actually hits, what will work afterwards. Keeping electronic gear in a tin box when you are not using it seems like a reasonable precaution.

The engine itself would be unharmed but an EMP is going to damage most electronics and most of the modern cars have electronic controls through out. The steering on mine is even electrical assist!!! Any electromagnetic tape would be damaged or the data on it would be erased so your credit cards etc. would be worthless. Hard drives are generally electromagnetic so even if the electronics of your computer made it the data would most likely be destroyed. CD's would be safe but the player would probably be damaged. In short a sizable EMP would bring most of our technology to a screeching halt. The positve is that an EMP is quite localized and it would require a very large EMP to cover very much area. If it is due to a nuclear blast the EMP would be the least to worry about.

You don't see many mainstream press articles on EMP these days, but I just read this Christian Science Monitor article on EMP last week. Some interesting tidbits in it, but only one "expert" is quoted so I don't know how authoritative the info is. Someone's been watching "24" reruns, eh? <img src="/images/graemlins/smile.gif" alt="" />

I am no expert, but from what I have read, should a nuke be exploded over the US at the right altitude, most everything electronic will be non-functional and we will be back in the days of the early west. Iran has already successfully detonated a missile at emp altitude, which was categorized as a missile failure by our ignorant media, but that was exactly what they need to do to detonate an emp blast over North America. Should that happen, an Ipod will be the least of your worries.

If anyone has any reliable stats or links please enlighten me...

It is my understanding that EMP is fairly localized. Meaning one pulse can not take out the US or even your state. If you work in, and carry your IPod in a high risk area - Military Post, Wall St., etc. - then your best solution happens to be prudent advice anyway - Keep an offsite backup!

There are three sure things in life... Death, Taxes and Data Loss. The first you cannot avoid, the second you can minimize and the third? Backups.

Offsite backups are cheap and simple. You just have to make yourself do it and update them regularly. DVD burners are cheap. DVDs are immune to the effects of EMP. And if you are really worried send a couple of backups to your brother-in-law on the opposite coast or in another country.

"And if you are really worried send a couple of backups to your brother-in-law on the opposite coast or in another country."

Only know about EMP what I've read here, and this was just an idle thought. If you send your data away, & you have E<P troubles, how do you get your units back?

Sue

Solid State circuitry is most prone to EMP. EMPs induce voltage fields that will blow the junction of most solid state devices unless the field can be effectively shunted to ground. Grounded cases don't work, because the field raises the ambient electrical environment and tends to cause a lot of eddy current activity on chassis and in suspended cables. Lightning generates an EMP, though not to the level obtained by airbursting nuclear weapons.

In short, if you are within the range of an effective EMP burst, you can say goodbye to anything electronic. Even assuming an old beater vehicle, you are going to lose the alternator because the diodes and the regulator are all semi-conductor solid state devices. A diesel can maybe keep running, but it must be completely mechanically based (including the injection controls) and none of the other electronic stuff on the vehicle will be funtional.

Coils can be nearly as vulnerable. A coil microphone element will probably eat itself, as will a tape recording/playback head.

Engine coils will likely take the juice, as will big speaker coils, but small engine windings may or may not make it, like that electric shaver, or the dremel tool, etc.

If you have adobe acrobat reader, here is the latest government report on emp

it is a link to a 62 page pdf file:

http://empcreport.ida.org/EMPCExecRpt_FinalToSandS.pdf

If we are hit by a nuclear attack and subsequent EMP, the last thing I'd be worried about would be my electronics.

It would be time to hoof it with my boots and BoB. <img src="/images/graemlins/shocked.gif" alt="" />

On a related note, how does the military protect their sensative electronics from EMP? I remember seeing pictures in books of aircraft carriers hosing the decks (although to remove fallout).

"how does the military protect their sensative electronics from EMP?"

Most military grade electronics are "hardened" both environmentally and electronically. This is why they are usually big, basic, and heavy. A GI issue GPS weighs in at several pounds for example.

Although I have a feeling it is more the equivalent of "water resistant" when it comes to EMP. You have to figure that if you are at ground zero then EMP is the least of your worries. It is only away that you have to worry about it.

"If you send your data away, & you have E<P troubles, how do you get your units back?"

I was thinking of long term data preservation but you always have the option of going to it or getting it sent to you either electronically or physically. Let us assume a single, massive EMP was able to take out your entire city... you may have to travel to a location unaffected to find a working terminal where you could download your data. That being said... for some data (not a 60 GB music library) it might be wise to pay for a bit of online storage.

How old would a vehicle have to be to be able to move after an EMP attack?

