by Duncan Long
June 23, 2005
EMP. The letters spell burnt out computers and other electrical
systems and perhaps even a return to the dark ages if it were to
mark the beginning of a nuclear war. But it doesn't need to be that
Once you understand EMP, you can take a
few simple precautions to protect yourself and equipment from it. In
fact, you can enjoy much of the "high tech" life style you've come
accustomed to even after the use of a nuclear device has been used
by terrorists - or there is an all-out WWIII.
Pulse), also sometimes known as "NEMP" (Nuclear
Electromagnetic Pulse), was kept secret from the public for a long
time and was first discovered more or less by accident when US
Military tests of nuclear weapons started knocking out phone banks
and other equipment miles from ground zero.
EMP is no longer "top secret" but information about it is still a
little sketchy and hard to come by. Adding to the problems is the
fact that its effects are hard to predict; even electronics
designers have to test their equipment in powerful EMP simulators
before they can be sure it is really capable of with standing the
EMP occurs with all nuclear explosions. With smaller explosions the
effects are less pronounced. Nuclear bursts close to the ground are
dampened by the earth so that EMP effects are more or less confined
to the region of the blast and heat wave. But EMP becomes more
pronounced and wide spread as the size and altitude of a nuclear
blast is increased since the ground; of these two, altitude is the
quickest way to produce greater EMP effects.
As a nuclear device is exploded higher
up, the earth soaks up fewer of the free electrons produced before
they can travel some distance.
The most "enhanced" EMP effects would occur if a nuclear weapon were
exploded in space, outside the Earth's atmosphere. In such a case,
the gamma radiation released during the flash cycle of the weapon
would react with the upper layer of the earth's atmosphere and strip
electrons free from the air molecules, producing electromagnetic
radiation similar to broad-band radio waves (10 kHz-100 MHz) in the
These electrons would follow the earth's
magnetic field and quickly circle toward the ground where they would
be finally dampened.
(To add to the confusion, we now have
two more EMP terms:
Tactically, a space-based nuclear attack
has a lot going for it.
The magnetic field of the earth tends to
spread out EMP so much that just one 20-MT bomb exploded at an
altitude of 200 miles could - in theory - blanket the continental US
with the effects of EMP. It's believed that the electrical surge of
the EMP from such an explosion would be strong enough to knock out
much of the civilian electrical equipment over the whole country.
Certainly this is a lot of "bang for the
buck" and it would be foolish to think that a nuclear attack would
be launched without taking advantage of the confusion a
high-altitude explosion could create.
Ditto with its use by terrorists should
the technology to get such payloads into space become readily
available to smaller countries and groups.
But there's no need for you to go back to the stone age if a nuclear
war occurs. It is possible to avoid much of the EMP damage that
could be done to electrical equipment - including the computer that
brought this article to you - with just a few simple precautions.
First of all, it's necessary to get rid of a few erroneous facts,
One mistaken idea is that EMP is like a powerful bolt of lightning.
While the two are alike in their end results - burning out
electrical equipment with intense electronic surges - EMP is
actually more akin to a super-powerful radio wave. Thus, strategies
based on using lightning arrestors or lightning-rod grounding
techniques are destined to failure in protecting equipment from EMP.
Another false concept is that EMP "out of the blue" will fry your
brain and/or body the way lightning strikes do. In the levels
created by a nuclear weapon, it would not pose a health hazard to
plants, animals, or man PROVIDED it isn't concentrated.
EMP can be concentrated. That could happen if it were "pulled in" by
a stretch of metal. If this happened, EMP would be dangerous to
living things. It could become concentrated by metal girders, large
stretches of wiring (including telephone lines), long antennas, or
similar set ups.
So - if a nuclear war were in the offing
- you'd do well to avoid being very close to such concentrations. (A
safe distance for nuclear-generated EMP would be at least 8 feet
from such stretches of metal.)
This concentration of EMP by metal wiring is one reason that most
electrical equipment and telephones would be destroyed by the
electrical surge. It isn't that the equipment itself is really all
that sensitive, but that the surge would be so concentrated that
nothing working on low levels of electricity would survive.
Protecting electrical equipment is simple if it can be unplugged
from AC outlets, phone systems, or long antennas.
But that assumes
that you won't be using it when the EMP strikes. That isn't all that
practical and - if a nuclear war were drawn out or an attack
occurred in waves spread over hours or days - you'd have to
either risk damage to equipment or do without it until things had
settled down for sure.
One simple solution is to use battery-operated equipment which has
cords or antennas of only 30 inches or less in length.
This short stretch of metal puts the
device within the troughs of the nuclear-generated EMP wave and will
keep the equipment from getting a damaging concentration of
electrons. Provided the equipment isn't operated close to some other
metal object (i.e., within 8 feet of a metal girder, telephone line,
etc.), it should survive without any other precautions being taken
If you don't want to buy a wealth of batteries for every appliance
you own or use a radio set up with longer than 30-inch antenna, then
you'll need to use equipment that is "hardened" against EMP.
