          ELECTROMAGNETIC PULSE (EMP) AND TEMPEST PROTECTION FOR FACILITIES

                      Table of Contents: http://jya.com/emp.htm

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                                       CHAPTER 4

                             SYSTEM ENGINEERING REQUIREMENTS

    4-1. Outline. This chapter is organized as follows:

         4-1. Outline
         4-2. Standards and specifications
         4-3. Electromagnetic integration
              a. Incompatible design approaches
              b. Correcting incompatibilities
              c. Electromagnetic shielding
              d. Surge protection
         4-4. HEMP and lightning protection integration
              a. Lightning rise time
              b. Frequency and current levels
              c. Induced transients and injected current
              d. Voltage surges
              e. Radiated and static fields
              f. Magnetic fields
              g. Summary
         4-5. HEMP/TEMPEST and electromagnetic integration
              a. Electromagnetic compatibility (E~CJ
              b. Electromagnetic interference (EMI)
                 (1) Natural radio noise
                 (2) Purposely generated signals
                 (3) Man-made noise
              c. Achieving electromagnetic compatibility
                 (1) Frequency ranges
                 (2) Spectra encompassed
                 (3) Interference within enclosures
                 (4) Exceptions
         4-6. Environmental requirements
              a. Corrosion
              b. Groundwater
              c. Thermal effects
              d. Vibration and acoustics
              e. Ground shock
         4-7. Cited references

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    4-2. Standards and specifications. Definitive standards and specifications
    for hardening facilities against HEMP/TEMPEST do not exist. However, efforts
    are underway to develop them and to integrate them with other HEMP/TEMPEST
    requirements and with electromagnetic compatibility (EM) standards. Results
    of some recent studies have been reported (refs 4-1 through 4-3). Campi et
    al. (ref 4-1) compiled a listing of Government and industrial standards,
    specifications, and handbooks related to HEMP/TEMPEST mitigation. Most of
    these standards pertain to EMC and TEMPEST (table 4-1). However, many of
    these specifications and standards may be useful in integrating EMP hardening
    requirements. A comprehensive listing of EMP-related standards is available
    in reference 4-4.

    4-3. Electromagnetic integration. Facilities often are required to be
    protected against several EM environments, including HEMP (or other EMP),
    electromagnetic interference (EMI), electromagnetic compatibility, and
    lightning. The facility may also have TEMPEST requirements that impose the
    need for communications security through control of compromising EM
    emanations.

       a. Incompatible design approaches. Vance et al. (ref 4-2) have examined
    70 related standards and specifications and tabulated areas in which the
    design approaches are not compatible for all EM protection requirements. Many
    of these incompatibilities are related to methods for grounding cable shields
    and allowances for penetrating conductors.

       b. Correcting incompatibilities. Graf et al. (ref 4-3) have recommended
    ways to correct these incompatibilities. In view of these studies and other
    programs, unified EM specifications and standards probably will eventually
    become available. Meanwhile, designers will find it necessary to integrate
    the EM design on a site-, facility-, and system-specific basis.

       c. Electromagnetic shielding. Generally, the main method used in EM
    protection is EM shielding. The shielding required for HEMP/TEMPEST is
    usually more than enough for all other EM protection. A comprehensive
    discussion of grounding and bonding technology for all EM protection is in
    MIL-HDBK-419A (ref 4-5). MIL-STD-188-124A gives specific grounding and
    bonding requirements (ref 4-6).

       d. Surge protection. An area in which care must be taken to ensure
    compatibility in EM integration is surge protection. Some surge arresters
    used for lightning do not clamp fast enough to protect against EMP. Some ESAs
    used for EMP may not have great enough current carrying capacity for lightning
    protection in all situations. Thus, for compatible lightning and EMP
    protection, a carefully selected combination of protection elements will be
    required.

