EMP Understanding and Practical Countermeasures
This article will address a much misunderstood subject, the effects of EMP (Electromagnetic Pulse) and some practical countermeasures against the damaging effects it can cause. When a nuclear weapon is detonated in the atmosphere, gamma radiation travels in all directions (spherically) and ionizes the air molecules around it, stripping the electrons in a cascade effect.
The interaction of these electrons with the earth’s magnetic field then generates EMP, which is actually three components. We will not go into the physics here, bit a search of EMP and Compton Effect will bring you all of the heavy-duty reading you can handle.
I am a degree electronic engineer with nearly 40 years in practice, and worked as a volunteer amateur radio operator in the MARS (Military Affiliate Radio System) from the early 1980’s into the mid 1990’s, a time in communications when we were migrating from vacuum tubes to solid state electronics and the military communication planners were well aware of the EMP issue, and produced quite a bit of documentation and training material on the subject.
EMP produces high voltages and currents via induction from a magnetic field across a conductor. If we think of the conductor as an antenna, then the smaller the antenna, the smaller the induced power will be.
What this means is that many small electronic items, from FRS radios, to cell phones may be untouched, because the voltages induced internally are small. Nearly any item plugged into the power from the electrical grid, will however most likely be compromised, because of the vast array of antennas (i.e., power lines) stretching across the country.
Nearly all modern electronics are hardened against induced voltages from things like static electricity and tested using both contact and air gap discharge tests with a minimum voltage in the range of 4000-8000 volts or more. Unfortunately, most devices connected to the power line will suffer damage, up to and including complete inoperability, due to the induced high voltages on the power grid, which then are presented to the outlets in your home. There is however both good and bad news here.
While your cell phone may be undamaged, the cell towers, and interconnections to the normal telephone network will most likely fail, leaving you with a rather useless communications device with perhaps a working mp3 player and camera. Keep in mind however that you may have antennas on some of your equipment that is not connected to the power grid.
A large solar electric panel has a large surface area and wiring, and makes a pretty good antenna for induced power, and I’m not sure you can really do anything to save them, other than a duplicate set stored in an EMP proof manner. In short, anything not connected to the power grid that has its own extended wiring (antenna) is vulnerable.
An analogy for this effect would be the following thought experiment. Take a collection of containers, from shot glasses, coffee cups, 5 gallon buckets, kid’s swimming pools, and the rain barrel attached to your downspout, and set them all over the yard. Lay some of them on their sides, and place some of them upside down.
Now imagine a heavy thunder shower coming over the area that lasts perhaps for only 15 seconds. Now walk amongst the containers and see how much water (i.e., damage) each received. Those that are upside down are probably dry inside, and represent equipment that was oriented with the smallest cross-section toward the oncoming storm front (e.g., EMP pulse wave). Those on their side are similar, but some of them nay contain water, based again on their orientation to the storm.
Of those that are upright, some of the smaller shot glasses may have a little water, or even be dry, but the buckets, pools, and especially the rain barrel, contain a lot of water. This is because they provide a larger surface area to collect it. The way EMP affects metal work similarly.
The larger the surface area of the antenna, and the more directly it faces the pulse wave front, the more energy is transferred and the more current gets induced. To some extent this may affect things in a seemingly random fashion, because it depends on a lot of factors that cannot be known when the event occurs.
In 1962 the United States detonated a 1.4 Megaton nuclear device in the upper atmosphere 250 miles above the earth’s surface in the middle of the Pacific Ocean, about 900 miles from Hawaii. The EMP effects damaged about 300 street lights. The lights were damaged precisely because they were part of a large antenna system which allowed large voltages and currents to be produced.
It is generally true that an EMP event will not harm most humans; the power induced by an EMP event can possibly harm someone with a pacemaker, the lead wires of which may make a good set of antennas. Even here, the location of the person and orientation to the pulse will have an (unpredictable) effect.
Mitigation: So what can we do to save at least some if our equipment if an event occurs? There are several things, a few of which will be outlined here.
Old stuff: My 30+ year old Stihl chainsaw and my 40+ year old generator both use magnetos and no electronics for the ignition. Keeping additional spark plugs, etc. is a good thing to do regardless of an EMP event, and is simply good practice. The same would also apply to older vehicles with carburetors and standard points & condenser, or maybe some of those old tube based radios. You get the point here. Use old stuff and keep critical spares on hand.
Spares: Keep EMP protected spares of equipment or repair components for newer equipment that you have decided is required equipment.