Sue

I cant remember where I read it or the exact detail, but before they knew that a nuclear blast caused an EMP, when they were testing on a Pasific atol they demaged the phone systems on another island about 1000 kilometers away. Unfortunately I cant remember the name of the island or the exact distance.

Heres something to try. Get an old CD and place it in a microwave oven data side facing up on a piece of cardboard. If you like try taking the microwaves globe out first so you can see the effects. Turn the microwave on for a few seconds (no more than 8 seconds)
Watch the mini lightning and then tell me how a DVD or CD will survive an EMP. Before you tell me that this is different that an EMP blast, I would like to state EMP damage will occure but may not be as dramatic as the microwave. As soon as the energy hits the CD its damaged, but the lightning effects take a fraction longer. You will also get to see how fast the magnatron turns on. In mine there is over a second delay but my friends is on before the finger has left the button.
Also the CD's will make pretty neat drink coasters after the microwave, but injurries may occure after your wife smells the microwave after doing this, so air it for a couple of hours.
You wont notice the smell after that.

You dont need a nuclear weapon to create an EMP. You can design a purpose built device to make an EMP, but it will be more localised. It is also much cheaper to make than a nuclear device, so would be easier to create multple devices to work together to achieve a bigger result.

I googled EMP+DAMAGE and these sites were on the first page. I just skimmed them, but some of the info on a couple of the sites seems to contradict the info on the other sites.... whatever:

http://www.aussurvivalist.com/nuclear/empprotection.htm

http://www.qsl.net/n9zia/emp.html

http://www.globalsecurity.org/org/news/2001/010930-attack04.htm

http://www.sonic.net/~doretk/Issues/00-03-SPR/theblack.html

Sue

EMP sheilding is like the escape trunk on a sub- if it is useful, you got lucky or they weren't in your weight class. You can always make a bigger bomb for a lot less than the other guy can add shielding.

OK, speaking as professional geek and someone who grew up in a house full of cold warriors, let me say that this is pretty much a nonissue. The probability of an EMP device or a near space nuke are a lot lower than battery failure.

You are probably right, but then again, how long ago was planes deliberately flying into tall buildings a non issue.
Considering how cheaply this could be done and how resourced terrorist are these days, all it needs is one of them to think of it and then pay off an electrcal engineer somewhere and ....
If they can learn to fly 767's and they already train to make bombs etc you never know whats next.

This thread could also lead into some more useful ideas about power protection and lightning protection which would be the first place to start to protect against an EMP.

it isn't that cheap, and it isn't that easy

trust me, I wanted to try one as my disertation :P Skipping the DOD interview woiuld have resulted if it ever got beyond the bad idea stage, the cost would be more than sending a dozen shmucks to Embry Riddle. (Flight and aircraft tech school in Florida my sister went to.)

And even if it was, let's say that the fear of EMP increases cost of consumer electronics 25%, and doubles thier weight. I can increse the cost of the device by 10% and smoke them. Or just let everyone be afraid, pushing thier paranoia until an iPod is the size and cost of ENIAC (adjusting for inflation). It which point RIAA is very, very happy.

Non issue, becuase realistically, there is nothing you can do to stop it passively. If there is real world EMP detonation, I'm more worried about my bank records than my mp3 player.

If by unit you mean your data, it's easy- copy the date to a new hard drive.

If by unit you mean the hardware, forget it. Big was right when said it can be simulated in the microwave. The solid state components will be smoked, all gone. You can save the frame, maybe the power supply, and that will be it. EMP = NCT (new computer time) <img src="/images/graemlins/smile.gif" alt="" />

Non fuel injected, certainly. Carberators would make it, though. Anything that old wouldn't have a chipped ignition or anythign like that.

and as soon as you attach your headphones, the faraday cage doesn't mean diddly <img src="/images/graemlins/smile.gif" alt="" /> speakers in the tin can, with shrodinger's gerbil on it's wheel for power

Yeah, if the engine is trashed, it's pretty easy.

You need a really big block of super high grade steel, a fully equipped machine shop, and an engineering degree. And time. And resources becuase you will screw it up the first time or three.