    4-4. HEMP and lightning protection integration. The EM environment generated
    by lightning differs from that of HEMP in energy spectral distribution rise
    time, current levels, pulse repetition and coverage area.

       a. Lightning rise time. Many early studies indicated that the typical
    rise time of lightning was almost three orders of magnitude slower than that
    of HEMP. More recent work, however, has shown that radiation fields produced
    by lightning can have much faster rise times. Step leaders in the initial
    stroke have had measured rise times reportedly approaching 30 nanoseconds.
    Return strokes have been determined to have initial portions with rise time in
    the 40- to 200-nanosecond range. A complete lightning flash contains a first
    stroke with a downward-moving step leader and usually numerous return strokes
    as shown in figure 4-1. The total flash time can be greater than 1 second.

       b. Frequency and current levels. A comparison of lightning and HEMP in
    the frequency domain shows that radiated lightning energy is higher at low
    frequencies and lower at high frequencies as indicated in figure 4-2. The
    current levels of lightning return strokes average nearly 35 kiloamps, but may
    be less than 10 kiloamps and as high as several hundred kiloamps for so-called
    "superbolts."

       c. Induced transients and injected current. Hazards common with both HEMP
    and lightning are induced transients coupled onto sensitive elements and
    injected current from exterior electrical conductors. Lightning also can
    strike directly with extreme damage potential. In rare cases, the direct
    strike has been known to cause structural damage as well as electrical damage,
    even to underground facilities. Thus, facilities need a system of lightning
    rods with suitable grounding to divert the extremely high currents (up to
    hundreds of kiloamperes peak) away.

       d. Voltage surges. Lightning can produce high voltage surges on power
    lines without a direct strike. Figure 4-3 shows some typical surge values
    versus distance from the stroke.

       e. Radiated and static fields. One study has identified radiated fields
    associated with lightning (ref 4-7). Figure 4-4 summarizes approximated typi-
    cal near-field radiated E-field values. Another study has identified radiated
    and static fields associated with lightning (ref 4-8). Figure 4-5 shows
    averages for these fields.

       f. Magnetic fields. Table 4-2 lists typical values of the H-field close
    to a stroke. The close in H-field from lightning thus has higher magnitude
    than the HEMP H-field (see table 4-2 for magnitudes); since it has greater
    energy content at low frequencies, shield thickness must be greater than for
    HEMP.

       g. Summary. In summary, integrating HEMP and lightning protection
    requires--

          (1) Greater shield thickness for lightning if protection from close-in
    strokes is required since the H-field magnitude can be greater, although this
    is not common practice.

          (2) More robust surge arresters for lightning.

          (3) Use of lightning rods.

          (4) High-frequency protection for HEMP using more sophisticated
    transient protection and filtering.

    4-5. HEMP/TEMPEST and electromagnetic integration. EMC is defined in ref 4-9
    as the ability of communications-electronics equipments, subsystems, and
    systems to operate in their intended environments without suffering or causing
    unacceptable degradation because of unintentional EM radiation or response.
    Electromagnetic interference (EMI) results when EM energy causes unacceptable
    or undesirable responses, malfunctions, degrades or interrupts the intended
    operation of electronic equipment, subsystems, or systems. RFI is a special
    case of EMI for which the radio frequency transmission (usually narrow-band)
    causes unintentional problems in equipment operation. For commercial
    electronic and electrical equipment, systems, or subsystems, the Federal
    Communications Commission (FCC) has regulations defining allowable emission
    and susceptibility levels. Military equipment is regulated by MIL STD 461 and
    MIL STD 462 (refs 4-10 and 4-11). MIL STD 461 defines allowable emission
    levels, both conducted and radiated, and allowable susceptibilities, also both
    conducted and radiated. Other specifications exist, but they apply to
    specific equipment.

       a. Electromagnetic compatibility (EMC). EMC requirements usually apply to
    individual equipment as well as to the overall system. Because of equipment
    level requirements, the equipment cabinets or racks often must have a degree
    of protection, which comprises part of the topological protection.

       b. Electromagnetic interference (EMI). The EMI environment has
    contributors from three main classes:

          (1) Natural radio noise. Natural radio noise originating mainly from
    atmospheric disturbances (including lightning) and partly from
    extraterrestrial sources.

