I was watching a old show on the SciFi network this afternoon and a question came to mind about a nuclear air blast that would create EMP waves knocking out all electrical circuits.  My question is this.  If an electronic device was off, would it still be damaged?  Would any electrical device survive such a blow.  Would it matter if the devices were in an underground shelter?  Just wondering about geiger counters and such and if they would work after an nuclear blast.

Quoted: I was watching a old show on the SciFi network this afternoon and a question came to mind about a nuclear air blast that would create EMP waves knocking out all electrical circuits.  My question is this.  If an electronic device was off, would it still be damaged?  Would any electrical device survive such a blow.  Would it matter if the devices were in an underground shelter?  Just wondering about geiger counters and such and if they would work after an nuclear blast.

there are so many factors which affect this question that it is nearly impossible to say, with any certainty, whether a given device will continue to function post-NEMP.  

as i wrote some time ago here in the SF,
archive.ar15.com/forums/topic.html?b=1&f=123&t=521338&page=3

i've been thinking about how to answer this question and others like it ("will X survive a NEMP?") for the past few days. i finally concluded that it might be a useful exercise to turn the situation into a physical, palpable one -- where you can see/feel the situation under discussion. imagine you are financially very well-off, retired in style from the money you made by shorting Enron shares at their peak. you are currently on a large ocean-going sailboat somewhere in the pacific, stretched out in a hammock in your bathing suit drinking sumptuous red wine out of a hefty glass. several brunette models from the Dutch Institute of Modeling are sunbathing on the foredeck, and a few blond beauties from Norway are playing drunk patty-cakes on the aft deck. life is good. about 1000 miles away, a meteorite the size of a house traveling over 25,000mph slams into the pacific ocean. like the proverbial stone thrown into a pond, large waves radiate outward from the point of impact. an immense first wave and smaller subsequent waves approach your far away boat. up to now folks have asked EMP-related questions which can be compared to "will a meteorite hitting the ocean spill the wine in my glass?" there are a million variables which affect the answer... the depth of the water at point of impact, the approach angle of the meteorite, the density of the meteorite, the makeup of the bottom of the ocean at point of impact, the varying depth of water as the wave progresses towards your boat, the prevailing wind, the shape of the wave when it arrives at the boat, the size of your boat, the orientation of the boat with respect to the wave, the center of gravity of the boat, the mass of the boat, the boat's current heel, the natural frequency of you in your hammock, the size and shape of your wine glass, the viscosity of the wine, your reaction time and reaction to the wave, and so on and so forth. put into nice, easy, phsyical terms, the above may help folks understand that there is no single answer to "will my Aimpoint fail?" or "will my ham radio fail" due to an EMP -- the same way we can't answer the question regarding the red wine above. there is also no way to create a protection scheme where the wine will NEVER spill (for example, if the boat itself overturns you will certainly lose the wine). moreover, there are condtions which would appear to be safe but in reality will cause loss of the red wine. a small seemingly "safe" wave with the right peak-to-trough distance may excite the dynamic system that is made up of you, the hammock, and the boat. your hammock will overturn despite the fact that the wave, from strictly an amplitude (height) perspective, seemed "safe". to continue the comparison with NEMP, it is therefore not enough to say that an RF field of "less than 200 V/m" will not cause an Aimpoint to fail. again, there are simply too many variables to conclude this. a field of 100V/m at a given frequency (or more appropriately, risetime) may be far more destructive than a 500V/m field at other frequencies. which leads me to this, as others who have BTDT (like CWO) will agree: there is a little black magic to go along with science in anything to do with this area. approaches to protection you think will work turn out not to, and vice versa. and knowing what will work is a matter of many years of experience and careful testing methods. even after the reports are written you know that given the right cicrcumstances, failures can still be induced. most any manufacturer who declares, "our product is EMP-proof" can be quickly found to be unknowing in this discipline.

that said, in all likelihood, most all portable, battery operated, handheld devices (such as ham HT's, geiger counters, and the like) will not be affected by EMP.  the distance-reduced field intensity and the minimal capture area will prevent any permanent damage, although there may be minor transient issues.