There is no quick fix, kid. Salvage what you can and start walking. You've just entered the TEOTWAWKI Zone. <img src="/images/graemlins/smile.gif" alt="" />

online storage not much good if a)internet is fried, b)electric grid is down, c)computer is fried, d)telephone lines fried -- perhaps this is the time to re-start the pony express, horse mail instead of email

EMP Electro Magnetic Pulse
By Rich “Raspy” Shawver

The way you make electricity require 3 things a conductor [Wire] a magnetic field and relative motion. A lightning strike generates an expanding [the moving] magnetic pulse or field that passes over power lines [the wire] generating a voltage spike in incoming services. The size of the spike is dependent on the strength of the field and the length of the wire involved. The resulting spike only has a duration of a very small fraction of a second but that is more than enough to damage electronic components. Circuit breakers are of no help. The spike is so short that it hits and does the damage long before the breaker has a chance to react and open. The spike resulting from a lightning strike can be 4 to 5 times as high the normal line voltage. The EMP of a nuclear weapon is exactly the same mechanism but with a much greater intensity. Depending on your distance from the detonation the field can be strong enough to generate damaging voltages in the internal wiring of the equipment.

If your equipment is hooked up but turned off, an incoming spike on the electrical power lines [and other attached lines, cable and phone] can arc over the switch if large enough. Also most electronic equipment now have circuits that have power running through them even when turned off for remote operation [even if it's not remote controlled]. Rather than building separate boards for each model companies have found it is cheaper to include many of the features on a common board. They just turn on the special features on the cheaper models.

The only safe way to keep equipment from being damaged is to enclose it in a metal structure that is grounded. The equipment has to be totally isolated from the cage and any outside connections. A structure of this type is called a Faraday Cage. A metal container [such as an ammo box] in which equipment can be stored if insulated from the container and the container is grounded will act as one. The way a Faraday cage works is the moving magnetic field strikes the cage. This starts to generate an electrical charge. As the electrical charge builds this in turn starts generating its own magnetic field that pushes back or repulses the original magnetic field. This then causes the original field to flow around the cage rather than through it. This is what keeps the EMP pulse from effecting the equipment inside the cage. While the best design for a cage is solid sheet it can be a fine mesh grid. The size of the openings in the grid is somewhat critical. If the openings or mesh size is too large the field the wires counter generate does not build up fast enough to block the field pulse. Something the size of chicken wire would be so large that there would be some leakage. The field on the cage has to build up fast enough to block the holes in the mesh. The cage does need to be grounded to dissipate the resulting electrical charge.

There are devices called lightning arresters among other names. That are sold on the market that are designed to stop or at least minimize the effects of such spikes. Many are good devices. But they are limited to the amount of protection they can supply. A large enough spike can overwhelm their capacity. While you can not shield wiring outside your own home. Inside it can and should be shielded. Some wiring is designed with shielding. This is a metallic or braided sheath surrounding the wiring. Another way is to run the wiring through EMT conduits. Both methods can be combined for better results. This shielding needs to be grounded. Just remember that this wiring is attached to wiring that is outside your control and probably not shielded.

The best way to build your shelter is to line the inside or outside with sheet metal. [Door included] The metal of the door must make electrical connection with the rest of the sheeting. For more reliability Line both inside and outside independently. A double Faraday cage. You do not have to do this for your entire house but should be done for a shelter, panic room, communication shack or a room that is a combination of any of the three. The best metal for making the cage is copper because it conducts better but any metal will work. [Gold and platinum would actually work even better but who could afford it.]

If you do run electrical or electronic conducting lines into your structure have them shielded but do not have your equipment connected to them except during actual use. I do not mean disconnected by a switch but physical distance such as pulling the plug out of the wall socket.

Remember if the moving magnetic field is strong enough the internal wires of the equipment itself can cause a voltage spike that will damage it. That is why most cars will be knocked out because the voltages would knock out any electronics. [Most cars are totally controlled by chips] That is why older vehicles [pre chip] are a better BOV. The voltages can be high enough to actually burn out the wiring itself.

I can see the question in your eyes. A car is basically a metal box wouldn’t that act like a faraday cage? If that is so how can a car be effected? Simple the box that is a car has some huge holes in it electrically speaking. That and many modern vehicles have gone to composite material mostly plastic for sheet material rather than steel to reduce weight. The engine compartment, that has much of the wiring running hither and yon to operate the engine. Plus you have the main power supply cables from the battery and alternator and they either hook into everything that uses electricity or that item does not have power. Look under the hood sometime even in the tight compartments today there are places you can see the ground. The passenger compartment has windows some real big holes in the box. Yeah, but the wires are under the dash. How much of the dash is plastic? Look at all the holes for gages and dials. In most cases the entire underside is open. Out your car in the bottom of your swimming pool. Just kidding. But if you did would the water be able to get to the wiring? If so then so could the pulse. While you could close off the engine area covering the windows with plate or mesh just wouldn’t be a workable solution. It would be difficult to say the least to see out and drive. But the local constabulary might have a comment or two.