Naturally shielded Equipment: whenever possible, purchase electronics in metal enclosures and not plastic. While not perfect, the metal enclosure will provide some amount of faraday shielding to your device. All of my Yaesu radios are build this way using heavy cast aluminum for the main body, although those connected to a power supply or antenna during an event would most likely be damaged.
Natural Faraday Shield: Storing equipment in naturally shielded enclosures can provide protection to varying degrees depending on the enclosure, and can make a good place to store commonly used devices. Metal desks, filing cabinets, metal storage boxes (tool box with tight-fitting lid), or even a 30 gallon metal trash can with a tight-fitting lid, can be convenient and are a better place to store things than laying out on the countertop or table. Make sure to remove paint and rust so the lid and the container have a solid electrical connection. When possible, line the edges of the container and lid with copper or other electrical braid to act as an electrical gasket.
Faraday Shielded cage or box: A Faraday shielded container is simply one that is completely covered with, or constructed of a conductive material (e.g., metal). Any metal will do, and although commercial cages are generally constructed with copper mesh, copper is not required. The problem with constructing a single Faraday Cage is that everything must be stored there, and may not be easily available for everyday use.
Also, since the container cannot have any holes in it, the only way to really be sure it is always protective, is to have an airlock type door system, ensuring that one of the two doors is always closed when accessing the contents. The simplest way to provide protection is to keep things in their original boxes, and wrap the boxes like Christmas or Birthday presents with several overlapping layers of aluminum foil, being careful not to tear the foil on the corners or any sharp edges.
Storing devices in anti-static bags is not a bad idea, but is unnecessary when the device is encased in foil. Additionally, you can store these wrapped (mini Faraday cages) in your other cages (e.g., trash can, filing cabinet, etc), to provide layered protection. BTW, the copper mesh is generally used due to weight concerns and to allow external light to penetrate the cage, since having anything but a battery-powered light in the cage would represent a break of the cage integrity to the outside world.
To ground or not to ground: There seems to always be heated discussion on whether or not to ground a Faraday cage. The short answer is that it isn’t necessary and indeed may be harmful in some configurations. Assuming the cage is constructed properly, which can be tested by placing a battery-powered radio inside (the radio should stop producing sound when the cage is closed). The magnetic field gradients within the box should always cancel out to zero, regardless of whether or not the cage is grounded.
Once you get the radio to stop, add, and remove a ground and you’ll see that the radio is not affected. If the cage is physically close to earth ground, a heavy breaded ground may not hurt anything, but is not required. Connecting a lighter (single copper wire) more than a few feet, may seem like a ground connection, but in reality can act like an antenna.
While this in itself won’t hurt anything, if it is long enough and enough power is induced into it, you could see arcing, in, around, and possibly through your cage barrier. The only real danger of leaving the cage ungrounded is that if you are touching it at the moment of an EMP event, you will likely receive a nasty shock.
If a ground was required to be functional, then is would not be possible to protect aircraft from EMP. Some people confused grounding for lightning with grounding for EMP. Lightning is generated as a high voltage differential between the upper atmosphere and the ground, and the lightning strike is natures attempt to bring the differential to zero. In this case, the electrical path is to ground, and a ground rod for lightning is useful
Final (random) thoughts: Keeping things protected from an EMP event isn’t all that hard, and dealing with individual items may provide some security, that may not be provided with a single large storage container. If 50% of your mini aluminum foil wrapped packages fail, you lose half your stuff.
If your Faraday storage room fails, you may lose all of it. Keep in mind that the LED’s in flashlights are solid state devices, and although superior in almost every way to the older light bulb based lights, may be susceptible to EMP when those old light bulbs are not. Keeping additional supplies (like the diodes for the vehicle alternator) wrapped in aluminum foil and tucked in the bottom of the drawer, will give you the ability to fix the broken things if an event actually breaks them.
Another event generally lumped into the EMP discussion is that of an EMP type event due to a solar storm. The good thing here is that NASA keeps a pretty close eye on the sun and we generally get some warning on future events. If this concerns you check out: http://spaceweather.com/ for forecasts and other interesting information.
Hopefully this information will give you a starting point to think about countermeasures for an EMP event, and give you some ideas on how to secure equipment in your own situation. The effects of an EMP event are in many ways theoretical, and all we can do is the best effort based on what we do understand if the physics involved. So, get some cheap aluminum foil and look around the house and I suspect you’ll find a lot of potential hidey holes that will fit the bill.
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SOURCE : www.thesurvivalistblog.net