The trick is that it must REALLY be hardened from the real thing,
not just EMP-proof on paper.
This isn't all that easy; the National
Academy of Sciences recently stated that tailored hardening is,
"not only deceptively difficult, but
also very poorly understood by the defense-electronics
Even the US Military has equipment which
might not survive a nuclear attack, even though it is designed to do
That said, there are some methods which will help to protect
circuits from EMP and give you an edge if you must operate ham
radios or the like when a nuclear attack occurs.
Design considerations include,
the use of
tree formation circuits (rather than standard loop formations)
use of induction shielding around components
the use of
self-contained battery packs
the use of loop antennas (with
the use of Zener diodes
These design elements can eliminate the
chance an EMP surge from power lines or long antennas damaging your
Another useful strategy is to use grounding wires for
each separate instrument which is coupled into a system so that EMP
has more paths to take in grounding itself.
A new device which may soon be on the market holds promise in
allowing electronic equipment to be EMP hardened.
Called the "Ovonic threshold device", it
has been created by Energy Conversion Devices of Troy, MI.
The Ovonic threshold device is a solid-state switch capable of
quickly opening a path to ground when a circuit receives a massive
surge of EMP.
Use of this or a similar device would
assure survival of equipment during a massive surge of electricity.
Some electrical equipment is innately EMP-resistant. This includes
large electric motors, vacuum tube equipment, electrical generators,
transformers, relays, and the like. These might even survive a
massive surge of EMP and would likely to survive if a few of the
above precautions were taking in their design and deployment.
At the other end of the scale of EMP resistance are some really
sensitive electrical parts. These include IC circuits, microwave
transistors, and Field Effect Transistors (FET's). If you have
electrical equipment with such components, it must be very well
protected if it is to survive EMP.
One "survival system" for such sensitive equipment is
A Faraday box is simply a metal box designed to divert and soak up
the EMP. If the object placed in the box is insulated from the
inside surface of the box, it will not be effected by the EMP
travelling around the outside metal surface of the box. The Faraday
box simple and cheap and often provides more protection to
electrical components than "hardening" through circuit designs which
can't be (or haven't been) adequately tested.
Many containers are suitable for make-shift Faraday boxes:
metal filing cabinets,
...etc., etc., can
all be used.
Despite what you may have read or heard,
these boxes do NOT have to be airtight due to the long wave length
of EMP; boxes can be made of wire screen or other porous metal.
The only two requirements for protection with a Faraday box are:
the equipment inside the box
does NOT touch the metal container (plastic, wadded paper,
or cardboard can all be used to insulate it from the metal)
the metal shield is continuous
without any gaps between pieces or extra-large holes in it
Grounding a Faraday box is NOT necessary
and in some cases actually may be less than ideal.
While EMP and lightning aren't the "same
animal", a good example of how lack of grounding is a plus can be
seen with some types of lightning strikes. Take, for example, a
lightning strike on a flying airplane. The strike doesn't fry the
plane's occupants because the metal shell of the plane is a Faraday
box of sorts.
Even though the plane, high over the
earth, isn't grounded it will sustain little damage.
In this case, much the same is true of small Faraday cages and EMP.
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
The thickness of the metal shield around the Faraday box isn't of
much concern, either.
This makes it possible to build
protection "on the cheap" by simply using the cardboard packing box
that equipment comes in along with aluminium foil. Just wrap the box
with the aluminium foil (other metal foil or metal screen will also
work); tape the foil in place and you're done.
Provided it is kept dry, the cardboard
will insulate the gear inside it from the foil; placing the
foil-wrapped box inside a larger cardboard box is also wise to be
sure the foil isn't accidentally ripped anywhere.
The result is an "instant" Faraday box
with your equipment safely stored inside, ready for use following a
Copper or aluminium foil can help you insulate a whole room from EMP
as well. Just paper the wall, ceiling and floor with metal foil.
Ideally the floor is then covered with a false floor of wood or with
heavy carpeting to insulate everything and everyone inside from the
shield (and EMP). The only catch to this is that care must be taken
NOT to allow electrical wiring connections to pierce the foil shield
(i.e., no AC powered equipment or radio antennas can come into the
room from outside).
Care must also be taken that the door is
covered with foil AND electrically connected to the shield with a
wire and screws or some similar set up.
Many government civil defense shelters are now said to have gotten
the Faraday box, "foil" treatment. These shelters are covered inside
with metal foil and have metal screens which cover all air vents and
are connected to the metal foil. Some of these shelters probably
make use of new optical fibre systems - protected by plastic pipe -
to "connect" communications gear inside the room to the "outside
world" without creating a conduit for EMP energy to enter the
Another "myth" that seems to have grown up with information on EMP
is that nearly all cars and trucks would be "knocked out" by EMP.
