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An Immediate Threat?
by Mark Armstrong
with Iran Soon?
by Michael Burkert
Nuclear bombs trigger a strange
effect that can fry your electronics here's how it works
---Nuclear blasts trigger an effect called electromagnetic pulse, or
---EMP can disrupt or even destroy electronics from miles away.
---Blasts miles above a country like the US might severely damage its
electric and telecommunications infrastructure.
A nuclear detonation creates plenty of terrifying effects, including a
blinding (and burning) flash of light, a building-toppling blast wave,
an incendiary fireball, and radioactive fallout that can drift for
hundreds of miles.
But there's a lesser-known consequence of a nuclear explosion that can
drastically expand its damage zone: an electromagnetic pulse, or EMP.
EMPs are rapid, invisible bursts of electromagnetic energy. They occur
in nature, most frequently during lightning strikes, and can disrupt or
destroy nearby electronics. However, nuclear EMPs can cover an entire
continent and cripple tiny circuits inside modern electronics on a
massive scale. The power grid, phone and internet lines, and other
infrastructure that uses metal is also prone to effects that resemble
those of a devastating geomagnetic storm.
Savvy readers called this to our attention after we published expert
advice on why you should never get in a car after a nuclear bomb is
detonated. Brooke Buddemeier, a radiation expert at Lawrence Livermore
National Laboratory, suggested sheltering deep within a building
instead, and tuning in to a radio for instructions.
But a reader named Taylor K. pointed out that "radios, computers,
anything that use[s] electrical transmission to power itself will be
effectively neutralized" by the bomb's EMP.
He's correct but fortunately only in certain situations.
How electromagnetic pulse works
Nuclear explosions don't make EMPs directly; the effect requires a
couple of key ingredients.
The first is a nuke's invisible burst of gamma rays, a form of light
typically emitted by the "hottest and most energetic objects in the
universe," according to NASA. A small fraction of a bomb's energetic
yield between 0.1% and 0.5% is emitted as gamma rays. These slam
into air molecules, knock off electrons, and accelerate the negatively
charged particles to about 90% of the speed of light.
Earth's magnetic field then shuttles many of these high-speed electrons
toward the planet's poles in a corkscrew-like pattern. The electrons
respond to this movement by letting off their newly acquired energy as a
powerful soup of electromagnetic radiation, including radio waves.
This is a nuclear electromagnetic pulse. It happens within a fraction of
a microsecond, and the surge of energy can overload or "shock" sensitive
electronic devices especially the kinds we heavily rely on today.
"[T]he radiation can be collected by metallic and other conductors at a
distance, just as radio waves are picked up by antennas," according to
an unclassified 1977 report from the Department of Defense and
Department of Energy. "The energy from the EMP is received in such a
very short time, however, that it produces a strong electric current
which could damage the equipment. An equal amount of energy spread over
a long period of time, as in conventional radio reception, would have no
When EMP passes through metal objects like a phone, computer, or radio,
they can "catch" this incredibly powerful pulse. This can generate a
rogue current of electricity that moves through a modern device's tiny
circuits and can disrupt or even destroy them. Power transmission or
telecommunications equipment, meanwhile, can overload from the excess
current, spark, and fail for miles around.
If you've ever turned on a microwave oven and noticed your phone's Wi-Fi
or Bluetooth connection momentarily drop out, you've experienced
disruptive electromagnetic waves and had a very small taste of what
could happen with an EMP.
The intensity of a nuclear detonation's EMP is about 30,000 to 50,000
volts per meter thousands of times greater than the one your microwave
Fortunately, not all nuclear blasts are created equal when it comes to
Why altitude is everything
Nuclear detonations that occur dozens or hundreds of miles above Earth
could have devastating consequences compared to those that happen on the
At a high elevation, gamma rays can more easily spread out, hitting many
upper-atmosphere air molecules over a large area at once. The low
density of air allows electrons to move more freely and maximize the
intensity of an EMP.
In fact, a 2008 report by the EMP Commission suggests that the right
nuclear device detonated at the right altitude could bathe the entire
continental US in EMP, disrupting telecommunications and power grid
infrastructure to "catastrophic" effect.
But if an explosion were to occur closer to the ground, many of the
gamma rays would slam into the earth. Those rays would have a harder
time creating a large electric field that could generate widespread EMP.
And the greater density of air wouldn't help, either.
The US government actively plans for 15 disaster scenarios, one of which
is a terrorist-caused nuclear detonation that occurs close to the ground
with a yield of about 10 kilotons roughly 66% as powerful as the
This setup is the one we discussed with Buddemeier, and in that case he
says the nuclear blast itself would give you a lot more to worry about
than bricked electronics or power loss.
"[T]here would be some localized EMP effects," he told Business Insider
in an email, "but if you were close enough for you equipment to be
damaged by EMP (within a couple miles), then you are also close enough
to be significantly impacted by the blast wave."
Put another way, you may not survive inside this zone, which can stretch
a couple of miles in diameter. And if you did, you'd have to worry about
climbing out of rubble before checking to see whether your radio still
It's more likely, Buddemeier says, that within about 5 miles of the
blast "you may have a disruptive impact, which doesnt 'fry' your
equipment, but can cause 'latch-up' (e.g., like the endless spinning
hourglass on your phone) until restarted."
There are hundreds of variables that determine whether or not an EMP
affects electronics, Buddemeier says, including "the size and
orientation of your device, the structure of the building you are in,
plug-in or battery, if it is behind a surge protector," and so on.
Because many radios have simpler, less sensitive circuitry than a phone,
they're likely to be a first line of information after a ground blast.
"There is a good chance that there will be plenty of functioning radios
even within a few miles of the event and that radio transmission towers
outside of the impacted area will still be able to send information on
the safest strategy to keep you and your family safe," Buddemeier says.