TM 58113/AFM 889, Chap. 3
2-7. Steel frame building with nonconducting
bonded to steel arch, and all will be grounded in con-
roof and sides. Air terminals will be provided and
formance with paragraph 24.
installed in conformance with figure 2-2 and para-
213. Fences. Metal fences that are electrically
graph 2-3. Not less than one steel column will be
continuous with metal posts extending at least 2 feet
grounded at each corner of building.
into the g-round normally require no additional
28. Metal clad building with steel framing.
grounding. Other fences should be made electrically
Steel columns of metal clad buildings will be bonded
continuous and grounded on each side of every gate.
top and bottom to metal siding. Except for facilities
Fences should all be grounded every 1,000 to 1500
used for storage of propellant type weapons and un-
feet when located in isolated areas; and every 500 to
less the using service guidelines or requirements dif-
750 feet when located within 100 feet of public roads,
fer, air terminals may be omitted from building con-
highways and buildings. All metal fences will be
taining no hazardous areas.
grounded at or near points crossed by overhead
powerlines in excess of 600 volts and also at distances
29. Building containing hazardous areas.
of 150 feet on each side of the line crossing.
Metal containers of hazardous materials will not be
214. Railroads. Rails that are not electrically con-
located within 10 feet of lightning protection system.
tinuous and that extend within 100 feet of facilities
Any metals within hazardous atmospheres having
used for storage, manufacturing, processing or han-
connections to other metals within 10 feet of light-
dling explosives, explosive ingredients. explosive
ning protection system will be bonded to the nearest
gases, or flammable liquids will be bonded together
lightning protection system down conductor. Metal
with flexible copper cables or straps and grounded.
doors and windows within hazardous areas will be in-
Switches will be bonded to rails. Where overhead
cluded in such grounding, and doors will be bonded to
power lines in excess of 600 volts crosses railroads,
metal framing by flexible braid-type copper conduct-
the rails will be made electrically continuous and
ors, and connected to lightning protection system.
grounded at a distance of 150 feet on each side of
210. Classified communications building.
overhead lines. Where tracks are located within 25
feet of structures with a grounding system, the
Lightning protection and grounding of communica-
tracks will be grounded to the structural grounding
tions facilities will comply with MIL-STD-188-124
system. This is to effectively discharge potentials
and MI LHDBK-419.
generated by static electricity and lightning before
21 1. Aircraft control-navigation aids.
such discharges are permitted to accumulate or oth-
erwise cause an air gap spark to ignite loose hazard-
a. General. These facilities are considered of such
ous materials. Isolation points should be provided in
importance that aircraft pilots must be assured of re-
the tracks outside of hazardous areas to avoid stray
liability, particular when landing during any light-
currents from being conducted into the bonded or
ning storm, and when pilot's visibility is severely lim-
grounded area.
ited. Counterpoise grid g-rounding system will be
provided for each building.
215. Weapon system electronic facilities
b. Instrument landing system (ILS), tactical air
aboveground
navigation (TACAN) and ground control approach
a. General. This guidance pertains to designs for
(GCA), facilities. One-floor frame buildings housing
the protection of radars, antennas, electronic equip-
equipment for ILS and TACAN facilities and other
ment vans, launchers, missile controls, and guided
similar type structures will be protected as described
missile batteries when permanently installed. Any
in paragraph 2-5; however no fewer than two air ter-
lightning stroke may damage or destroy such elec-
minals will be provided on each facility. Transmitter
tronic weapon facilities by blast effect or by creating
and receiver buildings for GCA facilities will be pro-
surges in connecting wiring. A direct stroke could ig-
tected as described in paragraph 2-6.
nite magnesium portions of van walls, cabinets, con-
c. Control towers. Protection will be provided inde-
soles, and radar antenna castings. When lightning oc-
pendently of antennas and other superstructure.
curs with rain, moisture encourages burning of
These terminals will be interconnected around top
magnesium and splattering of molten metal. Protec-
perimeter of control tower for connections to down
tion for weapon support buildings is as required by
conductors.
construction types discussed in previous paragraphs.
212. Igloos. Protection for corrugated steel arch
b. Protection pattern. Patterns will comply with
earth-mounted igloos, also called "magazines", will be
NFPA No. 78. When structure is a van type, pole
provided as required by the using agency. Metallic
will be located opposite middle of van's longest side,
conduits containing electrical conductors will be
and not less than 6 inches from concrete base of van
2-6
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