martin shielded rooms

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 seized the moment and have staged attacks

ETS-Lindgren in many First World countries. Recall 9/11,
Glendale Heights, IL the Madrid train bombings, the London
subway attack, and the attempt on Glasgow

T he most cursory assessment of

news and events around the globe dur-
ing this first decade of the Twenty-First
Airport. Terrorizing nations or people
has been achieved though conventional
weaponry such as explosives, or in the
Century leads to the inescapable conclu- case of 9/11, by turning our own technol-
sion that we live in perilous times. Around ogy against us. In today’s world, weapons
the globe, political, ethnic, and religious of mass destruction (WMD), so called
strife results in violence. This paper does “dirty bombs”, radio frequency weapons
not discuss the capabilities or readiness (RFW), and intentional electromagnetic
of the United States military or that of interference (IEMI) devices can generate
its allies, nor does it focus on developing localized electromagnetic pulse surges to
effective standards for first-responder disrupt everyday services.
communications both inside and outside Critical infrastructure facilities are a
challenging environments such as sky- vital part of everyday life. These facilities
scrapers and tunnels. (See accompanying include electric power facilities, oil re-
short article on page 87.) Instead, it lays out fineries, water treatment plants, banking
a more modern scenario that could be just systems, pipelines, transportation systems,
as devastating to our economy and way of emergency facilities, and communications
life as an all-out nuclear war and details facilities. Most critical infrastructure facili-
steps that the military, local government, ties depend upon electrical and electronic
utilities or industry itself can take to ward systems to function. These systems can be
off such a catastrophe. susceptible to a little known, yet significant
and growing threat, the radio frequency
THE THREAT weapons mentioned above. RFWs have
Confidence remains high that the United already been used to defeat security sys-
States military can and will defend Ameri- tems, to disable police communications,
ca from a missile attack originating outside to induce fires, and to disrupt banking
the country. The nation has an extensive computers. Many of these devices are small,
missile defense program, a legacy of the suitcase-sized or slightly larger devices
Cold War era; and the government has that could be smuggled into the country
had many years to prepare for whatever the same way drugs and other contraband
the future may hold, as well as plenty of penetrate our borders and become available
doctrines for guidance. Terrorism is the on the black market. These devices in the
Twenty-First century version of the last hands of a terrorist are capable of inflict-
century’s world wars. Terrorists have ing extreme damage and may be capable

interferencetechnology.com 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 to 80 dB at 10 MHz in accordance with MIL-STD-125-1

any location. and -2 (Figure 2).
Looking back to that fateful day in September 2001 Obviously, the HEMP shield and all POE protective
and realizing the magnificent job local, state, and federal devices are hardness critical items (HCIs). All devices
officials in New York did in managing the World Trade installed as special protective measures are also HCIs.
Center crisis makes one feel proud. Imagine what might Collectively, the HCIs constitute the HEMP protective
have occurred if the perpetrators of that vicious attack systems. Items such as shielded vestibules with inter-
had included in their suicide mission the detonation locked doors, waveguide honeycomb vents, various pipe
of an electromagnetic pulse device that could disrupt penetrations, power and signal line filters with surge
communications of the police, fire, and medical teams protection (electronic surge arrestors or ESAs), and fiber
responding to the emergency. Surely, many more lives optic penetrations are all HCIs—individually or as part
and properties would have been lost. The sudden inabil- of an assembly.
ity of the mayor and other city government officials to Generally, HEMP facilities are specified as welded
mobilize resources during such a chaotic event could be systems by the military to be installed during the initial
catastrophic. At present, homeland security, some local building stage. Warranties of 20 or 30 years are com-
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.