If your only choice for a BOV does rely on electronics there is a remedy. On any car you could pull the entire wiring harness and up grade it. This would be with heavier gage wiring and using shielded wire. Get a spare set of the control modules needed for you car. Not just the computer control boxes but also the sensors and the items that are controlled by the computer. [They are also susceptible to pulse damage.] Wrap them in insulation [Electrical not temperature type I.E. rubber] and store them in a metal box. Attach the box to the frame so that it makes good electrical contact. Then do as they do to movie stunt cars. Attach a grounding strap to the frame. The strap is usually a braided copper cable that then drags on the ground. This is to dissipate and charge that builds up on the vehicle. The strap needs to be checked regularly and replaced as needed.

Yes the entire national power grid would be knocked out. While the most of the grid components them selves would be able to withstand such a pulse all the electronic control equipment would be fried. The means of operating and monitoring the system. Local power may be restorable but an inter linked grid would take a long, long time to restore.

Will your car or home equipment be affected? Mainly it will depend on luck. How far you are from the source and intervening obstacles. Even the angle that the local grid or house wiring is to the source can have an effect.

Sorry to be so long winded but it is not a simple subject and needs some explanation on the hows and whys.

Here are a couple of web sites that have a more technical explanation of how the field is generated.
http://www.geocities.com/CapeCanaveral/5971/emp.html
http://www.geocities.com/HotSprings/Falls/1984/emp1.htm

the end of the world as we know it -- everybody is basically a walking circuit board now with all the gadgets, we'll all be a lot lighter it that emp event ever happens, talk about survival preparedness!

He's right. I'm in the marines. We have big, heavy stuff that in the civilian world are tiny. A GPS is a perfect example. We call our GPS's "Pluggers" - Pluggers are about the size of an average novel and just as thick. Correct again, its mainly designed for water proofness and rough use. The military's answer for all things nuclear related including EMP is to DIG! I guess they think it solves everything. See a flash from an explosion...if you didnt evaporate, DIG lol. No kidding. We have SOPs (standard operating procedures) for a lot of things pertaining to big events such as a nuclear explosion, biological attack and the like. But I think they will go where the SOPs in Iraq went, right out the window.

I personally hate iPods so I dont mind if they all go up in a EMP.
But as to the cost and ease of making one. A small scale device could be made for about $3000 then chucked on a back of a truck and parked and detonated.
It doesnt need the pinpoint accuracy and other features your military has built into theres to be effective. There are simple designs that could be used and they may not be the best design but it doesnt mean it wont be effective.
Buying the parts would attract very little attention because nobody would be looking out for most of the components.

I think you are underestimating how easily this could be done with the right design.

Another thought:

If any useful electronic device survives an EMP it will be worth 20 times it's weight in gold. Do you really want to have to protect your iPOD from murderous theives? Think "Waterworld" where dirt is priceless.

Not trying to go TEOTWAWKI, but you should consider what effect protecting/taking things with you will have. You do NOT want to stick out like a sore thumb after any event that effects ALOT of people.

Well, there are some problems with the physics of your statements. First, an EMP from a nuclear detonation is likely to generate ac fields in the EHF range. One component in the shunting ability of a faraday screen is wavelength, and the mesh size of a faraday screen determines the effective cutoff frequency efficiency of it's shunt. In short, unless your screen mesh size is approaching microscopic, it won't do much to protect against a nuke based emp.

Second, as the field intensity increases, the shunt capabilities of a faraday screen diminish because the ambient ground level goes up. Unless your ground plane is deep and is connected to the screen using massive conductors, the screen will develop a potential, or series of potentials that will induce fields in the equipment within. There are very few real true earth faraday screens in existence, at least ones capable of shunting major emp hits such as we are considering. Most faraday screens I know of are used to protect against lightning hit level emp. These can be big, but are localized and not nearly the magntiude a strategic emp attack would generate.

Third, cars are not grounded to earth, and therefore float on an insulating layer (four tires). They are not able to shunt an emf field at all, and provide virtually no protection to electronic gear contained within. To find a vehicle that would still run after an emp surge, it would have to have a generator instead of an alternator, because the diodes and the regulator in the alternator are semi-conductors and would be blown by an emp. You might get lucky and the battery would not take a hit, and the coil might not blow open, but anything silicon based is going to go after a few hundred electron volts. All those new LED lights everyone is toting these days will suddenly quit, leaving the good ole incandenscents. I dunno if the xenon and halogen lights will take the voltage or not, but my guess is certainly the new plasma based lights and the fluorescents are suspect.

