Mitigation of EMP effects using shielded rooms and - ETS

shielded rooms
martin
Mitigation of EMP effects using shielded
rooms and enclosures
Performance and reliability of a shielding system is essential
in times of emergency.
WAYNE D. MARTIN
ETS-Lindgren
Glendale Heights, IL
T
he most cursory assessment of
news and events around the globe during this first decade of the Twenty-First
Century leads to the inescapable conclusion that we live in perilous times. Around
the globe, political, ethnic, and religious
strife results in violence. This paper does
not discuss the capabilities or readiness
of the United States military or that of
its allies, nor does it focus on developing
effective standards for first-responder
communications both inside and outside
challenging environments such as skyscrapers and tunnels. (See accompanying
short article on page 87.) Instead, it lays out
a more modern scenario that could be just
as devastating to our economy and way of
life as an all-out nuclear war and details
steps that the military, local government,
utilities or industry itself can take to ward
off such a catastrophe.
THE THREAT
Confidence remains high that the United
States military can and will defend America from a missile attack originating outside
the country. The nation has an extensive
missile defense program, a legacy of the
Cold War era; and the government has
had many years to prepare for whatever
the future may hold, as well as plenty of
doctrines for guidance. Terrorism is the
Twenty-First century version of the last
century’s world wars. Terrorists have
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seized the moment and have staged attacks
in many First World countries. Recall 9/11,
the Madrid train bombings, the London
subway attack, and the attempt on Glasgow
Airport. Terrorizing nations or people
has been achieved though conventional
weaponry such as explosives, or in the
case of 9/11, by turning our own technology against us. In today’s world, weapons
of mass destruction (WMD), so called
“dirty bombs”, radio frequency weapons
(RFW), and intentional electromagnetic
interference (IEMI) devices can generate
localized electromagnetic pulse surges to
disrupt everyday services.
Critical infrastructure facilities are a
vital part of everyday life. These facilities
include electric power facilities, oil refineries, water treatment plants, banking
systems, pipelines, transportation systems,
emergency facilities, and communications
facilities. Most critical infrastructure facilities depend upon electrical and electronic
systems to function. These systems can be
susceptible to a little known, yet significant
and growing threat, the radio frequency
weapons mentioned above. RFWs have
already been used to defeat security systems, to disable police communications,
to induce fires, and to disrupt banking
computers. Many of these devices are small,
suitcase-sized or slightly larger devices
that could be smuggled into the country
the same way drugs and other contraband
penetrate our borders and become available
on the black market. These devices in the
hands of a terrorist are capable of inflicting extreme damage and may be capable
INTERFERENCE TECHNOLOGY 1
shielded rooms
m i t i g at i o n o f e m p e f f e c t s
of generating a localized intentional EMI disturbance at
any location.
Looking back to that fateful day in September 2001
and realizing the magnificent job local, state, and federal
officials in New York did in managing the World Trade
Center crisis makes one feel proud. Imagine what might
have occurred if the perpetrators of that vicious attack
had included in their suicide mission the detonation
of an electromagnetic pulse device that could disrupt
communications of the police, fire, and medical teams
responding to the emergency. Surely, many more lives
and properties would have been lost. The sudden inability of the mayor and other city government officials to
mobilize resources during such a chaotic event could be
catastrophic. At present, homeland security, some local
law enforcement agencies, and border patrol resources
have been stretched extremely thin. Unfortunately, they
are not credited for deterring potential attacks as much
as they will be remembered for the one they did not.
to 80 dB at 10 MHz in accordance with MIL-STD-125-1
and -2 (Figure 2).
Obviously, the HEMP shield and all POE protective
devices are hardness critical items (HCIs). All devices
installed as special protective measures are also HCIs.
Collectively, the HCIs constitute the HEMP protective
systems. Items such as shielded vestibules with interlocked doors, waveguide honeycomb vents, various pipe
penetrations, power and signal line filters with surge
protection (electronic surge arrestors or ESAs), and fiber
optic penetrations are all HCIs—individually or as part
of an assembly.
Generally, HEMP facilities are specified as welded
systems by the military to be installed during the initial
building stage. Warranties of 20 or 30 years are com-
AN EMP ATTACK DEFINED
The detonation of a nuclear device in or above the
Earth’s atmosphere produces an intense, time-varying
electromagnetic field (electromagnetic pulse or EMP).
