when a shielded facility requires a long
maintainable service life of high-level protection,
100 dB attenuation, or HEMP protection, 100 dB.
Bolted construction is associated with a lower level
(50 dB) of maintained shielding effectiveness.
Bolted construction will usually consist of modular
panels bolted together with metal strips or
channels. Panels are commonly plywood with steel
sheets laminated to one or both sides. Bolted
construction is used when a shielded facility's
service life is short, 10 years or less, or the
system is required to be demountable for change of
location. This system requires more maintenance
than a welded system and requires access to the
panels. The EM shield layout may restrict
attenuation testing of the enclosure. It is
desirable for large facilities to place the shield
at least 1 meter (3.3 feet) inside the exterior
walls, although cost and construction restrict this
consideration. The floor shielding can be tested by
SELDS test but not by IEEE Std 299 if it is on
grade. The facility layout must be carefully
planned to allow for testing and shield maintenance.
**************************************************************************
2.3.1
Welded Shielding Enclosure
**************************************************************************
NOTE: Shielding steel thickness should not be based
solely on the minimum thickness required for
HEMP/TEMPEST attenuation. Thicker steel may be
necessary because of structural factors and heat
deformation or burn-through from seam welding.
**************************************************************************
The intent of this section and the drawings is to provide a complete metal
enclosure including floor, walls, ceiling, doors, penetrations, welds, and
the embedded structural members to form a continuous EM shielded enclosure.
Shielding sheets and closures shall be [3.416] [_____] mm [10] [_____]
gauge thick hot-rolled steel conforming to ASTM A 568/A 568M. Steel
plates, channels, or angles of minimum 6 mm 1/4 inch thick shall be used to
reinforce shield sheets for attachments of ducts, waveguides, conduit,
pipes, and other penetrating items. Furring channels used to attach
shielding sheets to walls or floors shall be the minimum gauge of the
shielding steel. The shielding sheet steel gauge may be thicker at the
Contractor's option to reduce labor and welding effort only if structurally
tolerable with the existing design. Steel shall be free of oil, dents,
rust, and defects.
2.3.2
Metal Members
Structural steel shapes, plates, and miscellaneous metal shall conform to
ASTM A 36/A 36M.
2.3.3
Steel and Welding Material
Welding materials shall comply with the applicable requirements of AWS
D1.1/D1.1M and AWS D9.1M/D9.1. Steel and welding material shall conform to
AISC 316. Welding electrodes shall conform to AWS D1.1/D1.1M for metal
SECTION 13095A
Page 17
Previous Page