Perhaps one of the smartest things I've ever heard about emp threat was to use tube technology and keep whatever appliance you were planning on using disassembled like a kit and packed away in an airtight aluminum container. If an emp hit, likely the componentry would survive intact, you could reassemble the unit, and assuming alignmnet was not a problem put it into operation. There are more than a couple dedicated ham operators and a few government agencies that subscribe to this practice.

The botom line is consumer electronics are going to toast in an emp field. Only the truly dedicated technicians who planned ahead have any chance of operating electrical gear after the fact, and even then, they're going to have to come up with suitable electrical generating devices (you can pretty much say goodbye to all those new portable generators too, which are dynamically controlled with solid state electronics).

Just enclosing equipment in a metal structure will not keep it safe. I've witnessed a lightning strike take out a telco switch station from 1/4 mile away. This was a site that was in a metal building, with a good grounding system, and plenty of circuit protection. If it can happen to a $50k switch site, then it can happen just about anywhere.

> and as soon as you attach your headphones, the faraday cage doesn't mean diddly

That's why I said get 2 iPods. You listen to the one that isn't in the biscuit tin.

Bank records should be protected by the bank. It really shouldn't be that hard for them to store a backup in a Faraday cage.

It's true there would be bigger problems than iPods. Then again, there is a strong psychological component to survival and if music is what you think will get you through the disaster, I say go for it.

All that sounds a bit "worst case". An EMP will surely be subject to inverse square laws, so there will be a wide area, away from ground zero, where a little protection will be better than none at all.

HEY! Finally a situation where being poor is a benefit! All of your (non-electronic) stuff fits into the back seat and trunk of your 1964 VW bug and the road ahead is CLEAR! <img src="/images/graemlins/smile.gif" alt="" />

Sue

EMP works by induction in conductors. Microwaves work by stimulating molecules. If you put your hand in a microwave for 8 seconds it will be severely damaged, not true with EMP. I would be interested in any references you have for your claims.

Does anyone have any idea the range of a non-military EMP device? Are we getting worked up over nothing? If a "really big" home grown device is able to produce a pulse only 10 miles wide then we are getting all fired up over nothing.

Yep, and as Brangdon points out, inverse square laws apply. I'd figure the best non-nuke emp might make it to the horizon if popped at ground level, maybe 12 miles if they really pump the local field up and aren't in close proximity to any big conductors (including underground). The gauss level is what we would measure I reckon just to get a good basis. Figure it'd have to be about 100 times more voltage than your standard lightning bolt, so we're probably looking at a 10 to the 7th or 8th power voltage level with a high spiking square wave type leading edge. That'd generate enough harmonics to beat the slew rate on most solid state junctions within that range.

In contrast, it isn't all about the amount of voltage, but the type. Like I was saying before, when you get the frequency component up to ionizing levels, it can compound the effects. Propogational loss is diminished in this case (the inverse square law doesn't work quite the same, but still is a factor). Popping a nuke at 40 miles up with a 10 to the 11th or 12th order (we're talking a really good hydrogen bomb thermo-nuclear detonation, probably 15 megaton or larger) voltage level would probably effect at least a 200 mile radius on the ground, likely a whole lot more if the pulse finds it's way into the grid and surges down the line a lot further. The more x-ray and gamma ray generation, the more effective it will be at slamming all those transistors into oblivion (greater penetration of obstructions).

BTW, humans aren't immune to the emp. I believe that at 5,000 rem the central nervous system blows, and our switch gets abruptly flipped off. I can't remember what the conversion is from eV to rem, but it is not a small number.

Really? Wow, I had no idea. Do you have any scientific references? I would really like to learn a bit about this. Has anyone ever died solely because of EMP?

REM and Electron Volts are two completely different critters. EV is a measure of electrical energy not radiation such as gamma. Rem is radiation Equivalant Man. It is a conversion unit that measures the amount of damage to the human body which is different from electrical damage. There are several different types of radiation you can be exposed to.

Unless you are attached to a very large conductor EMP will not hurt you. Ionnizing radiation on the othere hand is when radiation passes through the body causing damage to the cells. LD 50/50 or the leathal dose where half the people exposed to it will die. Depending upon which study you read LD 50/50 is between 500 to 600 REM.

As soon as the magnatron powers up, the CD is stuffed. Wheres my reference? My kitchen and some of my friends kitchens. Ive put cd's that dont look damaged back into drives to try and read them. Feel free to come around and test. You dont need the 8 seconds. The 8 seconds was to let people know that it might get a little dangerous and that they look pretty cool after a few seconds.
The microwave is a high frequency eletro magnetic wave, an EMP is a electr magnetic pulse. Both will induce electical currents and not just in a wire conductor. In what way do you not think that a cd will not have any induced currents.

