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 MIL-HDBK-419A
3.8.3 Criticalness to System Mission.
If a strike to the facility poses a threat to human life, either to the occupants of the structure or to those.
persons whose safety is dependent upon reliable performance of the equipment and people inside the structure,
comprehensive lightning protection should be definitely provided even in areas of low thunderstorm activity. At
the other extreme, the need for the protection of buildings used primarily to store nonflammable or
nonexplosive items is doubtful unless the stored items are critical to system operation, the building is usually
exposed, etc. In between these extremes are those structures whose incapacitation would cause an
inconvenience or present other difficulties short of life-and-death situations. With these structures, a careful
analysis must be made to determine the relative likelihood of outages from lightning in comparison to normal
equipment failures, downtime for maintenance, and other routine occurrences.
Though not directly related to the protection of electrical or electronic installations, Reference 3-10 is
recommended for further guidance in performing the tradeoff analyses to determine the degree of lightning
protection required for specific facilities.
3.9 APPLICABLE CODES.
The Lightning Protection Code, NFPA No. 78, issued by the National Fire Protection Association (3-9) contains
the basic requirements for the minimization of personnel hazards in the event of a lightning strike to the
structure.
The requirements of NFPA No. 78, however, are not sufficient to protect the electrical distribution system,
signal and control cables, or sensitive electronic equipment from surges produced by either direct or indirect
strokes. Thus additional steps such as providing lightning arresters on power lines and on outside signal and
control cables, providing counterpoise cables for overhead and underground cables, providing comprehensive
electromagnetic shielding on sensitive cables, and installing fast response surge protection devices on circuits
exposed to lightning discharges should be taken. MIL-STD-188-124A refers.
3-27
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