TM-5-8554
Normally, the engine will be equipped with a viscous impingement-type filter in the combustion air
intake for normal operations.
(2) Design of hardened ports and combustion air duct work is covered in TM-5-858-5.
e. The location of combustion engines and other air-consuming equipment is also of primary
importance. Such equipment will be provided with a closed system with its own filtered air, or so located
within a structure that the filtered air required for personnel will exhaust through the equipment area and
be used for combustion. In an occupied structure without benefit of fresh air, any equipment requiring air
for combustion will soon create an untenable condition within the structure. Such equipment will be
isolated and provided with its own air supply and exhaust.
2-4. Vitiated air.
a. A concentration of 0.5 percent carbon monoxide in the air can cause death after one hour. The gas
from a high explosive bomb can contain from 60 to 70 percent carbon monoxide. The air intakes and
exhausts of a facility under attack will be sealed to protect against any such weapon effects. The length of
time a facility must remain sealed up in the attack mode without rejuvenation of air will be determined
during criteria development. Limiting parameters are temperature and humidity rise, oxygen depletion,
and carbon dioxide buildup. These factors reviewed below are further discussed in the ASHRAE
Handbook, Application.
b. The temperature and humidity rise in occupied unventilated spaces may be estimated by the
methods of chapter 3. The particular case of an underground facility isolated for one week is considered
in problem 5, paragraph 3-9e, using sedentary personnel metabolic emission rates (shown in table 2-1) as
the sole source of heat build up in the space. Depending on initial and boundary conditions it is estimated
that during the isolation period personnel will be exposed to temperature of 80 F to 90 F with humidities
approaching 100 percent. This is not beyond human endurance, but is beyond the range at which work
with paper, instruments, or electronic equipment can be reliably accomplished.
c. The hourly oxygen depletion rate under perfect mixing conditions is the ratio of the individual
oxygen consumption V02 in cubic feet per hour (cfh) to the space volume per capita V in cubic feet. As a
result, after t hours (h) of isolation, the oxygen volume fraction [0 2 ] drops from the initial 21 percent
normally present in the air to
(eq 2-1)
d. The hourly carbon dioxide buildup rate under perfect mixing conditions is the ration of the
individual carbon dioxide production V'
in cfh to V. As a result, after t hours of isolation, the carbon
dioxide volume fraction [CO] will rise from the initial 0.3 percent normally present in the air to
(eq 2-2)
e. Table 2-1 shows the various quantities of air, oxygen, and carbon dioxide used or given off under
various conditions.
(1) Variation of oxygen levels between the normal 21 percent and 17 percent are acceptable, but
carbon dioxide buildup is more serious because it acts on the human nervous system to maintain
involuntary respiration. TM 5-858-7 indicates that hyperventilation and increased oxygen consumption
will start above the 1 percent level and that carbon dioxide concentrations higher than about 4 percent are
toxic.
(2) If in the problem of b above, Vc = 1,500 cubic feet per seated occupant each releasing 0.67 cfh of
carbon dioxide, then equation 2-2 shows that the 4 percent critical carbon dioxide level is reached after
only 90 hours, at which point the oxygen consumed at the faster rate of 0.8 cfh has also dropped (equation 2-
1 ) below the 17 percent acceptable oxygen level. In other words, the occupants of the shelter will die
asphyxiated long before their scheduled rescue (after 192 hours of isolation) unless air-regeneration
processes are used.
f. A number of materials for chemically rejuvenating the air are given in table 2-2. These materials
are useful for relatively small capacity carbon dioxide removal requirements. These regeneration
processes also liberate heat and moisture as indicated. Their contribution to the latent and sensible heat
load will be taken into account in the design.
(1) As a rule oxygen will be provided under pressure in bottles, but small quantities of oxygen may
be generated by burning special chlorate candles. Oxygen to be generated or released can be estimated
based on 0.89 cfh per person.
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