Many misconceptions about
electromagnetic pulse (EMP) effects have circulated for years among technical
and policy experts, in press reports, on preparedness websites, and even in
technical journals. Because many aspects of EMP-generation physics and its effects
are obscure, misconceptions from those who do not perceive the seriousness of
the effects to those who predict a doomsday chain of events are inevitable.
However, not all EMPs are the same, with the most significant effects being
caused by E1 and E3 fields.
Nuclear bursts detonated at
altitudes above 40 km generate two principle types of EMPs that can debilitate
critical infrastructure systems over large regions:
- The first– a “fast-pulse” EMP field, also referred to as E1– is created by gamma ray interaction with stratospheric air molecules. The resulting electric field peaks at tens of kilovolts per meter in a few nanoseconds and lasts a few hundred nanoseconds. E1’s broadband power spectrum (frequency content from DC to 1 GHz) enables it to couple to electrical and electronic systems in general, regardless of the length of their cables and antenna lines. Induced currents range into the thousands of amperes, and exposed systems may be upset or permanently damaged.
- The second– a “slow-pulse” phenomenon referred to as magnetohydrodynamic (MHD) EMP, or E3– is caused by the distortion of Earth’s magnetic field lines due to the expanding nuclear fireball and the rising of heated, ionized layers of the ionosphere. The change of the magnetic field at the Earth’s surface induces a field in the tens of volts per kilometer, which, in turn, induces low-frequency currents of hundreds to thousands of amperes in long conducting lines only (a few kilometers or longer) that damage components of long-line systems, including the electric power grid and long-haul communication and data networks.
By over- and under-emphasizing
realistic consequences of EMPs, policymakers may delay actions or dismiss
arguments altogether. The six misconceptions about EMPs that are perhaps the
most harmful involve: (a) exposed electronic systems, (b) critical
infrastructure systems, (c) nuclear weapons, (d) cost of protection, (e) type
of EMPs, and (f) fiber-optic networks.
Based on the U.S. Department of
Defense (DOD) and Congressional EMP Commission’s EMP test databases, small,
self-contained systems, such as motor vehicles, hand-held radios, and
unconnected portable generators, tend not to be affected by EMPs. If there is
an effect on these systems, it is often temporary upset rather than component
burnout.
On the other hand, threat-level EMP
testing also reveals that systems connected to power lines are highly
vulnerable to component damage, requiring repair or replacement. Because the
strength of EMP fields is measured in volts per meter, the longer the
conducting line, the more EMP energy will be coupled into the system, and the
higher the probability of damage. As such, the electric power-grid network and landline
communication systems are almost certain to experience component damage when
exposed to an EMP with cascading effects to most other (dependent)
infrastructure systems.
EMP Effects Will Have Limited, Easily Recoverable,
“Nuisance” Effects on Critical Infrastructure Systems.
Although an EMP would not affect
every system, widespread failure of a significant fraction of electrical and
electronic systems will cause large-scale cascading failures of critical
infrastructure networks because of the interdependency among affected and
unaffected systems. Mathematician Paul Erdos’s “small-world” network theory
applies, which refers to most nodes– equipment attached to a network– being
accessible to all others through just a few connections. The fraction of all
nodes changes suddenly when the average number of links per single network
connection exceeds one. For example, a single component failure, where the
average links per node is two, can affect approximately half of the remaining
“untouched” network nodes.
For many systems, especially
unmanned systems, loss of control is tantamount to permanent damage, in some
cases causing machinery to self-destruct. Examples of this include:
- Lockup or not being able to change the “on” or “off” state of long-haul communication repeaters,
- Loss of remote pipeline pressure control in supervisory control and data acquisition (SCADA) systems, which communicate with remote equipment,
- Loss of generator controls in electric power plants, and
- Loss of machine process controllers in manufacturing plants.
Due to a limiting atmospheric
saturation effect in the EMP-generation process, low-yield weapons produce a
peak E1 field similar in magnitude to high-yield weapons if they are detonated
at altitudes of 50-80 km. The advantage of high-yield weapons is that their
range on the ground is affected less significantly when detonated at higher
altitudes.
Nuclear weapons with yields ranging
from three kilotons to three megatons (a three order of magnitude difference in
yield), when detonated at their optimum burst altitudes, exhibit a range of
peak E1 fields on the ground differing by only a factor of ~3, viz. 15-50
KV/meter. With respect to the late-time (E3, or low-amplitude, low-frequency
components) EMP field, a 30-KT nuclear weapon above 100 km would cause
geomagnetic disturbances as large as solar superstorms, although over smaller
regions. It also is worth noting that peak currents on long overhead lines
induced by E1 from 10 kiloton-class weapons can range in the kiloamperes with
voltages reaching into the hundreds of kilovolts.