As to how much damage a device will make depends on its design, size, location etc and how many of them there are.
As to the likely chance of this happening, I think I will be pretty safe where I am.
I am more worried about lighning around here, as this is a much greater risk. Protecting for lightning will provide some protection from a non nuclear EMP if the device doesnt go off close.

Some of the damage Ive seen caused by lightning has been a 1 inch bolt holding a plate on a wall blow itself apart and embed itself in a limestone wall on the other side of the room.
Ive also seen a builbing take a hit through an antenna on the roof which looked like an afro. Every computer in the 3 story building had its BIOS ROM chips wiped, even the ones not switched on.

Actually, the fundamental measurement of radiation is the electron volt. Gamma rays are measured in eV, although the higher the eV is, the shorter the wavelength and the higher the frequency. As the frequency increases, the energy increases. The threshold where the frequency becomes ionizing occurs at the UV range, ie it has the ability to strip electrons from atoms, about 10 eV, or 2,500 Terra Hertz (120 nanometer wavelength). This, you will note is independent of the amplitude of the wave. Since an emp is a function of both amplitude and frequency, a nuke emp has a lot of high extremely high frequency components, which means they can contain a lot of x-ray and gamma ray energy. I believe there is a formula for converting eV to RAD (Radiation Absorbed Dose), which can then be converted to REM (Rad Equivalent Man), which takes into consideration the type of exposure. It's been a few years since the college Rad Health Physics class I took, so I don't know the specific formulas anymore, but they are out there (I think it is 1 Rad =6.24E7 MeV, or 62.4 trillion electron volts). There is a table that shows what damage occurs to the human body at different REM doses. I believe the first to go are the crypt cells of the small intestine at something like 50 REM, then the marrow, and so on. Lethal doses aren't immediately lethal, so a 300 to 500 REM dose takes time to kill, whereas a 5,000 REM dose is going to shut you down before you can take a couple steps. Here's a link to an industry standard exposure table, which has the LD 50/50 actually slightly lower than you noted:

http://www.pimahealth.org/dmat/dmat_radiationchart.pdf

Basically, if you are close enough to hear the bright blue arcs going between the two PU spheres, you are toast before you can get out of the room.

The statement that you have to be attached to a very large conductor to be effected by an EMP is limited to the size of the field you are exposed to. If the field you are exposed to is intense enough, you don't need to be attached to anything and you will be cooked.

Here's another aspect to consider about popping a conventional EMP (forget the nuke aspects for a moment, let's just use non-ionizing fields). EMPs generate high momentary electromagnetic/electrostatic fields. Having induced emf fields using large coils, I can tell you that if the field is high enough, it can have nasty effects on the musculo-skeletal system. We had a coil that we put tools in to magnetize by pulsing the coil with a high voltage transient. We experimented with animals using this field and found out that the pulse at a close proximity fairly turned the critter (which was not electrically connected to the coil in any way) inside out!!! Now, while it's not likely that people will be that close to the source, it is important to note that the field we were creating was not nearly as big as the tactical EMPs we've been talking about here. Even at that, the coil blew an electrically isolated DMM up from over three feet away.

Another experiment used a cascading voltage multiplier to bump line voltage up to about 115kv. We called it the symphony box, because it made beautiful arcing noises if you moved the probe near any equipment that the return was clipped to. We clipped the return on a piece of equipment and without even arcing the probe we could just wave the tip around inside the chassis and all the semiconductors would blow. It was a good way of decommissioning some piece of junk that an owner wanted us to resurrect for more than the thing was worth. Some people just can't be convinced otherwise.

Nuke EMPs do contain an ionizing component, which has to be considered as part of the whole effect. Propagational loss due to high altitude detonation is likely going to keep them from generating a significant instantaneous dose, but it is still there. Likewise, propagational loss keeps the amplitude component from generating an acute biologic effect as well.

The bottom line is REM and eV are not two completely different critters. If it were, then there would be no such thing as ionizing rays, like UV, X-Ray and Gamma. EMPs do pose a health risk if the relative intensity of the exposure is high enough, regardless of the grounding potential of the individual exposed.

There's an awful lot of this sort of information on the internet, so I won't go any deeper (heck, I've probably walked off the deep end already). Do some more research if you really want to know, but I classify such information as "nice to know" trivia. <img src="/images/graemlins/grin.gif" alt="" />

Just an observation. I think it's been rather confusing (it has for me) that people have been talking about different kinds of EMP in this thread and it seems to be generating some frustration for some readers. For me, the word "EMP" means EMP from a high altitude nuclear detonation and that's the paradigm I was reading from. I think most of us are at least vaguely familiar with the characteristics of such a phenomenon from Cold War "common knowledge", such as massive damage to electrical systems but no damage to people. That's why benjammin's comment about EMP being harmful to people was perplexing to me at first.

