TM-5-855-4
passing through the filter, the air is collected and distributed within the installation by means of a supply
fan and a suitable duct system. Air distribution strategies given in the preceding paragraph will
maximize its utilization.
(3) Control of exhaust air and sealing air leaks will provide a degree of pressurization. Exhaust
air control is achieved by poppet valves or other valves calibrated to permit a fixed flow of air under
pressure or by volume control dampers on exhaust fans. The valves will be located as far as practicable
from the fresh air intake to provide a good circulation of air through the installation. Exhaust air control
of entrances is discussed in chapter 6.
c. Air scrubbing of openings. Many CB contaminants will tend to concentrate in subsurface
openings such as shafts and cut entrances. Such openings will be sealed off at or above ground level. For
some kinds of openings, such sealing will be impossible. To prevent or reduce the build-up of
contamination, provision should be made to scrub the openings with exhaust air from the tunnel or by other
means. Scavenging air of decontamination facilities are discussed in chapter 6.
d. Exclusion of solid and surface contaminants.
(1) Surface contaminants can enter an underground installation either by falling into openings
or, after they have been deposited on the ground, by being carried in accidentally by personnel or vehicles.
Shielding over openings will prevent such contaminants from falling into the installation. Offsets in
shafts are not enough protection against this danger, for they require that the contaminants be removed or
decontaminated, and until decontamination there is danger that the contamination may be moved on into
the installation.
(2) Dust removal devices are covered in TM 5-858-5, but ease of removal and disposal of
contaminated media must be considered in the equipment selection. In this respect, dry type traveling
curtain air filters are preferred to fabric-bag dust separators.
(3) Prevention of contamination by surface contaminants carried into the installation is a matter
of detection and decontamination. Decontamination is covered in chapter 6.
e. Air intakes.
(1) At least two air intakes will be provided whenever possible and given a maximum separation
to reduce the possibility of both intakes being destroyed by a single explosion. Each intake shaft will be
capable of handling the total air requirement of the installation with a minimum friction loss and will
extend above the structure or earth in such manner as to preclude areas of possible high concentration of
-
contamination.
(2) Air intake cross sections will vary from 1 to 5 square feet with the larger shafts used also as
normal air intake for ventilation and AC of occupied areas. For these areas, the incoming air must pass
through chemical filters prior to entering the distribution or conditioning equipment. Bypass of these CB
filters will not be allowed.
(3) Should it be necessary to duct contaminated air through protected areas within a structure, it is
essential that the internal duct pressure be less than that of the area through which it runs. This condition
will permit an inward flow of air into the duct in the event of a leak. Design of intake ports is covered in
TM 5-858-5.
f. CB filters.
(1) The filter units developed by AMCCOM-CRDC, described herein are a development of
Aberdeen Proving Ground, will be installed in all military structures that are to be provided with CBR
protection. HVAC designer will specify component particulate and gas filters, only as listed in table 2-4
and 2-5. When properly installed, these filter units will provide maximum protection against CBR
contaminants that may enter a structure through the ventilation air intake.
(2) The CB filters are composed of two units in series, one unit being a dense water-repellent paper
for the retention of particulate matter, which is the basic carrier of biological and radiological
contaminants. The second unit is an activated carbon unit for the adsorption, retention, and
neutralization of chemical agents.
(3) AS no neutralization of the biological and radiological contaminants can occur, the filter units
may become a secondary hazard to personnel in the immediate vicinity of the filter units. The
construction of the filters does not provide for the required radiation shielding. As a rule and for an
airflow V' in cfm, the shield surface density in pounds per square foot (psf) will be within 20 percent of
(12.6 (V') .3. ]. Shielding of the filters and the operating procedure to protect personnel when removing
contaminated filters will be coordinated with AMCCOM.
(4) Provisions will be made to transfer contaminated filters to the outside without moving through
protected areas. Proper location and installation of CB filters must be coordinated with the design of the
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