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 (high-
altitude 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 Figure 1. EMP area by bursts at 30, 120, and 300 miles.
interference (IEMI), has been defined as the “intentional Source: Gary Smith, “Electromagnetic Pulse Threats,” testimony to House National
malicious generation of electromagnetic energy introduc- Security Committee on July 16, 1997.
ing noise or signals into electric and electronic systems,
110
thus disrupting, confusing, or damaging these systems
for terrorist or criminal purposes.” Nature’s contribution, 100

lightning EMP (LEMP), like HEMP and other forms of 90

Resonant Range/Plane Wave
SE R = SEPW = 80
10-cm Waveguide
Below Cutoff
EMP, involves a brief but intense electromagnetic dis- 7
2 x 10 < f < 10
9
SEPW =
80
turbance in the atmosphere and thus presents another
Shielding Effectiveness- SE (dB)

9 2
107.3 1- (f/1.5x10 )
potential threat to the operation of electronic systems. 70
9 9
10 < f < 1.5 x 10

60
SYSTEM SURVIVABILITY
Magnetic
The U.S. military bears the responsibility of establishing 50 3 7
SEM = 20 log f-60 = 80 10 < f < 10
a HEMP-hardened electrical parameter barrier for mis- 107 < f < 2 x 107
sion critical military operations that will ensure system 40

survivability during a HEMP event. Creating an electro-

30
magnetic barrier that will prevent or limit HEMP or local-
ized EMP fields or conducted transients from entering 20

the shielded area is primary. The shield and all points of

10
entry (POE) must be treated properly to maintain shield
0
integrity. They must be hardened to provide at least 80 10
3
10
4
10
5
10
6
10
7
10
8
10
9
10
10
10
11

Frequency- f (Hz) 1.5 x 10 9

dB attenuation in the plane wave field from 10 MHz to
1.5 GHz and magnetic attenuation of 2 dB at 1 kHz rising Figure 2. HEMP performance graph based on MIL-STD-188-125.

2  INTERFERENCE TECHNOLOGY EMC DIRECTORY & DESIGN GUIDE 2009

martin shielded rooms

mon, i.e., the same as for the parent and ambulances are all vulnerable to
building. Smaller facilities, upgrades electromagnetic pulse.
or retrofits may involve other forms To protect the overall functioning
of shielding, particularly modular of an emergency system, the vital
shielded panels. Industry standard equipment linking first responders to
modular shielding systems are avail- the command system must be shield-
able in single-shield copper or steel, ed as well. Today’s shielding industry
double-layer steel cell type, or steel produces small copper enclosures
pan form enclosures and are easily fitted with shock mounts that can
installed in existing facilities needing be installed in all mobile field units.
HEMP or EMP protection. These shielded boxes will exceed Figure 3. Command and control room.
the MIL-STD-188-125 performance
AN ALTERNATIVE SOLUTION requirement and will protect field
One alternative to relying entirely on radios from electromagnetic pulse
the military and federal government (Figure 4).
protection and intervention involves As standard operating procedure
a “Plan B” solution—i.e., the cost-ef- (SOP) as defined by the user, members
fective shielding of high value assets.
Specific areas within a facility con-
taining critical high value hardware, Confidence remains
software, or other equipment should high that the United
be hardened to the effects of IEMI
or other deleterious electromagnetic
States military
conditions. can and will defend Figure 4. Mobile unit enclosure.
America from a
Shielding protection
Present shielding technology can missile attack
be used to protect existing Regional originating outside
Emergency Management Control
Centers (REMCCs) or the combined
the country.
regular and emergency communica-
tions facilities from the effects of of mobile units at the fire or police
EMP. Single- or double-layer steel precinct could exchange the emer-
enclosures, steel pan form designs, gency walkie-talkie radios in their
and single-layer copper systems are vehicles with freshly charged units
available in modular designs that will at the fire house or police precinct
exceed the HEMP/IEMI performance every 24 hours, or as necessary. Simi-
requirements of the military stan- larly, ambulance crews could have an
dard. These modular systems can be alternate exchange point at a local
installed within an existing facility to hospital or other appropriate location. Figure 5. Fixed station recharging unit.
meet the dimension and operational Those radios in need of recharging
needs of a particular entity. Even the could be placed in a secure shielded shielding system construction choices
aesthetic expectations of customers enclosure with a battery charging include welded steel rooms or build-
can be met with a choice of interior/ system. Since radios are a high cost ings, modular systems made of galva-
exterior finishes (Figure 3). item, the recharging stations should nized steel or copper-clad panels, and
Still, shielding the dispatch or be in tamper-proof security contain- modular pan form designed systems
command/control room is only the ers (Figure 5). for retrofitting or for establishing
first part of forestalling EMP dam- shielding within an existing facility.
age to vital communications. Vital SYSTEM RELIABILITY Pin-pointing any possible weak links
communications equipment is, of The selection process during the design stage of a shielding
necessity, deployed throughout the Several critical aspects of the pro- system helps to assure reliable perfor-
community when emergency strikes. posed system merit careful consid- mance after procurement. Enclosures
The equipment of first-responders eration. These include maintenance, without seams or penetration may
could be damaged or rendered to- installation timing and cost, life cycle be ideal, but they are impractical.
tally inoperable during an initial parameters, and the system’s adapt- Still, to achieve the most reliable
surge. Fire houses, police precincts, ability vis-à-vis a number of physical shielding system, it is always good
hospitals, fire trucks, police cars, requirements. As noted above, typical policy to minimize penetrations and