The EMP environment produced by an exo-atmospheric
event is caused by the sudden entrance of energy (chiefly
gamma rays) into the atmosphere. When such an event
takes place above 30 km, it is defined as a HEMP (highaltitude electromagnetic pulse) effect and can affect
a vast area. Detonation of a weapon at lower altitudes
will produce an electromagnetic pulse that may be less
intense, but will still be strong enough to induce fields
that can cause critical systems in a smaller more localized
area to malfunction because of circuit damage (Figure
1). Another form of attack, intentional electromagnetic
interference (IEMI), has been defined as the “intentional
malicious generation of electromagnetic energy introducing noise or signals into electric and electronic systems,
thus disrupting, confusing, or damaging these systems
for terrorist or criminal purposes.” Nature’s contribution,
lightning EMP (LEMP), like HEMP and other forms of
EMP, involves a brief but intense electromagnetic disturbance in the atmosphere and thus presents another
potential threat to the operation of electronic systems.
Figure 1. EMP area by bursts at 30, 120, and 300 miles.
Source: Gary Smith, “Electromagnetic Pulse Threats,” testimony to House National
Security Committee on July 16, 1997.
110
100
Shielding Effectiveness- SE (dB)
7
SYSTEM SURVIVABILITY
The U.S. military bears the responsibility of establishing
a HEMP-hardened electrical parameter barrier for mission critical military operations that will ensure system
survivability during a HEMP event. Creating an electromagnetic barrier that will prevent or limit HEMP or localized EMP fields or conducted transients from entering
the shielded area is primary. The shield and all points of
entry (POE) must be treated properly to maintain shield
integrity. They must be hardened to provide at least 80
dB attenuation in the plane wave field from 10 MHz to
1.5 GHz and magnetic attenuation of 2 dB at 1 kHz rising
2 INTERFERENCE TECHNOLOGY
Resonant Range/Plane Wave
SE R = SEPW = 80
90
2 x 10 < f < 10
80
10-cm Waveguide
Below Cutoff
9
SEPW =
9 2
1- (f/1.5x10 )
107.3
70
9
10 < f < 1.5 x 10
9
60
50
40
Magnetic
3
7
SEM = 20 log f-60 = 80 10 < f < 10
107 < f < 2 x 107
30
20
10
0
3
10
10
4
10
5
10
6
10
7
Frequency- f (Hz)
10
8
10
9
10
10
1.5 x 10 9
10
11
Figure 2. HEMP performance graph based on MIL-STD-188-125.
EMC DIRECTORY & DESIGN GUIDE 2009
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mon, i.e., the same as for the parent
building. Smaller facilities, upgrades
or retrofits may involve other forms
of shielding, particularly modular
shielded panels. Industry standard
modular shielding systems are available in single-shield copper or steel,
double-layer steel cell type, or steel
pan form enclosures and are easily
installed in existing facilities needing
HEMP or EMP protection.
AN ALTERNATIVE SOLUTION
One alternative to relying entirely on
the military and federal government
protection and intervention involves
a “Plan B” solution—i.e., the cost-effective shielding of high value assets.
Specific areas within a facility containing critical high value hardware,
software, or other equipment should
be hardened to the effects of IEMI
or other deleterious electromagnetic
conditions.
Shielding protection
Present shielding technology can
be used to protect existing Regional
Emergency Management Control
Centers (REMCCs) or the combined
regular and emergency communications facilities from the effects of
EMP. Single- or double-layer steel
enclosures, steel pan form designs,
and single-layer copper systems are
available in modular designs that will
exceed the HEMP/IEMI performance
requirements of the military standard. These modular systems can be
installed within an existing facility to
meet the dimension and operational
needs of a particular entity. Even the
aesthetic expectations of customers
can be met with a choice of interior/
exterior finishes (Figure 3).
Still, shielding the dispatch or
command/control room is only the
first part of forestalling EMP damage to vital communications. Vital
communications equipment is, of
necessity, deployed throughout the
community when emergency strikes.
The equipment of first-responders
could be damaged or rendered totally inoperable during an initial
surge. Fire houses, police precincts,
hospitals, fire trucks, police cars,
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and ambulances are all vulnerable to
electromagnetic pulse.
To protect the overall functioning
of an emergency system, the vital
equipment linking first responders to
the command system must be shielded as well. Today’s shielding industry
produces small copper enclosures
fitted with shock mounts that can
be installed in all mobile field units.
These shielded boxes will exceed
the MIL-STD-188-125 performance
requirement and will protect field
radios from electromagnetic pulse
(Figure 4).