          (2) Purposely generated signals. Signals that are generated purposely
    to convey information but that may interfere with the operation of other
    equipment.

          (3) Man-made noise. Man-made noise such as spectral components
    generated incidentally by various electrical and electronic devices, motors,
    generators, and other machinery.

       c. Achieving electromagnetic compatibility. Achieving EMC involves the
    same principles as protection against HEMP/TEMPEST. Generally, a
    HEMP/TEMPEST-protected facility will provide EMC protection as well over most
    of the desired frequency range. Some exceptions are--

          (1) Frequency ranges. EMC encompasses the low frequencies, including
    the power frequency spectrum (5 to 400 hertz), and therefore, may have
    shielding and filtering requirements different than those for HEMP or TEMPEST
    protection.

          (2) Spectra encompassed. EMC includes the VHF and microwave spectra as
    well as system-specific radiators or susceptibilities requiring special
    treatment. Examples are susceptibilities to high power radars beyond the
    HEMP/TEMPEST frequency range and switching transients below the HEMP/TEMPEST
    frequency range.

          (3) Interference within enclosures. EMC also can include interference
    between equipment within the same shielded enclosures.

       d. Exceptions. Clearly, EMC integration requires that special engineering
    attention be given to these stated exceptions. For further guidance, see
    references 4-9 and 4-12.

    4-6. Environmental requirements. HEMP/TEMPEST protection must withstand
    adverse environmental conditions that may occur at the facility. The major
    concern is corrosion of buried grounding or shielding system elements,
    including exterior steel sheets and buried water pipe or conduit. Other
    environments of concern include those with high temperatures, excessive
    vibration, and potential ground shock.

       a. Corrosion. Design details and the materials used for external
    grounding systems and underground shielding elements will affect the corrosion
    of all exterior exposed metal installed underground throughout the facility
    complex. Galvanic cells are the main cause of corrosion associated with
    grounding system and adjacent underground metal objects. A galvanic cell is
    produced when two dissimilar metals are immersed in an electrolyte and the
    potential difference between electrodes causes a current to flow in a low-
    resistance path between them. For HEMP/TEMPEST-protected facilities, the many
    grounding connections between steel objects, including shielding and
    reinforcing bars in contact with the shield, and the external grounding system
    provide a low-resistance conductive path between interconnected metals in the
    soil. Current will flow from cathodic material, such as copper or concrete-
    encased steel, through these connections to bare steel, such as pipes and
    conduits (anodic material). The current flow carries ferrous ions into the
    earth electrolyte, resulting in galvanic corrosion of the pipes and conduits.
    Conventional design practice for corrosion protection is to electrically
    isolate the ferrous metal to be protected from buried copper and concrete
    embedded steel. The protected metal often is coated with a dielectric
    material. Conventional procedures must be modified to meet the restrictions
    and limitations imposed by HEMP/TEMPEST requirements for electrically
    continuous and grounded pipes, conduit, and electrical equipment. Close
    coordination is required between grounding system design and that for
    corrosion protection. Through such coordination, it is often possible to
    design grounding systems that avoid corrosion problems, reduce corrosion
    protective requirements, and simultaneously improve the grounding system.

       b. Groundwater. In areas with high water tables, groundwater presents a
    threat to underground shielding elements. Careful design is required to
    obtain water-tight penetrations of the floor, roof, and exterior walls. This
    includes piping, conduit, and utilitY or access tunnel connections.

       c. Thermal effects. If the metallic shield is subjected to temperatures
    somewhat higher than adjacent concrete, the sheets will tend to buckle
    outward. This condition could occur during construction or during building
    operation. Shield buckling is undesirable because welds can be damaged,
    compromising the shield and possibly the steel envelope's structural
    integrity. To eliminate buckling, provisions for expansion, temperature
    control, and/or securing the plates must be included in shielding design.