interferencetechnology.com INTERFERENCE TECHNOLOGY  3

shielded rooms m i t i g at i o n o f e m p e f f e c t s

seams. This premise underlies a use- few active components subject to

ful management philosophy that can daily wear and tear. To preserve the
be applied throughout the shielding integrity of a shielded enclosure, doors
system selection process. Consider must include a durable means for
these key factors affecting modular making repeatable seals around their
shielding system performance—mate- entire perimeter. Shielded door perfor-
rial characteristics, quality of seams mance should provide a safety factor
and penetrations, door performance, of up to 20 dB both initially and after
accessory performance, and the quan- a reasonable number of cycles for all
tity of seams and penetrations. requirements up to 100 dB at 10 GHz.
Achieving a 20-dB factor of safety at
Material characteristics and 1 GHz is no problem. The industry
seam quality standard RF door most suitable for
While the goal of achieving a cost- modular cell or pan form enclosures
effective shielding solution may begin is the Single Knife Edge (SKE) door
with a consideration of the attenua- (Figure 7). As a safety factor, MIL-
tion characteristics of the shielding STD-188-125-1 requires a vestibule Figure 7. SKE door.
material, once a decision regarding to maintain shield integrity. The SKE
all-welded steel vs. modular steel/ door can be set up for semi-automatic
copper panels has been made, the next operation with a door interlock system
crucial consideration is seam quality. that prevents both doors from being
While fewer seams would logically opened at the same time.
mean less potential for degradation,
it is seam quality that is absolutely Accessories
vital. An analysis of shielding alter- Accessories are needed to transmit
natives indicates that some seaming power and signals, HVAC, liquids,
techniques require fewer seams per or gases into or out of a shielded en-
shielding surface area. For example, vironment. While accessories have
“Pan Form” construction requires only an important impact on total system
one seam per joint. In contrast, the performance, their performance can
standard “Double Electrically Isolated” be controlled by following proven
(DEI) construction requires two seams techniques and by applying the ap-
per joint. Standard modular plywood propriate design principles. Necessary Figure 8. RF filters.
(cell-type) construction requires four penetrations that do not compromise
seams per joint. Generally, two layers shielding effectiveness can be achieved be tested to confirm shielding per-
of shielding are used simply because by using a combination of power line formance in accordance with MIL-
seam quality makes it difficult to filtering combined with ESA and MOV STD-188-125-1 and -2. Shielding
achieve the shielding objective with (metal oxide varistor) protection or effectiveness testing is generally a
just one layer of shielding. Still, with with waveguide below cut off and field test at the highest frequency of
high quality seaming, one layer should fiber optic concepts (Figure 8). Signal usage. The shield and all points of
be sufficient (Figure 6). line interfaces, penetrating the shield, entry must be hardened to provide
should use a fiber optic system for at least 80 dB of attenuation in the
Shielded doors optimum EMP security. plane wave field from 10 MHz to 1.5
Once a material and construction GHz and magnetic attenuation of
type has been chosen, shielded doors Performance testing 2 dB at 1 kHz, rising to 80 dB at 10
become the most critical component As a minimum at the time of accep- MHz. Overtime, all shielding systems
in the system. Doors are one of the tance, all shielding systems should 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 EMC DIRECTORY & DESIGN GUIDE 2009