As standard operating procedure
(SOP) as defined by the user, members
Confidence remains
high that the United
States military
can and will defend
America from a
missile attack
originating outside
the country.
of mobile units at the fire or police
precinct could exchange the emergency walkie-talkie radios in their
vehicles with freshly charged units
at the fire house or police precinct
every 24 hours, or as necessary. Similarly, ambulance crews could have an
alternate exchange point at a local
hospital or other appropriate location.
Those radios in need of recharging
could be placed in a secure shielded
enclosure with a battery charging
system. Since radios are a high cost
item, the recharging stations should
be in tamper-proof security containers (Figure 5).
SYSTEM RELIABILITY
The selection process
Several critical aspects of the proposed system merit careful consideration. These include maintenance,
installation timing and cost, life cycle
parameters, and the system’s adaptability vis-à-vis a number of physical
requirements. As noted above, typical
Figure 3. Command and control room.
Figure 4. Mobile unit enclosure.
Figure 5. Fixed station recharging unit.
shielding system construction choices
include welded steel rooms or buildings, modular systems made of galvanized steel or copper-clad panels, and
modular pan form designed systems
for retrofitting or for establishing
shielding within an existing facility.
Pin-pointing any possible weak links
during the design stage of a shielding
system helps to assure reliable performance after procurement. Enclosures
without seams or penetration may
be ideal, but they are impractical.
Still, to achieve the most reliable
shielding system, it is always good
policy to minimize penetrations and
INTERFERENCE TECHNOLOGY 3
shielded rooms
seams. This premise underlies a useful management philosophy that can
be applied throughout the shielding
system selection process. Consider
these key factors affecting modular
shielding system performance—material characteristics, quality of seams
and penetrations, door performance,
accessory performance, and the quantity of seams and penetrations.
Material characteristics and
seam quality
While the goal of achieving a costeffective shielding solution may begin
with a consideration of the attenuation characteristics of the shielding
material, once a decision regarding
all-welded steel vs. modular steel/
copper panels has been made, the next
crucial consideration is seam quality.
While fewer seams would logically
mean less potential for degradation,
it is seam quality that is absolutely
vital. An analysis of shielding alternatives indicates that some seaming
techniques require fewer seams per
shielding surface area. For example,
“Pan Form” construction requires only
one seam per joint. In contrast, the
standard “Double Electrically Isolated”
(DEI) construction requires two seams
per joint. Standard modular plywood
(cell-type) construction requires four
seams per joint. Generally, two layers
of shielding are used simply because
seam quality makes it difficult to
achieve the shielding objective with
just one layer of shielding. Still, with
high quality seaming, one layer should
be sufficient (Figure 6).
Shielded doors
Once a material and construction
type has been chosen, shielded doors
become the most critical component
in the system. Doors are one of the
m i t i g at i o n o f e m p e f f e c t s
few active components subject to
daily wear and tear. To preserve the
integrity of a shielded enclosure, doors
must include a durable means for
making repeatable seals around their
entire perimeter. Shielded door performance should provide a safety factor
of up to 20 dB both initially and after
a reasonable number of cycles for all
requirements up to 100 dB at 10 GHz.
Achieving a 20-dB factor of safety at
1 GHz is no problem. The industry
standard RF door most suitable for
modular cell or pan form enclosures
is the Single Knife Edge (SKE) door
(Figure 7). As a safety factor, MILSTD-188-125-1 requires a vestibule
to maintain shield integrity. The SKE
door can be set up for semi-automatic
operation with a door interlock system
that prevents both doors from being
opened at the same time.
Figure 7. SKE door.
Accessories
Accessories are needed to transmit
power and signals, HVAC, liquids,
or gases into or out of a shielded environment. While accessories have
an important impact on total system
performance, their performance can
be controlled by following proven
techniques and by applying the appropriate design principles. Necessary
penetrations that do not compromise
shielding effectiveness can be achieved
by using a combination of power line
filtering combined with ESA and MOV
(metal oxide varistor) protection or
with waveguide below cut off and
fiber optic concepts (Figure 8). Signal
line interfaces, penetrating the shield,
should use a fiber optic system for
optimum EMP security.
Performance testing
As a minimum at the time of acceptance, all shielding systems should
Figure 8. RF filters.
be tested to confirm shielding performance in accordance with MILSTD-188-125-1 and -2. Shielding
effectiveness testing is generally a
field test at the highest frequency of
usage. The shield and all points of
entry must be hardened to provide
at least 80 dB of attenuation in the
plane wave field from 10 MHz to 1.5
GHz and magnetic attenuation of
2 dB at 1 kHz, rising to 80 dB at 10
MHz. Overtime, all shielding systems
will degrade with normal wear and
Figure 6. Pan form shield system, single shield hybrid frame system, and cell type or “hat & flat” system.