       d. Vibration and acoustics. Shielded rooms in which the audible noise
    level is high should be studied for possible acoustical treatment because of
    steel's low sound absorption. Likewise, shielded rooms that have vibrating
    equipment should be given special consideration to avoid resonant vibration of
    shield panels or shielding elements. Excessive panel vibration could
    eventually damage welded seams, thus compromising the shielding.

       e. Ground shock. If the hardened facility will be in an area of high
    seismic activity, or if it must withstand nuclear strikes with high
    overpressures, requirements will be defined for ground shock resistance.
    Expansion joints may be required between linear plate shielded structures to
    protect against differential motion from ground shock. Design for ground
    shock protection should be delegated to structural engineers who have
    appropriate experience and expertise.

    4-7. Cited references.

       4-1.      Campi, M., G. L. Roffman, and J. R. Miletta, Standardization for
                 Mitigation of High Altitude Electromagnetic Pulse (HEMP), HDL-
                 TM-80-33 (U.S. Army Electronics Research and Development
                 Command, Harry Diamond Laboratories, December 1980).

       4-2.      Vance, E. F., W. Graf, and J. E. Nanevicz, Unification of
                 Electromagnetic Specifications and Standards Part I -- Evaluation
                 of Existing Practices, SRI International AFWL Interaction Note
                 420 Defense Nuclear Agency [DNA], July 1981).

       4-3.      Graf, W., J. M. Hamm, and E. F. Vance, Nitrification of
                 Electromagnetic Specifications and Standard Part II:
                 Recommendations for Revisions of Existing Practices, DNA 5433F-2
                 (DNA, February 1983).

       4-4.      Schulz, R. B., EMC Standards Manual, ECAC-HDBK-82-043 (U.S.
                 Department of Defense [DOD], November 1982).

       4-5.      MIL-HDBK-419A, Grounding, Bonding, and Shielding for Electronic
                 Equipments and Facilities (DOD, 21 January 1982).

       4-6.      MIL-STD-188-124A, Grounding, Bonding, and Shielding (DOD, 2
                 February 1984).

       4-7.      Uman, M. A., M. J. Master, and E. P. Krider, "A Comparison of
                 Lightning Electromagnetic Fields With Nuclear ELectromagnetic
                 Pulse in the Frequency Range 104-10-7Hz," IEEE Transactions on
                 Electromagnetic Compatibility, EMC-24 (4) (Institute of
                 Electrical and Electronic Engineers [IEEE], November 1982).

       4-8.      Cianos, N., and E. T. Pierce, A Ground-Lightning Environment for
                 Engineering Usage, Technical Report 1 (Stanford Research
                 Institute, August 1972).

       4-9.      Engineering Design Handbook, Electromagnetic Compatibility,
                 DARCOM Pamphlet P 706-410 (U.S. Army Materiel Command [AMC],
                 March 1977).

       4-10.     MIL-STD-461B, Electromagnetic Emission and Susceptibility
                 Requirements for the Control of Electromagnetic Interference
                 (DOD, 1 April 1980).

       4-11.     MIL-STD-462, (U) Measurement of Electromagnetic Interference
                 Characteristics (DOD, 9 February 1971). (C)

       4-12.     USAF Design Handbook DH-1.

       4-13.     NACSEM 5204, (U) Shielded Enclosures (National Security Agency,
                 May 1978). (C)

       4-14.     NACSEM 5203, (U) Guidelines for Facility Design and Red/Black
                 Installation, (National Security Agency, June 1982). (C)

       4-15.     MIL-HDBK-232A, (U) Red/Black Engineering Installation Guidelines
                 (Draft). (C)

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    Table 4-1. HEMP/TEMPEST-related standards and specifications. (Sheet 1 of 3)

    ____________________________________________________________________________

    Specifications
     and Standards    Issuer    Superseded by      Short title.
    ____________________________________________________________________________