martin shielded rooms

tear. Retesting should be an annual

scheduled requirement—a fail-safe Measurements to Support Improved Wireless Communication for
measure that will detect any problems Emergency Responders
before system failure occurs and thus
assures ongoing EMP protection. Dr. Kate A. Remley
NIST RF Fields Group 818.02
Boulder, CO
Maintenance
One of the critical problems with the When emergency responders enter large structures (such as apartment and office buildings,
use of a shielding system is the lack of sports stadiums, stores, malls, hotels, convention centers, warehouses), radio communication
any clear-cut understanding of exactly 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
who is responsible for maintaining the attenuation of radio signals caused by losses in the building materials, scattering from structural
integrity of the system. At too many features (multipath), and the waveguiding effects of corridors and tunnels.
facilities, there is an ongoing power
The National Institute of Standards and Technology (NIST) is involved in a multi-year project to
struggle to shift shield maintenance investigate wireless communications problems faced by emergency responders (firefighters,
responsibility from the facilities to police, and medical personnel) in disaster situations involving large building structures. The work,
operations department and vice versa. funded by the Justice Department’s Community Oriented Police Services (COPS) program through
Unfortunately, without clearly defined 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
responsibility for preventative main- York. Emergency personnel outside the buildings could not communicate with those inside.
tenance, shield integrity will diminish
The work has involved collecting a large body of open-literature data of quantities used to
rapidly. Even when a problem is finally assess wireless communication channels. To provide statistics on signal level and variability in
noticed, there is a tendency to resort to representative environments, NIST researchers measured the received signal strength outside
untested, “band-aid” or quick fix solu- the various structures while a transmitter was carried throughout the interior. The researchers
tions. These solutions may satisfy the also collected data on the level of reflectivity (multipath) a signal encounters as it travels from
within the structure to the outside.
primary objective of meeting shielding
requirements temporarily, but may not Because lives may be at stake in emergency response scenarios, a higher standard for reliability
provide an adequate factor of safety to 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
assure long-term reliability. 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
SUMMARY methods within the context of the unique needs of the emergency response environment.
Absolute performance and reliabil- This work placed NIST researchers in some interesting non-laboratory environments, including
ity of a shielding system is essential buildings schedule for implosion, [1-3 ] oil refineries and tunnels, [4-5] several large public buildings, [4]
in times of emergency. The key to and, in related work, automotive manufacturing facilities. [6]
obtaining a good shielding system is N.B.—These documents may be downloaded from the NIST website at: http://www.boulder.
an understanding that seams, doors, nist.gov/div818/81802/MetrologyForWirelessSys/ under the heading “Wireless System
and other penetrations are the criti- Measurements for Industry and the Public Safety Sector.”
cal elements that must function as a
whole to create an effective shielding REFERENCES:
system. It is the design of the shield-
[1] C.L. Holloway, G. Koepke, D. Camell, K.A. Remley, D.F. Williams, S.A. Schima, S. Canales, D.T.
ing system and the quality of the Tamura, “Propagation and Detection of Radio Signals Before, During, and After the Implosion
installation that will determine its of a 13-Story Apartment Building,” Natl. Inst. Stand. Technol. Note 1540, May 2005.
long-term reliability. In many cases, [2] C.L. Holloway, G. Koepke, D. Camell, K.A. Remley, D.F. Williams, S.A. Schima, S. Canales, D.T.
single-shield, “Pan Form” modular Tamura, “Propagation and Detection of Radio Signals Before, During, and After the Implosion
steel, double-shield galvanized steel of a Large Sports Stadium (Veterans’ Stadium in Philadelphia),” Natl. Inst. Stand. Technol.
cell-type panels, or a lightweight 12 or Note 1541, October 2005.
24 ounce copper system can provide [3] C.L. Holloway, G. Koepke, D. Camell, K.A. Remley, S.A. Schima, M. McKinley, R.T. Johnk,
a reliable, cost-effective solution for “Propagation and Detection of Radio Signals Before, During, and After the Implosion of a Large
EMP applications. Convention Center,” Natl. Inst. Stand. Technol. Note 1542, June 2006.
There are many shielding vendors [4] C.L. Holloway, W.F. Young, G. Koepke, K.A. Remley, D. Camell, Y. Becquet, “Attenuation
in the market today. To protect a of Radio Wave Signals Coupled Into Twelve Large Building Structures,” Natl. Inst. Stand.
Technol. Note 1545, Apr. 2008.
shielded system investment, look
for a full service, turn-key designer, [5] K.A. Remley, G. Koepke, C.L. Holloway, C. Grosvenor, D. Camell, J. Ladbury, D. Novotny,
manufacturer, installer, and tester of 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.
shielding systems with years of expe- Stand. Technol. Note 1546, Apr. 2008.
rience in the military and government
[6] K.A. Remley, G. Koepke, C. Grosvenor, R.T. Johnk, J. Ladbury, D. Camell, J. Coder, “NIST
arena and a strong background in Tests of the Wireless Environment in Automobile Manufacturing Facilities,” Natl. Inst. Stand.
the EMP field. Insist on seeing test Technol. Note 1550, Oct. 2008.
reports from previous installations

