Because LOX is stored at its boiling point, it is
constitutes a potential fire and explosion hazard if
either the flammability or solubility limit of the
concentrating the less volatile impurities present in the
hydrocarbon is exceeded. Some of the more important
L OX . T h i s g r a d u a l p r o c e s s o f i n c r e a s i n g
hydrocarbons are discussed in the following text.
ACETYLENE.--Acetylene, a colorless gas, is
contaminants are introduced during handling and
the most hazardous hydrocarbon contaminant because
transfer operations. As noted above, "procurement
it is highly insoluble in LOX (does not dissolve).
standards" of purity are set slightly higher than "use
A c e t y l e n e a l s o s o l i d i fi e s a t ex t r e m e l y l ow
standards" to provide a small margin of safety. This
concentrations. Once in its solid state, acetylene can be
margin of safety, however, does not provide a margin
readily triggered into ignition. And since it is
for error. Never relax your vigilance in quality control
chemically unstable, acetylene can decompose and
against the ever present sources of increasing
become its own source of ignition. The presence of
acetylene in LOX has been the cause of several major
explosions at LOX generating plants.
I N E RT S O L I D C O N S T I T U E N T S . -- I n e r t
solids are classified as "inert" because they do not react
the air we breathe, which is the major source of oxygen
with oxygen to create a fire or explosion hazard. They
u s e d i n t h e p r o d u c t i o n o f L OX . A s a r e s u l t ,
are also classified as inert to distinguish them from
hydrocarbons are always present in LOX, but in small
other hydrocarbons that become solids when their
amounts. Our goal is to keep the amount of
solubility limits are exceeded. Inert solids in LOX are
hydrocarbons that come in contact with LOX as small
hazardous for a number of reasons. First, they may
as possible. The following is a list of some of the
cause mechanical malfunctions or failures. Second,
materials that react violently with oxygen under the
inert solids can cause filters, lines, injectors, and valves
right conditions of temperature and pressure:
to plug. Third, inert solids may accumulate charges of
static electricity, and thus become sources of ignition.
Inert solids consist of three distinct forms: moisture,
carbon dioxide, and particulate matter.
Moisture.--Water vapor condenses to ice on
contact with LOX, and is always present in the form of
atmospheric moisture. Like other substances that
solidify in LOX, ice can cause filters, lines, injectors,
and valves to plug.
cloth and wood
Carbon Dioxide.--Carbon dioxide is slightly
soluble in LOX, but at high concentrations it generally
If exposed to liquid oxygen, organic materials,
exists as a solid.
such as those listed above (including dirt soaked with
Particulate Matter.--Particulate matter consists
oil or grease), will burn violently when ignited. For that
of rust, metal fragments, dust, and fibers derived from
matter, all combustibles are potential explosion
the equipment or the environment of the LOX supply
hazards when mixed with liquid oxygen. The mere
mixture of LOX with powdered organic materials
temperatures as well as at LOX temperatures.
under certain conditions may cause an explosion. If the
In addition to the hydrocarbons there are other
vapor from LOX mixes with fuel vapor in the right
constituents, which if present in LOX, may also affect
the mental and physical well-being of aircrews.
therefore, every fire involving LOX must be regarded
as an explosion hazard.
NITROUS OXIDE.--Nitrous oxide may present
such hazards as those listed above, as well as the
Hydrocarbon fumes may also be added by the
inherent danger of chemical mixture with acetylene
when both exceed their saturation limits. The mixture
p l a n t . T h e p r e s e n c e o f h y d r o c a r b o n s i n L OX