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 Section 3:
PLANNING PHASE
3.1
Introduction. It is extremely important that the requirements for
EMI shielding be identified during the planning phase of the project. The
requirements must be identified to allow the EMI shielding to be integrated
into the structure at the lowest possible cost while meeting the operational
requirements of the sponsor and user. It is also important that the shielding
cost be established as early as possible during the project development to
ensure that adequate funding has been established to cover project cost and
avoid delays in the facilities procurement process.
3.1.1
Construction Requirements. There are a number of requirements which
dictate the construction of EMI shielded enclosures. These include: safety
for personnel, ordnance and fuel (HERP, HERO AND HERF); protection of
sensitive communication-electronic (C-E) equipment from ambient
electromagnetic EM energy or the intense EM energy generated by the detonation
of a nuclear device (EMP); preventing classified information (compromising
emanation) from radiating or being conducted out of a controlled area
(TEMPEST).
3.1.2
EMC Surveys and Studies. Any required electromagnetic compatibility
(EMC) surveys and studies should be conducted during the planning phase. The
EMI shielding requirements are established in the BESEP which is prepared by
the SPAWARSYSCOM at the request of the sponsor. The results of the efforts
expended during the planning phase to completely and accurately define the EMI
shielding requirements should not be underestimated. Defining the shielding
requirements (attenuation versus frequency) for the project during the
planning phase will minimize the possibility of costly changes during project
design and construction phase. Not including well defined shielding
requirements during the Facility Study could be costly in terms of money, time
and shielding effectiveness; the project budget may be greatly exceeded, the
completion of the facility may be delayed, the required shielding
effectiveness may not be reached, or more often than not a combination of all
of the above may occur.
3.2
Types of Shielded Enclosures. There are a number of programs,
directives and instructions from various commands that require shielding to
eliminate or reduce the electronic energy in a critical area. The TEMPEST
program is of primary concern in this publication but the material presented
is appropriate for other EMI enclosures.
3.2.1
TEMPEST. One of the most critical shielding programs is the TEMPEST
program. TEMPEST shielding may be required in facilities that house
communication-electronics (C-E) equipment that process classified information.
Facilities which contain this type of equipment must conform to the policies
and regulations contained in OPNAVINST C5510.93, and to the appropriate
National Security Agency COMSEC Publications. The shielding effectiveness
(SE) requirements include both attenuation and frequency for the TEMPEST
shield and should be contained in the BESEP. In the absence of defined
frequency and shielding effectiveness limits in the BESEP, the cost estimate
and construction techniques for the shield should provide for the shielding
effectiveness defined in NSA 65-6, with the shielding effectiveness versus
frequency as shown in Figure 15 and power filter insertion loss shown in
Figure 10.
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