heat cannot easily escape, the temperature will rise and
TYPES OF OXYGEN
a fire may break out. This fire is the result of
Aviators breathing oxygen (ABO) (MIL-0-27210)
spontaneous combustion.
is supplied in two types--type I and type II. Type I is
Oxygen does not burn, but it does support
gaseous oxygen and type II is liquid oxygen. Oxygen
combustion. Nitrogen neither burns nor supports
procured under this specification is required to be 99.5
combustion. Therefore, combustible materials burn
percent pure. The water vapor content must not be more
more readily and vigorously in oxygen than in air, since
than 0.02 milligrams per liter when tested at 21.1C
air is composed of about 78 percent nitrogen by volume
(70F) and at sea level pressure.
and only about 21 percent oxygen.
Technical oxygen, both gaseous and liquid, is
procured under specification BB-O-925A. The
In addition to existing as a gas, oxygen can exist as
moisture content of technical oxygen is not as rigidly
a liquid and as a solid. Liquid oxygen is pale blue in
controlled as is breathing oxygen; therefore, the
color. It flows like water, and weighs 9.52 pounds per
technical grade should never be used in aircraft oxygen
gallon.
systems.
EFFECTS OF LACK OF OXYGEN
The extremely low moisture content required of
breathing oxygen is not to avoid physical injury to the
A decrease in the amount of oxygen per unit
body, but to ensure proper operation of the oxygen
volume of air results in an insufficient amount of
system. Air containing a high percentage of moisture
oxygen entering the bloodstream. The body reacts to
can be breathed indefinitely without any serious ill
this condition rapidly. This deficit in oxygen is called
effects. The moisture affects the aircraft oxygen system
hypoxia. When the body regains its normal oxygen
in the small orifices and passages in the regulator.
supply, one may recover from hypoxia. A complete
Freezing temperatures can clog the system with ice and
lack of oxygen, which results in permanent physical
prevent oxygen from reaching the user. Therefore,
damage or death, is called anoxia.
extreme precautions must be taken to safeguard against
the hazards of water vapor in oxygen systems.
Hypoxia
CHARACTERISTICS OF OXYGEN
There is an enormous increase in oxygen
requirements caused by an increase in physical activity.
Oxygen in its natural state is a colorless, odorless,
Strenuous exercise like long distance running greatly
and tasteless gas. Oxygen is considered to be the most
increases the need for oxygen, which is evidenced by
important of all the elements to life. It forms about 21
deep and rapid breathing. Even mild exercise like
percent of the atmosphere by volume and 23 percent by
getting up and walking around a room may double the
weight. The remainder of the atmosphere consists of
air intake. In the case of the aviator, leaking of an
nitrogen (78 percent) and inert gases (1 percent), of
oxygen mask, which may go completely unnoticed
which argon is the most abundant.
while the wearer is at rest, may lead to collapse and
Of all the elements in our environment, oxygen is
unconsciousness when an attempt is made to move
the most plentiful. It makes up nearly one-half of the
from one station to another in the aircraft. A
Earth's crust and approximately one-fifth of the air we
walkaround (portable) oxygen bottle that is sufficient
breath.
for 24 minutes of quiet breathing may be emptied by 17
minutes of use when the user is moving around inside
Oxygen combines with most of the other elements.
the aircraft.
The combining of an element with oxygen is called
oxidation. Combustion is simply rapid oxidation. In
Effects of Hypoxia
almost all oxidations, heat is given off. In combustion,
the heat is given off so rapidly it does not have time to
People differ in their reactions to hunger, thirst, and
be carried away; the temperature rises extremely high,
other sensations. An individual's reactions vary from
and a flame appears.
time to time under similar circumstances. Illness, pain,
fear, excessive heat or cold, and many other factors
Some examples of slow oxidation are rusting of
govern what the response will be in each particular
iron, drying of paints, and the change of alcohol into
case. The same thing is true of individual reactions to
vinegar. Even fuels in storage slowly oxidize, the heat
oxygen starvation. The effects of hypoxia on a given
usually being rapidly carried away. However, when the
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