But then as posters elaborated some more and I did some Googling, it's evident that some are referring to other kinds of EMP, like from High Power Microwave devices that can use batteries or explosives to generate their energy (a "suitcase EMP"). And some people are referring to intense EM fields created in the lab under controlled conditions. For example, a field that lasts long enough to wave a probe two inches from equipment to destroy it is different than the 10 nanosecond EMP of a high altitude detonation 250 miles up and 1,000 miles away. Yes, all of them are intense EM fields, but we're talking about pretty different phenomenon in terms of frequency, intensity, duration, exposure, range, how they're generated, etc.

Anyway, in case there are other people who know just enough physics to be confused like I was, I think much of the confusion is because we're talking apples and oranges in some cases. It's like having a discussion on the dangers of and defense against "biological weapons" and one person is thinking of the characteristics of anthrax spores and the other person is thinking of small pox virus.

Actually, there's not as much difference as you might think between all of the above.

What kills the solid state circuits really is the voltage. Whether the duration of exposure is 10 nanoseconds or 10 seconds won't make much difference. I relate the probe story because it was the voltage that killed the transistors, and not how long I held the probe in the case. BTW, the duration of the EMP for a nuclear detonation is quite a bit longer than 10 nanoseconds. That's more like the duration of the spike from a lightning strike. But like I say, it isn't the duration, but the intensity.

In the remake of Ocean's Eleven (with George Clooney), they demonstrated the use of a "pinch", which was a chemically induced emp generator. While the characteristics were a bit embellished, the idea was about right (I'd wanted to avoid that reference, but I guess it is the only good one I can cite for the layman).

My point was precisely that not all EMPs are created equal, or have the same characteristics, though they share many attributes, the most noteworthy of which is the high intensity transitory electromagnetic field. You really could put all other arguments aside and just state that the purpose of EMPs is to blow solid state electronics all to heck.

This isn't an apples and oranges comparison, more like a Macintosh to Golden Delicious to Granny Smith type comparison. We are not nearly so divurgent here as the biologic references you refer to.

I guess the bottom line here is, "If the lights go out and your watch quits, you got greater concerns than checking your Ipod, and I hope you brought a good pair of walking shoes with you. <img src="/images/graemlins/smirk.gif" alt="" />

quote You really could put all other arguments aside and just state that the purpose of EMPs is to blow solid state electronics all to heck.
I guess the bottom line here is, "If the lights go out and your watch quits, you got greater concerns than checking your Ipod, and I hope you brought a good pair of walking shoes with you. unquote

I agree with Ben, that pretty much sums it up, I too was going from the high altitude nuke airburst perspective, which is a very real threat and has been for some time from a variety of enemies, just now it is more likely with terrorists rather than a country like Russia or China. The technology is now available to just about anybody with enough money to buy or build a nuke and a delivery system such as a SCUD missle.

Ok. So great. Everything I own is going to be screwed. How far away do I have to send my backup DVDs? With an "Oceans 11" type or an airburst? Are we talking miles or hundreds of miles or cross continents?

Ben you are still mixing apples and oranges. I speak from a considerable amount of experiance. 9 years in the navy nuclear power program 2 of which were as an instructor.

Yes there are components of radiation involved if the pulse is generated by a nuclear explosion. But it is not the Electro MAGNETIC pulse. And it is a moving magnetic field that generates the damage in electrical equipment. By creating a voltage spike in the wiring. And that is generally of very short duration.

If you are exposed to high levels of radiation along with a pulse it is the radiation that fries you.

A strong enough magnetic field can effect the body directly. That is because hemoglobin in the blood contains iron.It can literally pull that iron or your blood out of you. The level though is tremendously high. That is why you are not allowed near cyclotrons while in operation. To get that kind of magnetic level even from a nuclear blast. Well let's just say the field might affect the floating ash of your body because you are at ground zero. Well inside the fireball.

Actually, it is the burst of high energy gamma rays from the nuclear blast that induces the EMP, by what's called Compton Scattering. Relative to our perception, the duration of the EMP generation cycle is quite short (typically 10 milliseconds or so), on a timescale calibrated to such events, 10 milliseconds is way longer than 10 nanoseconds (kinda like comparing minutes to eons on our timescale).