Of the 14 critical infrastructure
sectors, EMP risk is highest for electric power grids and telecommunication
grids, because of their network connections and criticality to the operation
and recovery of other critical infrastructure sectors. Attention to hardening
these infrastructure grids alone would provide significant benefits to national
resilience.
The electric power grid is essential
for sustaining population “life-support” services. However, some major grid
components could take months, or years, to replace, if many components are
damaged. The primary example is high-voltage transformers, which can
irreparably fail during major solar storms and are thus likely to fail during
an EMP event. Protection of these large transformers would reduce the time
required to restore the grid and restore the necessary services it enables.
According to Emprimus– a
manufacturer of transformer protection devices– the unit cost for high-voltage
transformer protection is estimated to be $250,000, with the total number of
susceptible, large, high-voltage units ranging from 300 to 3,000, according to
Oak Ridge National Laboratory. The requirement and cost for generator facility
protection are still undetermined but are likely to be similar to transformer
protection costs. To protect SCADA systems, replacement parts are readily
available and repairs are relatively uncomplicated. Protection costs for
heavy-duty grid components are in the $10 billion range, which is a small
fraction of the value of losses should they fail. When amortized, protection
costs to consumers amount to pennies per month.
Oak Ridge National Laboratory’s
January 2010 report on its E1 tests of 7.2-KV distribution transformers produced
permanent damage to transformer windings in seven of the 20 units tested. The
failures were due to transformer winding damage caused by electrical breakdown
across internal wire insulation. As an important side note, transformers with
direct-mounted lightning surge arrestors were not damaged during the tests.
Similar tests of high-voltage transformers are needed.
In general, fiber-optic networks are
less susceptible than metallic line networks; however, fiber-optic multipoint
line driver and receiver boxes, which are designed to protect against ground
current, may fail in EMP environments. Long-haul telecommunication and regional
Internet fiber-optic repeater amplifiers’ power supplies are particularly
vulnerable to EMP environments (Figure 1). Terrestrial fiber-optic cable
repeater amplifier power is provided by the electric power grid and, thus,
vulnerable to grid failure as well as to direct EMP/E1 effects. Undersea cable
repeater amplifiers also are vulnerable to EMP/E3 effects, since they are
connected to a coaxial metallic power conductor that runs the length of the
line. Because of its low-frequency content, E3 penetrates to great ocean
depths, which subjects undersea power amplifiers to high risk of burnout. On
the positive side, line drivers/receivers and repeater amplifiers are
relatively easy to protect using shielding, shield-penetration treatment, and
power-line filters and/or breakers.
From a risk-based priority
standpoint, the electric power grid is a high priority for EMP protection.
Hardening this infrastructure alone would have major benefits for national
resilience– the ability to sustain, reconstitute, and restart critical
services. EMP engineering solutions have been implemented and standardized by
DOD since the 1960s and are well documented:
- MIL-STD-188-125-1 – “DOD Interface Standard – High-Altitude Electromagnetic Pulse (HEMP) Protection for Ground-Based C4I Facilities Performing Critical, Time-Urgent Missions – Part 1 – Fixed Facilities” (17 July 1998);
- MIL-STD-188-125-2 – “DOD Interface Standard – High-Altitude Electromagnetic Pulse (HEMP) Protection for Ground-Based C4I Facilities Performing Critical, Time-Urgent Missions – Part 1 – Transportable Systems” (3 March 1999); and
- MIL-HDBK-423 – “Military Handbook – High-Altitude Electromagnetic Pulse (HEMP) Protection for Fixed and Transportable Ground-Based C4I Facilities Vol. 1 – Fixed Facilities” (15 May 1993).
With respect to the power grid, the
installation of blocking devices in the neutral-to-ground conductors of large
electric distribution transformers will significantly reduce the probability of
damage from slow EMP/E3. Transformer protection against E1 over-voltages is
achievable by installing common metal-oxide varistors (control elements in
electrical circuits) on transformers from each phase to ground. Costs for
protecting the power grid are small, compared to the value of the systems and
services at risk.
The author of this article is a
professor emeritus who consults on critical infrastructure assurance,
specializing in EMP and other nuclear effects for various government agencies.
From the Survival Blog
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