TM58554
d. Attack conditions. Attack conditions exists when weapons have been detonated in the area. The
atmosphere may be contaminated and weapon effects may have rendered external cooling water
equipment inoperative.
(1) In the attack mode, the facility is closed to protect filters, personnel, and pertinent equipment
from blast pressure. The HVAC system is totally isolated from the outside. Ventilation and exhaust air is
recirculated through carbon filters for odor removal. The prime mover combustion air is ducted through
the primary dust separator and a scrubber for dust removal and temperature control. Contaminated dust
slurry from the scrubber is piped to the outside. Facility operation is independent of commercial power.
(2) The seal-up period begins with attack warning and continues until the outside environment is
tolerable. Fuel is supplies from hardened tanks, and cooling water is supplied from hardened heat sinks
and cooling towers.
e. Disaster conditions. Under disaster conditions, the installation is inoperative due to damage or
exhaustion of cooling water, fuel, or oxygen. To sustain life it may be necessary to utilize oxygen
generation and carbon dioxide absorption equipment.
f. Postattack conditions After an all clear signal from an attack has been given, the facility can
return to an alert condition The post-attack conditions end when the facility objectives are completed.
g. Other conditions. The period from button-up or weapon detonation to attack completion is also
known as transattack and may range from minutes to days. Together with the postattack it is collectively
referred to as the facility endurance period or simply facility endurance.
1-5.
Hardened configuration.
a. The primary objective of a hardened structure is to withstand the effects of hostile weapons and
complete the missions for which it was designed. Depending on the degree of hardening and the nature of
this mission, hardened structures may be above or underground.
b. A structure is aboveground when all or a portion of the structure projects above the ground.
Structures mounded over with slopes steeper than 1:4 are considered aboveground.
c. With respect to the ground surface, a structure is flush or partially buried when its rooftop is flush
or buried less than half the structure diameter. Below these levels the structure is deep or shallow-buried
depending on whether or not the buried depth enables it to absorb a direct overhead burst. Fortifications
and air raid shelters are usually the shallow-buried type and equipped with blast doors, baffles, and
labyrinth entrances to provide some blast attenuation.
d. A deep buried facility so defined is a structure buried deep enough that the direct induced ground
motion effects govern design rather than air induced effects. Deep-buried installations can be made
almost invulnerable and are generally used for protection of large one-of-a-kind facilities such as
command and control centers, which cannot risk relying on redundancy or dispersion to ensure
operability. Such important installations are invariable located in hard rock to use the strength of rock
for protection and because rock is usually found at the depths of burial necessitated by nuclear weapons of
the megaton class.
(1) Deep underground structures are the most costly and present the most operational problems.
Deep-underground facilities typically can be several hundred or thousand feet below the surface. Deep-
underground facilities must have survivable entrances, exits, communication links, etc., which will be
.
shallow-buried or aboveground facilities. The designer must ensure that the appropriate weapon effects
are considered for each component of the facility.
(2) Some features of the structural arrangement of a depe-underground installation affect the size
and design of the air-conditioning system. Relevant definitions are as follows:
(a) Bare chamber. An underground chamber with no covering on the rock walls or ceiling that
appreciable affects heat transfer. Walls painted to improve illumination of the chamber are considered
bare from the heat-transfer standpoint A chamber with a concrete floor poured on the underlying rock is
also considered a bare chamber.
(b) Lined chamber. An underground chamber with a wall covering of concrete or other
material in contact with the rock walls and ceiling. Liners may consist of insulating or acoustical
material and may contain a vapor barrier.
(c) Internal structure. A building or enclosure erected within an underground chamber to
house equipment or facilities. The internal structure reduces the heat transfer from the occupied space to
the rock and influences the dehumidification load.
(d) Annular space. The space around an internal structure, between the structure and the rock
walls, floor, and ceiling of an underground chamber
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