Radiation hardening is a legitimate concern. Radiation can cause as much or more damage than the EMP. TTL was not as susceptible to radiation induced transient failure, but the current commercial technology is based more on MOS semiconductors, which are susceptible to ionizing radiation at levels below 1 RAD, which is a possible exposure level in an airburst at 20-40 km, which happens to be where nuke EMPs are targeted to detonate because that's where the Gamma radiation induces the highest EMP level in the atmosphere. Of course, all this information is published on the internet. Typically with EMPs, the solid state device blows at the semiconductor junction because the Peak Inverse Voltage is exceeded. An EMP creates a voltage spike in all the conductors, including the lans of the circuit boards, the compnent leads, the internal substrates, and the external circuit wiring as you noted. Of course, you can electrically shield these circuits against the EMP, but that shield may not prevent the radiation exposure, especially if it is mostly Gamma, and the circuit will blow anyways. Given that most electronic circuits still employ lead based solder, high energy nuetrons (also present in nuke emp detonations) which also are difficult to shield against can induce a secondary x-ray emission due to the Bremstralung effect, at a fairly close proximity to the semiconductor junction I might add, which said junctions are also susceptible to (x-rays ionize substrate atoms liberating electrons, which induce an emf at the junction, and also a photonic emission that deteriorates the junction). These are all factors that have to be sheided against when putting electronic equipment in space as well, very real concerns that have little to do with shielding against EMPs. There's a good deal of technology devoted to it, so it must be a design factor for a reason.

I'll agree that the radiation surge from a nuke EMP will get you long before the strength of the electromagnetic field does. I'm not sure what your counterpoint was in that statement.

I would add that an electromagnetic field does more than just act on the hemoglobin. High transient spike EMPs induce a temporary field in the skeletal structure. This transient has the effect of rippling the bones as eddy fields develop, and the result is signficant fracture of the structure. As before, I would agree that the radiation will get you before the electromagnetic field does in a Nuke EMP, but in a conventional EMP, lacking the radiation component, it is advisable that you keep your distance from the point of origin. Let's put it this way, I wouldn't want to be holding on to a suitcase containing a non-nuke emp when the thing went off, unless I want to know real, unequivocal pain. Our experiments indicated that significant bone fracture occurred using transient fields that were lower than what was needed to rupture or extract hemoglobin. Independent variables made it hard to predict or determine what gaussian level was needed, but it was distinctly lower.

I think it is still apples and apples.

As I also discovered after my Naval tour in the Cryptologic program, they don't teach you everything there. <img src="/images/graemlins/grin.gif" alt="" />

So, uh, you basically have more important things to worry about than your iPOD!

Can you burying electronic devices and have them unaffected by an EMP?

Yes, if you go deep enough that the emp and the radiation level diminishes below a significant threat level. As to what particular depth that will occur, well, that's what engineers and scientists get paid to figure out.

While the threat of a terroristic use of a nuclear weapon is very real, I do not believe anything short of all-out nuclear war (and MAD) would motivate any party to employ a high altitude nuclear detonation (generally required for EMP).

There's just too much bang for the buck in targeting people and buildings and such to worry about electronics.

If one is unfortunate enough to be affected by a terrorist act, there are more likely threats to your IPOD, e.g., blast, metling due to fire, being crushed or, most likely of all, being dropped as you bug out to the hills with your PSK to take on TEOTWAWKI to the strains of that Dallas-area band, Bloodrock. <img src="/images/graemlins/cool.gif" alt="" />

Actually, the greatest threat to the IPOD devices will likely come from viruses, but that is altogether a different paranoia. <img src="/images/graemlins/grin.gif" alt="" /> <img src="/images/graemlins/shocked.gif" alt="" /> <img src="/images/graemlins/laugh.gif" alt="" />

The counter point was that if you are close enough to the blast for the magneteic field to be high enough to serious effect you the other aspects of the detonation are going o get yiou first.

And yes I know how a nuclear blast generates the magnetic field. I didn't go into how because I was discussing the effects of EMP and didn't want to cause too much confusion. Besides it was getting long as it was.

Gravity and really heavy people are probably just as dangerous for iPods. I suspect that the washer-drier combo might become the natural predator of the Nano though. <img src="/images/graemlins/smile.gif" alt="" />

Well then, your counterpoint complements my point rather nicely. <img src="/images/graemlins/grin.gif" alt="" />

Yeah, I was kinda hoping to avoid all the long haired stuff as well. Like I said before, it is all just trivia that won't have much value to anyone if such an incident actually occurred.

As concerns IPODS, there are more immediate threats out there to worry about. Really though, nothing lasts forever.