4 INTERFERENCE TECHNOLOGY
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tear. Retesting should be an annual
scheduled requirement—a fail-safe
measure that will detect any problems
before system failure occurs and thus
assures ongoing EMP protection.
Maintenance
One of the critical problems with the
use of a shielding system is the lack of
any clear-cut understanding of exactly
who is responsible for maintaining the
integrity of the system. At too many
facilities, there is an ongoing power
struggle to shift shield maintenance
responsibility from the facilities to
operations department and vice versa.
Unfortunately, without clearly defined
responsibility for preventative maintenance, shield integrity will diminish
rapidly. Even when a problem is finally
noticed, there is a tendency to resort to
untested, “band-aid” or quick fix solutions. These solutions may satisfy the
primary objective of meeting shielding
requirements temporarily, but may not
provide an adequate factor of safety to
assure long-term reliability.
SUMMARY
Absolute performance and reliability of a shielding system is essential
in times of emergency. The key to
obtaining a good shielding system is
an understanding that seams, doors,
and other penetrations are the critical elements that must function as a
whole to create an effective shielding
system. It is the design of the shielding system and the quality of the
installation that will determine its
long-term reliability. In many cases,
single-shield, “Pan Form” modular
steel, double-shield galvanized steel
cell-type panels, or a lightweight 12 or
24 ounce copper system can provide
a reliable, cost-effective solution for
EMP applications.
There are many shielding vendors
in the market today. To protect a
shielded system investment, look
for a full service, turn-key designer,
manufacturer, installer, and tester of
shielding systems with years of experience in the military and government
arena and a strong background in
the EMP field. Insist on seeing test
reports from previous installations
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Measurements to Support Improved Wireless Communication for
Emergency Responders
Dr. Kate A. Remley
NIST RF Fields Group 818.02
Boulder, CO
When emergency responders enter large structures (such as apartment and office buildings,
sports stadiums, stores, malls, hotels, convention centers, warehouses), radio communication
to other responders on the outside is often impaired. Wireless communication from within
large buildings and other structures can be complicated by several factors, including the strong
attenuation of radio signals caused by losses in the building materials, scattering from structural
features (multipath), and the waveguiding effects of corridors and tunnels.
The National Institute of Standards and Technology (NIST) is involved in a multi-year project to
investigate wireless communications problems faced by emergency responders (firefighters,
police, and medical personnel) in disaster situations involving large building structures. The work,
funded by the Justice Department’s Community Oriented Police Services (COPS) program through
the NIST Office of Law Enforcement Standards, has grown out of communications problems such
as those encountered during the September 11, 2001, collapse of the World Trade Center in New
York. Emergency personnel outside the buildings could not communicate with those inside.
The work has involved collecting a large body of open-literature data of quantities used to
assess wireless communication channels. To provide statistics on signal level and variability in
representative environments, NIST researchers measured the received signal strength outside
the various structures while a transmitter was carried throughout the interior. The researchers
also collected data on the level of reflectivity (multipath) a signal encounters as it travels from
within the structure to the outside.
Because lives may be at stake in emergency response scenarios, a higher standard for reliability
of service must be applied compared to those that might be deemed adequate for commercial
applications. As a result, some specifications must either be modified or newly developed. The
experiments were carried out at emergency responder frequencies to gather germane and
useful data for those developing and assessing new technologies and creating standardized test
methods within the context of the unique needs of the emergency response environment.
This work placed NIST researchers in some interesting non-laboratory environments, including
buildings schedule for implosion, [1-3 ] oil refineries and tunnels, [4-5] several large public buildings, [4]
and, in related work, automotive manufacturing facilities. [6]
N.B.—These documents may be downloaded from the NIST website at: http://www.boulder.
nist.gov/div818/81802/MetrologyForWirelessSys/ under the heading “Wireless System
Measurements for Industry and the Public Safety Sector.”
REFERENCES:
[1] C.L. Holloway, G. Koepke, D. Camell, K.A. Remley, D.F. Williams, S.A. Schima, S. Canales, D.T.
Tamura, “Propagation and Detection of Radio Signals Before, During, and After the Implosion
of a 13-Story Apartment Building,” Natl. Inst. Stand. Technol. Note 1540, May 2005.
[2] C.L. Holloway, G. Koepke, D. Camell, K.A. Remley, D.F. Williams, S.A. Schima, S. Canales, D.T.
Tamura, “Propagation and Detection of Radio Signals Before, During, and After the Implosion
of a Large Sports Stadium (Veterans’ Stadium in Philadelphia),” Natl. Inst. Stand. Technol.