here is what an ARRL report on the EMP effects to ham radios says:


as you can see, as long as there are no long power cables or antennas connected to the device, it should survive an EMP.

ar-jedi
former EMC/EMI/ESD/EFT/TEMPEST engineer.

ps:
i have a test chamber where i work:  

ETA:
from page one of the link posted above:

Quoted: Don't take it personally! I was just ribbing you a little! That formula doesn't really explain how the electro magnetic waves will effect a circuit that is off. I wouldn't know what to do with it if it did. Pretend I am a little slow, and explain it to me in a way that would effect our lives. It sure won't affect your toaster oven. Will it effect a small circuit like a calculator with its tiny short wires and circuits. Will it effect a 12 v. car computer if it isn't on and the computer isn't charged. What kind of voltage will it generate in realy world conditions. Please!

Quoted: ok, i am going to try to make this as simple as possible. however, i'm quite sure my simplification will result in AR15.com going down from the massive number of "corrections" offered by my peers. but let me attempt it anyway in nice, easy, practical terms. let's start with something you know, an FM car radio. but first we have to start at the source, the FM radio station. the transmitter at your favorite station takes an audio signal (say from a CD player) and modulates it onto an RF (radio frequency) carrier at a frequency of say 100 MHz. modulate, in case you were wondering, in this context means that the input audio changes very slightly the output frequency that the radio station is transmitting on. you can read more on how FM (frequency modulation) works via google -- i can't explain it to you here without typing for 10 more minutes. thousands of watts of RF are sent up a piece of coax into an antenna -- where that power is radiated as an electromagnetic wave. for our purposes, we can use a lightbulb for an analogy -- there electrical power gets turned into visible light, which is a type of electromagnetic energy. an electromagnetic wave carries with it energy, just as a wave of water on the ocean carries with it kinetic energy. this EM energy, as you will see in a moment, is what makes all this radio stuff happen. the EM wave that you are most familiar with is in your kitchen: EM waves in what is called the microwave region bombard whatever is placed in the appliance, rapidly spinning the boomerang shaped water molecules. this creates a lot of friction, which then produces heat -- as anyone who has used a belt sander knows. so you see, strong EM fields can boil water! so back at our FM station, EM waves "spring" from the transmitter's antenna, radiating in all directions. btw, the strength of these waves decay as the square of the distance, and therefore are quite weak after a trip of many miles. at your car, a long metal rod is used to capture these waves. the EM waves that impinge on the antenna create a very tiny varying current along the surface, and a very sensitive circuit built into the radio detects this current. that current is changed into a small voltage, and then amplified, and fed into another circuit which ultimately delivers the low frequency audio back to an audio amplifier and finally to a set of speakers. the voltage seen by the radio at the antenna input is on the order of 10's of microvolts (millionths of a volt). the circuits are thus very sensitve and correspondinly quite delicate. moreover, even if the power to the radio is off these circuits still lie in the path of the applied voltage. suppose, instead of a very weak EM wave being captured by the antenna, a strong EM wave is. what do think the effects might be? what if the EM wave is so strong that the sensitive circuit is not able to cope with the applied voltage? the answer is that the delicate transistors used in these circuits will fail, usually because of thermal reasons (tiny conductors fusing open) or a situation called dielectric breakdown (translated: insulator punch-through). what is going on inside a transistor's tiny body is conceptually no different that what is going on inside the hydraulics of a tractor. apply too much pressure (=voltage) or too high of a flow rate (=current) somewhere in the system and there will be a pop. --- i have described how an FM radio with an exposed antenna might be susceptible to fail if the passing EM wave carries enough energy. the fact is that ANY exposed metal captures these same currents/voltages from EM waves. your house gutter, for example, at this very moment is receiving the Voice of America shortwave station. that energy goes nowhere, but suppose we take another example. your ADSL or cable modem sits on the end of a very long piece of wire (that's our antenna). a very strong passing EM wave can either temporarily interrupt (bit errors) or permanently damage (blown receiver) these devices. it will be useful for you to know that a lightning strike, besides the immediately visible bolt, produces a very strong EM wave that can damage equipment quite far from the actual strike point. a toaster over, per your comment above, has no delicate circuits like a PC or radio both have. a toaster oven is basically a big resistor designed to get hot, sucking down 1000 to 1500W in the process. a radio is not designed for this! any delicate circuit with long wires attached it can be affected by strong EM waves like the type produced by a nuclear EMP. how the equipment reacts is a function of dozens of factors, including how strong the EM field is, how long the attached wires are, how robust the circuit design is, and so and so forth. thus there is no way to answer the question, "will X be affected by an EMP?". that's enough for now.

