TM
5-858-7
riodically, dry process absorption is a batch proc-
OSHA (1972) and others. Where potential sources
ess and therefore has had limited industrial use.
cannot be eliminated, strict regulations controlling
However, dry lithium hydroxide, LiOH, has been
their storage and use should be mandatory provi-
used as a carbon dioxide absorber in both sub-
sions of the facility operating procedures. Specify
the installation of monitoring sensors near poten-
marines and space capsules. Dry LiOH absorbers
tial sources and at possible concentration points
remove moisture as well as carbon dioxide from the
and provide suitable air-treatment equipment ei-
air; this may necessitate the air be dehumidified to
maintain a 50 percent humidity level. The heat
ther as part of the full-time air processing system
or for use as required.
generated by water absorption could be several
times greater than the heat of carbonate formation.
(1) Most gases and vapors are somewhat solu-
ble in water and tend to dissolve in the condensate
f. An absorption system based on Baralyme (a
in dehumidification equipment or in wet-scrubber
trade name for a mixture of 20 percent barium hy-
solutions. Additionally, acid gases such as the ox-
droxide hydrate and 80 percent calcium hydroxide)
ides of nitrogen will be removed by chemical reac-
was designed and tested by NCEL (Williams, 1968)
tion in carbon dioxide scrubbers. Many gases and
as a carbon dioxide control system for survival
vapors, particularly organics, are effectively re-
shelters. The LiOH-based system is the more ex-
moved by activated charcoal filters. Restrict maxi-
tensively tested and the more efficient in terms of
mum permissible concentrations of gases and
carbon dioxide absorbed per unit weight and per
vapors to 25 percent of their lower flammability
unit volume. The cost (1978) is about the same (on
limit, unless the maximum allowable concentration
the order of .10 for LiOH compared with about
must be further reduced because of their toxic
.50 for Baralyme per man-day).
properties.
( 2 ) Catalytic oxidation is effective for
47. Contaminants.
eliminating combustible gases. However, use cau-
a. Particulates. Control of particles such as dust
tion in specifying oxidation devices where the air
and lint is of great importance for good control of
may contain contaminants that could break down to
airborne bacteria in closed ventilation systems.
release still more hazardous compounds (e. g., chlo-
Extensive tests in hospitals and barracks have
roform releases phosgene gas). Specify the use of
demonstrated that a high percentage of infectious
catalytic oxidation devices on an "as required" ba-
bacteria are transported by dust or lint and can be
sis, since they operate at elevated temperatures
eliminated by effective dust control. Particles will
(usually with electrical heating) and add to both
be eliminated by regularly serviced, high-efficiency
electrical-power and waste-heat loads. Provide bat-
filter sytems in supply ducts to all manned areas.
tery installations in closed ventilation systems with
Prefilters can be treated with a bactericidal emul-
one or more standard US Navy catalytic hydrogen
sion spray. Electrostatic precipitators cannot be
eliminators. The poison gas antimony hydride can
used because of the problem caused by ozone
be completely eliminated by restricting batteries to
buildup.
those using calcium rather than antimony as a
b. Flammable and toxic gases. Internally gener-
hardening agent in the lead alloy.
ated gases can build up to significant concentration
c. Ozone control. The low allowable concentra-
levels in closed systems. Potentially combustible or
tion of ozone in ventilation air (0.1 ppm) can make
toxic vapors and gases can be released by numer-
this gas a problem in closed ventilation systems.
ous very ordinary products including cleaners, sol-
The principal sources are high-voltage corona dis-
vents, inks, anesthetics, antiseptics, disinfectants,
charge and electrical arcs. Smooth, non-weathered,
refrigerants, and photocopy chemicals. In open
insulation of high-voltage lines will minimize coro-
ventilation systems, most of these contaminants
na discharge. Arcing in motor and generator
are minor problems that require, at most, in-
brushes and control switches, relays and circuit
creased air flow for dilution and direct discharge to
breakers can be minimized by use of solid-state
outside air. In closed systems, however, control
b r u s h l e s s motors; s o l i d - s t a t e zero-current
measures should include prevention, monitoring,
switching; solid-state transient suppressors; and
and treatment, with the emphasis on prevention.
various surge voltage protectors, gas discharge de-
All liquid and gaseous products used in facilities
vices, and vacuum spark gaps available in the elec-
having closed-ventilation systems should be inves-
trical power and communications fields.
tigated as potential sources of the more than 200
d. Odors. Control of odors will require use of ac-
toxic and flammable gases for which concentration
tivated charcoal filters.
limits in ventilation air have been established by
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