Note 1541, October 2005.
[3] C.L. Holloway, G. Koepke, D. Camell, K.A. Remley, S.A. Schima, M. McKinley, R.T. Johnk,
“Propagation and Detection of Radio Signals Before, During, and After the Implosion of a Large
Convention Center,” Natl. Inst. Stand. Technol. Note 1542, June 2006.
[4] C.L. Holloway, W.F. Young, G. Koepke, K.A. Remley, D. Camell, Y. Becquet, “Attenuation
of Radio Wave Signals Coupled Into Twelve Large Building Structures,” Natl. Inst. Stand.
Technol. Note 1545, Apr. 2008.
[5] K.A. Remley, G. Koepke, C.L. Holloway, C. Grosvenor, D. Camell, J. Ladbury, D. Novotny,
W.F. Young, G. Hough, M.D. McKinley, Y. Becquet, J. Korsnes, “Measurements to Support
Broadband Modulated-Signal Radio Transmissions for the Public-Safety Sector,” Natl. Inst.
Stand. Technol. Note 1546, Apr. 2008.
[6] K.A. Remley, G. Koepke, C. Grosvenor, R.T. Johnk, J. Ladbury, D. Camell, J. Coder, “NIST
Tests of the Wireless Environment in Automobile Manufacturing Facilities,” Natl. Inst. Stand.
Technol. Note 1550, Oct. 2008.
INTERFERENCE TECHNOLOGY 5
shielded rooms
m i t i g at i o n o f e m p e f f e c t s
that document the vendor’s ability to
provide a reliable shielding system.
ACKNOWLEDGEMENT
The author would like to thank Dr.
William A. Radask y of Metatech
Corporation for his invaluable review
of this article.
END NOTES
Those who wish to read further on
this topic might wish to consult:
1. Report of the Commission to Assess the
Threat to the United States from Electromagnetic Pulse Attack: Executive Report,
2004. Visit http://w w w.globalsecurity.
org/wmd/library/congress/2004_r/04-0722emp.pdf
2. Presidential Decision Directive/NSC-63,
May 22, 1998. Visit http://www.fas.org/
irp/offdocs/pdd/pdd-63.htm
BIBLIOGRAPHY
MIL-STD-2169B – High-Altitude Electromagnetic Pulse (HEMP) Environment (U)
MIL-STD-188-125-1- DOD Interface Standard
– High Altitude Electromagnetic Pulse
(HEMP) Protection for Ground-Based
C4I Facilities Performing Critical, TimeUrgent 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, TimeUrgent Missions – Part 1 – Transportable
Systems ( 3 March, 1999 )
MIL-HDBK-423 Military Handbook - High
Altitude Electromagnetic Pulse (HEMP)
Protection for Fixed and Transportable
Ground-based C4I Facilities Vol. 1 – Fixed
Facilities ( 15 May1993 )
William E. Curran and Wayne D. Martin,
“Shielding for HEMP/TEMPEST Requirements” Lindgren RF Enclosures, Inc. Addison, IL, ITEM Annual Guide 1988.
“Commission to Assess the Threat to the
Un ited St ates f rom Elec t romag net ic
Pulse (EMP) Attack - Statement Before
the House Armed Services Committee,”
July 10, 2008
“The Threat of Radio Frequency Weapons to
Critical Infrastructure Facilities” – TSWG
& DETO Publications, August 2005.
Wayne D. Martin retired as a Chief Radioman from the U.S. Navy in 1984 having gained
20 years’ experience working in HEMP and
TEMPEST environments. Following his time in
the Navy, he joined the RCA Service Company
as a visual TEMPEST inspector/instructor and
later joined Contel Federal Systems (a government contractor) and worked as a TEMPEST
engineer. In 1987, he joined Lindgren RF Enclosures (now ETS-Lindgren) in Glendale Heights,
IL. Since joining the company, Mr. Martin has
continued to lend his expertise to the company’s
RF shielding systems for government and commercial industries requiring protection from
critical EMP and IEMI. As the Government
Sales Manager and Facilities Security Officer, he
also assists ETS-Lindgren’s sales, R&D, manufacturing, and installation departments in providing solutions to general EMI and RFI issues.
He is currently at work on an article on specific
shielding solutions for HEMP. The author may
be contacted by phone at 630-307-7200 or via
email at wayne.martin@ets-lindgren.com. n
Reprinted from the 2009 Interference Technology EMC Directory & Design Guide.
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EMC DIRECTORY & DESIGN GUIDE 2009