ar-jedi

Thanks for your answers.  I was just wondering what would survive a blast of massive EMP in planning for the aftermath.  Radios, newer electronic geiger counters, computers, vehicles are some of the items that rely on electronics that come to mind.

Thank you for an informed post. It's great to get info from people who actually have real knowledge in the area. "Weaponology" demonstrated an EMP effect on a car by driving one directly under an EMP generator. So if I get this right then many vehicles (and other devices) may survive a high altitude EMP burst due to distance from point-of-origin, atmospherics and other variables ?

Quoted: So if I get this right then many vehicles (and other devices) may will survive a high altitude EMP burst due to distance from point-of-origin, atmospherics and other variables ?

yes.

ar-jedi

I've read a lot of conflicting info. Do you or don't you have to ground your homemade Faraday Cage. Some sites say not necessary (as long as it's not on concrete) and some say it's a must. Whats the truth???

"Consequently, storage of equipment in Faraday boxes on wooden shelves or the like does NOT require that everything be grounded. (One note: theoretically non-grounded boxes might hold a slight charge of electricity; take some time and care before handling ungrounded boxes following a nuclear attack.) "
www.aussurvivalist.com/nuclear/empprotection.htm

Quoted: Do you or don't you have to ground your homemade Faraday Cage.

you don't.

ar-jedi

Why not? I'm not doubting you but just curious. Where does the surge then go?

Quoted: Why not? I'm not doubting you but just curious. Where does the surge then go?

If you don't ground it the surge doesn't go anywhere. The Faraday cage could act like a (crappy) capacitor until the charge bleeds off naturally. A grounded cage would get rid of its charge much faster. BSW

Quoted: Quoted: Why not? I'm not doubting you but just curious. Where does the surge then go? If you don't ground it the surge doesn't go anywhere. The Faraday cage could act like a (crappy) capacitor until the charge bleeds off naturally.

no.

Quoted: A grounded cage would get rid of its charge much faster. BSW

no.

let's work up an example.  what happens when an airplane in flight is struck by lightning?  clearly, the airplane isn't grounded.  

ar-jedi

Quoted: Quoted: Quoted: Why not? I'm not doubting you but just curious. Where does the surge then go? If you don't ground it the surge doesn't go anywhere. The Faraday cage could act like a (crappy) capacitor until the charge bleeds off naturally. no. Quoted: A grounded cage would get rid of its charge much faster. BSW no. let's work up an example.  what happens when an airplane in flight is struck by lightning?  clearly, the airplane isn't grounded.   ar-jedi

I'm not an airplane guy:

I suppose that a charge builds up on the skin of the airplane. As long as there is no path to ground, no potential, no current flow. It's the same reason birds can sit on a 50kV HV line, the bird is at 50kV in respect to ground, but at 0V with respect to the line. BSW

file this under "Sucks to be me" -
In the case of a EMP, there is one device that is quite sensitive to an EMP. The Pacemaker...... Yup, you will be able to tell who is pacemaker dependent when it hits.... Folks like me, not as big a deal as it could be. BUT - there are many, many people of ALL ages (some as young as 14) who are 100% pacemaker dependent. That means EVERY beat of their heart is instructed by the device. Therefore, when the EMP scrambles the pacer, - they're done. Many of those people may be driving cars when it happens.....

