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 MIL-HDBK-232A
equipment. Such sweeps should provide information to establish the ERTZ of
that equipment. Where the ERTZ is unknown or of uncontrollable size,
countermeasures to reduce or contain those emanations are indicated. Such
methods may include encapsulation of the equipment, use of racks and
cabinets, placing of equipment in screen rooms, or shielding of the facility.
NACSI 5004 and NACSI 5005 should be consulted to determine the anticipated
threat. That threat defines the level of required protection.
5.7.2.1.1 Encapsulation. Encapsulation of equipment to contain emanations
involves surrounding the equipment with a stand alone RFI enclosure. Such
encapsulation must include provision for the entrance of signal and power
cables and provide adequate ventilation. Total encapsulation may not be
practical if operators must have ready access to controls and indicators.
5.7.2.1.2 Cabinets. Equipment which is rack mountable should be mounted in
cabinets. This method is effective if the front panels of equipment, when
properly mounted, provide an adequate degree of RFI attenuation, Equipment
should make bare-metal contact with the cabinet. All unused front rack space
should be closed by blank panels. Closed-door operation of the cabinet
provides further protection. Adequate warning is required that a TEMPEST
hazard may exist when the door is open or panels are removed.
5.7.2.1.3 Screen rooms. Where a quantity of equipment requires ready
operator access to controls and indicators, such equipment may be placed in a
screen room within the REA. Screen rooms are commercially available to
provide attenuation and containment of emanations and provide proper
treatment of signal and power cables required to operate the equipment.
5.7.2.1.4 Shielded facilities. An entire facility may be shielded to
contain emanations. While this method reduces or eliminates numerous
problems in designing a facility, it may be quite expensive and may not be
necessary. As pointed out in paragraph 5.7.1.7, the size of the CS may be
such that by using other methods, shielding may not be required. The
decision to shield must be made after careful study of the equipment being
used, the adequacy of other methods, the physical plant, and the potential
threat, coupled with cognizant agency regulations and policies. Shielding is
easier to accomplish and has better protective capability when done
concurrently with new construction. Shielding in new construction typically
attains 100-dB or better attenuation, while retrofitting typically achieves
about 60-dB attenuation. Additional measures may then be required.
Facilities designed and hardened to HEMP threats are shielded to prevent
damage to equipment. That shielding also provides TEMPEST protection to the
facility.
5.7.2.2 Other exploitation prevention. The use of TEMPEST equipment and
protective measures for nonTEMPEST equipment may be offset by emanations from
interconnecting cables. Signals may be induced on cables passing through an
ERTZ. These cables may egress the facility. To reduce this hazard, proper
attention to cable protection is required. The use of shielded cables and
metallic wire ways provides such protection by providing an EM barrier
between the cable and the radiated signals.
5.7.2.2.1 Shielded cable. All signal cables in a facility should have at
least one overall shield. The use of individually shielded pairs within a
cable should be considered if signal characteristics of clock and data lines
and supportive tests indicate a high likelihood of crosstalk. From a
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