TM-5-855-4
hardened AES covered in TM 5-858-5. Any questions regarding the types of prefilters that should be used
in a particular system will be referred to AMCCOM.
(5) The filter units will be installed in a readily accessible location and be provided with an
overhead hoist for periodic removal and replacement. The filters will be located as close as possible to an
exit and remote from the occupied portions of a structure. In structures not provided with blast protection, --
the filter units will be located outside the structure in the vicinity of the main air intake.
(6) When filters are located outside a structure or in an otherwise contaminated area, the supply
fan will be place on the influent side of the filters to preclude the infiltration of contamination in the event
of system leakage. When filters are located inside a structure or in an otherwise clean or protected area,
the supply fan will be place on the eflluent side of the filters. This arrangement will eliminate the
infiltration of contamination since any leakage will be that of clean air.
(7) All intake air will be filtered continuously unless the total requirements necessary for normal
operations of a structure make such filtration uneconomical. Automatic CBR detection devices cannot be
relied upon to put the CB filters on the line when bypassing these filters is allowed; this operation will have
to be accomplished manually at the start of the alert and in advance of pending attack.
(8) Normally, a standby system of filter units identical to the main units will be installed for
occasions when the filters become contaminated and require replacement and when such replacement
cannot be accomplished by shutting down the fresh-air supply. In certain important structures, such as
deep buried ones, the standby filters will be on a completely separate system of supply fans and intake
shafts in case one system becomes inoperable as a result of equipment failure or air-intake shaft damage.
In other instances the standby filters may be stored in readiness for replacement rather than being
initially installed in the duct system. The methods of providing standby filter units will depend on the
importance of the mission to be accomplished within the structure as determined by the using agency.
g. Filter equipment room. A separate area or room will be provided for the air-filtering equipment,
and when AC is required, portions of the AC equipment will also be placed in this room. This room will be
pressurized with clean air, and the filter units and fans will be arranged so that any leakage into the room
will be that of clean air. The refrigerant compressors and evaporative condensers of any AC system will
be placed outside the pressurized area in order to reduce heat buildup, filtered-air requirements, and
possible refrigerant leakage.
h. Protective closures.
(1) Protective closures are required at air intake and exhaust openings, plumbing vents, or other
openings to the atmosphere to prevent a pressure buildup within the facility greater than 2 psi above
atmosphere pressure. Blast closures, valves, ducts, attenuation chambers, debris traps, penetration
protection, and hydraulic surge protection are covered in TM 5-858-5.
(2) In view of the complications involved in design and the variations in requirements for
protective closures in a single given structure, it is strongly recommended that the entire system of air
intakes and exhausts, soil vents, boiler stacks, engine combustion intakes, and exhausts be designed to
reduce the number and types of closures required. This will be accomplished by consolidating a variety of
exhausts or intakes into a common plenum having its own protective closure.
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