    AFSC DM 1-4       USAF            -            Electromagnetic Compact
    AFSC DH2-7        USAF            -            Sys Survivability
    AFSCN 500-6       USAF            -            EMP Ef on Air Force
    AIR-STD-20/16     USAF            -            Des Gde Haz of EMR-Argon
                                                     Wpn Sys
    AIR 1221          SAE             -            EMC Sys Des Require
    AIR 1255          SAE                          Spect An for EMI Mgmt
    AIR 1173          SAE             -            Test Proc-Mar RF Shldng Char
    AIR 1404          SAE             -            DC Resis vs. RF IMP-EMI Gask
    AIR 1500          SAE             -            Bib Lossy Filters
    AN-J-1            USN/USAF    MS 2508          Bonding Jumpers
    ANS C63.2         ANSI        IF               RI-FI Meters < 30 MHz
    ANS C63.3         ANSI        IF               Msrmts, < 25 MHz
    ANS C63.5         ANSI        IP               Msrmt 20 MHz-1 GHz
    ANS C63.8         ANSI        IP               Msrmt < 30 MHz
    ANS C63.9         ANSI        IP               RI-FI Meters 0.01-15 kHz
    ARP 935           SAE             -            Sugg EMI Cntl Plan Outline
    ARP 936           SAE             -            EMI 10-microF Capacitor
    ARP 958           SAE         IF               Antenna Factors
    ARP 1172          SAE             -            Filt. Conv EMI Gen Spec
    DCA-330-190-1     DCA             -            Equip Performance
    DCAC-330-175-2    DCA             -            DCS Engr Installation
    DIAM-50-3A        DIA             -            Phy Security Stds for
                                                     Sensitive Compartmented
                                                     Information Facilities
    DNA 2114H-l       DNA             -            EMP Hdbk, Des Principles
    DNA 2114H-2       DNA             -            EMP Hdbk, Anal & Treating
    DNA 2114H-3       DNA             -            EMP Hdbk, Env & Applications
    DNA 2114H-4       DNA             -            EMP Hdbk, Resources
    DNA 3286-H        DNA             -            EMP Preferred Test Proc.
    D65/9371          BSI             -            RFI Aircraft Require
    FED-STD-222       All Feds    NACSEM-5100      Info Process Emissions
    FED-STD-1030A     DCA/NCS     Proposed         Balanced Dig. Interface Ckts
    FED-STD-1030A     DCA/NCS     Proposed         Unbalanced Dig Interface Ckts
    FED-STD-1040      DCA/NCS     Proposed         Data Term, Data Ckt Interface
    JAN-I-225         USA/USN     MIL-I-6181       Interfer Cntl/Test
    J551              SAE         J551A            Vehicle RFI
    J551A             SAE         IF               Vehicle RFI
    MIL-B-5087B(ASG)  USN/USAF    Amend #2         Aerospace Bonding
    MIL-C-11693A      USANAR      MIL-C-11693B     R-I Feedthru Capacitor
    MIL-C-11693B      USANAF      IF               R-I Feedthru Capacitor
    MIL-C-12889       USA SC      MIL-C-12889A     R-I Bypass Capacitors
    MIL-C-12899A      USANAF      IF               R-I Bypass Capacitors
    MIL-C-19080       USAN SHIPS  MIL-C-11693B     R-9 Bypass Capacitors
    MIL-C-39011       USANAF      IF               Feedthru Capacitors