interferencetechnology.com 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 – High Altitude Electromagnetic Pulse Critical Infrastructure Facilities” – TSWG
provide a reliable shielding system. (HEMP) Protection for Ground-Based & DETO Publications, August 2005.
C4I Facilities Performing Critical, Time-
ACKNOWLEDGEMENT Urgent Missions – Part 1 – Fixed Facilities Wayne D. Martin retired as a Chief Radio-
The author would like to thank Dr. ( 17 July, 1998 ) man from the U.S. Navy in 1984 having gained
William A. Radask y of Metatech MIL-STD-188-125-2- DOD Interface Standard 20 years’ experience working in HEMP and
Corporation for his invaluable review – High Altitude Electromagnetic Pulse TEMPEST environments. Following his time in
of this article. (HEMP) Protection for Ground-Based the Navy, he joined the RCA Service Company
C4I Facilities Performing Critical, Time- as a visual TEMPEST inspector/instructor and
END NOTES Urgent Missions – Part 1 – Transportable later joined Contel Federal Systems (a govern-
Those who wish to read further on Systems ( 3 March, 1999 ) ment contractor) and worked as a TEMPEST
this topic might wish to consult: MIL-HDBK-423 Military Handbook - High engineer. In 1987, he joined Lindgren RF Enclo-
1. Report of the Commission to Assess the Altitude Electromagnetic Pulse (HEMP) sures (now ETS-Lindgren) in Glendale Heights,
Threat to the United States from Electro- Protection for Fixed and Transportable IL. Since joining the company, Mr. Martin has
magnetic Pulse Attack: Executive Report, Ground-based C4I Facilities Vol. 1 – Fixed continued to lend his expertise to the company’s
2004. Visit http://w w w.globalsecurity. Facilities ( 15 May1993 ) RF shielding systems for government and com-
org/wmd/library/congress/2004_r/04-07- William E. Curran and Wayne D. Martin, mercial industries requiring protection from
22emp.pdf “Shielding for HEMP/TEMPEST Require- critical EMP and IEMI. As the Government
2. Presidential Decision Directive/NSC-63, ments” Lindgren RF Enclosures, Inc. Ad- Sales Manager and Facilities Security Officer, he
May 22, 1998. Visit http://www.fas.org/ dison, IL, ITEM Annual Guide 1988. also assists ETS-Lindgren’s sales, R&D, manu-
irp/offdocs/pdd/pdd-63.htm “Commission to Assess the Threat to the facturing, and installation departments in pro-
Un ited St ates f rom Elec t romag net ic viding solutions to general EMI and RFI issues.
BIBLIOGRAPHY Pulse (EMP) Attack - Statement Before He is currently at work on an article on specific
MIL-STD-2169B – High-Altitude Electro- the House Armed Services Committee,” shielding solutions for HEMP. The author may
magnetic Pulse (HEMP) Environment (U) July 10, 2008 be contacted by phone at 630-307-7200 or via
MIL-STD-188-125-1- DOD Interface Standard “The Threat of Radio Frequency Weapons to email at wayne.martin@ets-lindgren.com.  n

Reprinted from the 2009 Interference Technology EMC Directory & Design Guide.

6  INTERFERENCE TECHNOLOGY EMC DIRECTORY & DESIGN GUIDE 2009