This seems logical, but is one of those
cases where "real world" experiments contradict theoretical answers
and I'm afraid this is the case with cars and EMP. According to
sources working at Oak Ridge National Laboratory, cars have proven
to be resistant to EMP in actual tests using nuclear weapons as well
as during more recent tests (with newer cars) with the US Military's
One reason for the ability of a car to resist EMP lies in the fact
that its metal body is "insulated" by its rubber tires from the
ground. This creates a Faraday cage of sorts.
(Drawing on the analogy of EMP being
similar to lightning, it is interesting to note that cases of
lightning striking and damaging cars is almost non-existent; this
apparently carries over to
EMP effects on vehicles as well.)
Although Faraday boxes are generally made so that what is inside
doesn't touch the box's outer metal shield (and this is especially
important for the do-it-yourself since it is easy to inadvertently
ground the Faraday box - say by putting the box on metal shelving
sitting on a concrete floor), in the case of the car the "grounded"
wiring is grounded only to the battery.
In practice, the entire system is not
grounded in the traditional electrical wiring sense of actually
making contact to the earth at some point in its circuitry. Rather
the car is sitting on insulators made of rubber.
It is important to note that cars are NOT 100 percent EMP proof;
some cars will most certainly be effected, especially those with
fibreglass bodies or located near large stretches of metal. (I
suspect, too, that recent cars with a high percentage of IC
circuitry might also be more susceptible to EMP effects.)
The bottom line is that all vehicles probably won't be knocked out
by EMP. But the prudent survivalist should make a few contingency
plans "just in case" his car (and other electrical equipment) does
not survive the effects of EMP.
Discovering that you have one of the few
cars knocked out would not be a good way to start the onset of
terrorist attack or nuclear war.
Most susceptible to EMP damage would be cars with a lot of IC
circuits or other "computers" to control essential changes in the
engine. The very prudent may wish to buy spare electronic ignition
parts and keep them a car truck (perhaps inside a Faraday box). But
it seems probable that many vehicles WILL be working following the
start of a nuclear war even if no precautions have been taken with
One area of concern are explosives connected to electrical discharge
wiring or designed to be set off by other electric devices.
These might be set off by an EMP surge.
While most citizens don't have access to such equipment, claymore
mines and other explosives would be very dangerous to be around at
the start of a nuclear box if they weren't carefully stored away in
a Faraday box.
Ammunition, mines, grenades and the like
in large quantities might be prone to damage or explosion by EMP,
but in general aren't all that sensitive to EMP.
A major area of concern when it comes to EMP is nuclear reactors
located in the US. Unfortunately, a little-known Federal dictum
prohibits the NRC from requiring power plants to withstand the
effects of a nuclear war. This means that, in the event of a nuclear
war, many nuclear reactors' control systems might will be damaged by
an EMP surge.
In such a case, the core-cooling
controls might become inoperable and
a core melt down and breaching
of the containment vessel by radioactive materials into the
surrounding area might well result. (If you were needing a reason
not to live down wind from a nuclear reactor, this is it.)
Provided you're not next door to a nuclear power plant, most of the
ill effects of EMP can be over come. EMP, like nuclear blasts and
fallout, can be survived if you have the know how and take a few
precautions before hand.
And that would be worth a lot, wouldn't it?
Some initial thoughts on EMP protection from the US military
A continuously sealed metal barrier has proven to be very effective
in preventing EM/HPM energy from reaching susceptible electronic or
explosive components. Exterior packaging fabricated from plastic,
wood or other fibre materials provides almost no protection form EM/HPM
threats. The metal enclosure can be very thin provided there are no
openings (tears, pin holes, doors, incomplete seams) that would
allow microwaves to enter.
Sealed barrier bags that incorporate a
thin layer of aluminium foil and are primarily used to provide water
vapour proof protection to an item, can add a great deal of
resistance to EM/HPM penetration.
A number of cylindrical and rectangular steel containers have been
developed by the Packaging Division for a wide range of munitions,
weapon systems and associated components. The cylindrical containers
are end opening and the rectangular containers are top opening. All
the containers have synthetic rubber gaskets that allow them to
maintain a +3 psi environmental seal to the outside environment.
The containers are constructed using
seam welding to provide for continuous metal contact on all surfaces
of the body assembly.
The cover openings have been held to a
minimum and the sealing gaskets positioned in a manner to allow
overlapping metal parts to add additional protection to these areas.
Microwaves are very adept at bouncing around and working their way
into even the smallest opening. Tests of the cylindrical and
rectangular steel containers used by this organization have
demonstrated a high level of protection in preventing EM/HPM energy
from entering the container.
The key is to use a metal enclosure and eliminate or minimize any
Where openings are needed they should be
surrounded to the greatest extent possible by continuous metal and
in the case of a gasket, metal sheathing or mesh can be placed
around the elastometer material or conductive metal molded into the
gasket. The closer the surrounding container comes to a continuous
metal skin the more protection that will be provided.
High quality gaskets, utilizing either a mesh or embedded conductive
metal design, are very expensive.
They add a magnitude of cost to a normal
gasket and can easily double the price of a container similar to the
ones mentioned above.