Quoted: Quoted: Quoted: Quoted: Why not? I'm not doubting you but just curious. Where does the surge then go? If you don't ground it the surge doesn't go anywhere. The Faraday cage could act like a (crappy) capacitor until the charge bleeds off naturally. no. Quoted: A grounded cage would get rid of its charge much faster. BSW no. let's work up an example.  what happens when an airplane in flight is struck by lightning?  clearly, the airplane isn't grounded.   ar-jedi I'm not an airplane guy: I suppose that a charge builds up on the skin of the airplane. As long as there is no path to ground, no potential, no current flow. It's the same reason birds can sit on a 50kV HV line, the bird is at 50kV in respect to ground, but at 0V with respect to the line. BSW

No, birds can do this because their feet and legs are made out of protein and can't conduct unless they also touch a ground but in the example of electrified bird feeders the birds aren't bothered but the squirrels get zapped.

Quoted: Quoted: Quoted: Why not? I'm not doubting you but just curious. Where does the surge then go? If you don't ground it the surge doesn't go anywhere. The Faraday cage could act like a (crappy) capacitor until the charge bleeds off naturally. no. Quoted: A grounded cage would get rid of its charge much faster. BSW no. let's work up an example.  what happens when an airplane in flight is struck by lightning?  clearly, the airplane isn't grounded.   ar-jedi

So, it's all about protecting whats inside but were does the surge go, say if everything was in a metal cabinet (not directly touching the metal but sitting on cardboard)on a cement floor?

Quoted: No, birds can do this because their feet and legs are made out of protein and can't conduct unless they also touch a ground but in the example of electrified bird feeders the birds aren't bothered but the squirrels get zapped.

I hope you are joking.  His statement was correct.
These guys are working on a live line by raising the potential of their insulated truck to the line's potential:

Quoted: I suppose that a charge builds up on the skin of the airplane. As long as there is no path to ground, no potential, no current flow.

but consider that a moment later the airplane is now charged at a potential which can ionize the air in the gap to the ground.  there is another discharge, originating at the plane and ending on the ground.  

www.youtube.com/watch?v=w69vfMvpeBc

so there is current flow (and a high current flow at that) through the plane, specifically through the skin of the plane.  if the surface area of the plane is sufficiently conductive, and there is enough conductive area to avoid localized heating (i.e., melting of aluminum), there will be no damage to the aricraft.  

what we've talked about so far is a situation where a large current passes through an ungrounded structure.  let's take this onward.  suppose the bolt does not hit the plane, but instead passes some 100yards to one side of it.  what happens then?

we know that any current flow (especially a big current flow like a lightning bolt) produces electromagnetic (EM) energy -- turn on an AM/FM radio during a thunderstorm and you can hear it (much more so on AM than FM, btw, for the simple reason that FM is much more resistant to atmospheric disturbances).  the current flow in the bolt creates an electric field (conceptually a wave front, sometimes referred to as a "flux") and a magnetic field.  these two are referred to as an E-field and an H-field respectively.  for simplicity here, take my word that the E-field and H-field travel together but at a right angle to one another.  if you want to learn more about EM energy, google for Maxwell, Gauss, Faraday, and Michelson.

the lightning discharge can be thought of as an impulse; that is, a very short duration high energy pulse.  again, for reasons a bit complicated to type up, such an impulse generates a broad range of electromagnetic energy -- which i'll translate to say that the lightning produces a wide bandwidth "bump" of powerful EM energy that spans many frequencies.

as the invisible electromagnetic wave produced by the lightning passes by the airplane, a current is generated on the surface of the plane.  this is conceptually no different than the current that is produced on the antenna of your car -- an EM wave is transmitted by your favorite radio station, and your car antenna picks up this signal and converts it to audio.  

the magnitude of the current on the skin of the airplane is a product of many factors, including the E- and H-field strengths, the spectral content of the wave, the angle of incidence, and the conductivity of the aluminum skin.  nevertheless, because of a principle put forth by Faraday, assuming the skin is reasonably electrically contiguous up to the highest frequency impinging on it, the inside of the structure will not suffer any effects of the wave.  this is true whether the structure is grounded or not.

Quoted: It's the same reason birds can sit on a 50kV HV line, the bird is at 50kV in respect to ground, but at 0V with respect to the line. BSW

this is correct.  the protein nonsense written above is just that, nonsense.

ar-jedi