CHAPTER 6.
LIFE SUPPORT SYSTEMS
1.
SCOPE. This chapter presents criteria for the design, fabrication, and
protection of the life support systems which furnish the PV with the bodily
requirements of human occupants at elevated pressures. The atmosphere for
breathing is supplied by the air system, gas system, and auxiliary breathing
system. Food is supplied by the nutrient system. Water for drinking,
washing, shower, and toilet is supplied by the potable water system and the
waste water is removed by the sanitary system. All of these systems must be
controlled and monitored.
Section 1.
ATMOSPHERE REQUIREMENTS
1.
ATMOSPHERE. The mixture and quantity requirements for breathing gas in
hyperbaric facilities are determined by the physiological response of the
human body when exposed to elevated pressures. The breathing mechanisms that
serve to regulate partial pressures of oxygen and carbon dioxide in the blood
at sea level serve equally well at higher pressures if the partial pressures
of oxygen, nitrogen, and carbon dioxide, as well as the respiratory volume,
are similar to those at sea level. Medical research has provided sufficient
information on physical tolerance to partial-pressure levels to permit safe
selection of both composition and consumption requirements of breathing gas
for hyperbaric facilities. This section suggests ranges and limits for
composition, consumption, and temperature-humidity of required breathing gas
for chamber occupants.
2.
BREATHING GAS COMPOSITION REQUIREMENTS. Gas, in order to serve as a
breathing medium, must conform to certain limits. The various problems
connected with specification of gas composition are discussed below.
a.
Oxygen Concentration. Air is used as a breathing gas only for
relatively low pressures (to 300 feet seawater for hyperbaric facilities)
because nitrogen and oxygen become toxic at the elevated partial pressures of
compressed air, The percentage of oxygen in the breathing mixture must be
reduced with increasing pressure to maintain the oxygen partial pressure
within a range of about 0.21 to 1.2 atm (atmospheres absolute pressure). For
long exposure periods, the mixture should contain oxygen at a partial
pressure between 0.21 and 0.50 atm. U.S. Navy practice for saturation diving
missions is to maintain the oxygen partial pressure between 0.30 and 0.32
atm. In order to maintain blood oxygen levels within acceptable limits,
oxygen partial pressure is held nearly constant regardless of total pressure,
and the remaining pressure is provided by increasing the proportion and
partial pressure of the diluent gas.
b.
Anoxia an Oxygen Toxicity. Figure 6-1 relates the percentage of
oxygen in the breathing mixture to pressure depth, and to oxygen partial
pressure in both psia and atm. The curves show a large area within which
mixtures are physiologically acceptable, bounded on the lower side by curves
defining different levels of anoxia (oxygen deficiency) and on the upper side
by levels of oxygen toxicity. It will be noted in Figure 6-1 that the first
symptoms of anoxia occur where oxygen partial pressure falls to 0.16 atm, and
Previous Page