    MIL-E-4957A       USAF        MIL-E-4957A(ASG) EMI Shielded Enclosure
    MIL-E-4957(ASG)   USN/USAF    Cancelled        EMI Shielded Enclosure
    MIL-E-55301(EL)   USA         MIL-STD-461/462  EM Compatibility
    MIL-E-6051C       USANAF      MIL-E-6051D      Sys EMC Require
    MIL-E-6051D       USANAF      IF               Sys EMC Require
    MIL-E-8669        USN BuA     MIL-E-4957A(ASG) EM Shielded Enclosure
    MIL-E-8881        USANAF      IF               Shielded EnclosureMIL-F-
    15733C            USANAF      NIL-F-15733D     Radio Interf Filters
    MIL-F-15733D      USANAF      NIL-F-15733E     Radio Interf Filters
    MIL-F-15733G      USANAF      IF               Radio Interf Filters
    MIL-F-18327C      USANAF          -            Filter Specs
    MIL-F-18344A      USN         MIL-F-15733C     Radio Interf Filters
    MIL-HDBK-232A     USANAF          -            RED/BLACK Engr Instal Gdlines
    MIL-HDBK-411      USANAF          -            Long Haul Comm & Env Cntl
    MIL-HDBK-419A     USANAF      IP               GBS for Telecomm Facilities
    MIL-I-6051        USANAF      MIL-I-6051C      Aircraft EMI Limits
    MIL-I-6051A       USAF        MIL-E-006051B    Aircraft EMI Limits
    MIL-I-006051B     USAF        MIL-E-6051C      Sys EMC Require
    MIL-I-6181        USANAF      MIL-I-6181B      EMI Cntl Aircraft
    MIL-STD-188-124A  DOD             -            Grounding, Bonding and
                                                     Shielding
    MIL-STD-202A      DOD             -            Test Methods for Electronic
                                                     and Electrical Component
                                                     Parts
    MIL-STD-220A      DOD             -            Method of Insertion--
                                                     Less Measurement
    MIL-STD-248C      DOD             -            Welding and Brazing Procedure
                                                     and Performance Qualifi-
                                                     cation
    MIL-STD-285       DOD             -            Attenuation Measurements for
                                                     Enclosures, etc. Methods
    MIL-STD-461C      DOD             -            Electromagnetic Emission and
                                                     Susceptibility Requirements
                                                     for Control of EMT
    MIL-STD-1542      DOD             -            EMC and Grounding Reqmts
                                                     for Space Sys Facilities
    NACSEM 5109       NSA             -            Tempest Testing Fundamentals
    NACSEM 5110       NSA             -            Facilities Evaluation Cri-
                                                     teria--TEMPEST
    NACSEM 5201       NSA             -            TEMPEST Guidelines for
                                                     Equipment/System Design
    NACSEM 5204       NSA             -            Shielding Enclosures
    NACSI 5004        NSA             -            TEMPEST Countermeasures for
    NASCI 5005        NSA             -            TEMPEST Countermeasures for
                                                     Facilities Outside the U.S.
    NACSIM 5000       NSA             -            TEMPEST Fundamentals
    NACSIM 5100A      NSA             -            Compromising Emanations
                                                     Laboratory Test Reqmts,
                                                     Electromagnetics
    NACSIM 5203       NSA             -            Guidelines for Facility
                                                     Design and RED/BLACK
                                                     Installation
    NSA 65-5          NSA             -            NSA Specification for RF-
                                                     Shielded Acoustical
                                                     Enclosures for Communica-
                                                     tions Equipment
    NSA 65-6          NSA             -            NSA Specification for RF-
                                                     Shielded Enclosure for
                                                     Communications Equipment
    NSA 73-2A         NSA             -            NSA Specification for Foil
                                                     RF-Shielded Enclosure

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    Table 4-2. Peak magnetic field values for close lightning strokes.

    _____________________________________________________________
                               Magnetic fields
                                 (amps/meters)
       Peak    _______________________________________________
      current      10 m          100 m             10 km
       (kA)     from flash    from flash        from flash
    _____________________________________________________________

        10      1.6 x 10^2         16             1.9 x 10^-2
        20      3.2 x 10^2         32             3.8 x 10^-2
        30      4.8 x 10^2         48             5.8 x 10^-2
        70      1.1 x 10^3      1.1 x 10^2         1.3 x 10^-2
       100      1.6 x 10^3      1.6 x 10^2          19 x 10^-2
       140      2.2 x 10^3      2.2 x 10^2          27 x 10^-2
       200      3.2 x 10^3      3.2 x 10^2          38 x 10^-2

    [Figures 4-1 through 4-5 not digitized here.]

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    [End Chapter 4]